U.S. patent application number 14/342467 was filed with the patent office on 2014-09-25 for bonded abrasive article.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Walter Flaschberger, Andrea Veronika Kirschner.
Application Number | 20140287658 14/342467 |
Document ID | / |
Family ID | 46980906 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140287658 |
Kind Code |
A1 |
Flaschberger; Walter ; et
al. |
September 25, 2014 |
BONDED ABRASIVE ARTICLE
Abstract
The present invention relates to a bonded abrasive article
comprising specific shaped abrasive particles and a bonding medium
comprising a vitreous bond. The present invention also relates to
the use of an article according to the present invention in
grinding applications, in particular in high performance grinding
applications and to the use of an article according to the present
invention for abrading a workpiece material particularly a
workpiece material selected from steels, non-ferrous metals, and
alloys. In addition, the present invention relates to a method for
abrading a workpiece, the method comprising frictionally contacting
at least a portion of an abrasive article according to the
invention with a surface of a workpiece; and moving at least one of
the workpiece or the abrasive article to abrade at least a portion
of the surface of the workpiece.
Inventors: |
Flaschberger; Walter;
(Villach, AT) ; Kirschner; Andrea Veronika;
(Villach, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
46980906 |
Appl. No.: |
14/342467 |
Filed: |
September 6, 2012 |
PCT Filed: |
September 6, 2012 |
PCT NO: |
PCT/EP2012/067426 |
371 Date: |
March 31, 2014 |
Current U.S.
Class: |
451/47 ; 451/28;
451/51; 451/541; 451/552; 51/307; 51/308; 51/309 |
Current CPC
Class: |
B24D 3/14 20130101; B24D
5/06 20130101; C09K 3/1409 20130101; B24D 5/02 20130101; B24D 5/14
20130101 |
Class at
Publication: |
451/47 ; 451/541;
451/552; 451/28; 451/51; 51/307; 51/309; 51/308 |
International
Class: |
B24D 3/14 20060101
B24D003/14; B24D 5/06 20060101 B24D005/06; B24D 5/14 20060101
B24D005/14; B24D 5/02 20060101 B24D005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2011 |
EP |
11180479.5 |
Sep 8, 2011 |
EP |
11180639.4 |
Claims
1. A bonded abrasive article comprising shaped abrasive particles
and a bonding medium comprising a vitreous bond, said shaped
abrasive particles each comprising a first side and a second side
separated by a thickness t, wherein said first side comprises a
first face having a perimeter of a first geometric shape, wherein
the thickness t is equal to or smaller than the length of the
shortest side-related dimension of the particle.
2. The article according to claim 1, wherein the shaped abrasive
particles are ceramic shaped abrasive particles.
3. The article according to claim 1, wherein the shaped abrasive
particles comprise alpha alumina.
4. The article according to claim 1, wherein the shaped abrasive
particles comprise seeded or non-seeded sol-gel derived alpha
alumina.
5. The article according to claim 1, wherein said shaped abrasive
particles comprise a major portion of aluminum oxide.
6. The article according to claim 5, wherein said aluminum oxide is
fused aluminum oxide.
7. The article according to claim 1, further comprising secondary
abrasive particles.
8. The article according to claim 7, wherein the shaped and
secondary abrasive particles are independently selected from
particles of fused aluminum oxide materials, heat treated aluminum
oxide materials, ceramic aluminum oxide materials, sintered
aluminum oxide materials, silicon carbide materials, titanium
diboride, boron carbide, tungsten carbide, titanium carbide,
diamond, cubic boron nitride, garnet, fused alumina-zirconia,
sol-gel derived abrasive particles, cerium oxide, zirconium oxide,
titanium oxide or a combination thereof.
9. The article according to claim 7, wherein the secondary abrasive
particles are selected from crushed abrasive particles having a
specified nominal grade.
10. The article according to claim 9, wherein the crushed abrasive
particles are of a smaller size than the shaped abrasive
particles.
11. The article according to claim 7 wherein said secondary
abrasive particles are selected from particles of fused aluminum
oxide materials, particles of superabrasive materials or particles
of silicon carbide materials.
12. The article according to claim 1 comprising 10 to 80% by volume
of said shaped abrasive particles and 1 to 60% by volume of said
bonding medium.
13. The article according to claim 1, wherein said vitreous bond
comprises, based on the total weight of the vitreous bond, 25 to
90% by weight of SiO.sub.2; 0 to 40% by weight of B.sub.2O.sub.3; 0
to 40% by weight of Al.sub.2O.sub.3; 0 to 5% by weight of
Fe.sub.2O.sub.3, 0 to 5% by weight of TiO.sub.2, 0 to 20% by weight
of CaO; 0 to 20% by weight of MgO; 0 to 20% by weight of K.sub.2O;
0 to 25% by weight of Na.sub.2O; 0 to 20% by weight of Li.sub.2O; 0
to 10% by weight of ZnO; 0 to 10% by weight of BaO; and 0 to 5% by
weight of metallic oxides.
14. The article according to claim 1, wherein the vitreous bond is
obtainable from a vitreous bond precursor composition comprising
frit.
15. The article according to claim 1, comprising porosity.
16. The article according to claim 7 wherein the shaped abrasive
particles and the secondary abrasive particles are comprised in a
blend, wherein the content of the secondary abrasive particles is
up to 95% by weight based on the total amount of abrasive particles
present in the blend.
17. The article according to claim 1, wherein said first geometric
shape is selected from polygonal shapes, lense-shapes, lune-shapes,
circular shapes, semicircular shapes, oval shapes, circular
sectors, circular segments, drop-shapes and hypocycloids.
18. The article according to claim 1 wherein said first geometric
shape is selected from triangular shapes and quadrilateral
shapes
19. The article according to claim 1, comprising at least one
sidewall.
20. The article according to claim 19, wherein the at least one
sidewall is a sloping sidewall.
21. The article according to claim 1, wherein said shaped abrasive
particles each comprise at least one shape feature selected from:
an opening, at least one recessed (or concave) face; at least one
face which is shaped outwardly (or convex); at least one side
having a plurality of grooves or ridges; at least one fractured
surface; a low roundness factor; a perimeter of the first face
comprising one or more corner points having a sharp tip; a second
side comprising a second face having a perimeter comprising one or
more corner points having a sharp tip; or a combination of one or
more of said shape features.
22. The article according to claim 1, wherein the shaped abrasive
particles each have an opening.
23. The article according to claim 1, wherein the shaped abrasive
particles further comprise a plurality of grooves and/or ridges on
the second side.
24. The article according to claim 1 wherein the second side
comprises a vertex or a ridge line or a second face.
25. The article according to claim 24, wherein the second side
comprises a second face separated from the first side by thickness
t and at least one sidewall connecting the second face and the
first face.
26. The article according to claim 25, wherein the second face has
a perimeter of a second geometric shape which may be the same or
different to the first geometric shape.
27. The article according to claim 26 wherein said first and second
geometric shapes are independently selected from regular polygons,
irregular polygons, lenses, lunes, circulars, semicirculars, ovals,
circular sectors, circular segments, drop-shapes and
hypocycloids.
28. The article according to claim 26 wherein the first and second
geometric shapes have identical geometric shapes which may or may
not be different in size.
29. The article according to claim 28, wherein said identical
geometric shapes are both selected either from triangular shapes or
from quadrilateral shapes.
30. The article according to claim 25, wherein the first face and
the second face are substantially parallel or non-parallel to each
other.
31. The article according to claim 25, wherein the first and/or the
second face are substantially planar.
32. The article according to claim 25, wherein at least one of the
first and second face is a non-planar face.
33. The article according to claim 32, wherein at least one of the
first and the second face is shaped inwardly.
34. The article according to claim 33, wherein the first face is
shaped inwardly and the second face is substantially planar or the
first face is shaped outwardly and the second face is shaped
inwardly or the first face is shaped inwardly and the second face
is shaped inwardly.
35. The article according to claim 25, wherein the second side
comprises a second face and four facets intersecting the second
face at a draft angle alpha forming a truncated pyramid.
36. The article according to claim 24, wherein the second side
comprises a vertex separated from the first side by thickness t and
at least one sidewall connecting the vertex and the perimeter of
the first face.
37. The article according to claim 36, wherein the perimeter of the
first face is trilateral, quadrilateral or higher polygonal and
wherein the second side comprises a vertex and the corresponding
number of facets for forming a pyramid.
38. The article according to claim 37, wherein the perimeter of the
first face is trilateral and wherein the shaped abrasive particles
have four major sides joined by six common edges, wherein each one
of the four major sides contacts three other of the four major
sides, and wherein the six common edges have substantially the same
length.
39. The article according to claim 24, wherein the second side
comprises a ridge line separated from the first side by thickness t
and at least one sidewall connecting the ridge line and the
perimeter of the first face.
40. The article according to claim 39, wherein the sidewall
comprises one or more facets connecting the ridge line and the
perimeter of the first face.
41. The article according to claim 39, wherein the first geometric
shape is selected from quadrilateral geometric shapes and the
sidewall comprises four facets forming a roof-shaped particle.
42. The article according to claim 1 having a three-dimensional
shape selected from the shape of a wheel, honing stone, grinding
segment, mounted points, or other shapes.
43. The article according to claim 1, wherein the article comprises
a wheel.
44. The article according to claim 43, wherein the wheel is
selected from grinding wheels for cylindrical grinding, centerless
grinding, surface and profile grinding, reciprocating grinding,
creep-feed grinding, grinding in generating methods of gears,
threads, tools, camshafts, crankshafts bearings, and guard
rails.
45. The article according to claim 1, wherein the shaped abrasive
particles are homogeneously distributed in the abrasive
article.
46. The article according to claim 1, wherein the shaped abrasive
particles are non-homogeneously distributed in the abrasive
article.
47. The article according to claim 46, which is or comprises a
bonded abrasive wheel, the wheel comprising an outer zone and an
inner zone, wherein the compositions of the inner and outer zone
differ in one or more aspects selected from the composition of the
bond, the shape of abrasive particles, the grit size of abrasive
particle, and the amount of abrasive particles.
48. A bonded abrasive article according to claim 1, wherein the
article comprises a blend of said shaped abrasive particles and
secondary abrasive particles, wherein the amount of shaped abrasive
particles ranges from 20 to 60% by weight, based on the total
weight of abrasive particles in the blend.
49. A bonded article according to claim 1, wherein the article is
an article for gear grinding.
50. Use of an article according to claim 1 in high performance
grinding applications.
51. Use according to claim 50 for outer diameter grinding with a
Q'.sub.w of at least 1.5 mm.sup.3/mm/sec, inner diameter grinding
with a Q'.sub.w of at least 1 mm.sup.3/mm/sec, surface grinding
with a Q'.sub.w of at least 1.5 mm.sup.3/mm/sec, profile grinding
with a Q'.sub.w of at least 3 mm.sup.3/mm/sec, profile grinding
with generating method with a Q'.sub.w of at least 8
mm.sup.3/mm/sec, creep-feed grinding with a Q'.sub.w of at least 4
mm.sup.3/mm/sec, and camshaft grinding with a Q'.sub.w of at least
8 mm.sup.3/mm/sec.
52. Use of an article according to claim 1 for abrading a workpiece
material selected from steels, non-ferrous metals, alloys, hard
metals, ceramics and glasses.
53. Method for abrading a workpiece, the method comprising
frictionally contacting at least a portion of the abrasive article
according to claim 1 with a surface of a workpiece; and moving at
least one of the workpiece or the abrasive article to abrade at
least a portion of the surface of the workpiece.
54. Method of gear grinding characterized by using a bonded
abrasive article according to claim 1.
55. Method of creep-feed grinding characterized by using a bonded
abrasive article according to claim 1.
56. Method of surface grinding characterized by using a bonded
abrasive article according to claim 1.
57. Method of cylindrical grinding characterized by using a bonded
abrasive article according to claim 1.
58. A method of grinding characterized by using a bonded abrasive
article according to claim 1, wherein the specific chip volume
V'.sub.w is at least 20% higher, than the specific chip volume
achieved when using a comparable bonded abrasive article at the
same specific material removal rate Q'.sub.w.
Description
[0001] The present invention relates to bonded abrasive articles,
particularly those which are useful in high performance
grinding.
[0002] Abrasive machining using bonded abrasive articles (such as
grinding wheels) continues to develop its capabilities. This
development has created an increasing demand for high-performance
grinding wheels: wheels which can remove material faster at
exacting tight tolerances, but without causing damage at the
workpiece, thus able to provide reductions in grinding cycle time
and lower grinding costs per part.
[0003] Bonded abrasive articles have abrasive particles bonded
together by a bonding medium. The main types of bonding systems
used to make bonded abrasive articles are: resinoid, vitrified, and
metal. Resinoid bonded abrasives utilize an organic binder system
(e.g., phenolic binder systems) to bond the abrasive particles
together to faint the shaped mass. Another major type are bonded
abrasive articles (for example vitrified bonded wheels) in which a
vitreous binder system is used to bond the abrasive particles
together. These bonds are usually vitrified at temperatures between
700.degree. C. to 1500.degree. C. Metal bonded abrasive articles
typically utilize sintered or plated metal to bond the abrasive
particles. Vitrified bonded abrasive articles are different from
resinoid bonded abrasive articles in that they use a vitreous phase
to bond the abrasive grain and thus are processed at substantially
higher temperatures. Vitrified bonded abrasive articles can
withstand higher temperatures in use and are generally more rigid
and brittle than resinoid bonded wheels.
[0004] Bonded abrasives are three-dimensional in structure and
typically include a shaped mass of abrasive particles, held
together by the binder. Such shaped mass can be, for example, in
the form of a wheel, such as a grinding wheel. Ideal bonded
abrasive articles have a long life time and are able to abrade the
workpiece with constant cut over time. However, when the abrasive
particles are worn and dulled, these abrasive particles are
expelled from the bonded abrasive to expose new, fresh cutting
abrasive particles. In the ideal situation, the bonded abrasive
article is self-sharpening. However, in reality, particularly, when
the forces get high enough, the bonded abrasive articles can break
down, breaking and ejecting grit particles and the grinding power
drawn decreases beyond the starting value of the grinding
application as the bonded abrasive article wears away rapidly and
looses its preferred shape. Bonded abrasive articles therefore
typically show cyclical grinding curves (grinding power consumption
as a function of grinding time). At the end point of a grinding
cycle dressing of the bonded abrasive article (such as a grinding
wheel) has to be set up in order to avoid defects at the workpiece
to be abraded and in order to provide for constant abrading
performance of the bonded abrasive article. Dressing is typically
performed using a dressing tool such as a diamond dressing tool.
Frequent dressing cycles are undesirable since the production
process has to be interrupted frequently which will add on costs,
besides reducing service life of the wheel. What is desired in the
industry is a bonded abrasive article requiring a minimum of
dressing cycles resulting in a long total service life of the
wheel. Such an article typically draws a minimum of power when
operating.
[0005] Vitrified bonded grinding wheels incorporating irregularly
shaped (for example, crushed) abrasive particles are known to be
useful for abrading workpieces such as hardened and unhardened
metal components. However, the dressing cycles of these abrasives
articles can be more frequent than desired, i.e., resharpening has
to be set up more frequently to avoid dulling of the grains.
Sometimes constant grinding performance in terms of workpiece
quality and/or long dressing cycles cannot be provided,
particularly under severe grinding conditions, e.g., high feed
rates. In particular, in case of a grinding cycle not having a
phase of substantially constant grinding performance (for example
in terms of material removal rate) over a period of time it can be
difficult to achieve constant grinding results of the workpiece to
be abraded.
[0006] What is desired in the industry is a bonded abrasive
article, for example, a grinding wheel, that has an improved
service life and can provide constant grinding results
(particularly in terms of surface quality of the workpiece) over a
long period of time, particularly under severe grinding
conditions.
[0007] Surprisingly, it has been found that shaped abrasive
particles in combination with a vitrified bond can provide abrasive
articles which can solve the aforementioned problems. In
particular, such articles have been found to be particularly
effective in high performance grinding applications.
[0008] The present invention relates to a bonded abrasive article
comprising shaped abrasive particles and a bonding medium
comprising a vitreous bond, said shaped abrasive particles each
comprising a first side and a second side separated by a thickness
t, wherein said first side comprises a first face having a
perimeter of a first geometric shape. The thickness t is preferably
equal to or smaller than the length of the shortest side-related
dimension of the particle.
[0009] Typically, the ratio of the length of the shortest side
related dimension to the thickness of said particle is at least
1:1.
[0010] The present invention also relates to the use of the bonded
abrasive articles in high performance grinding applications and to
a method for abrading a workpiece.
[0011] FIG. 1 illustrates a graph of the grinding power consumption
as a function of the grinding time for Type III Wheels of Example I
(Examples 1A-1, 1A-2, 2A-1 and 3A-1 and Comparative Examples Ref.
1A-2, Ref. 2A-1, Ref. 3A-1, and Ref. 3A-2) using the conditions of
Test Series (I).
[0012] FIG. 2 illustrates a graph of the grinding power consumption
as a function of the grinding time for the Type VII Wheels of
Example I (Examples 1B-1, 1B-2, 2B-1 and 3B-1) using the conditions
of Test Series (I).
[0013] FIG. 3 illustrates a graph of the grinding power consumption
as a function of the grinding time for Type III Wheels of Example 1
(Examples 1A-1, 1A-2, 2A-1 and 3A-1 and Comparative Examples Ref.
1A-2, Ref. 2A-1, Ref. 3A-1, and Ref. 3A-2) using the conditions of
Test Series (II).
[0014] FIG. 4 illustrates a graph of the grinding power consumption
as a function of the grinding time for Type VII Wheels of Example I
(Examples 1B-1, 1B-2, 2B-1 and 3B-1) using the conditions of Test
Series (II).
[0015] FIG. 5 shows a graph illustrating the surface roughness Ra
obtained for Type III Wheels of Example I (Examples 1A-1, 1A-2,
2A-1, 3A-1, and Comparative Examples Ref. 1A-2, Ref. 2A-1, Ref.
3A-1, and Ref. 3A-2).
[0016] FIG. 6A is a schematic top view of exemplary shaped abrasive
particle 320.
[0017] FIG. 6B is a schematic side view of exemplary shaped
abrasive particle 320.
[0018] FIG. 6C is a cross-sectional top view of plane 3-3 in FIG.
6B.
[0019] FIG. 6D is an enlarged view of side edge 327a in FIG.
6C.
[0020] While the above-identified drawing figures set forth several
embodiments of the present disclosure, other embodiments are also
contemplated, as noted in the discussion. The figures may not be
drawn to scale. Like reference numbers may have been used
throughout the figures to denote like parts.
[0021] As used herein, forms of the words "comprise", "have", and
"include" are legally equivalent and open-ended. Therefore,
additional non-recited elements, functions, steps or limitations
may be present in addition to the recited elements, functions,
steps, or limitations.
[0022] As used herein, the term "abrasive dispersion" means a
precursor (in typical cases an alpha alumina precursor) that can be
converted into an abrasive material (for example, alpha alumina)
that is introduced into a mold cavity. The composition is referred
to as an abrasive dispersion until sufficient volatile components
are removed to bring about solidification of the abrasive
dispersion.
[0023] As used herein, the term "precursor shaped abrasive
particle" means the unsintered particle produced by removing a
sufficient amount of the volatile component from the abrasive
dispersion, when it is in the mold cavity, to form a solidified
body that can be removed from the mold cavity and substantially
retain its molded shape in subsequent processing operations.
[0024] As used herein, the term "shaped abrasive particle", means
an abrasive particle with at least a portion of the abrasive
particle having a predetermined shape that is replicated from a
mold cavity used to form the shaped precursor abrasive particle.
Except in the case of abrasive shards (e.g. as described in US
Patent Application Publication Nos. 2009/0169816 and 2009/0165394),
the shaped abrasive particle will generally have a predetermined
geometric shape that substantially replicates the mold cavity that
was used to form the shaped abrasive particle. Shaped abrasive
particle as used herein excludes abrasive particles obtained by a
mechanical crushing operation.
[0025] As used herein, the term "nominal" means: of, being, or
relating to a designated or theoretical size and/or shape that may
vary from the actual.
[0026] With respect to the three-dimensional shape of the abrasive
particles in accordance with the present invention, the length
shall mean the longest particle dimension, the width shall mean the
maximum particle dimension perpendicular to the length. The
thickness as referred to herein is also typically perpendicular to
length and width.
[0027] As used herein, the term "thickness", when applied to a
particle having a thickness that varies over its planar
configuration, shall mean the maximum thickness. If the particle is
of substantially uniform thickness, the values of minimum, maximum,
mean, and median thickness shall be substantially equal. For
example, in the case of a triangle, if the thickness is equivalent
to "a", the length of the shortest side of the triangle is
preferably at least "2a". In the case of a particle in which two or
more of the shortest facial dimensions are of equal length, the
foregoing relationship continues to hold. In most cases, the shaped
abrasive particles are polygons having at least three sides, the
length of each side being greater than the thickness of the
particle. In the special situation of a circle, ellipse, or a
polygon having very short sides, the diameter of the circle,
minimum diameter of the ellipse, or the diameter of the circle that
can be circumscribed about the very short-sided polygon is
considered to be the shortest facial dimension of the particle.
[0028] For further illustration, in case of a tetrahedral-shaped
abrasive particle, the length would typically correspond to the
side length of one triangle side, the width would be the dimension
between the tip of one triangle side and perpendicular to the
opposite side edge and the thickness would correspond to what is
normally referred to as "height of a tetrahedron", that is, the
dimension between the vertex and perpendicular to the base (or
first side).
[0029] If an abrasive particle is prepared in a mold cavity having
a pyramidal, conical, frusto-pyramidal, frusta-conical, truncated
spherical, or a truncated spheroidal shape, the thickness is
determined as follows: (1) in the case of a pyramid or cone, the
thickness is the length of a line perpendicular to the base of the
particle and running to the apex of the pyramid or cone; (2) in the
case of a frusto-pyramid or frusto-cone, the thickness is the
length of a line perpendicular to the center of the larger base of
the frusto-pyramid or of the frusto-cone and running to the smaller
base of the frusto-pyramid or of the frusto-cone; (3) in the case
of a truncated sphere or truncated spheroid, the thickness is the
length of a line perpendicular to the center of the base of the
truncated sphere or truncated spheroid and running to the curved
boundary of the truncated sphere or truncated spheroid.
[0030] The length of the shortest side-related dimension of the
particle is the length of the shortest facial dimension of the base
of the particle (if the particle has only one base, typically the
first face) or the length of the shortest facial dimension of the
larger base of the particle (if the particle has two bases, for
example in cases where the second side comprises a second
face).
[0031] As used herein in referring to shaped abrasive particles,
the term "length" refers to the maximum dimension of a shaped
abrasive particle. In some cases the maximum dimension may be along
a longitudinal axis of the particle, although this is not a
necessary requirement. "Width" refers to the maximum dimension of
the shaped abrasive particle that is perpendicular to the length.
"Thickness" refers to the dimension of the shaped abrasive particle
that is perpendicular to the length and width.
[0032] As used herein the term "circular sector" or "circle sector"
refers to the portion of a disk enclosed by two radii and an arc,
including minor sectors and major sectors.
[0033] As used herein the term "circular segment" refers to an area
of a circle informally defined as an area which is "cut off" from
the rest of the circle by a secant or a chord. The circle segment
constitutes the part between the secant and an arc, excluding the
circle's center. This is commonly known as Meglio's Area.
[0034] As used herein the term "drop shape" is intended to refer to
a shape having a perimeter (the path that surrounds the drop shape
area) that can be described as consisting of one vertex and one
curved line, wherein the vertex is formed at the point wherein the
ends of the curved line meet.
[0035] As used herein the term "rhombus" refers to a quadrilateral
having four edges of equal length and wherein opposing vertices
have included angles of equal degrees as seen in FIGS. 1 and 3 of
WO 2011/068714.
[0036] As used herein the term "rhomboid" refers to a parallelogram
wherein the two intersecting edges on one side of the longitudinal
axis are of unequal lengths and a vertex between these edges has an
oblique included angle as seen in FIG. 4 of WO 2011/068714.
[0037] As used herein the term "kite", as seen in FIG. 5 of WO
2011/068714, refers to a quadrilateral wherein the two opposing
edges above a transverse axis are of equal length and the two
opposing edges below the transverse axis are of equal length, but
have a different length than the edges above the transverse axis.
If one took a rhombus and moved one of the opposing major vertices
either closer to or further away from the transverse axis a kite is
formed.
[0038] As used herein the term "superellipse" refers to a geometric
figure defined in the Cartesian coordinate system as the set of all
points (x, y) defined by Lame's curve having the formula
x a n + y b n = 1 ##EQU00001##
where n, a and b are positive numbers. When n is between 0 and 1,
the superellipse looks like a four-armed star with concave edges
(without the scallops) as shown in FIG. 2 of WO 2011/068714. When n
equals 1, a rhombus a=b or a kite a< >b is formed. When n is
between 1 and 2 the edges become convex.
[0039] As used herein the term "secondary abrasive particles" is
intended to generally refer to abrasive particles which differ from
the shaped abrasive particles to be used in accordance with the
present invention
[0040] The term "hard materials" as used in the present invention
is intended to refer to materials which can typically be
characterized as having a Knoop Hardness of 3500 kg.sub.f/mm.sup.2
or less (typically, about 1500 to about 3000 kg.sub.f .mu.mnf).
[0041] The term "superhard materials" as used in the present
invention is intended to refer to materials which can be typically
characterized as having a Knoop Hardness of more than 3500
kg.sub.f/mm.sup.2 (typically, about 4000 to about 9000
kg.sub.f/mm.sup.2).
[0042] The term "superabrasives" as used in the present invention
is intended to refer to abrasive materials which can be typically
characterized as having a Knoop Hardness of 4500 or more than 4500
kg.sub.f/mm.sup.2) (typically 4700 to about 9000
kg.sub.f/mm.sup.2).
[0043] Most oxide ceramics have a Knoop hardness in the range of
1000 to 1500 kg.sub.f/mm.sup.2 (10-15 GPa), and many carbides are
over 2000 kg.sub.f/mm.sup.2 (20 GPa). The method for determining
Knoop Hardness is specified in ASTM C849, C1326 & E384.
[0044] The present invention relates to a bonded abrasive article
comprising specific shaped abrasive particles (which can be
typically characterized as thin bodies) and a bonding medium
comprising a vitreous bond. The present invention also relates to
the use of an article according to the present invention in
grinding applications, in particular in high performance grinding
applications and to the use of an article according to the present
invention for abrading a workpiece material particularly a
workpiece material selected from steels, non-ferrous metals, and
alloys. In addition, the present invention relates to a method for
abrading a workpiece, the method comprising frictionally contacting
at least a portion of an abrasive article according to the
invention with a surface of a workpiece; and moving at least one of
the workpiece or the abrasive article (while in contact) to abrade
at least a portion of the surface of the workpiece.
[0045] In accordance with the present invention, the bonded
abrasive article comprises shaped abrasive particles. Three basic
technologies that have been employed to produce abrasive grains
having a specified shape are (1) fusion, (2) sintering, and (3)
chemical ceramic.
[0046] Any one of these basic technologies or any combination of
two or all of these technologies may be used in order to provide
shaped abrasive particles for use in the present invention.
[0047] The materials that can be made into shaped abrasive
particles of the invention include any suitable hard or superhard
material known to be suitable for use as an abrasive particle.
[0048] Accordingly, in one embodiment, the shaped abrasive
particles comprise a hard abrasive material. In another embodiment,
the shaped abrasive particles comprise a superhard abrasive
material. In yet other embodiments, the shaped abrasive particles
comprise a combination of hard and superhard materials.
[0049] Specific examples of suitable abrasive materials include
known ceramic materials, carbides, nitrides and other hard and
superhard materials such as aluminum oxide (for example alpha
alumina) materials (including fused, heat treated, ceramic and
sintered aluminum oxide materials), silicon carbide, titanium
diboride, titanium nitride, boron carbide, tungsten carbide,
titanium carbide, diamond, cubic boron nitride (CBN), garnet,
alumina-zirconia, sol-gel derived abrasive particles, cerium oxide,
zirconium oxide, titanium oxide or a combination thereof.
[0050] The most useful of the above are typically based on aluminum
oxide, and: in the specific descriptions that follow the invention
may be illustrated with specific reference to aluminum oxide. It is
to be understood, however, that the invention is not limited to
aluminum oxide but is capable of being adapted for use with a
plurality of different hard and superhard materials.
[0051] With respect to the three basic technologies for preparing
shaped abrasive particles (i.e., fusion, sintering and chemical
ceramic technologies), in the present invention, the shaped
abrasive particles may be based on one or more material(s) prepared
by any one of these technologies, i.e. on one or more fused,
sintered or ceramic materials, with a preferred material being
aluminum oxide (preferably alpha aluminum oxide). In other words,
preferred shaped abrasive particles according to the invention are
based on alumina, i.e. such particles either consist of alumina or
are comprised of a major portion thereof, such as for example
greater than 50%, for example 55 to 100%, or 60 to 80%, more
preferably 85 to 100% by weight of the total weight of the abrasive
particle. The remaining portion may comprise any material which
will not detract from the shaped abrasive particle acting as an
abrasive, including but not limited to hard and superhard materials
as outlined in the foregoing. In some preferred embodiments, the
shaped abrasive particles consist of 100% aluminum oxide. In yet
other preferred embodiments, the shaped abrasive particles comprise
at least 60% by weight aluminum oxide or at least 70% by weight of
aluminum oxide. Useful shaped abrasive particles may, for example,
include but are not limited to particles which comprise a major
portion (for example 50% or more and preferably 55% or more by
weight) of fused aluminum oxide and a minor portion (for example,
less than 50% and preferably less than 45% by weight) of an
abrasive material different from fused aluminum oxide (for example
zirconium oxide).
[0052] It is also within the scope of the present invention to use
abrasive particles that have a surface coating for example of
inorganic particles thereon. Surface coatings on the shaped
abrasive particles may be used to improve the adhesion between the
shaped abrasive particles and a binder material in abrasive
articles, or can be used to aid in electrostatic deposition of the
shaped abrasive particles. In one embodiment, surface coatings as
described in U.S. Pat. No. 5,352,254 (Celikkaya) in an amount of
0.1 to 2 percent surface coating to shaped abrasive particle weight
may be used. Such surface coatings are described in U.S. Pat. No.
5,213,591 (Celikkaya et al.); U.S. Pat. No. 5,011,508 (Wald et
al.); U.S. Pat. No. 1,910,444 (Nicholson); U.S. Pat. No. 3,041,156
(Rowse et al.); U.S. Pat. No. 5,009,675 (Kunz et al.); U.S. Pat.
No. 5,085,671 (Martin et al.); U.S. Pat. No. 4,997,461
(Markhoff-Matheny et al.); and U.S. Pat. No. 5,042,991 (Kunz et
al.). Additionally, the surface coating may prevent the shaped
abrasive particle from capping. Capping is the term to describe the
phenomenon where metal particles from the workpiece being abraded
become welded to the tops of the shaped abrasive particles. Surface
coatings to perform the above functions are known to those skilled
in the art.
[0053] In the present invention, it is preferred to use shaped
abrasive particles produced by chemical ceramic technology, i.e.,
ceramic shaped abrasive particles. However, the present invention
is not limited to the use of such particles.
[0054] In one embodiment, the ceramic shaped abrasive particles
comprise alpha alumina, i.e. the particles are alpha alumina based
ceramic shaped particles.
[0055] In one embodiment, the ceramic shaped abrasive particles
comprise sol-gel derived alumina based abrasive particles. Both
seeded and non-seeded sol-gel derived alumina based abrasive
particles can be suitably used in accordance with the present
invention. However, in some instances, it may be preferred to use
non-seeded sol-gel derived alumina based abrasive particles.
[0056] The shaped abrasive particles of the present invention each
have a substantially precisely formed three-dimensional shape.
Typically, the shaped abrasive particles generally have a
predetermined geometric shape, for example one that substantially
replicates the mold cavity that was used to form the shaped
abrasive particle.
[0057] Typically, the shaped abrasive particles can be
characterized as thin bodies. As used herein the term thin bodies
is used in order to distinguish from elongated or filamentary
particles (such as rods), wherein one particle dimension (length,
longest particle dimension) is substantially greater than each of
the other two particle dimensions (width and thickness) as opposed
to particle shapes useful in the present invention wherein the
three particle dimensions (length, width and thickness as defined
herein) are either of the same order of magnitude or two particle
dimensions (length and width) are substantially greater than the
remaining particle dimension (thickness). Conventional filamentary
abrasive particles can be characterized by an aspect ratio, that is
the ratio of the length (longest particle dimension) to the
greatest cross-sectional dimension (the greatest cross-sectional
dimension perpendicular to the length) of from about 1:1 to about
50:1, preferably of from about 2:1 to about 50:1 and more typically
greater than about 5:1 to about 25:1. Furthermore, such
conventional filamentary abrasive particles are characterized by a
cross-sectional shape (the shape of a cross section taken
perpendicular to the length or longest dimension of the particle)
which does not vary along the length.
[0058] In contrast hereto, shaped abrasive particles according to
the present invention can be typically characterized by a
cross-sectional shape that varies along the length of the particle.
Variations can be based on size of the cross-sectional shape or on
the form of the cross-sectional shape.
[0059] The abrasive particles generally each comprise a first side
and a second side separated by a thickness t. The first side
generally comprises (and more typically is) a first face (in
typical cases a planar face) having a perimeter of a first
geometric shape.
[0060] Preferably, the thickness t is equal to or smaller than the
length of the shortest side-related dimension of the particle (the
shortest dimension of the first side and the second side of the
particle; the length of the shortest side-related dimension of the
particle may also be referred to herein as the length of the
shortest facial dimension of the particle).
[0061] In typical cases, the second side comprises a vertex
separated from the first side by thickness t, or the second side
comprises a ridge line separated from the first side by thickness
t, or the second side comprises a second face separated from the
first side by thickness t. For example, the second side may
comprise a vertex and at least one sidewall connecting the vertex
and the perimeter of the first face (illustrative examples include
pyramidal shaped particles, for example tetrahedral-shaped
particles). Alternatively, the second side may comprise a ridge
line and at least one sidewall connecting the ridge line and the
perimeter of the first face (illustrative examples include
roof-shaped particles). Alternatively, the second side may comprise
a second face and at least one sidewall (which may be a sloping
sidewall) connecting the second face and the first face
(illustrative examples include triangular prisms or truncated
pyramids).
[0062] Blends of different shaped abrasive particles in accordance
with the present invention can be used in the bonded abrasive
articles of the present invention. A blend of shaped abrasive
particles can comprise a first plurality of shaped abrasive
particles in accordance with the present invention and a second
plurality of shaped abrasive particles in accordance with the
present invention wherein the particles of the first plurality are
different from the second plurality. Differences can for example be
selected based on the shape or grade or chemical composition of the
abrasive particle.
[0063] The thickness t may be the same (for example in embodiments
wherein the first and second sides comprise parallel planar faces)
or vary over the planar configuration of the particle (for example
in embodiments wherein one or both of the first and second sides
comprise non-planar faces or in embodiments wherein the second side
comprises a vertex or a ridge line as discussed in more detail
later herein).
[0064] In most cases, the ratio of the length of the shortest
side-related dimension of the shaped abrasive particle to the
thickness of the shaped abrasive particle is at least 1:1 but can
range from 1:1 to 10:1, more preferably from 2:1 to 8:1 and most
preferably from 3:1 to 6:1. This ratio is also referred to herein
as primary aspect ratio.
[0065] The dimension of the thickness of the particles is not
particularly limited. For example in typical cases, the thickness
can be about 5 micrometers or more, or about 10 micrometers or
more, or about 25 micrometers or more, or about 30 micrometers or
more, or even about 200 micrometers or more. The upper limit of the
thickness can be selected to be about 4 mm or less, or about 3 mm
or less for large particles, or about 1600 micrometers or less, or
about 1200 micrometers or less, or about 100 micrometers or less,
or about 500 micrometers or less or about 300 micrometers or less
or even about 200 micrometers or less.
[0066] The shaped abrasive particles are typically selected to have
a length in a range of from 0.001 mm to 26 mm, more typically 0.1
mm to 10 mm, and more typically 0.5 mm to 5 mm, although other
lengths may also be used. In some embodiments, the length may be
expressed as a fraction of the thickness of the bonded abrasive
article in which it is contained. For example, the shaped abrasive
particle may have a length greater than half the thickness of the
bonded abrasive wheel. In some embodiments, the length may be
greater than the thickness of the bonded abrasive wheel.
[0067] The shaped abrasive particles are typically selected to have
a width in a range of from 0.001 mm to 26 mm, more typically 0.1 mm
to 10 mm, and more typically 0.5 mm to 5 mm, although other
dimensions may also be used.
[0068] The shaped abrasive particles can have various volumetric
aspect ratios. The volumetric aspect ratio is defined as the ratio
of the maximum cross sectional area passing through the centroid of
a volume divided by the minimum cross sectional area passing
through the centroid.
[0069] For some shapes, the maximum or minimum cross sectional area
may be a plane tipped, angled, or tilted with respect to the
external geometry of the shape. For example, a sphere would have a
volumetric aspect ratio of 1.000 while a cube will have a
volumetric aspect ratio of 1.414. A shaped abrasive particle in the
form of an equilateral triangle having each side equal to length A
and a uniform thickness equal to A will have a volumetric aspect
ratio of 1.54, and if the uniform thickness is reduced to 0.25 A,
the volumetric aspect ratio is increased to 2.64. It is believed
that shaped abrasive particles having a larger volumetric aspect
ratio have enhanced cutting performance.
[0070] In various embodiments of the invention, the volumetric
aspect ratio for the shaped abrasive particles can be greater than
about 1.15, or greater than about 1.50, or greater than about 2.0,
or between about 1.15 to about 10.0, or between about 1.20 to about
5.0, or between about 1.30 to about 3.0.
[0071] The abrasive particles are preferably in the shape of thin
three-dimensional bodies having various three-dimensional shapes.
Typical examples include particles (typically, thin bodies) in the
form of flat triangles, flat rectangles, flat triangles which have
at least one face and more preferably two faces that is/are shaped
inwardly (for example recessed or concave), as discussed in more
detail later herein.
[0072] The first side generally comprises (and more typically is) a
first face having a perimeter of a first geometric shape.
[0073] For example, the first geometric shape can be selected from
geometric shapes having at least one vertex, more typically two or
more, preferably three or more, most preferably three or four
vertices.
[0074] Suitable examples for geometric shapes having at least one
vertex include polygons (including equilateral, equiangular,
star-shaped, regular and irregular polygons), lense-shapes,
lune-shapes, circular shapes, semicircular shapes, oval shapes,
circular sectors, circular segments, drop-shapes and hypocycloids
(for example super elliptical shapes). Specific examples for
suitable polygonal geometric shapes include triangular shapes and
quadrilateral shapes (for example a square, a rectangle, a rhombus,
a rhomboid, a trapezoid, a kite, or a superellipse).
[0075] The vertices of suitable quadrilateral shapes can be further
classified as a pair of opposing major vertices that are
intersected by a longitudinal axis and a pair of opposing minor
vertices located on opposite sides of the longitudinal axis. Shaped
abrasive particles having a first side having this type of
quadrilateral shape can be characterized by an aspect ratio of a
maximum length along a longitudinal axis divided by the maximum
width transverse to the longitudinal axis of 1.3 or greater,
preferably 1.7 to about 5. This aspect ratio is also referred to
herein as secondary aspect ratio.
[0076] In some embodiments it is particularly preferred that the
first geometric shape is selected from triangular shapes, such as
an isosceles triangular shape or, more preferably, an equilateral
triangular shape.
[0077] In other embodiments, the first geometric shape is selected
from quadrilateral shapes, preferably from the group of a square, a
rectangle, a rhombus, a rhomboid, a trapezoid, a kite, or a
superellipse, more preferably from the group of a rectangle, a
rhombus, a rhomboid, a kite or a superellipse.
[0078] For the purposes of this invention geometric shapes are also
intended to include regular or irregular polygons or stars wherein
one or more edges (parts of the perimeter of the face) can be
arcuate (either of towards the inside or towards the outside, with
the first alternative being preferred). Hence, for the purposes of
this invention, triangular shapes also include three-sided polygons
wherein one or more of the edges (parts of the perimeter of the
face) can be arcuate, i.e., the definition of triangular extends to
spherical triangles and the definition of quadrilaterals extends to
superellipses.
[0079] The second side may comprise (and preferably is) a second
face. The second face may have a perimeter of a second geometric
shape.
[0080] The second geometric shape may be the same or be different
to the first geometric shape. Preferably the second geometric shape
is selected to have substantially the same shape as the first
geometric shape and is preferably arranged in a congruent way with
the first geometric shape (although the size or area of the
geometric shapes may be different, i.e. the one face may be larger
than the other one).
[0081] In other words, as used herein the terms "substantially the
same shape" or "substantially identical shapes" are intended to
include the case wherein the area encompassed by said shapes may be
different in size.
[0082] As used herein with respect to the preferred case of
substantially identical first and second geometric shapes, the term
"arranged in a congruent way with the first geometric shape" is
intended to include the case wherein the first and the second
geometric shapes are slightly rotated against each other, although
it is preferred that said substantially identical first and second
geometric shapes are perfectly aligned or only slightly rotated
against each other. The degree (or angle of rotation) depends on
the particular geometric shape of the first face and of the second
face and the thickness of the particle. Acceptable angles of
rotation may range from 0 to +/-30 degrees, preferably from 0 to
+/-15, more preferably from 0 to +/-10 degrees. Most preferably,
the angle of rotation is about 0 degrees (for example 0+/-5
degrees).
[0083] Examples of suitable geometric shapes of the perimeter of
the second face include shapes as exemplified in the foregoing with
respect to the first geometric shapes.
[0084] It is particularly preferred that the first and preferably
also the second geometric shape is selected from triangular shapes,
such as an isosceles triangular shape or, more preferably, an
equilateral triangular shape.
[0085] The first face may be substantially planar or the second
face (if present) may be substantially planar. Also, both faces may
be substantially planar. In many typical cases, the first face is
planar (and identical to the first side).
[0086] Alternatively, at least one of the first and the second face
(if present) may be a non-planar face. Also both faces may be
non-planar faces.
[0087] For example, one or both of the first and the second face
(if present) could be shaped inwardly (for example recessed or
concave) or could be shaped outwardly (for example convex).
[0088] For example, the first face (or the second face, if present)
can be shaped inwardly (for example be recessed or concave) and the
second face (if present, or the first face) can be substantially
planar. Alternatively, the first face (or the second face, if
present) can be shaped outwardly (for example be convex) and the
second face (if present, or the first face) can be shaped inwardly
(for example be recessed or concave), or, the first face can be
shaped inwardly (for example be recessed or concave) and the second
face (if present) can also be shaped inwardly (for example be
recessed or concave).
[0089] The first face and the second face (if present) can be
substantially parallel to each other. Alternatively, the first face
and the second face (if present) can be nonparallel, for example
such that imaginary lines tangent to each face would intersect at a
point (as in the exemplary case wherein one face is sloped with
respect to the other face).
[0090] The second face is typically connected to the perimeter of
the first face by at least one sidewall which may be a sloping
sidewall, as will be discussed later in more detail. The sidewall
may comprise one or more facets, which are typically selected from
quadrilateral facets.
[0091] Specific examples of shaped particles having a second face
include prisms (for example triangular prisms) and truncated
pyramids.
[0092] In some embodiments, the second side comprises a second face
and four facets that form a sidewall (draft angle alpha between the
sidewall and the second face equals 90 degrees) or a sloping
sidewall (draft angle alpha between the sidewall and the second
face greater than 90 degrees). As the thickness, t, of the shaped
abrasive particle having a sloping sidewall becomes greater, the
shaped abrasive particle resembles a truncated pyramid when the
draft angle alpha is greater than 90 degrees.
[0093] The shaped abrasive particles can comprise at least one
sidewall, which may be a sloping sidewall. Typically, the first
face and the second face are connected to each other by the at
least one sidewall.
[0094] In other embodiments the ridge line and the first face are
connected to each other by the at least one sidewall.
[0095] In even other embodiments, the vertex and the first face are
connected to each other by the at least one sidewall.
[0096] In some embodiments, more than one (for example two or
three) sloping sidewall can be present and the slope or angle for
each sloping sidewall may be the same or different. In some
embodiments, the first face and the second face are connected to
each other by a sidewall. In other embodiments, the sidewall can be
minimized for particles where the faces taper to a thin edge or
point where they meet instead of having a sidewall.
[0097] The sidewall can vary and it generally forms the perimeter
of the first face and the second face (if present). In case of a
sloping sidewall, it forms a perimeter of the first face and a
perimeter of the second face (if present). In one embodiment, the
perimeter of the first face and the second face is selected to be a
geometric shape (preferably a triangular shape), and the first face
and the second face are selected to have the same geometric shape,
although, they may differ in size with one face being larger than
the other face.
[0098] A draft angle alpha between the second face and the sloping
sidewall of the shaped abrasive particle can be varied to change
the relative sizes of each face. In various embodiments of the
invention, the area or size of the first face and the area or size
of the second face are substantially equal. In other embodiments of
the invention, the first face or second face can be smaller than
the other face.
[0099] In one embodiment of the invention, draft angle alpha can be
approximately 90 degrees such that the area of both faces are
substantially equal. In another embodiment of the invention, draft
angle alpha can be greater than 90 degrees such that the area of
the first face is greater than the area of the second face. In
another embodiment of the invention, draft angle alpha can be less
than 90 degrees such that the area of the first face is less than
the area of the second face. In various embodiments of the
invention, the draft angle alpha can be between approximately 95
degrees to approximately 130 degrees, or between about 95 degrees
to about 125 degrees, or between about 95 degrees to about 120
degrees, or between about 95 degrees to about 115 degrees, or
between about 95 degrees to about 110 degrees, or between about 95
degrees to about 105 degrees, or between about 95 degrees to about
100 degrees.
[0100] The first face and the second face can also be connected to
each other by at least a first sloping sidewall having a first
draft angle and by a second sloping sidewall having a second draft
angle, which is selected to be a different value from the first
draft angle. In addition, the first and second faces may also be
connected by a third sloping sidewall having a third draft angle,
which is a different value from either of the other two draft
angles. In one embodiment, the first, second and third draft angles
are all different values from each other. For example, the first
draft angle could be 120 degrees, the second draft angle could be
110 degrees, and the third draft angle could be 100 degrees.
[0101] Similar to the case of an abrasive particle having one
sloping sidewall, the first, second, and third sloping sidewalls of
the shaped abrasive particle with a sloping sidewall can vary and
they generally form the perimeter of the first face and the second
face.
[0102] In general, the first, second, and third, draft angles
between the second face and the respective sloping sidewall of the
shaped abrasive particle can be varied with at least two of the
draft angles being different values, and desirably all three being
different values. In various embodiments of the invention, the
first draft angle, the second draft angle, and the third draft
angle can be between about 95 degrees to about 130 degrees, or
between about 95 degrees to about 125 degrees, or between about 95
degrees to about 120 degrees, or between about 95 degrees to about
115 degrees, or between about 95 degrees to about 110 degrees, or
between about 95 degrees to about 105 degrees, or between about 95
degrees to about 100 degrees.
[0103] The sloping sidewall can also be defined by a radius, R,
instead of the draft angle alpha (as illustrated in FIG. 5B of US
Patent Application No. 2010/0151196). The radius, R, can be varied
for each of the sidewalls.
[0104] Additionally, the various sloping sidewalls of the shaped
abrasive particles can have the same draft angle or different draft
angles. Furthermore, a draft angle of 90 degrees can be used on one
or more sidewalls. However, if a shaped abrasive particle with a
sloping sidewall is desired, at least one of the sidewalls is a
sloping sidewall having a draft angle of about greater than 90
degrees, preferably 95 degrees or greater.
[0105] The sidewall can be precisely shaped and can be for example
either concave or convex. Alternatively, the sidewall (top surface)
can be uniformly planar. By uniformly planar it is meant that the
sidewall does not have areas that are convex from one face to the
other face, or areas that are concave from one face to the other
face. For example, at least 50%, or at least 75%, or at least 85%
or more of the sidewall surface can be planar. The uniformly planar
sidewall provides better defined (sharper) edges where the sidewall
intersects with the first face and the second face, and this is
also thought to enhance grinding performance.
[0106] The sidewall may also comprise one or more facets, which are
typically selected from triangular and quadrilateral facets or a
combination of triangular and quadrilateral facets.
[0107] The angle beta between the first side and the sidewall can
be between 20 degrees to about 50 degrees, or between about 10
degrees to about 60 degrees, or between about 5 degrees to about 65
degrees.
[0108] The second side may comprise a ridge line. The ridge line is
typically connected to the perimeter of the first face by at least
one sidewall which may be a sloping sidewall, as discussed in the
foregoing. The sidewall may comprise one or more facets, which are
typically selected from triangular and quadrilateral facets or a
combination of triangular and quadrilateral facets.
[0109] The ridge line may be substantially parallel to the first
side. Alternatively, the ridge line may be non-parallel to the
first side, for example such that an imaginary line tangent to the
ridge line would intersect the first side at a point (as in the
exemplary case wherein the ridge line is sloped with respect to the
first face).
[0110] The ridge line may be straight lined or may be non-straight
lined, as in the exemplary case wherein the ridge line comprises
arcuate structures.
[0111] The facets may be planar or non-planar. For example at least
one of the facets may be non-planar, such as concave or convex. In
some embodiments, all of the facets can be non-planar facets, for
example concave facets.
[0112] Specific examples of shaped particles having a ridge line
include roof-shaped particles, for example particles as
illustrated, in FIG. 4A to 4C of WO 2011/068714). Preferred
roof-shaped particles include particles having the shape of a hip
roof, or hipped roof (a type of roof wherein any sidewalls facets
present slope downwards from the ridge line to the first side. A
hipped roof typically does not comprise vertical sidewall(s) or
facet(s)).
[0113] In some embodiments, the first geometric shape is selected
from a quadrilateral having four edges and four vertices (for
example from the group consisting of a rhombus, a rhomboid, a kite,
or a superellipse) and the second side comprises a ridge line and
four facets forming a structure similar to a hip roof. Thus, two
opposing facets will have a triangular shape and two opposing
facets will have a trapezoidal shape.
[0114] The second side may comprise a vertex and at least one
sidewall connecting the vertex and the perimeter of the first face.
The at least one sidewall may be a sloping sidewall, as discussed
in the foregoing. The sidewall may comprise one or more facets,
which are typically selected from triangular facets. The facets may
be planar or non-planar. For example at least one of the facets may
non-planar, such as concave or convex. In some embodiments, all of
the facets can be non-planar facets, for example concave
facets.
[0115] Illustrative examples include pyramidal-shaped particles,
for example tetrahedral-shaped particles or particles as
illustrated in FIG. 1A to 1C and FIG. 2A to 2C of WO 2011/068714.
The thickness, t, of the shaped abrasive particles can be
controlled to select an angle, beta, between the first side and the
sidewall (or facets). In various embodiments of the invention, the
angle beta between the first side and the sidewall (or facets) can
be between 20 degrees to about 50 degrees, or between about 10
degrees to about 60 degrees, or between about 5 degrees to about 65
degrees.
[0116] In typical embodiments the second side comprises a vertex
and a sidewall comprising and more typically consisting of
triangular facets forming a pyramid. The number of facets comprised
by the sidewall will depend on the number of edges present in the
first geometric shape (defining the perimeter of the first face).
For example, pyramidal shaped abrasive particles having a first
side characterized by a trilateral first geometric shape will
generally have three triangular facets meeting in the vertex
thereby forming a pyramid, and pyramidal shaped abrasive particles
having a first side characterized by a quadrilateral first
geometric shape will generally have four triangular facets meeting
in the vertex thereby forming a pyramid, and so on.
[0117] In some embodiments, the second side comprises a vertex and
four facets forming a pyramid. In exemplary embodiments, the first
side of the shaped abrasive particle comprises a quadrilateral
first face having four edges and four vertices with the
quadrilateral preferably being selected from the group consisting
of a rhombus, a rhomboid, a kite, or a superellipse. The shape of
the perimeter of the first face (i.e., the first geometric shape)
can be preferably selected from the above groups since these shapes
will result in a shaped abrasive particle with opposing major
vertices along the longitudinal axis and in a shape that tapers
from the transverse axis toward each opposing major vertex.
[0118] The degree of taper can be controlled by selecting a
specific aspect ratio for the particle as defined by the maximum
length, L, along the longitudinal axis divided by the maximum
width, W, along the transverse axis that is perpendicular to the
longitudinal axis. This aspect ratio (also referred to herein as
"secondary aspect ratio") should be greater than 1.0 for the shaped
abrasive particle to taper as may be desirable in some
applications. In various embodiments of the invention, the
secondary aspect ratio is between about 1.3 to about 10, or between
about 1.5 to about 8, or between about 1.7 to about 5. As the
secondary aspect ratio becomes too large, the shaped abrasive
particle can become too fragile.
[0119] In some embodiments, it is possible to slightly truncate one
or more of the vertices as shown by dashed lines 42 in FIG. 1 of WO
2011/068714 and mold the shaped abrasive particles into such a
configuration. In these embodiments, if the edges where the
truncation occurs can be extended to form one or more an imaginary
vertices that then completes the claimed quadrilateral, the first
side is considered to be the claimed shape. For example, if both of
the major opposing vertices were truncated, the resulting shape
would still be considered to be a rhombus because when the edges
are extended past the truncation they form two imaginary vertices
thereby completing the rhombus shape for the first side.
[0120] Another exemplary class of shaped abrasive particles having
a second side comprising a vertex are tetrahedral shaped particles.
A tetrahedral shape generally comprises four major sides joined by
six common edges, wherein one of the four major sides contacts
three other of the four major sides, and wherein the six common
edges have substantially the same length. According to the
definitions used herein a tetrahedral shape can be characterized by
a first side comprising a equilateral triangle as a first face and
a second side comprising a vertex and a sidewall comprising three
equilateral triangles as facets connecting the first face and the
vertex, thereby forming a tetrahedron.
[0121] At least one of the four major sides (i.e. the group
consisting of the first side and the three facets) can be
substantially planar. At least one of the four major sides can be
concave, or all the four major sides can be concave. At least one
of the four major sides can be convex or all the four major sides
can be convex.
[0122] The shaped particles of this embodiment typically have
tetrahedral symmetry. The shaped abrasive particles of this
embodiment are preferably substantially shaped as regular
tetrahedrons.
[0123] It is preferred that the shaped abrasive particles comprise
at least one shape feature selected from: an opening (preferably
one extending or passing through the first and second side); at
least one recessed (or concave) face or facet; at least one face or
facet which is shaped outwardly (or convex); at least one side
comprising a plurality of grooves; at least one fractured surface;
a low roundness factor (as described later herein); a perimeter of
the first face comprising one or more corner points having a sharp
tip; a second side comprising a second face having a perimeter
comprising one or more corner points having a sharp tip; or a
combination of one or more of said shape features.
[0124] In preferred embodiments the shaped abrasive particles
comprise at least one of the aforementioned shape features in
combination with a substantially triangular shape of the perimeter
of the first and optionally the second face.
[0125] In other preferred embodiments the shaped abrasive particles
comprise at least one of the aforementioned shape features in
combination with a substantially quadrilateral first geometric
shape.
[0126] In other preferred embodiments, the shaped abrasive particle
comprises a combination of two or more (for example, of three,
four, five or more) of the recited shape features. For example, the
abrasive particle can comprise an opening and a first face that is
shaped outwardly (or convex) and a recessed (or concave) second
face; a second face comprising a plurality of grooves and a low
roundness factor; or an opening and a first face that is shaped
outwardly (or convex) and a recessed (or concave) second face.
[0127] The shaped abrasive particles preferably have a perimeter of
the first and optionally of the second face that comprises one or
more corner points having a sharp tip. Preferably, all of the
corner points comprised by the perimeter(s) have sharp tips. The
shaped abrasive particles preferably also have sharp tips along any
edges that may be present in a sidewall (for example between two
meeting facets comprised by a sidewall).
[0128] The sharpness of a corner point can be characterized by the
radius of curvature along said corner point, wherein the radius
extends to the interior side of the perimeter (as illustrated for
the exemplary shaped abrasive particle shown in FIG. 6D).
[0129] In various embodiments of the invention, the radius of
curvature (also referred to herein as average tip radius) can be
less than 75 microns, or less than 50 microns, or less than 25
microns. It is believed that a sharper edge promotes more
aggressive cutting and improved fracturing of the shaped abrasive
particles during use.
[0130] A smaller radius of curvature means that the particle more
perfectly replicates the edge or corner features of the mold used
to prepare the particle (i.e. of the ideal shape of the particle),
i.e. the shaped abrasive particles are much more precisely made.
Typically, shaped abrasive articles (in particular, ceramic shaped
abrasive particles) made by using a mold of the desired shape
provide more precisely made particles than methods based on other
methods for preparing shaped abrasive particles, such as methods
based on pressing, punching or extruding.
[0131] FIGS. 6C-6D show the radius of curvature 329a for sidewall
edge 327a. In general, the smaller the radius of curvature, the
sharper the sidewall edge will be.
[0132] The shaped abrasive particles may comprise an opening. The
opening can pass completely through the first side and the second
side. Alternatively, the opening can comprise a blind hole which
may not pass completely through both sides.
[0133] In one embodiment, the size of the opening can be quite
large relative to the area defined by the perimeter of the first
face or the second face (if present).
[0134] The opening can comprise a geometric shape which may be the
same or a different geometric shape than that of the first
geometric shape and the second geometric shape.
[0135] An opening ratio of the opening area divided by the face
area of the larger of either the first face or the second face can
be between about 0.05 to about 0.95, or between about 0.1 to about
0.9, or between about 0.1 to about 0.7, between about 0.05 to about
0.5, or between about 0.05 to about 0.3. For the purposes of this
calculation, the face area is based on the area enclosed by the
perimeter without subtracting any area due to the opening.
[0136] Shaped abrasive particles with an opening can have several
benefits over solid, shaped abrasive particles without an opening.
First, the shaped abrasive particles with an opening have an
enhanced cut rate as compared to solid, shaped abrasive particles.
Shaped abrasive particles having a larger opening relative to the
face size may have enhanced grinding performance.
[0137] The inner surface of the opening can have varying contours.
For example, the contour of the inner surface may be planar,
convex, or concave depending on the shape of the upstanding mold
element used for the manufacture of the shaped abrasive particle
with an opening. Additionally, the inner surface can be tapered
such that the size of the opening in each face is different. It is
preferred that the inner surface is a tapered surface such that the
opening is narrower at the top of the mold cavity and wider at the
bottom of the mold cavity for best release of the shaped abrasive
particles from the mold and to prevent cracking of the shaped
abrasive particles during drying.
[0138] The opening can be selected to have substantially the same
shape as the first perimeter. The opening can also be selected to
have substantially the same shape as the perimeter of the first
face and of the perimeter of the second face. Thus, the shaped
abrasive particles with an opening can comprise an integral
connection of a plurality of bars joined at their respective ends
to form a closed polygon as illustrated for example in FIG. 1A or
FIG. 5A of US patent Application Publication 2010/0151201.
Alternatively, the shape of the opening can be selected to be
different than the shape of the first and optionally of the second
perimeter, as illustrated for example in FIG. 5B of US patent
Application Publication 2010/0151201. The size and/or shape of the
opening can be varied to perform different functions more
effectively. In one embodiment, the shape of the opening comprises
a substantially triangular shape, more preferably the shape of an
equilateral triangle.
[0139] Another feature of the shaped abrasive particles with an
opening can be an extremely low bulk density as tested by ANSI
B74.4-1992 Procedure for Bulk Density of Abrasive Grains. Since the
opening can significantly reduce the mass of the shaped abrasive
particles without reducing their overall size, the resulting bulk
density can be extremely low. Moreover, the bulk density of the
shaped abrasive particles can be readily changed and controlled by
simply varying the size and shape of the opening in the particles.
In various embodiments of the invention, the bulk density of the
shaped abrasive particles with an opening can be less than 1.35
g/cm.sup.3, or less than 1.20 g/cm.sup.3, or less than 1.00
g/cm.sup.3, or less than 0.90 g/cm.sup.3. The shaped abrasive
particles may comprise at least one non-planar face. For example,
the first face may be a non-planar face or both of the first face
and the second face may be a non-planar face, or one or both of the
first face and the second face could be shaped inwardly (for
example recessed or concave) or shaped outwardly (for example
convex).
[0140] For example, the first face can be shaped inwardly (for
example be recessed or concave) and the second face can be
substantially planar. Alternatively, the first face can be shaped
outwardly (for example be convex) and the second face can be shaped
inwardly (for example be recessed or concave), or, the first face
can be shaped inwardly (for example be recessed or concave) and the
second face can also be shaped inwardly (for example be recessed or
concave).
[0141] A face which is shaped inwardly (for example a recessed
face) may comprise a substantially planar center portion and a
plurality of raised corners or upturned points. To further
characterize such a face, the curvature of the first face of the
shaped abrasive particles can be measured by fitting a sphere using
a suitable image analysis program such as a non-linear regression
curve-fitting program "NLREG", available from Phillip Sherrod,
Brentwood, Tenn., obtained from www.NLREG.com. A recessed face may
comprise a radius of a sphere curve fitted to the recessed face by
image analysis. The radius can be between about 1 mm to about 25
mm, more preferably about 1 mm to about 14 mm or between about 2 mm
to about 7 mm, when the center of the sphere is vertically aligned
above the midpoint of the first face 24. In one embodiment, the
radius of the fitted sphere to the dish-shaped abrasive particles
measured 2.0 mm, in another embodiment 3.2 mm, in another
embodiment 5.3 mm, and in another embodiment 13.7 mm.
[0142] In one embodiment, the abrasive particles may be described
as dish-shaped abrasive particles. In general, the dish-shaped
abrasive particles comprise typically thin bodies having a first
face, and a second face separated by a sidewall having a varying
thickness t. In general, the sidewall thickness is greater at the
points or corners of the dish-shaped abrasive particles and thinner
at the midpoints of the edges. As such, Tm is less than Tc. In some
embodiments, the sidewall is a sloping sidewall having a draft
angle alpha greater than 90 degrees as discussed in more detail in
the foregoing. More than one sloping sidewall can be present and
the slope or draft angle for each sloping sidewall may be the same
or different for each side of the dish-shaped abrasive particle, as
discussed in the foregoing.
[0143] In some embodiments, the first face is shaped inwardly (for
example recessed) and the second face and sidewall are
substantially planar. By recessed it is meant that that the
thickness of the interior of the first face, Ti, is thinner than
the thickness of the shaped abrasive particle at portions along the
perimeter.
[0144] As mentioned, in some embodiments, the recessed face can
have a substantially flat center portion and a plurality of
upturned points or a plurality of raised corners. The perimeter of
the dish-shaped abrasive particle can be flat or straight at
portions between the upturned points or corners and the thickness
Tc can be much greater than Tm.
[0145] In other embodiments, the recessed first face is
substantially concave with three upturned points or corners and a
substantially planar second face (the shaped abrasive particle is
plano-concave). The difference between Tc and Tm is less and there
can be a more gradual transition from the interior of the first
face to each upturned point as compared to the embodiment wherein
the first face is recessed and the second face and sidewall are
substantially planar. A recessed face may be the result from the
use of a manufacturing method involving sol-gel in a mold cavity
and forming a meniscus leaving the first face recessed. As
mentioned, the first face can be recessed such that the thickness,
Tc, at the points or corners tends to be greater than the
thickness, Ti, of the interior of the first face. As such, the
points or corners are elevated higher than the interior of the
first face.
[0146] In various embodiments of the invention, a thickness ratio
of Tc/Ti can be between 1.25 to 5.00, or between 1.30 to 4.00, or
between 1.30 to 3.00. The thickness ratio can be calculated as
described in [0036] of US Patent Application Publication No.
2010/0151195. Triangular dish-shaped abrasive particles have been
measured to have thickness ratios between 1.55 to 2.32 in some
embodiments. Triangular shaped particles produced by the prior art
method disclosed in U.S. Pat. No. 5,366,523 (Rowenhorst et al.)
have been measured to have thickness ratios between 0.94 to 1.15
meaning they are essentially flat and are just as likely to be
slightly thicker in the middle as they are to be slightly thinner
in the middle. Dish-shaped abrasive particles having a thickness
ratio greater than 1.20 are statistically different from the
Rowenhorst particles at the 95% confidence interval.
[0147] One or more draft angle(s) alpha between the second face and
the sidewall of the dish-shaped abrasive particle can be varied to
change the relative sizes of each face as described in the
foregoing.
[0148] A preferred embodiment of a dish-shaped abrasive particle is
one with a recessed face. The draft angle alpha is approximately 98
degrees and the dish-shaped abrasive particle's perimeter comprises
an equilateral, triangle. The sides of each triangle measured
approximately 1.4 mm long at the perimeter of the first face.
[0149] In one embodiment the thickness t can be more uniform. As
such, Tm can be approximately equal to Tc.
[0150] In one embodiment, the first face is convex and the second
face is concave (concavo-convex), for example such that the
dish-shaped abrasive particle substantially comprises a triangular
section of a spherical shell.
[0151] It is believed that the convex face is formed by the sol-gel
in the mold cavity releasing from the bottom surface of the mold
due to the presence of a mold release agent such as peanut oil
during evaporative drying of the sol-gel. The rheology of the
sol-gel then results in the convex/concave formation of the first
and second face while the perimeter is formed into shape
(preferably, a triangular shape) during evaporative drying.
[0152] In various embodiments of the invention, the radius of a
sphere fitted to the concave second face can be between about 1 mm
to about 25 mm, or between about 1 mm to about 14 mm, or between
about 2 mm to about 7 mm, when the center of the sphere is
vertically aligned above the midpoint of the second face.
[0153] In other embodiments of the invention, the first face and
the second face of the dish-shaped abrasive particles can both be
recessed. In some embodiments, the dish shaped abrasive particles
can be biconcave having a concave first face and a concave second
face. Alternatively, other recessed structural geometries can be
formed on the second face. For example, a plurality of upturned
points or a plurality of raised corners on the second face. In such
embodiments, the degree of curvature or flatness of the first face
can be controlled to some extent by how the dish-shaped abrasive
particles are dried thereby resulting in a recessed or curved first
face or a substantially planar first face.
[0154] The shaped abrasive particles can comprise a plurality of
grooves on one or both of the first side and the second side.
Preferably, the second side (i.e., one or more sidewalls, faces or
facets comprised by the second side, and more preferably the second
face) comprises a plurality of grooves.
[0155] The shaped abrasive particles can comprise a plurality of
ridges on one or both of the first side and the second side.
Preferably, the second side (i.e., one or more sidewalls, faces or
facets comprised by the second side, and more preferably the second
face) comprises a plurality of ridges.
[0156] The plurality of grooves (or ridges) can be formed by a
plurality of ridges (or grooves) in the bottom surface of a mold
cavity that have been found to make it easier to remove the
precursor shaped abrasive particles from the mold.
[0157] The plurality of grooves (or ridges) is not particularly
limited and can, for example, comprise parallel lines which may or
may not extend completely across the side. In terms of this aspect
ratio, the shaped abrasive particles for use in the invention can
be characterized as having a ratio of the length of the greatest
cross-sectional dimension, of from about 2:1 to about 50:1 and more
typically greater than about 5:1 to about 25:1. In one embodiment,
the plurality of grooves (or ridges) comprises parallel lines
extending completely across the second side (preferably across the
second face). Preferably, the parallel lines intersect with the
perimeter along a first edge at a 90 degree angle. The cross
sectional geometry of a groove or ridge can be a truncated
triangle, triangle, or other geometry as further discussed in the
following. In various embodiments of the invention, the depth, D,
of the plurality of grooves can be between about 1 micrometer to
about 400 micrometers. Furthermore, a percentage ratio of the
groove depth, D, to the dish-shaped abrasive particle's thickness,
Tc, (D/Tc expressed as a percent) can be between about 0.1% to
about 30%, or between about 0.1% to 20%, or between about 0.1% to
10%, or between about 0.5% to about 5%.
[0158] In various embodiments of the invention, the spacing between
each groove (or ridge) can be between about 1% to about 50%, or
between about 1% to 40%, or between about 1% to 30%, or between
about 1% to 20%, or between about 5% to 20% of a face dimension
such as the length of one of the edges of the dish-shaped abrasive
particle.
[0159] According to another embodiment the plurality of grooves
comprises a cross hatch pattern of intersecting parallel lines
which may or may not extend completely across the face. A first set
of parallel lines intersects one edge of the perimeter at a 90
degree angle (having a percent spacing of for example 6.25%) of the
edge length of the triangle, and a second set of parallel lines
intersects a second edge of the perimeter at a 90 degree angle
(having a percent spacing of for example 6.25%) creating the cross
hatch pattern and forming a plurality of raised diamonds in the
second face. In various embodiments, the cross hatch pattern can
use intersecting parallel or non-parallel lines, various percent
spacing between the lines, arcuate intersecting lines, or various
cross-sectional geometries of the grooves.
[0160] In other embodiments of the invention the number of ridges
(or grooves) in the bottom surface of each mold cavity can be
between 1 and about 100, or between 2 to about 50, or between about
4 to about 25 and thus form a corresponding number of grooves (or
ridges) in the shaped abrasive particles.
[0161] The shaped abrasive particles may have a low Average
Roundness Factor. Such shaped abrasive particles comprise a
longitudinal axis extending from a base to the grinding tip of the
abrasive article (for example, as shown in FIG. 1 of US Patent
Application Publication No. 2010/0319269). The Average Roundness
Factor for the shaped abrasive particles can be between about 15%
to 0%, or between about 13% to 0%, or between about 12% to 0%, or
between about 12% to about 5%.
[0162] The geometric shape of the cross-sectional plane resulting
from the transverse cut (i.e., the cut transversely at 90 degrees
to the longitudinal axis, also simply referred to as
cross-sectional shape) of the shaped abrasive particles is not
particularly limited and can also vary. A non-circular
cross-sectional shape is most preferably used. A circular
cross-sectional shape is round, which is believed to be duller. It
is believed that a non-circular cross-sectional shape has improved
grinding performance since one or more sharp corners can be present
and one or more sides could be generally linear similar to a chisel
blade. Desirably, the cross-sectional shape is a polygonal shape,
including but not limited to, a triangle, a rectangle, a trapezoid,
or a pentagon.
[0163] In preferred embodiments (such as in the case of particles
having a second face wherein at least one or preferably both of the
first and second faces is/are shaped inwardly), the size of the
cross-sectional shape diminishes from the perimeter of the second
face towards the center of the second face. In this connection, the
term "center" is not restricted to the exact geometric centre of
the geometric shape of second face (i.e. the second geometric
shape), although this option is also contemplated and may be
preferred in some instances, but is intended to encompass an area
generally located in the inside of the geometric shape of the
second face as opposed to the boundaries of the second face as
defined by the second geometric shape.
[0164] In one embodiment, the perimeter of the first and of the
second side of the (and preferably of the first and of the second
face) of the shaped abrasive particle is triangular and the
cross-sectional shape is trapezoidal.
[0165] The shaped abrasive particles can also comprise at least one
fractured surface (shaped abrasive particles having at least one
fractured surface are also referred to herein as fractured shaped
abrasive particle or abrasive shard). In other words, the abrasive
particles can be shaped abrasive particles, as described in the
foregoing, but wherein at least one surface is a fractured
surface.
[0166] As compared to the same shaped abrasive particle without at
least one fractured surface, the fractured abrasive particle can be
considered to comprise the major part of the original shape of the
comparison particle, such as for example, at least 60%, or 70% or
80% or 90% by volume of the original shape. The term original shape
means the same shape but without at least one fractured surface.
Typically, the original shape will correspond to the shape of a
mold cavity used to prepare the comparative ideally shaped abrasive
particle.
[0167] Apart from the at least one fractured surface the fractured
shaped abrasive particles comprise only precisely formed surfaces
defining the major part of the original shape, and thus exclude
particles obtained by a mechanical crushing operation.
[0168] In one embodiment, the fractured shaped abrasive particle
does not comprise more than three, preferably more than two
fractured surfaces. In another embodiment, the fractured shaped
abrasive particle comprises one fractured surface.
[0169] The original shape is not particularly limited and can be
selected from geometric shapes as defined in the foregoing with
respect to abrasive particles which do not comprise at least one
fractured surface.
[0170] Fractured shaped abrasive particles can be formed in a mold
having the original shape, such as a triangular cavity. Typically,
the mold has a plurality of cavities to economically produce the
abrasive shards.
[0171] In one example, the shaped abrasive particles can comprise a
first precisely formed surface, a second precisely formed surface
intersecting with the first precisely formed surface at a
predetermined angle alpha, a third surface opposite the first
precisely formed surface, and a fractured surface.
[0172] The first precisely formed surface can be formed by contact
with a bottom surface of a cavity in a mold (corresponding to the
original shape). The first precisely formed surface substantially
replicates the surface finish and shape of the bottom surface of
the cavity. The second precisely formed surface of the abrasive
shard can be formed by contact with a sidewall of the cavity in the
mold. The sidewall is designed to intersect the bottom surface at a
predetermined angle alpha (also referred to as draft angle alpha in
the present invention). The second precisely formed surface
substantially replicates the surface finish and shape of the
sidewall of the cavity. The second precisely formed surface is
molded by contact with the sidewall of the cavity. As such, at
least two surfaces of the resulting abrasive shard are precisely
formed and the angle of intersection alpha between the two surfaces
is a predetermined angle based on the selected mold geometry. The
third surface of the abrasive shard opposite the first precisely
formed surface can be randomly wavy or undulating in appearance
since it is in contact with the air after the cavity is filled with
an abrasive dispersion. The third surface is not precisely formed
since it is not molded by contact with the cavity. Often, the third
surface is created by scraping or doctoring a top surface of the
mold to remove excessive abrasive dispersion from the mold. The
doctoring or scraping step results in a subtle waviness or
irregularity of the third surface that is visible under
magnification. As such, the third surface is similar to a surface
created by extrusion, which is also not precisely formed. In the
extrusion process, the sol-gel is forced out of a die. As such, the
surfaces of the sol-gel exhibits scrape marks, gouges, and/or score
lines as a result of the extrusion process. Such marks are created
by the relative motion between the sol-gel and the die.
Additionally, extruded surfaces from a die can be generally a
smooth plane. In contrast, the precisely formed surfaces can
replicate a sinusoidal or other more complex geometrical surface
having significant variations in height along the length of the
surface.
[0173] The fractured surface of the abrasive shard generally
propagates between the first precisely formed surface and the
opposing third surface and between opposing sidewalls of the cavity
when the cavity depth is relatively small compared to the area of
the bottom surface. The fractured surface is characterized by
sharp, jagged points typical of a brittle fracture. The fractured
surface can be created by a drying process that cracks or fractures
at least the majority of the shaped abrasive particle precursors
into at least two pieces while residing in the cavity. This
produces abrasive shards having a smaller size than the mold cavity
from which they were made. The abrasive shards, once formed, could
be reassembled like jigsaw puzzle pieces to reproduce the original
cavity shape of the mold from which they were made. The cracking or
fracturing of the precursor abrasive particles is believed to occur
by ensuring that the surface tension of the abrasive dispersion to
the walls of the cavity is greater than the internal attractive
forces of the abrasive dispersion as the abrasive dispersion is
dried in the cavity.
[0174] Another embodiment is a shaped abrasive particle
respectively bounded by a polygonal first face (or base), a
polygonal second face (or top), and a plurality of sidewalls
connecting the base and the top, wherein adjacent sidewalls meet at
respective sidewall edges having an average radius of curvature of
less than 50 micrometers. For example, referring to FIGS. 6A-6B,
exemplary shaped abrasive particle 320 is bounded by a trigonal
base 321, a trigonal top 323, and plurality of sidewalls 325a,
325b, 325c connecting base 321 and top 323. Base 321 has sidewall
edges 327a, 327b, 327c, having an average radius of curvature of
less than 50 micrometers. FIGS. 6C-6D show radius of curvature 329a
for sidewall edge 327a. In general, the smaller the radius of
curvature, the sharper the sidewall edge will be. Typically, the
base and the top of the shaped abrasive particles are substantially
parallel, resulting in prismatic or truncated pyramidal (as shown
in FIGS. 6A-6B) shapes, although this is not a requirement. As
shown, sides 325a, 325b, 325c have equal dimensions and form
dihedral angles with base 321 of about 82 degrees. However, it will
be recognized that other dihedral angles (including 90 degrees) may
also be used. For example, the dihedral angle between the base and
each of the sidewalls may independently range from 45 to 90
degrees, typically 70 to 90 degrees, more typically 75 to 85
degrees.
[0175] According to particularly preferred embodiments, the shaped
abrasive particles have a three-dimensional shape of flat
triangular platelets or flat rectangular platelets, with flat
triangular platelets being preferred. Such shaped abrasive
particles may also be simply referred to as flat triangles or flat
rectangles.
[0176] Hence, in particularly preferred embodiments, the shaped
abrasive particles each comprise a first side and a second side
separated by a thickness t, wherein said thickness t is preferably
equal to or smaller than the length of the shortest side-related
dimension of the particle, wherein said first side comprises (or
preferably is) a first face having a perimeter of a first geometric
shape, wherein said second side comprises (or preferably is) a
second face having a perimeter of a second geometric shape, and
wherein said second side is separated from said first side by
thickness t and at least one sidewall connecting said second face
and said first face, wherein said first geometric shape and said
second geometric shapes have substantially identical geometric
shapes which may or may not be different in size, wherein said
identical geometric shapes are both selected either from triangular
shapes or from quadrilateral shapes.
[0177] Said first geometric shape is preferably congruent to said
second geometric shape, as described previously.
[0178] It is also preferred that the first and second face of such
particles are substantially planar and substantially parallel to
each other.
[0179] Preferred triangular and quadrilateral or rectangular shapes
are as defined in the foregoing.
[0180] The sidewall can also be as defined in the foregoing. For
example, the sidewall can be a non-sloping sidewall (i.e., the size
of the first geometric shape is identical to the size of the second
geometric, shape; for example triangular or rectangular prisms) or
a sloping sidewall (i.e., the size of the first geometric shape is
not identical to and typically larger than the size of the second
geometric shape; as, for example, in the case of particles having
the shape of truncated triangular or rectangular pyramids, as
described herein).
[0181] According to another particularly preferred embodiment, the
shaped abrasive particles are flat triangular platelets (also
simply referred to as flat triangles) or flat rectangular platelets
(also simply referred to as flat rectangles), as described above,
but wherein at least one of the first and the second face is shaped
inwardly (for example recessed or concave).
[0182] For example, the first face can be shaped inwardly (for
example be recessed or concave) and the second face can be
substantially planar or shaped outwardly (for example be convex),
or the second face can be shaped inwardly (for example be recessed
or concave) and the first face can be substantially planar or
shaped outwardly (for example be convex).
[0183] Alternatively and more preferably, the first face can be
shaped inwardly (for example be recessed or concave) and the second
face can also be shaped inwardly (for example be recessed or
concave).
[0184] For particles according to this embodiment, the thickness
typically varies over the planar configuration of the particle and
diminishes towards the "center of the particle".
[0185] Particles according to this embodiment are also typically
characterized by a diminishing area of the cross-sectional shape
(perpendicular to the length) towards the center of the
particle.
[0186] The term "center of the particle" as used in this connection
is to be understood in a general way and does not necessarily have
to be the geometric center of the particle, although there might be
cases where the minimum thickness or the minimum area of the
cross-sectional shape can be found at the geometric center of the
particle, as described previously.
[0187] The shaped abrasive particles used in the present invention
can have an abrasives industry specified nominal grade or a nominal
screened grade.
[0188] Abrasive particles are generally graded to a given particle
size distribution before use. Such distributions typically have a
range of particle sizes, from coarse particles to fine particles.
In the abrasive art this range is sometimes referred to as a
"coarse", "control", and "fine" fractions. Abrasive particles
graded according to abrasive industry accepted grading standards
specify the particle size distribution for each nominal grade
within numerical limits. Such industry accepted grading standards
(i.e., abrasive industry specified nominal grade) include those
known as the American National Standards Institute, Inc. (ANSI)
standards, Federation of European Producers of Abrasive Products
(FEPA) standards, and Japanese Industrial Standard (JIS)
standards.
[0189] ANSI grade designations (i.e., specified nominal grades)
include: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI
46, ANSI 54, ANSI 60, ANSI 70, ANSI 80, ANSI 90, ANSI 100, ANSI
120, ANSI 150, ANSI 180, ANSI 220, ANSI 240, ANSI 280, ANSI 320,
ANSI 360, ANSI 400, and ANSI 600. FEPA grade designations include
F4, F5, F6, F7, F8, F10, F12, F14, F16, F20, F22, F24, F30, F36,
F40, F46, F54, F60, F70, F80, F90, F100, F120, F150, F180, F220,
F230, F240, F280, F320, F360, F400, F500, F600, F800, F1000, F1200,
F1500, and F2000. JIS grade designations include JIS8, JIS12,
JIS16, JIS24, JIS36, JIS46, JIS54, JIS60, JIS80, JIS100, JIS150,
JIS180, JIS220, JIS240, JIS280, JIS320, JIS360, JIS400, JIS600,
JIS800, JIS1000, JIS1500, JIS2500, JIS4000, JIS6000, JIS8000, and
JIS10,000.
[0190] Alternatively, the shaped abrasive particles can be graded
to a nominal screened grade using U.S.A. Standard Test Sieves
conforming to ASTM E-11 "Standard Specification for Wire Cloth and
Sieves for Testing Purposes." ASTM E-11 proscribes the requirements
for the design and construction of testing sieves using a medium of
woven wire cloth mounted in a frame for the classification of
materials according to a designated particle size. A typical
designation may be represented as -18+20 meaning that the shaped
abrasive particles pass through a test sieve meeting ASTM E-11
specifications for the number 18 sieve and are retained on a test
sieve meeting ASTM E-11 specifications for the number 20 sieve. In
one embodiment, the shaped abrasive particles have a particle size
such that most of the particles pass through an 18 mesh test sieve
and can be retained on a 20, 25, 30, 35, 40, 45, or 50 mesh test
sieve. In various embodiments of the invention, the shaped abrasive
particles can have a nominal screened grade comprising: -18+20,
-20+25, -25+30, -30+35, -35+40, -40+45, -45+50, -50+60, -60+70,
-70+80, -80+100, -100+120, -120+140, -140+170, -170+200, -200+230,
-230+270, -270+325, -325+400, -400+450, -450+500, or -500+635.
[0191] The shaped abrasive particles in accordance with the present
invention may be comprised in a fraction of abrasive particles (or
abrasive fraction), also referred to as blend of abrasive particles
in the present invention (for ease of reference the term "blend" as
used herein is also intended to include the case that the fraction
of abrasive particles comprises 100% by weight of shaped abrasive
particles, based on the total amount of abrasive particles present
in the fraction (or blend).
[0192] A blend can comprise one or more types of shaped abrasive
particles in accordance with the present invention and optionally
one or more types of abrasive particles which are generally
referred to herein as "secondary abrasive particles" (abrasive
particles which differ from the shaped abrasive particles to be
used in accordance with the present invention). For example,
abrasive particles having a shape not in accordance with the
present invention (for example filamentary abrasive particles or
elongated rods) or conventional non-shaped abrasive particles could
be used as secondary abrasive particles.
[0193] A blend can comprise shaped abrasive particles in accordance
with the present invention and secondary abrasive particles in any
amount. Accordingly, the shaped abrasive particles and the
secondary abrasive particles may be comprised in a blend, wherein
the content of the secondary abrasive particles may be up to 95% by
weight based on the total amount of abrasive particles present in
the blend or even higher. Thus, in other highly preferred
embodiments, the article does not contain secondary abrasive
particles.
[0194] In some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40,
45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by
weight of the blend are shaped abrasive particles according to the
present invention, based on the total weight of the blend of
abrasive particles.
[0195] The secondary abrasive particles may have any suitable
particle form (as long as it is different from the shape of the
abrasive particle for use in the invention). Exemplary particle
forms include but are not limited to particle forms obtained by
mechanical crushing operation, agglomerated forms and any other
forms that differ from the specific abrasive particle shapes as
defined herein.
[0196] The materials constituting the secondary abrasive particles
are not particularly limited and include any suitable hard or
superhard material known to be suitable for use as an abrasive
particle. Accordingly, in one embodiment, the secondary abrasive
particles comprise a major portion of a hard abrasive material. For
example, at least 30%, or at least 50%, or 60% to 100%, or 90% or
more, or 100% by weight of the total weight of the secondary
abrasive particles are comprised of a hard material. In another
embodiment, the secondary abrasive particles comprise a major
portion of a superhard abrasive material. For example, at least
30%, or at least 50%, or 60% to 100%, or 90% or more, or 100% by
weight of the total weight of the secondary abrasive particles are
comprised of a superhard material.
[0197] Examples of suitable abrasive materials of secondary
abrasive particles include but are not limited to known ceramic
materials, carbides, nitrides and other hard and superhard
materials and include materials, as exemplified herein with respect
to shaped abrasive particles, and the shaped abrasive particles of
the invention and the secondary abrasive particles can be
independently selected from particles of such exemplified materials
or any combination thereof.
[0198] Representative examples of materials of secondary abrasive
particles include for example particles of fused aluminum oxide,
e.g., white fused alumina, heat treated aluminum oxide, ceramic
aluminum oxide materials such as those commercially available under
the trade designation 3M CERAMIC ABRASIVE GRAIN from 3M Company of
St. Paul, Minn., sintered aluminum oxide, silicon carbide
(including black silicon carbide and green silicon carbide),
titanium diboride, boron carbide, tungsten carbide, titanium
carbide, diamond, cubic boron nitride, garnet, fused
alumina-zirconia, sol-gel derived abrasive particles (including
sol-gel-derived aluminum oxide particles), cerium oxide, zirconium
oxide, titanium oxide. Examples of sol-gel derived abrasive
particles can be found in U.S. Pat. No. 4,314,827 (Leitheiser et
al.), U.S. Pat. No. 4,623,364 (Cottringer et al.); U.S. Pat. No.
4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.); and
U.S. Pat. No. 4,881,951 (Monroe et al.).
[0199] In a preferred embodiment, the secondary abrasive particles
are selected from particles of fused oxide materials, including
fused aluminum oxide materials or fused alumina-zirconia,
preferably fused aluminum oxide.
[0200] In another preferred embodiment, the secondary abrasive
particles are selected from particles of superabrasive materials,
for example cubic boron nitride and natural or synthetic diamond.
Suitable diamond or cubic boron nitride materials can be
crystalline or polycrystalline. A preferred superabrasive material
for use as secondary abrasive particles is cubic boron nitride.
[0201] In yet another embodiment, the secondary abrasive particles
are selected from particles of silicon carbide materials.
[0202] The secondary abrasives particles comprised in the blend may
have an abrasives industry specified nominal grade or a nominal
screened grade. As mentioned, the shaped abrasive particles may
also have an abrasive industry specified nominal grade or a nominal
screened grade and the grade(s) of the secondary abrasive particles
and the grade(s) of the shaped abrasive particles of the present
invention can be independently selected from any useful grade.
[0203] For example, the abrasive article may further comprise
crushed abrasive particles (excluding abrasive shards as defined
herein) which can optionally correspond to an abrasive industry
specified nominal graded or combination thereof. The crushed
abrasive particles can be of a finer size grade or grades (e.g., if
a plurality of size grades are used) than the shaped abrasive
particles. In some embodiments, the crushed abrasive particles can
be of a coarser size grade or grades (e.g., if a plurality of size
grades are used) than the shaped abrasive particles.
[0204] Typically, conventional crushed abrasive particles are
independently sized according to an abrasives industry recognized
specified nominal grade. Exemplary abrasive industry recognized
grading standards and grades for secondary abrasive particles
include those as mentioned with respect to shaped abrasive
particles.
[0205] Methods to provide shaped abrasive particles are known in
the art and include technologies based on (1) fusion, (2)
sintering, and (3) chemical ceramic. While preferred shaped
abrasive particles can be obtained by using chemical ceramic
technology, non-ceramic shaped abrasive particles are also included
within the scope of the present invention. In the description of
the invention, methods for preparing shaped abrasive particles may
be described with specific reference to ceramic shaped abrasive
particles, particularly alumina based ceramic shaped abrasive
particles. It is to be understood however that the invention is not
limited to alumina but is capable of being adapted for use with a
plurality of different hard and superhard materials.
[0206] The shaped abrasive particles used in the present invention
can typically be made using tools (i.e., molds), cut using diamond
tooling, which provides higher feature definition than other
fabrication alternatives such as, for example, stamping or
punching. Typically, the cavities in the tool surface have planar
faces that meet along sharp edges, and form the sides and top of a
truncated pyramid. The resultant shaped abrasive particles have a
respective nominal average shape that corresponds to the shape of
cavities (e.g., truncated pyramid) in the tool surface; however,
variations (e.g., random variations) from the nominal average shape
may occur during manufacture, and shaped abrasive particles
exhibiting such variations are included within the definition of
shaped abrasive particles as used herein.
[0207] Shaped abrasive particles (for example alpha-alumina based
ceramic particles) can be made according to a multistep process
typically using a dimensionally stable dispersion of a suitable
precursor (for example a ceramic precursor).
[0208] The dispersion that is typically employed in the process may
be any dispersion of a suitable precursor and by this is intended a
finely dispersed material that, after being subjected to a process
suitable in the invention, is in the form of a shaped abrasive
particle. The precursor may be chemically a precursor, as for
example boehmite is a chemical precursor of alpha alumina; a
morphological precursor as for example gamma alumina is a
morphological precursor of alpha alumina; as well as (or
alternatively), physically a precursor in the sense of that a
finely divided form of alpha alumina can be formed into a shape and
sintered to retain that shape. In typical cases, the dimensionally
stable dispersion of a suitable precursor is a sol-gel.
[0209] Where the dispersion comprises a physical or morphological
precursor as the term is used herein, the precursor is in the form
of finely divided powder grains that, when sintered together, form
an abrasive particle of utility in conventional bonded and coated
abrasive applications. Such materials generally comprise powder
grains with an average size of less than about 20 microns,
preferably less than about 10 microns and most preferably less than
about a micron. The solids content of a dispersion of a physical or
a morphological precursor is preferably from about 40 to 65% though
higher solids contents of up to about 80% can be used. An organic
compound is frequently used along with the finely divided grains in
such dispersions as a suspending agent or perhaps as a temporary
binder until the particle has been dried sufficiently to maintain
its shape. This can be any of those generally known for such
purposes such as polyethylene glycol, sorbitan esters and the
like.
[0210] The solids content of a chemical precursor that changes to
its final stable (for example, ceramic) form upon heating may need
to take into account water that may be liberated from the precursor
during drying and firing to sinter the particles. In such cases the
solids content is typically somewhat lower such as about 75% or
lower and more preferably between about 30% and about 50%. With a
boehmite gel a maximum solids content of about 60% or even 40% is
preferred and a gel with a peptized minimum solids content of about
20% may also be used.
[0211] Particles made from physical precursors will typically need
to be fired at higher temperatures than those formed from a seeded
chemical precursor. For example, whereas particles of a seeded
boehmite gel form an essentially fully densified alpha alumina at
temperatures below about 1250.degree. C., particles made from alpha
alumina gels require a firing temperature of above about
1400.degree. C. for full densification.
[0212] By way of example, a method suitable for use in the present
invention comprises chemical ceramic technology involving
converting a colloidal dispersion or hydrosol (sometimes called a
sol), optionally in a mixture with solutions of other metal oxide
precursors, to a gel or any other physical state that restrains the
mobility of the components, drying, and firing to obtain a ceramic
material. A sol can be prepared by any of several methods,
including precipitation of a metal hydroxide from an aqueous
solution followed by peptization, dialysis of anions from a
solution of metal salt, solvent extraction of an anion from a
solution of a metal salt, hydrothermal decomposition of a solution
of a metal salt having a volatile anion. The sol optionally
contains metal oxide or precursor thereof and is transformed to a
semi-rigid solid state of limited mobility such as a gel by, e.g.,
partial extraction of the solvent, e.g., water, the gel can be
shaped by any convenient method such as pressing, molding, or
extruding, to provide a shaped abrasive grain.
[0213] An exemplary method involving chemical ceramic technology
comprises the steps of making a dimensionally stable dispersion of
a ceramic precursor (which may for example include either a seeded
or non-seeded sol-gel alpha alumina precursor dispersion that can
be converted into alpha alumina); filling one or more mold cavities
having the desired outer shape of the shaped abrasive particle with
the dimensionally stable dispersion of a ceramic precursor, drying
the stable dispersion of a ceramic precursor to form precursor
ceramic shaped abrasive particles; removing the precursor ceramic
shaped abrasive particles from the mold cavities; calcining the
precursor ceramic shaped abrasive particles to form calcined,
precursor ceramic shaped abrasive particles, and then sintering the
calcined, precursor ceramic shaped abrasive particles to form
ceramic shaped abrasive particles. The process is described in more
detail in U.S. Pat. No. 5,201,916 (Berg et al.).
[0214] The materials that can be made into shaped particles of the
invention include physical precursors such as finely divided
particles of known ceramic materials, carbides, nitrides such as
alpha alumina, tungsten carbide, silicon carbide, titanium nitride,
alumina/zirconia and cubic boron nitride (CBN). Also included are
chemical and/or morphological precursors such as aluminum
trihydrate, boehmite, gamma alumina and other transitional aluminas
and bauxite. The most useful of the above are typically based on
alumina, and its physical or chemical precursors and in the
specific descriptions that follow a method suitable for use in the
invention is illustrated with specific reference to alumina.
[0215] Other components that have been found to be desirable in
certain circumstances for the production of alumina-based particles
include nucleating agents such as finely divided alpha alumina,
ferric oxide, chromium oxide and other materials capable of
nucleating the transformation of precursor faints to the alpha
alumina form; oxides of magnesium; titanium; zirconium; yttrium;
and other rare earth metal oxides. Such additives often act as
crystal growth limiters or boundary phase modifiers. The amount of
such additives in the precursor is usually less than about 10% and
often less than 5% by weight (solids basis).
[0216] It is also possible to use, instead of a chemical or
morphological precursor of alpha alumina, a slip of finely divided
alpha alumina itself together with an organic compound that will
maintain it in suspension and act as a temporary binder while the
particle is being fired to essentially full densification. In such
cases it is often possible to include in the suspension materials
that will form a separate phase upon firing or that can act as an
aid in maintaining the structural integrity of the shaped particles
either during drying and firing, or after firing. Such materials
may be present as impurities. If for example the precursor is
finely divided bauxite, there will be a small proportion of
vitreous material present that will form a second phase after the
powder grains are sintered together to form the shaped
particle.
[0217] Ceramic shaped abrasive particles composed of crystallites
of alpha alumina, magnesium alumina spinel, and a rare earth
hexagonal aluminate may also be used. Such particles may be
prepared using sol-gel precursor alpha alumina particles according
to methods described in, for example, U.S. Pat. No. 5,213,591
(Celikkaya et al.) and U.S. Publ. Patent Appl. Nos. 2009/0165394 A1
(Culler et al.) and 2009/0169816 A1 (Erickson et al.).
[0218] In some embodiments, ceramic shaped abrasive particles can
be made according to a multistep process. The process will now be
described in greater detail with specific reference to alumina.
Generally, alpha alumina based shaped abrasive particles can be
made from a dispersion of aluminum oxide monohydrate that is
gelled, molded to shape, dried to retain the shape, calcined, and
sintered as is known in the art. The shaped abrasive particle's
shape is retained without the need for a binder.
[0219] The first process step of the multi-step process involves
providing either a seeded or non-seeded dispersion of an alpha
alumina precursor that can be converted into alpha alumina. The
alpha alumina precursor dispersion often comprises a liquid that is
a volatile component. In one embodiment, the volatile component is
water. The dispersion should comprise a sufficient amount of liquid
for the viscosity of the dispersion to be sufficiently low to
enable filling mold cavities and replicating the mold surfaces, but
not so much liquid as to cause subsequent removal of the liquid
from the mold cavity to be prohibitively expensive. In one
embodiment, the alpha alumina precursor dispersion comprises from 2
percent to 90 percent by weight of the particles that can be
converted into alpha alumina, such as particles of aluminum oxide
monohydrate (boehmite), and at least 10 percent by weight, or from
50 percent to 70 percent, or 50 percent to 60 percent, by weight of
the volatile component such as water. Conversely, the alpha alumina
precursor dispersion in some embodiments contains from 30 percent
to 50 percent, or 40 percent to 50 percent, by weight solids.
[0220] Aluminum oxide hydrates other than boehmite can also be
used. Boehmite can be prepared by known techniques or can be
obtained commercially. Examples of commercially available boehmite
include products having the trade designations "DISPERAL", and
"DISPAL", both available from Sasol North America, Inc, of Houston,
Tex., or "HiQ-40" available from BASF Corporation of Florham Park,
N.J. These aluminum oxide monohydrates are relatively pure; that
is, they include relatively little, if any, hydrate phases other
than monohydrates, and have a high surface area.
[0221] The physical properties of the resulting ceramic shaped
abrasive particles will generally depend upon the type of material
used in the alpha alumina precursor dispersion. In one embodiment,
the alpha alumina precursor dispersion is in a gel state. As used
herein, a "gel" is a three-dimensional network of solids dispersed
in a liquid.
[0222] The alpha alumina precursor dispersion may contain a
modifying additive or precursor of a modifying additive. The
modifying additive can function to enhance some desirable property
of the abrasive particles or increase the effectiveness of the
subsequent sintering step.
[0223] Modifying additives or precursors of modifying additives can
be in the form of soluble salts, typically water soluble salts.
They typically consist of a metal-containing compound and can be a
precursor of oxide of magnesium, zinc, iron, silicon, cobalt,
nickel, zirconium, hafnium, chromium, yttrium, praseodymium,
samarium, ytterbium, neodymium, lanthanum, gadolinium, cerium,
dysprosium, erbium, titanium, and mixtures thereof. The particular
concentrations of these additives that can be present in the alpha
alumina precursor dispersion can be varied based on skill in the
art.
[0224] Typically, the introduction of a modifying additive or
precursor of a modifying additive will cause the alpha alumina
precursor dispersion to gel. The alpha alumina precursor dispersion
can also be induced to gel by application of heat over a period of
time. The alpha alumina precursor dispersion can also contain a
nucleating agent (seeding) to enhance the transformation of
hydrated or calcined aluminum oxide to alpha alumina. Nucleating
agents suitable for this invention include fine particles of alpha
alumina, alpha ferric oxide or its precursor, titanium oxides and
titanates, chrome oxides, or any other material that will nucleate
the transformation. The amount of nucleating agent, if used, should
be sufficient to effect the transformation of alpha alumina.
Nucleating such alpha alumina precursor dispersions is disclosed in
U.S. Pat. No. 4,744,802 (Schwabel).
[0225] A peptizing agent can be added to the alpha alumina
precursor dispersion to produce a more stable hydrosol or colloidal
alpha alumina precursor dispersion. Suitable peptizing agents are
monoprotic acids or acid compounds such as acetic acid,
hydrochloric acid, formic acid, and nitric acid. Multiprotic acids
can also be used but they can rapidly gel the alpha alumina
precursor dispersion, making it difficult to handle or to introduce
additional components thereto. Some commercial sources of boehmite
contain an acid titer (such as absorbed formic or nitric acid) that
will assist in forming a stable alpha alumina precursor
dispersion.
[0226] The alpha alumina precursor dispersion can be formed by any
suitable means, such as, for example, by simply mixing aluminum
oxide monohydrate with water containing a peptizing agent or by
forming an aluminum oxide monohydrate slurry to which the peptizing
agent is added.
[0227] Defoamers or other suitable chemicals can be added to reduce
the tendency to form bubbles or entrain air while mixing.
Additional chemicals such as wetting agents, alcohols, or coupling
agents can be added if desired. The alpha alumina abrasive
particles may contain silica and iron oxide as disclosed in U.S.
Pat. No. 5,645,619 (Erickson et al.). The alpha alumina abrasive
particles may contain zirconia as disclosed in U.S. Pat. No.
5,551,963 (Larmie). Alternatively, the alpha alumina abrasive
particles can have a microstructure or additives as disclosed in
U.S. Pat. No. 6,277,161 (Castro).
[0228] The second process step involves providing a mold having at
least one mold cavity, and preferably a plurality of cavities. The
mold can have a generally planar bottom surface and a plurality of
mold cavities. The plurality of cavities can be formed in a
production tool. The production tool can be a belt, a sheet, a
continuous web, a coating roll such as a rotogravure roll, a sleeve
mounted on a coating roll, or die. In one embodiment, the
production tool comprises polymeric material. Examples of suitable
polymeric materials include thermoplastics such as polyesters,
polycarbonates, poly(ether sulfone), poly(methyl methacrylate),
polyurethanes, polyvinylchloride, polyolefin, polystyrene,
polypropylene, polyethylene or combinations thereof, or
thermosetting materials. In one embodiment, the entire tooling is
made from a polymeric or thermoplastic material. In another
embodiment, the surfaces of the tooling in contact with the sol-gel
while drying, such as the surfaces of the plurality of cavities,
comprises polymeric or thermoplastic materials and other portions
of the tooling can be made from other materials. A suitable
polymeric coating may be applied to a metal tooling to change its
surface tension properties by way of example.
[0229] A polymeric or thermoplastic tool can be replicated off a
metal master tool. The master tool will have the inverse pattern
desired for the production tool. The master tool can be made in the
same manner as the production tool. In one embodiment, the master
tool is made out of metal, e.g., nickel and is diamond turned. The
polymeric sheet material can be heated along with the master tool
such that the polymeric material is embossed with the master tool
pattern by pressing the two together. A polymeric or thermoplastic
material can also be extruded or cast onto the master tool and then
pressed. The thermoplastic material is cooled to solidify and
produce the production tool. If a thermoplastic production tool is
utilized, then care should be taken not to generate excessive heat
that may distort the thermoplastic production tool limiting its
life. More information concerning the design and fabrication of
production tooling or master tools can be found in U.S. Pat. No.
5,152,917 (Pieper et al.); U.S. Pat. No. 5,435,816 (Spurgeon et
al.); U.S. Pat. No. 5,672,097 (Hoopman et al.); U.S. Pat. No.
5,946,991 (Hoopman et al.); U.S. Pat. No. 5,975,987 (Hoopman et
al.); and U.S. Pat. No. 6,129,540 (Hoopman et al.).
[0230] Access to cavities can be from an opening in the top surface
or bottom surface of the mold. In some instances, the cavities can
extend for the entire thickness of the mold. Alternatively, the
cavities can extend only for a portion of the thickness of the
mold. In one embodiment, the top surface is substantially parallel
to bottom surface of the mold with the cavities having a
substantially uniform depth. At least one side of the mold, that
is, the side in which the cavities are formed, can remain exposed
to the surrounding atmosphere during the step in which the volatile
component is removed.
[0231] The cavities have a specified three-dimensional shape to
make the ceramic shaped abrasive particles. The depth dimension is
equal to the perpendicular distance from the top surface to the
lowermost point on the bottom surface. The depth of a given cavity
can be uniform or can vary along its length and/or width. The
cavities of a given mold can be of the same shape or of different
shapes.
[0232] The third process step involves filling the cavities in the
mold with the alpha alumina precursor dispersion (e.g., by a
conventional technique). In some embodiments, a knife roll coater
or vacuum slot die coater can be used. A mold release can be used
to aid in removing the particles from the mold if desired. Typical
mold release agents include oils such as peanut oil or mineral oil,
fish oil, silicones, polytetrafluoroethylene, zinc stearate, and
graphite. In general, mold release agent such as peanut oil, in a
liquid, such as water or alcohol, is applied to the surfaces of the
production tooling in contact with the sol-gel such that between
about 0.1 mg/in.sup.2 (0.02 mg/cm.sup.2) to about 3.0 mg/in.sup.2
0.46 mg/cm.sup.2), or between about 0.1 mg/in.sup.2 (0.02
mg/cm.sup.2) to about 5.0 mg/in.sup.2 (0.78 mg/cm.sup.2) of the
mold release agent is present per unit area of the mold when a mold
release is desired. In some embodiments, the top surface of the
mold is coated with the alpha alumina precursor dispersion. The
alpha alumina precursor dispersion can be pumped onto the top
surface.
[0233] Next, a scraper or leveler bar can be used to force the
alpha alumina precursor dispersion fully into the cavity of the
mold. The remaining portion of the alpha alumina precursor
dispersion that does not enter cavity can be removed from top
surface of the mold and recycled. In some embodiments, a small
portion of the alpha alumina precursor dispersion can remain on the
top surface and in other embodiments the top surface is
substantially free of the dispersion. The pressure applied by the
scraper or leveler bar is typically less than 100 psi (0.7 MPa),
less than 50 psi (0.3 MPa), or even less than 10 psi (69 kPa). In
some embodiments, no exposed surface of the alpha alumina precursor
dispersion extends substantially beyond the top surface to ensure
uniformity in thickness of the resulting ceramic shaped abrasive
particles.
[0234] The fourth process step involves removing the volatile
component to dry the dispersion. Desirably, the volatile component
is removed by fast evaporation rates. In some embodiments, removal
of the volatile component by evaporation occurs at temperatures
above the boiling point of the volatile component. An upper limit
to the drying temperature often depends on the material the mold is
made from. For polypropylene tooling the temperature should be less
than the melting point of the plastic. In one embodiment, for a
water dispersion of between about 40 to 50 percent solids and a
polypropylene mold, the drying temperatures can be between about
90.degree. C. to about 165.degree. C., or between about 105.degree.
C. to about 150.degree. C., or between about 105.degree. C. to
about 120.degree. C. Higher temperatures can lead to improved
production speeds but can also lead to degradation of the
polypropylene tooling limiting its useful life as a mold.
[0235] The fifth process step involves removing resultant precursor
ceramic shaped abrasive particles from the mold cavities. The
precursor ceramic shaped abrasive particles can be removed from the
cavities by using the following processes alone or in combination
on the mold: gravity, vibration, ultrasonic vibration, vacuum, or
pressurized air to remove the particles from the mold cavities.
[0236] The precursor abrasive particles can be further dried
outside of the mold. If the alpha alumina precursor dispersion is
dried to the desired level in the mold, this additional drying step
is not necessary. However, in some instances it may be economical
to employ this additional drying step to minimize the time that the
alpha alumina precursor dispersion resides in the mold. Typically,
the precursor ceramic shaped abrasive particles will be dried from
10 to 480 minutes, or from 120 to 400 minutes, at a temperature
from 50.degree. C. to 160.degree. C., or at 120.degree. C. to
150.degree. C.
[0237] The sixth process step involves calcining the precursor
ceramic shaped abrasive particles. During calcining, essentially
all the volatile material is removed, and the various components
that were present in the alpha alumina precursor dispersion are
transformed into metal oxides. The precursor ceramic shaped
abrasive particles are generally heated to a temperature from
400.degree. C. to 800.degree. C., and maintained within this
temperature range until the free water and over 90 percent by
weight of any bound volatile material are removed. In an optional
step, it may be desired to introduce the modifying additive by an
impregnation process. A water-soluble salt can be introduced by
impregnation into the pores of the calcined, precursor ceramic
shaped abrasive particles. Then the precursor ceramic shaped
abrasive particles are pre-fired again. This option is further
described in U.S. Pat. No. 5,164,348 (Wood).
[0238] The seventh process step involves sintering the calcined,
precursor ceramic shaped abrasive particles to form alpha alumina
particles. Prior to sintering, the calcined, precursor ceramic
shaped abrasive particles are not completely densified and thus
lack the desired hardness to be used as ceramic shaped abrasive
particles. Sintering takes place by heating the calcined, precursor
ceramic shaped abrasive particles to a temperature of from
1000.degree. C. to 1650.degree. C. and maintaining them within this
temperature range until substantially all of the alpha alumina
monohydrate (or equivalent) is converted to alpha alumina and the
porosity is reduced to less than 15 percent by volume. The length
of time to which the calcined, precursor ceramic shaped abrasive
particles must be exposed to the sintering temperature to achieve
this level of conversion depends upon various factors but usually
from five seconds to 48 hours is typical.
[0239] In another embodiment, the duration for the sintering step
ranges from one minute to 90 minutes. After sintering, the ceramic
shaped abrasive particles can have a Vickers hardness of 10 GPa, 16
GPa, 18 GPa, 20 GPa, or greater.
[0240] Other steps can be used to modify the described process such
as, for example, rapidly heating the material from the calcining
temperature to the sintering temperature, centrifuging the alpha
alumina precursor dispersion to remove sludge and/or waste.
Moreover, the process can be modified by combining two or more of
the process steps if desired. Conventional process steps that can
be used to modify the process of this disclosure are more fully
described in U.S. Pat. No. 4,314,827 (Leitheiser). More information
concerning methods to make ceramic shaped abrasive particles is
disclosed in US Patent Application Publication No. 2009/0165394 A1
(Culler et al.).
[0241] Methods for making shaped abrasive particles having at least
one sloping sidewall are for example described in US Patent
Application Publication Nos. 2010/0151196 and 2009/0165394. Methods
for making shaped abrasive particles having an opening are for
example described in US Patent Application Publication No.
2010/0151201 and 2009/0165394. Methods for making shaped abrasive
particles having grooves on at least one side are for example
described in US Patent Application Publication No. 2010/0146867.
Methods for making dish-shaped abrasive particles are for example
described in US Patent Application Publication Nos. 2010/0151195
and 2009/0165394. Methods for making shaped abrasive particles with
low Roundness Factor are for example described in US Patent
Application Publication No. 2010/0319269. Methods for making shaped
abrasive particles with at least one fractured surface are for
example described in US Patent Application Publication Nos.
2009/0169816 and 2009/0165394. Methods for making abrasive
particles wherein the second side comprises a vertex (for example,
dual tapered abrasive particles) or a ridge line (for example, roof
shaped particles) are for example described in WO 2011/068714.
[0242] The bonding medium of a bonded abrasive article serves to
retain the shaped abrasive particles (and any optional components,
such as secondary abrasive particles, fillers and additives) in the
abrasive article. According to the present invention, the bonding
medium comprises a vitreous (also referred to as vitrified) bond
phase. In a preferred embodiment, the bonding medium is a vitreous
bond (phase). The vitreous bond serves to retain the shaped
abrasive particles (and any optional secondary abrasive particles
as described herein) in the article. The vitreous bond phase which
binds together the abrasive particles (shaped abrasive particle and
any optional secondary abrasive particles) can be of any suitable
composition.
[0243] The vitreous bond phase, also known in the art as a
"vitrified bond", "vitreous bond", "ceramic bond" or "glass bond",
may be produced from a vitreous bond precursor composition
comprising a mixture or combination of one or more raw materials
that when heated to a high temperature melt and/or fuse to form an
integral vitreous matrix phase. Typical raw materials for forming a
vitreous bond phase can be selected from metal oxides (including
metalloid oxides), non-metal oxides, non-metal compounds, silicates
and naturally occurring and synthetic minerals, and combinations of
one or more of these raw materials.
[0244] Metal oxides can for example be selected from silicon oxide,
aluminium oxide, magnesium oxide, calcium oxide, barium oxide,
lithium oxide, sodium oxide, potassium oxide, iron oxide, titanium
oxide, manganese oxide, zinc oxide, and metal oxides that can be
characterized as pigments such as cobalt oxide, chromium oxide, or
iron oxide, and combinations thereof.
[0245] Non-metal oxides can for example be selected from boron
oxide or phosphorous oxide and combinations thereof.
[0246] Suitable examples for non-metal compounds include boric
acid.
[0247] Silicates can for example be selected from aluminum
silicates, borosilicates, calcium silicates, magnesium silicates,
sodium silicates, magnesium silicates, lithium silicates, and
combinations thereof.
[0248] Minerals can for example be selected from clay, feldspar,
kaolin, wollastonite, borax, quartz, soda ash, limestone, dolomite,
chalk, and combinations thereof.
[0249] In the present invention, the vitreous bond phase may also
be formed from a frit, i.e. a composition that has been prefired
prior to its employment in a vitreous bond precursor composition
for forming the vitreous bond phase of a bonded abrasive article.
As used herein, the term "fit" is a generic term for a material
that is formed by thoroughly blending a mixture comprising one or
more frit forming components, followed by heating (also referred to
as prefixing) the mixture to a temperature at least high enough to
melt it; cooling the glass and pulverizing it. The frit forming
components are usually mixed together as powders, fired to fuse the
mixture and then the fused mixture is cooled. The cooled mixture is
crushed and screened to a fine powder to then be used as a frit
bond. The fineness of the powder is not particularly limited.
Examples of illustrative particle sizes include but are not limited
to particle sizes of .ltoreq.35 .mu.m or .ltoreq.63 .mu.m. It is
this final powder that may be used in a vitreous bond precursor
composition to prepare the vitreous bond of a bonded abrasive
article of the invention, such as a grinding wheel.
[0250] Frits, their sources and compositions are well known in the
art. Frit forming components include materials which have been
previously referred to as raw materials for forming a vitreous
bond. Frits are well known materials and have been used for many
years as enamels for coating, for example, porcelain, metals and
jewellery, but also for vitreous bonds of technical ceramics and
grinding wheels. Frits as well as ceramic bonds for vitrified
bonded abrasive articles are commercially available from suppliers
such as Ferro Corporation, 1000 Lakeside Avenue, Cleveland, Ohio,
USA 44114-7000 and Reimbold & Strick, Cologne, Germany. Frits
for the use in vitrified bonded abrasive articles typically show
melting temperatures in the range of 500 to 1300.degree. C.
[0251] In accordance with the present invention, frits may be used
in addition to the raw materials or in lieu of the raw materials.
Alternatively, the vitreous bond may be derived from a non-frit
containing composition.
[0252] For example, a vitreous bond can be formed from a vitreous
bond precursor composition comprising from more than 0 to 100% by
weight frit, although more typically the composition comprises 3 to
70% frit. The remaining portion of the vitreous bond precursor
composition can be a non-fit material.
[0253] Suitable ranges for vitrified bond compositions can be
specified as follows: 25 to 90% by weight, preferably 35 to 85% by
weight, based on the total weight of the vitreous bond, of
SiO.sub.2; 0 to 40% by weight, preferably 0 to 30% by weight, based
on the total weight of the vitreous bond, of B.sub.2O.sub.3; 0 to
40% by weight, preferably 5 to 30% by weight, based on the total
weight of the vitreous bond, of Al.sub.2O.sub.3; 0 to 5% by weight,
preferably 0 to 3% by weight, based on the total weight of the
vitreous bond, of Fe.sub.2O.sub.3, 0 to 5% by weight, preferably 0
to 3% by weight, based on the total weight of the vitreous bond, of
TiO.sub.2, 0 to 20% by weight, preferably 0 to 10% by weight, based
on the total weight of the vitreous bond, of CaO; 0 to 20% by
weight, preferably 0 to 10% by weight, based on the total weight of
the vitreous bond, of MgO; 0 to 20% by weight, preferably 0 to 10%
by weight, based on the total weight of the vitreous bond, of
K.sub.2O; 0 to 25% by weight, preferably 0 to 15% by weight, based
on the total weight of the vitreous bond, of Na.sub.2O; 0 to 20% by
weight, preferably 0 to 12% by weight, based on the total weight of
the vitreous bond, of Li.sub.2O; 0 to 10% by weight, preferably 0
to 3% by weight, based on the total weight of the vitreous bond, of
ZnO; 0 to 10% by weight, preferably 0 to 3% by weight, based on the
total weight of the vitreous bond, of BaO; and 0 to 5% by weight,
preferably 0 to 3% by weight, based on the total weight of the
vitreous bond, of metallic oxides [e.g. CoO, Cr.sub.2O.sub.3
(pigments)].
[0254] It is known in the art to use various additives in the
making of vitreous bonded abrasive articles both to assist in the
making of the abrasive article and/or improve the performance of
such articles. Such conventional additives which may also be used
in the practice of this invention include but are not limited to
lubricants, fillers, temporary binders and processing aids.
[0255] Organic binders are preferably used as temporary binders.
Typical temporary binders are dextrins, urea resins (including urea
formaldehyde resins), polysaccharides, polyethylene glycol,
polyacrylates, and any other types of glue etc. These binders may
also include a liquid component, such as water or polyethylene
glycol, viscosity or pH modifiers and mixing aids. The use of
temporary binders may improve homogeneity and the structural
quality of the pre-fired or green pressed body as well as of the
fired article. Because the binders are burned out during firing,
they do not become part of the finished bond or abrasive
article.
[0256] Bonded abrasive articles according to the present invention
can be made according to any suitable method. Procedures and
conditions well known in the art for producing vitrified bonded
abrasive articles (e.g., grinding wheels) and especially procedures
and conditions for producing vitreous bonded sol-gel alumina-based
abrasive articles may be used to make the abrasive article of this
invention. These procedures may employ conventional and well known
equipment in the art.
[0257] An exemplary method for manufacturing a bonded abrasive
article of the invention comprises the steps of: [0258] (a)
providing a precursor composition comprising shaped abrasive
particles in accordance with the present invention and a vitreous
bond precursor composition and optionally one or more components
selected from a temporary binder composition (including for example
one or more components selected from one or more temporary
binder(s) and pore inducing agent(s)) and secondary abrasive
particles; [0259] (b) forming the precursor composition to a
desired shape so as to obtain a green structure; [0260] (c)
optionally, drying the green structure; [0261] (d) firing the green
structure obtained in step (b) or (c) at temperatures suitable to
produce a vitreous bond (for example at temperatures selected from
about 700.degree. C. to about 1500.degree. C.) so as to obtain a
vitrified bonded abrasive article having a first shape (for example
a straight wheel shape, e.g., T1 type); [0262] (e) optionally,
further altering the first shape in one or more shape features (for
example bore, diameter, thickness, face profile) so as to obtain a
bonded abrasive article having a second shape (for example a shape
resulting from customer needs).
[0263] For example, during manufacture of a vitrified bonded
abrasive article, the vitreous bond precursor composition, in a
powder form, may be mixed with a temporary binder (typically an
organic binder) which does not form part of the fired vitrified
bonding medium. Bonded abrasive articles are typically prepared by
forming a green structure comprised of abrasive grain, the vitreous
bond precursor composition, and optionally, a temporary binder and
other optional additives and fillers. Forming can for example be
accomplished by molding with or without pressing. Typical forming
pressures can vary within wide ranges and may be selected from
pressures ranging from 0 to 400 kg/cm.sup.2, depending on the
composition of the green structure. The green structure is then
fired. The vitreous bond phase is usually produced in the firing
step, typically at a temperature(s) in the range from about
700.degree. C. to about 1500.degree. C., preferably in the range
from about 750.degree. C. to about 1350.degree. C. and most
preferably in the range from about 800.degree. C. to about
1300.degree. C. Good results may be also obtained at temperatures
of about 1000.degree. C. or less, or from about 1100 to about
1200.degree. C. The actual temperature at which the vitreous bond
phase is formed depends, for example, on the particular bond
chemistry. Firing of the vitreous bond precursor composition is
typically accomplished by raising the temperature from room
temperature to the maximum temperature over a prolonged period of
time (e.g., about 10-130 hours), holding at the maximum
temperature, e.g., for 1-20 hours, and then cooling the fired
article to room temperature over an extended period of time, e.g.,
10-140 hours. It should be understood that the temperature selected
for the firing step and the composition of the vitreous bond phase
must be chosen so as to not have a detrimental effect on the
physical properties and/or composition of the abrasive particles
(shaped and optional secondary particles) contained in the abrasive
article.
[0264] A bonded abrasive article according to the present invention
comprises shaped abrasive particles (as defined in accordance with
the present invention) and a bonding medium comprising a vitreous
bond. In addition, the bonded abrasive article may comprise one or
more optional components selected from secondary abrasive
particles, fillers and additives.
[0265] The amounts of abrasive particles (which may be comprised in
a blend including one or more secondary abrasive particles) may
vary widely and can range for example from 10 to 80%, more
preferably from 25 to 60% by volume.
[0266] While the invention has a most pronounced effect when the
abrasive fraction (or blend) includes 100% by weight of shaped
abrasive particles in accordance with the present invention based
on the total weight of abrasive particles present in the abrasive
fraction (or blend), it is also effective when the article contains
for example as little as 5% by weight of shaped abrasive particles
in accordance with the present invention and up to 95% by weight of
secondary abrasive particles, based on the total weight of abrasive
particles present in the abrasive fraction. Hence, the abrasive
article can contain a total amount of abrasive particles of up to
100% by weight of the abrasive particles according to this
invention, based on the total weight of abrasive particles. In some
embodiments, the bonded abrasive article can include from about 5
to 100, preferably 10 to 80 percent by weight of shaped abrasive
particles; typically 20 to 60 percent by weight, and more typically
30 to 50 percent by weight, based on the total weight of abrasive
particles. In some grinding applications the addition of a
secondary abrasive particle is for the purpose of reducing the cost
of the abrasive article by reducing the amount of premium priced
shaped abrasive particles. In other applications a mixture with a
secondary abrasive particle may have a synergistic effect.
[0267] The amount of bonding medium may also vary widely and can
range for example from 1 to 60% by volume, more preferably 2.5 to
40% by volume.
[0268] Optionally, the bonded abrasive article can comprise
porosity. Bonded abrasive articles containing porosity have an open
structure (interlinked or interconnected porosity) which can
provide chip clearance for high material removal, transport more
coolant into the contact area while decreasing friction, and
optimizes the self-sharpening process. Porosity enables the bonded
abrasive article to shed used or worn abrasive particles to expose
new cutting edges or fresh abrasive particles.
[0269] Bonded abrasive articles according to the present invention
can have any useful range of porosity; such as from about 5 to
about 80% by volume, preferably from about 20 to about 70% by
volume.
[0270] Preferably, the bonded abrasive article according to the
present invention contains porosity. The porosity can be formed by
the natural spacing provided by the packing density of the
materials comprised in the bonded abrasive articles and by pore
inducing components, as known in the art, or by both.
[0271] Pore inducing components can be selected from temporary
components (i.e. components not present in the final article)
non-temporary components (i.e. (components present in the final
article) and combinations thereof. Preferred pore inducing
components should not leave any chemical traces in a finished
abrasive article (i.e. be temporary components), do not expand upon
removal, mix well with the abrasive particles and can provide the
desired type (e.g. interconnected) and extent of porosity. Pore
inducing components are typically used in amounts ranging from 0-40
Vol.-% of the total article. Typical non-temporary pore inducing
components may be selected from materials such as hollow spheres
made of materials such as glass, ceramic (aluminium oxide) and
glass particles. Typical temporary pore inducing components may be
selected from materials such as polymeric materials (including
foamed polymeric materials) cork, ground walnut shells, wood
particles, organic compounds (such as naphthalene or
paradichlorbenzene) and combinations thereof. In a preferred
embodiment, the abrasive article contains porosity induced by using
naphthalene (as a temporary pore inducing component).
[0272] Bonded abrasive articles according to the present invention
may contain additional components such as, for example, fillers and
additives, as is known in the art. Examples of optional additives
contained in the bonded abrasive article include non-temporary pore
inducing agents, as described in the foregoing, and any components
used when making the vitreous bond, including but not limited to
lubricants, fillers, temporary binders and processing aids.
[0273] Bonded abrasive articles in accordance with the present
invention have a three-dimensional shape, which is not particularly
limited. Typically, the shape of a bonded abrasive article
according to the invention is selected depending on factors such as
the intended grinding application (including grinding method,
grinding conditions and workpiece) as well as customer needs.
[0274] By way of exemplification, International Standard ISO
603:1999 lists suitable shapes of bonded abrasive articles all of
which are useful in the present invention. Standard types according
to standards of FEPA (Federation of European Producers of
Abrasives) or other standards as well as non-standard types can
also be used.
[0275] By way of illustration, typical shapes can for example
include but are not limited to the shape of a wheel, honing stone,
grinding segment, mounted point or other types according to
standard forms of FEPA or ISO 603:1999 and other standards as well
as non-standard individual types.
[0276] A preferred bonded abrasive article is a vitrified bonded
abrasive wheel, in particular, a vitrified bonded grinding
wheel.
[0277] The diameter of abrasive wheels in accordance with the
present invention is not particularly limited and can for example
be selected to range from 1 ram to 2000 mm, or from 10 mm to 1200
mm or from 100 mm to 750 mm, although other dimensions may also be
used. Likewise, the thickness of abrasive (grinding) wheels is not
particularly limited. For example, the thickness can typically be
selected to range from 2 to 600 mm, or from 5 to 350 mm, or from 10
mm to 300 mm, although other dimensions may also be used. For
example, a bore diameter may range from 0 mm to 800 mm, more
typically from 4 mm to 400 or from 8 mm to 350 mm.
[0278] The particular design of the abrasive article (preferably
grinding wheel) is not limited and can be selected from
"monolithic" designs and "zonal" design (such as segmented and
layered designs). Both designs can include the reinforcement of the
bore by using glues such as thermosetting resins, for example
resins selected from epoxy resins, polycondensates, and phenolic
resins.
[0279] The abrasive particles (i.e. one or more type of shaped
abrasive particles and optionally one or more types of secondary
abrasive particles) may be homogeneously or non-homogeneously
distributed in the abrasive article, for example be distributed or
concentrated in selected areas, layers, segments or portions of the
abrasive article. Homogeneous or non-homogeneous distribution may
be either as a homogeneous blend or in a way that different types
of abrasive particles are located and distributed only in selected
areas, layers, segments or portions of the abrasive article.
[0280] For example, a bonded abrasive wheel, may comprise at least
two distinct sections, including an outer zone (also often referred
to as rim or periphery) and an inner zone (also often referred to
as core or center portion). The distinct sections may be provided
based on differences in one or more aspects selected from the
composition of the bond (for example the type of bonding material
or the amount of porosity present), the shape of abrasive particles
(for example shaped versus crushed or first shape versus second
shape), the grit size of abrasive particle (for example, finer
versus coarser) and the amount of abrasive particles (for example
presence or absence of abrasive particles or first (for example
high) amount versus second (for example low) amount).
[0281] In some embodiments the outer zone comprises shaped abrasive
particles according to the present invention whereas the inner zone
does not.
[0282] In other embodiments, the inner zone comprises shaped
abrasive particles according to the present invention whereas the
outer zone does not.
[0283] An abrasive wheel may also contain an inner zone made of a
non-vitreous bonding material (such as plastics etc.).
[0284] If the bonded abrasive article is an abrasive wheel, such as
a grinding wheel, the abrasive particles may be concentrated
towards the middle, or only in the outer zone, i.e., the periphery,
of the wheel. The center portion may contain a different (higher or
lower) amount of abrasive particles.
[0285] Another example for a zonal design is an abrasive wheel,
such as a grinding wheel, having a rim containing shaped abrasive
particles in accordance with the present invention and an inner
zone optionally containing and preferably not containing shaped
abrasive particles in accordance with the present invention. The
inner zone of this design may optionally contain secondary abrasive
particles (e.g, fused alumina, sintered alumina) that may have the
same or different grit size. This design is also referred to as
special centre design which is intended to minimize the grinding
wheel costs due to the lack of shaped abrasive particles and at the
same time to increase the bursting speed.
[0286] In another variation, an abrasive wheel may include two or
more types of abrasive particles positioned on different sides of
the abrasive wheel. For example, first abrasive particles may be on
one side of the wheel with different abrasive particles on the
opposite side. Either the first or the second abrasive particles or
both are selected from shaped abrasive particles in accordance with
the present invention. However, typically all the abrasive
particles are homogenously distributed among each other, because
the manufacture of the wheels is easier, and the grinding effect is
optimized when the abrasive particles or the two or more types
thereof are closely positioned to each other.
[0287] In one embodiment, abrasive particles according to the
present invention are homogeneously distributed throughout the
bonded abrasive article.
[0288] The present invention also relates to a method for abrading
a workpiece, the method comprising frictionally contacting at least
a portion of an abrasive article in accordance with the invention
with a surface of a workpiece; and moving (for example rotating) at
least one of the workpiece or the abrasive article to abrade at
least a portion of the surface of the workpiece.
[0289] The bonded abrasive articles of this invention can be
advantageously used in a wide range of grinding applications.
[0290] Beneficial effects may be in particular achieved in grinding
applications which involve high material removal rates, in
particular grinding applications selected from roughing and
semi-roughing operations, i.e. applications typically involving
high material removal rates.
[0291] The present invention is however not limited to grinding
applications which involve high material removal rates but may also
be beneficially used in grinding applications which do not involve
high material removal rates, such as finishing operations.
[0292] Hence, the bonded abrasive articles of this invention can be
suitably used in a wide range of grinding applications ranging from
roughing operations via semi-roughing to finishing operations.
[0293] Exemplary grinding applications include but are not limited
to standardized and non-standardized grinding applications, for
example methods according to DIN-8589:2003.
[0294] The bonded abrasive articles of this invention are
particularly suitable for applications including but not limited to
cylindrical grinding (outer diameter or OD grinding as well as
internal diameter or ID grinding), centerless grinding, gear
grinding, generating gear grinding, surface and profile grinding,
reciprocating grinding, creep-feed grinding, grinding in generating
method as well as by other methods of gears, threads, tools,
camshafts, crankshafts, bearings, guard rails, etc. Cut-off
operations are less preferred but included within the scope of the
present invention. Preferred applications include gear grinding,
creep-feed grinding, surface grinding, profile grinding,
reciprocating grinding, grinding in generating method, cylindrical
grinding (OD and ID grinding) and centerless grinding, and
particularly preferred applications include cylindrical grinding
applications, gear grinding applications, surface grinding
applications and particularly creep-feed-grinding applications. The
applied force during abrading is not particularly limited and can
be selected on the basis of the grinding application.
[0295] During use, the bonded abrasive article can be used dry or
wet. During wet grinding, the bonded abrasive article is typically
used in conjunction with a grinding fluid which may for example
contain water or commercially available lubricants (also referred
to as coolants). During wet grinding lubricants are commonly used
to cool the workpiece and wheel, lubricate the interface, remove
swarf (chips), and clean the wheel. The lubricant is typically
applied directly to the grinding area to ensure that the fluid is
not carried away by the grinding wheel. The type of lubrication
used depends on the workpiece material and can be selected as is
known in the art.
[0296] Common lubricants can be classified based on their ability
to mix with water. A first class suitable for use in the present
invention includes oils, such as mineral oils (typically petroleum
based oils) and plant oils. A second class suitably for use in the
present invention includes emulsions of lubricants (for example
mineral oil based lubricants; plant oil based lubricants and
semi-synthetic lubricants) and solutions of lubricants (typically
semi-synthetic and synthetic lubricants) with water.
[0297] Abrasive articles in accordance with the present invention
can be used on any grinding machine specific for the grinding
method The grinding machine can be electrically, hydraulically or
pneumatically driven, at any suitable speed, generally at speeds
from about 10 to 250 m/s.
[0298] Bonded abrasive articles according to the present invention
are useful, for example, for abrading a workpiece. The bonded
abrasive article can be particularly suitable for use on workpieces
made of metal, such as steel (including powder metallurgical steel
and steel alloys, carbon steels, mild steels, tool steels,
stainless steel, hardened steel, ball bearing steel, cold working
steel, cast iron), non-ferrous metals and alloys (such as aluminum,
titanium, bronze, etc.), hard metals (such as tungsten carbide,
titanium carbide, titanium nitride, cenimets, etc), ceramics
(technical ceramics such as oxide ceramics, silicate ceramics,
non-oxide ceramics), and glasses. The use of the bonded abrasive
articles is however not restricted to the use on these exemplified
workpiece materials.
[0299] Preferred grinding methods according to the present
invention include but are not limited to cylindrical grinding
applications, gear grinding applications and surface grinding
applications including creep feed grinding applications.
Gear Grinding
[0300] The term gear grinding as used in the present invention
generally refers to a method of generative grinding and profile
grinding of gears. Gear wheels determine the transmission ratios of
gearboxes; according to the second fundamental law of gearing, this
ratio will only remain constant if the next tooth is already
engaged before the previous tooth disengages. The more perfectly
ground the surface of the tooth flanks, the better is the form fit,
and the more smoothly and quietly the gearbox runs. The process of
machining the tooth flanks brings with it tough demands in terms of
dimensional accuracy and shape accuracy--and also places tough
demands particularly on the edge zone properties of the component.
Whereas very slight deviations in terms of the macro and
micro-geometry--which influence the amount and type of noise
generated by the teeth--may be tolerable within strict limits
depending on the quality requirements, a "zero tolerance" policy
applies to the edge zone of the tooth flank. Damage to the edge
zone as a result of influence on the structure will contribute to
faster wear of the teeth and can, in extreme cases, cause the tooth
to fracture and break off. In the context of these requirements,
different techniques may be useful all of which are included within
the scope of the present invention.
[0301] Exemplary gear grinding techniques include: [0302] Gear
grinding with the continuous generative grinding technique using
grinding worms: The bonded abrasive article (typically a grinding
wheel) has a shape that corresponds to a grinding worm, the basic
tooth profile of which should always be seen as a rack profile. The
involute form is generated through continuous generative grinding
of the grinding worm and the gearing). The process lends itself
very well to the series production of gear wheels. [0303] Gear
grinding with globoidal grinding worms (continuous profile
grinding): unlike the continuous generative grinding technique, the
shape of the bonded abrasive article in this case does not
correspond to a grinding worm with a rack profile as the basic
tooth profile. Instead, a globoidal grinding worm maps the contour
of the tooth flank. During the grinding process the tooth form is
produced through virtually linear engagement of the tool in the
tooth gap. This method is predestined for grinding bevel gears
which are used primarily in differential gears and can optionally
be combined with a subsequent honing step. [0304] Single flank
generating grinding: The involute shape is produced in a generative
grinding process in which the grinding wheel only machines a single
flank in the direction of grinding per tooth gap. This method
allows the machining of different moduli with an unchanged wheel
width and allows different infeeds for the left or right-hand tooth
flank. [0305] Form or profile grinding with radial infeed: The
involute form is transferred to the bonded abrasive article (most
typically a grinding wheel), which then generates the form in the
tooth gap of the workpiece. [0306] Form or profile grinding with
rotative infeed: The involute form is transferred to the bonded
abrasive article (typically a grinding wheel), which then generates
the form in the tooth gap of the workpiece.
[0307] Bonded abrasive articles for use in the gear grinding
applications are not particularly limited and as described in the
foregoing. In preferred embodiments, the bonded abrasive articles
for use in gear grinding applications may be characterized by a
particle shape selected from flat triangles or flat rectangles
wherein optionally at least one face is shaped inwardly, as
described in the foregoing with respect to particularly preferred
particle shapes.
Creep-Feed Grinding
[0308] Creep-feed grinding can be considered as a specific case of
surface grinding. However, in contrast to surface grinding with a
reciprocating linear cutting motion, creep-feed grinding uses
relatively large cutting depths but comparatively low feed rates.
The total grinding allowance is generally achieved in a few passes.
With creep-feed grinding, a distinction is made between surface
grinding and cylindrical grinding operations. One special form of
creep-feed grinding is outside-diameter longitudinal grinding (peel
grinding).
[0309] Creep-feed grinding typically uses rotating dressing devices
and is typically operated wet. With creep-feed grinding, the
workpiece form can be produced with large infeeds of up to 15 mm in
a single grinding pass. As with increasing infeed the length of
contact between the workpiece and the bonded abrasive article
increases significantly, the processes of transporting the grinding
fluid and carrying away the grinding detritus is made more
difficult. As a result, creep-feed grinding requires open-pored
abrasive articles with a low hardness and a continuous supply of
grinding fluid in large quantities. This method is particularly
well suited to the final cutting of high-precision profiles like
guideways and clamping profiles of turbine vanes.
[0310] Bonded abrasive articles for use in creep-feed grinding
applications are not particularly limited and as described in the
foregoing. In preferred embodiments, the bonded abrasive articles
for use in creep-feed grinding applications may be characterized by
a particle shape selected from flat triangles or flat rectangles
wherein optionally at least one face is shaped inwardly, as
described in the foregoing with respect to particularly preferred
particle shapes.
Surface Grinding (Except Creep-Feed Grinding)
[0311] Surface grinding or face grinding techniques are commonly
divided into peripheral-longitudinal surface grinding (surface
grinding, face grinding of large surfaces) and
peripheral-transverse surface grinding (flute grinding, profile
grinding).
[0312] In the case of peripheral-longitudinal grinding, the
grinding wheel engages at right angles and advances by the selected
feed increment into the workpiece, which is moved by the machine
table. In the process, the infeed and feed rate define the grinding
result.
[0313] Peripheral-transverse surface grinding is ideally suited to
producing large, flat surfaces. With this method, the bonded
abrasive article is also positioned at right angles to the
workpiece, but it is fed in by the amount which exactly corresponds
to the width of the bonded abrasive article. Both methods can be
used for reciprocating grinding and creep-feed grinding.
[0314] With reciprocating grinding, the bonded abrasive article
moves over the workpiece "backwards and forwards" at right angles
to the reference edge--the resulting motion is described as being
"reciprocating". This method is seen as the oldest variant of
surface grinding and is characterised by low cutting depths (for
example as low as 0.005 to 0.2 mm) and high table speeds (for
example ranging from 15 to 30 m/min). The technique is particularly
useful for materials which are easy to grind, small batch sizes and
low amounts of material removal, as well in cases of relatively low
machine investment.
[0315] Bonded abrasive articles for use in surface grinding
applications are not particularly limited and as described in the
foregoing. In preferred embodiments, the bonded abrasive articles
for use in surface grinding applications may be characterized by a
particle shape selected from flat triangles or flat rectangles
wherein optionally at least one face is shaped inwardly, as
described in the foregoing with respect to particularly preferred
particle shapes
Cylindrical Grinding
[0316] Cylindrical grinding is a grinding technique which is
commonly characterized by having one or more and preferably all of
the following four features:
(1) The workpiece is constantly rotating; (2) The grinding wheel is
constantly rotating; (3) The grinding wheel is fed towards and away
from the work; (4) Either the work or the grinding wheel is
traversed with the respect to the other.
[0317] While the majority of cylindrical grinding applications
employ all four movements, there are applications that only employ
three of the four actions. Three main types of cylindrical grinding
are outside diameter (OD) grinding, inside diameter (ID) grinding,
and centerless grinding and any one of these techniques can be
suitably used in the present invention: [0318] Outside diameter
(OD) grinding is one of the most frequently used grinding
techniques--for example in the automotive industry, where it is
used in the grinding of camshafts and crankshafts. During the
course of industrial development and in response to the
requirements which have emerged as a result, outside diameter
grinding has been divided into different variants of the technique
which differ depending on the way in which the workpiece is mounted
and according to the principle feed direction. [0319]
Peripheral-transverse outer diameter (OD) grinding between centers
(also known as plunge grinding) [0320] Centerless
peripheral-transverse outer diameter (OD) grinding [0321]
Peripheral-longitudinal outer diameter (OD) grinding between
centers (also known as throughfeed grinding) [0322] Centerless
peripheral-longitudinal outer diameter (OD) grinding
[0323] In processes of grinding between centers, the workpiece is
clamped firmly between two centers in centering fixtures on its end
faces, and in this position the workpiece is driven by the grinding
machine. Depending on the principle feed direction of the
wheel--right-angled plunge feed or parallel movement along the
workpiece--this is referred to as transverse or longitudinal
grinding. [0324] In the process of peripheral-transverse outer
diameter grinding, the grinding wheel is generally at right angles
to the workpiece. This technique is generally used to machine
bearing seats, shoulders and grooves using straight plunge
grinding. Often the cut-in is divided into several process steps
which are performed in sequence with ever decreasing chip removal
rates. Depending on the particular task and the size of the batch,
angle plunge grinding is another variant which may be more
productive. [0325] The process of peripheral-longitudinal outer
diameter grinding is particularly suitable for applications
requiring cylindrical or conical workpieces which are significantly
longer than the width of the grinding wheel. Examples include but
are not limited to the machining of press cylinders and rollers for
paper production, as well as rollers for use in rolling mills in
the steel industry. In this technique the grinding wheel moves
parallel to the workpiece and is fed in at the reversal point at
right angles to the workpiece. The required finished dimension can
either be attained in several passes or in just a single pass--the
latter being referred to as peel grinding. These methods are
comparable to creep-feed grinding and reciprocating grinding. In
the automotive industry, peel grinding is used for example in the
production of drive shafts. [0326] Centerless grinding: If the
challenge is to machine large quantities of long and/or thin, round
components made of pliable or brittle materials, centerless
grinding might be the solution. In addition, centerless grinding is
a technique which can allow multiple tasks--e.g. roughing and
finishing--to be performed in a single pass. The machining process
itself corresponds to the other cylindrical grinding techniques
like the ones previously mentioned with respect to "Outside
diameter grinding"--even without centers the process still involves
plunge grinding and through feeding techniques. [0327] Internal
diameter (ID) grinding provides perfect functional surfaces in
components which need to establish a non-positive connection with
an axle or shaft. Similarly to outer diameter (OD) grinding, this
method is split into two different techniques according to the
direction of grinding: [0328] Peripheral-transverse internal
diameter (ID) grinding (plunge grinding) [0329]
Peripheral-longitudinal internal diameter (ID) grinding [0330] In
terms of the behaviour of the grinding wheel and the workpiece,
both techniques display virtually identical properties to outer
diameter (OD) grinding between centres. Application examples where
ID grinding is commonly used include but are not limited to the
refining of bores with a high-precision fit; for the machining of
hard and super-hard materials, to machine different diameters in a
single pass as well as to produce tapered fits and in situations
where the grinding wheel needs to be narrower than the surface
which is to be machined and a combination of longitudinal and
plunge grinding is required. In typical cases the grinding wheel
diameter should not exceed 2/3 or a maximum of 4/5 of the bore
diameter.
[0331] Bonded abrasive articles for use in cylindrical grinding
applications are not particularly limited and as described in the
foregoing. In preferred embodiments, the bonded abrasive articles
for use in cylindrical grinding applications may be characterized
by a particle shape selected from flat triangles or flat rectangles
wherein optionally at least one face is shaped inwardly, as
described in the foregoing with respect to particularly preferred
particle shapes.
[0332] Surprisingly, bonded abrasive articles in accordance with
the present invention have been found to provide excellent results
in a wide range of grinding applications and in particular in high
performance grinding applications.
[0333] For the purposes of the present invention, the term high
performance grinding application is intended to refer to higher
material removal rates than is commonly possible with present day
conventional abrasives. Conventional abrasives encompass all types
of aluminium oxide including so-called ceramic abrasives, and
silicon carbide.
[0334] High performance grinding can be established for a specific
grinding application based on the knowledge of sound grinding
engineering and adequate modern CNC (Computerized Numerical
Control) machinery. One parameter to define high performance
grinding could be the specific material removal rate Q'.sub.W also
called Q-prime. Q'.sub.W indicates how many mm.sup.3 of workpiece
material one mm wheel width removes per second (mm.sup.3/mm/sec).
Q'.sub.w can be calculated based on two parameters, namely the
depth of cut a.sub.e and the feed rate v.sub.w, according to the
formula Q'.sub.W=[a.sub.e.times.v.sub.w]/60. The specific material
removal rate Q'.sub.w can be increased by increasing the feed rate
v.sub.W and/or the depth of cut a.sub.e. [The peripheral speed
v.sub.c does not have an influence on Q'.sub.w]. Values for
Q'.sub.w are typically indicated by using the unit mm.sup.3/mm/s or
mm.sup.3/(mms).
[0335] Typical ranges for Q'.sub.W for exemplary high performance
grinding applications can be specified as follows: Inner diameter
(ID-) grinding 1-15, preferably 2-12, most preferably 4-11
mm.sup.3/mm/s; outer diameter (OD-) grinding 1.5-25, preferably
3-22, most preferably 4-20 mm.sup.3/mm/s; surface grinding 1.5-20,
preferably 2-17, most preferably 4-19 mm.sup.3/mm/s; profile
grinding 3-60, for example 3-50, preferably 5-45, most preferably
7-50 or 7-40 mm.sup.3/mm/s; profile grinding with generating method
8-60, preferably 10-55, most preferably 14-50 mm.sup.3/mm/s;
creep-feed grinding 4-100, preferably 6-90, most preferably 9-80
mm.sup.3/mm/s; and camshaft grinding 8-100, preferably 12-95, most
preferably 1.5-90 mm.sup.3/mm/s.
[0336] While the values mentioned above refer to roughing and
semi-roughing operations, in finishing operations the Q'.sub.W
values may be <1 mm.sup.3/mm/s.
[0337] Bonded abrasive articles of the present invention have been
found to provide constant grinding results over a long period of
time and particularly under severe grinding conditions (for example
at high specific material removal rates).
[0338] In addition, bonded abrasive articles in accordance with the
present invention can provide a better surface finish (decreased
surface roughness R.sub.a) on the workpiece used in a wide range of
grinding applications ranging from roughing via semi-roughing to
finishing operations. In some instances, bonded abrasive articles
incorporating a coarser particle size of shaped abrasive particles
may surprisingly provide better surface quality as compared to a
finer particle size.
[0339] During use the bonded abrasive articles can also ensure a
reduced risk of damaging the workpiece (such as by workpiece
burning or discoloration) while at the same time minimizing the
clogging of the bonded abrasive article during use.
[0340] Bonded abrasive articles of the present invention are
characterized by long dressing cycles thus allowing more workpiece
parts to be finalized between dressing cycles as well as a long
total serve life of the bonded abrasive article.
[0341] Due to the high material removal rates which can be realized
using bonded abrasive articles of the present invention, shorter
grinding times can be accomplished contributing to a higher
workpiece flow in overall.
[0342] Another parameter which is often used to characterize the
performance of a grinding application is the specific chip volume
V'.sub.w. V'.sub.w indicates the total amount of workpiece material
[mm.sup.3] that is removed in a grinding application before
dressing has to be set up (i.e. during one grinding cycle). The
time after which dressing has to be set up (i.e., the end of the
grinding cycle) can be easily recognized by a person skilled in the
art of grinding. By way of example, the end of a grinding cycle is
typically indicated by a somewhat prominent drop in the power drawn
by the grinding machine. Other factors which can be used as
additional or alternative indicators for recognizing the end of a
grinding cycle include but are not limited to the loss of the form
and profile holding of the bonded abrasive article, decrease of
workpiece quality, for example burning or discoloration of the
workpiece, or worse surface finish indicated by an increased
surface roughness Ra.
[0343] At the end of a grinding cycle, the specific chip volume can
be easily calculated by a skilled person, as is known in the art.
For the purpose of determining the specific chip volume, the actual
start of grinding is taken as the starting point of the grinding
cycle. For evaluating the performance of a specific grinding
application, the specific material removal rate Q'.sub.w is
typically set constant and the performance of the grinding
application is evaluated with respect to the specific chip volume
V'.sub.w.
[0344] In practice, the specific chip volume is commonly based on
the effective width of the active abrasive article's profile used
in the grinding application (i.e. the specific chip volume
indicates the total volume of workpiece material removed per 1 mm
of width of the bonded abrasive article, for example 1 mm wheel
width during one grinding cycle).
[0345] Bonded abrasive articles in accordance with the present
invention have surprisingly been found to provide excellent results
with respect to the specific chip volume V'.sub.w, in particular in
applications such as gear grinding, thus for example leading into
higher set limits for redressing. It is to be emphasized that such
excellent results with respect to the chip volume surprisingly can
also be achieved at high material removal rates i.e., when using a
high constant value of Q'.sub.w during the grinding cycle, for
example when using gear grinding (such as single rib ear grinding)
with a specific material removal rate Q'.sub.w of at least 5
mm.sup.3/mm/s, typically of at least 10 mm.sup.3/mm/s, more
typically of at least 14 mm.sup.3/mm/s or at least 16 mm.sup.3/mm/s
and even more typically of at least 20 mm.sup.3/mm/s, preferably of
at least 25 mm.sup.3/mm/s and more preferably of at least 30
mm.sup.3/mm/s. Typically, abrasive articles based on conventional
abrasive particles show lower specific chip volumes at a higher
specific material removal rate Q'.sub.w as compared to the same
grinding application at a lower specific material removal rate
Q'.sub.w and typically show adverse effects with respect to the
workpiece such as burning or discoloration when used at higher
specific material removal rates. Even under these severe grinding
conditions no workpiece burning or discoloration was observed when
using bonded abrasive articles in accordance with the present
invention.
[0346] While in particular grinding applications such as gear
grinding applications have been found to provide such excellent
results with respect to the specific chip volume, other grinding
applications are expected to provide similar pronounced
effects.
[0347] Bonded abrasive articles in accordance with the present
invention incorporating shaped abrasive particles as defined herein
can provide specific chip volumes that are substantially higher
than those commonly achieved with present day conventional
abrasives (as defined with respect to high performance grinding
applications). In other words, using a given set of grinding
conditions [given workpiece, given grinding application at constant
Q'.sub.w; for example 17CrNiMo6, gear grinding at a constant
specific material removal rate Q'.sub.W of 14 mm.sup.3/mm/s (or
even with a specific material removal rate Q'.sub.W as high as 30
mm.sup.3/mm/s)], a bonded abrasive article in accordance with the
present invention typically provides a specific chip volume that is
at least 20% higher, more typically at least 50%, higher, even more
typically at least 100% higher, even more typically at least 200%
higher and most typically at least 300% higher than the specific
chip volume achieved when using a comparable bonded abrasive
article using the same set of grinding conditions (in particular
the same specific material removal rate Q'.sub.W).
[0348] A person skilled in the art of grinding can easily ascertain
an appropriate comparable bonded abrasive article. A bonded
abrasive article suitable for use as a comparable bonded abrasive
article can for example be based on the same abrasive material but
with the only difference that the abrasive particles are not
shaped. For example, the same bonded abrasive article but wherein
the shaped abrasive particles according to the invention are
replaced with the same nominal size and weight of crushed abrasive
particles having the same chemical composition could be used as a
comparable bonded abrasive article. A comparable bonded abrasive
article should also contain the same nominal size(s) and weight(s)
of any optional secondary abrasive particles having the same
chemical composition(s) as used in the bonded abrasive article to
be evaluated. Hence, the shaped abrasive particles as defined
herein contained in the bonded abrasive article to be evaluated
preferably represent the only difference to the comparable bonded
abrasive article used when evaluating the specific chip volume
V'.sub.w. That means that the same type (particularly with respect
to the chemical composition) and volume amount of bonding medium
(and optionally the same volume amount of porosity, if any) is
preferably used for the bonded abrasive article to be evaluated and
the comparable bonded abrasive article.
[0349] By way of illustration, specific chip volumes as achievable
in the present invention are typically higher by factor 2, or 5, or
10, or 15 and even 20 than what is commonly achieved with a
comparable bonded abrasive article based on such present day
conventional abrasives.
[0350] For example, using a bonded abrasive article of the present
invention, a grinding application [such as gear grinding
(particularly single rib gear grinding) a workpiece made of for
example 17CrNiMo6 with a specific material removal rate Q'.sub.w of
for example 14 mm.sup.3/mm/s] can easily provide specific chip
volumes of at least 850 mm.sup.3/mm, particularly of at least 1500
mm.sup.3/mm greater, more particularly of at least 2500
mm.sup.3/mm, even more particularly of at least 10000 mm.sup.3/mm
and even more particularly of 15 000 mm.sup.3/mm or greater or of
even 30 000 mm.sup.3/mm or greater.
[0351] The present invention thus also relates to a method of
grinding (in particular, a method of gear grinding, more
particularly single rib gear grinding) characterized by using a
bonded abrasive article according to the present invention, wherein
the specific chip volume V'.sub.w is at least 20% higher,
preferably at least 50% higher, more typically at least 100%
higher, even more typically at least 200% higher and most typically
at least 300% higher than the specific chip volume achieved when
using a comparable bonded abrasive article under the same set of
grinding conditions, in particular at the same specific material
removal rate Q'.sub.w.
[0352] The present invention also relates to a method of grinding
(in particular, a method of single rib gear grinding at a specific
material removal rate of Q'.sub.w of 14) characterized by using a
bonded abrasive article according to the present invention, wherein
the specific chip volume is at least 850 mm.sup.3/mm, particularly
at least 1 500 mm.sup.3/mm greater, preferably at least 2 500
mm.sup.3/mm, more preferably at least 10 000 mm.sup.3/mm and even
more preferably 15 000 mm.sup.3/mm or greater or at least 30 000
mm.sup.3/mm or greater. In other preferred embodiments, the present
invention relates to a method of grinding (in particular, a method
of single rib gear grinding at a specific material removal rate of
Q'.sub.w of 16) characterized by using a bonded abrasive article
according to the present invention, wherein the specific chip
volume is at least 850 mm.sup.3/mm, particularly at least 1 500
mm.sup.3/mm greater, preferably at least 2500 mm.sup.3/mm, more
preferably at least 10 000 mm.sup.3/mm and even more preferably 15
000 mm.sup.3/mm or greater or at least 30 000 mm.sup.3/mm or
greater, and in other preferred embodiments is more than 10 000
mm.sup.3/mm, preferably at least 11 000, even more preferably 15
000 mm.sup.3/mm or greater and most preferably 30 000 mm.sup.3/mm
or greater.
[0353] Other effects achieved in the present invention are high
form or profile holding of the bonded abrasive article. This
translates into less dressing, and therefore better process and
tool consumption economics.
[0354] The use of shaped abrasive particles (such as flat triangles
and flat rectangles as described herein, optionally having one or
more faces shaped inwardly), in vitrified bonded abrasive articles
allows these beneficial effects to be achieved for a wide range of
different compositions of the bonded abrasive article as well as
for a wide variety of applications. Although in some applications a
most pronounced effect might be achieved when the abrasive article
comprises 100% shaped abrasive particles in accordance with the
present invention based on the total amount of abrasive particles
present in the article, articles containing for example as little
as 5% by weight of shaped abrasive particles in accordance with the
present invention and up to 95% by weight of secondary abrasive
particles, based on the total amount of abrasive particles present
in the article, have also been shown to provide excellent
performance over a wide range of applications.
[0355] The effects achieved in the present invention are also
unexpected in view of the fact that the bonded abrasive article
typically does not have to comprise the shaped abrasive in any
specific orientation. Unlike the situation in comparatively thin
coated abrasive articles where orientation may be of advantage, the
bonded abrasive article (for example, wheel, segment, layer or part
thereof) typically comprises the shaped abrasive particles in a
random orientation, although orientation of the particles is not
excluded from the scope of the present invention.
[0356] In embodiments, the present invention relates to the
following items: [0357] 1. A bonded abrasive article comprising
shaped abrasive particles and a bonding medium comprising a
vitreous bond, said shaped abrasive particles each comprising a
first side and a second side separated by a thickness t, wherein
said first side comprises a first face having a perimeter of a
first geometric shape. [0358] 2. The article of item 1, wherein the
thickness t is equal to or smaller than the length of the shortest
side-related dimension of the particle. [0359] 3. The article
according to items 1 or 2, wherein the shaped abrasive particles
are ceramic shaped abrasive particles. [0360] 4. The article
according to any of items 1 to 3, wherein the shaped abrasive
particles comprise alpha alumina. [0361] 5. The article according
to any of items l to 4, wherein the shaped abrasive particles
comprise non-seeded sol-gel derived alpha alumina. [0362] 6. The
article according to any of items 1 to 4, wherein the shaped
abrasive particles comprise seeded sol-gel derived alpha alumina.
[0363] 7. The article according to any of items 1 to 6, further
comprising secondary abrasive particles. [0364] 8. The article
according to item 7, wherein the shaped and secondary abrasive
particles are independently selected from particles of fused
aluminum oxide materials, heat treated aluminum oxide materials,
ceramic aluminum oxide materials, sintered aluminum oxide
materials, silicon carbide materials, titanium diboride, boron
carbide, tungsten carbide, titanium carbide, diamond, cubic boron
nitride, garnet, fused alumina-zirconia, sol-gel derived abrasive
particles, cerium oxide, zirconium oxide, titanium oxide or a
combination thereof. [0365] 9. The article according to item 7 or
8, wherein the secondary abrasive particles are selected from
crushed abrasive particles having a specified nominal grade. [0366]
10. The article according to item 9, wherein the crushed abrasive
particles are of a smaller size than the shaped abrasive particles.
[0367] 11. The article according to any of items 1 to 10 comprising
10 to 80% by volume of said shaped abrasive particles. [0368] 12.
The article according to any of items 1 to 11 comprising 1 to 60%
by volume of said bonding medium. [0369] 13. The article according
to any of items 1 to 12, wherein said vitreous bond comprises,
based on the total weight of the vitreous bond, 25 to 90% by weight
of SiO.sub.2; 0 to 40% by weight of B.sub.2O.sub.3; 0 to 40% by
weight of Al.sub.2O.sub.3; 0 to 5% by weight of Fe.sub.2O.sub.3, 0
to 5% by weight of TiO.sub.2, 0 to 20% by weight of CaO; 0 to 20%
by weight of MgO; 0 to 20% by weight of K.sub.2O; 0 to 25% by
weight of Na.sub.2O; 0 to 20% by weight of Li.sub.2O; 0 to 10% by
weight of ZnO; 0 to 10% by weight of BaO; and 0 to 5% by weight of
metallic oxides. [0370] 14. The article according to any of items 1
to 13, wherein the vitreous bond is obtainable from a vitreous bond
precursor composition comprising fit. [0371] 15. The article
according to any of item 14, wherein the vitreous bond precursor
composition comprises 3 to 70% by weight of a fit based on the
total weight of the vitreous bond precursor composition. [0372] 16.
The article according to any of items 1 to 15, comprising porosity.
[0373] 17. The article according to any of items 1 to 1.6
comprising, based on the volume of the article, 1 to 60% by volume
of a vitreous bond, 10 to 80% by volume of shaped abrasive
particles and 5 to 80% by volume of porosity. [0374] 18. The
article according to any of items 7 to 17 wherein the shaped
abrasive particles and the secondary abrasive particles are
comprised in a blend, wherein the content of the secondary abrasive
particles is up to 95% by weight based on the total weight of
abrasive particles present in the blend. [0375] 19. The article
according to any of items 1 to 18, wherein the ratio of the length
of the shortest side-related dimension to the thickness of said
particle is at least 1:1. [0376] 20. The article according to any
of items 1 to 19, wherein said first geometric shape is selected
from polygonal shapes, lense-shapes, lune-shapes, circular shapes,
semicircular shapes, oval shapes, circular sectors, circular
segments, drop-shapes and hypocycloids. [0377] 21. The article
according to any of items 1 to 20 wherein said first geometric
shape is selected from triangular shapes and quadrilateral shapes.
[0378] 22. The article according to any of items 1 to 21 wherein
said first geometric shape is a quadrilateral shape selected from a
rectangle, a rhombus, a rhomboid, a kite, or a superellipse. [0379]
23. The article according to any of items 1 to 21 wherein said
first geometric shape is a triangular shape selected from isosceles
triangular shapes and equilateral triangular shapes. [0380] 24. The
article according to any of items 1 to 23, wherein the shaped
abrasive particles have a volumetric aspect ratio and the
volumetric aspect ratio is greater than about 1.15. [0381] 25. The
article according to any of items 1 to 24, comprising at least one
sidewall. [0382] 26. The article according to item 25, wherein the
sidewall comprises one or more facets. [0383] 27. The article
according to item 26, wherein the one or more facets have a shape
independently selected from triangular and quadrilateral geometric
shapes and combinations thereof. [0384] 28. The article according
to any of items 25 to 27, wherein the at least one sidewall is a
sloping sidewall. [0385] 29. The article according to any of items
25 to 28, further comprising a draft angle alpha between the second
face and the sidewall, the draft angle alpha being greater than 90
degrees. [0386] 30. The article of item 29, wherein the draft angle
alpha is between about 95 to about 135 degrees. [0387] 31. The
article according to any of items 25 to 28, wherein the sidewall
intersects the first side at an angle beta of between 5 to about 65
degrees. [0388] 32. The article according to any of items 1 to 31,
wherein said shaped abrasive particles each comprise at least one
shape feature selected from: an opening, at least one recessed (or
concave) face; at least one face which is shaped outwardly (or
convex); at least one side having a plurality of grooves or ridges;
at least one fractured surface; a low roundness factor; a perimeter
of the first face comprising one or more corner points having a
sharp tip; a second side comprising a second face having a
perimeter comprising one or more corner points having a sharp tip;
or a combination of one or more of said shape features. [0389] 33.
The article according to any of items 1 to 32, wherein the shaped
abrasive particles each have an opening. [0390] 34. The article
according to any of item 33, wherein the opening passes through the
first side and the second side. [0391] 35. The article according to
any of items 1 to 34, wherein the shaped abrasive particles further
comprise a plurality of grooves and/or ridges on the second side.
[0392] 36. The article according to any of items 1 to 35 wherein
the second side comprises a vertex or a ridge line or a second
face. [0393] 37. The article according to item 36, wherein the
second side comprises a second face separated from the first side
by thickness t and at least one sidewall connecting the second face
and the first face. [0394] 38. The article according to item 37,
wherein the thickness is equal to or smaller than the length of the
shortest facial dimension of the particle. [0395] 39. The article
according to item 37 or 38, wherein the second face has a perimeter
of a second geometric shape which may be the same or different to
the first geometric shape. [0396] 40. The article according to item
39, wherein said first and second geometric shapes are
independently selected from regular polygons, irregular polygons,
lenses, lunes, circulars, semicirculars, ovals, circular sectors,
circular segments, drop-shapes and hypocycloids. [0397] 41. The
article according to items 39 or 40, wherein the first and second
geometric shapes have identical geometric shapes which may or may
not be different in size. [0398] 42. The article according to item
41, wherein the first and second geometric shapes are selected from
substantially triangular shapes. [0399] 43. The article according
to item 42, wherein the substantially triangular shape comprise the
shape of an equilateral triangle. [0400] 44. The article according
to any of items 37 to 43, wherein the first face and the second
face are substantially parallel to each other. [0401] 45. The
article according to any of items 37 to 44, wherein the first face
and the second face are nonparallel to each other. [0402] 46. The
article according to any of items 37 to 45, wherein the sidewall is
a sloping sidewall. [0403] 47. The article according to any of
items 37 to 46, further comprising a draft angle alpha between the
second face and the sidewall, and the draft angle alpha is greater
than 90 degrees. [0404] 48. The article according to item any of
items 37 to 47 comprising a first sloping sidewall having a first
draft angle, a second sloping sidewall having a second draft angle,
and a third sloping sidewall having a third draft angle. [0405] 49.
The article according to item 48, wherein the first draft angle,
and the second draft angle, and the third draft angle have
different values from each other. [0406] 50. The article according
to item 48, wherein the first draft angle, the second draft angle,
and the third draft angle are equal. [0407] 51. The article
according to any of items 37 to 50, wherein the first and the
second face are substantially planar. [0408] 52. The article
according to any of items 37 to 50, wherein at least one of the
first and second face is a non-planar face. [0409] 53. The article
according to item 52, wherein the first face is recessed or concave
and the second face is substantially planar. [0410] 54. The
articles according to item 52, wherein the first face is convex and
the second face is recessed or concave. [0411] 55. The article
according to item 52, wherein the first face is recessed or concave
and the second face is recessed or concave. [0412] 56. The article
according to item 52, wherein the particles are dish-shaped
abrasive particles each having a sidewall and a varying thickness
t, wherein the first face is recessed and a thickness ratio of
Tc/Ti for the dish-shaped abrasive particles is between 1.25 to
5.00. [0413] 57. The article according to item 52 or 56, wherein
the first face comprises a substantially planar center portion and
a plurality of raised corners. [0414] 58. The article according to
any of items 37 to 57, wherein the second side comprises a second
face and four facets intersecting the second face at a draft angle
alpha forming a truncated pyramid. [0415] 59. The article of item
58, wherein the draft angle alpha is between about 95 to about 135
degrees. [0416] 60. The article according to item 36, wherein the
second side comprises a vertex separated from the first side by
thickness t and at least one sidewall connecting the vertex and the
perimeter of the first face. [0417] 61. The article according to
item 60, wherein the sidewall comprises one or more facets
connecting the vertex and the perimeter of the first face. [0418]
62. The article according to item 60 or 61, wherein the perimeter
of the first face is trilateral, quadrilateral or higher polygonal
and wherein the second side comprises a vertex and the
corresponding number of facets for forming a pyramid. [0419] 63.
The article according to any of items 60 to 62, wherein the first
side comprises a quadrilateral having four edges and four vertices
with the quadrilateral being selected from the group consisting of
a rectangle, rhombus, a rhomboid, a kite, or a superellipse. [0420]
64. The article according to any of items 60 to 62, wherein the
first side comprises a trilateral having three edges and three
vertices and the second side comprise a vertex and three triangular
facets forming a pyramid. [0421] 65. The article according to item
64, wherein the trilateral is an equilateral triangle. [0422] 66.
The article according to any of items item 60 to 65, wherein the
sidewall and/or or facets intersect the first side at an angle beta
of between about 5 to about 65 degrees. [0423] 67. The article
according to item 64, wherein the shaped abrasive particles have
four major sides joined by six common edges, wherein each one of
the four major sides contacts three other of the four major sides,
and wherein the six common edges have substantially the same
length. [0424] 68. The article according to item 67, wherein at
least one of the four major sides is substantially planar. [0425]
69. The article according to item 67 or 68, wherein at least one of
the four major sides is concave. [0426] 70. The article according
to item 67, wherein all of the four major sides are concave. [0427]
71. The article according to item 67 or 68, wherein at least one of
the four major sides is convex. [0428] 72. The article according to
any of items 67 to 71, wherein the shaped abrasive particles have
tetrahedral symmetry. [0429] 73. The article according to any of
items 67 to 72, wherein the shaped particles are substantially
shaped as regular tetrahedrons. [0430] 74. The article according to
item 36, wherein the second side comprises a ridge line separated
from the first side by thickness t and at least one sidewall
connecting the ridge line and the perimeter of the first face.
[0431] 75. The article according to item 74, wherein the sidewall
comprises one or more facets connecting the ridge line and the
perimeter of the first face. [0432] 76. The article according to
any of item 74 or 75 wherein the sidewall and/or facets intersect
the first side at an angle beta of between about 5 to about 65
degrees. [0433] 77. The article according to any of items 74 to 76,
wherein the first geometric shape is selected from quadrilateral
geometric shapes and the sidewall comprises four facets forming a
roof-shaped particle. [0434] 78. The article according to item. 77
wherein the quadrilateral shape is selected from the group
consisting of a rectangle, a rhombus, a rhomboid, a kite, or a
superellipse. [0435] 79. The articles according to any of items 1
to 78, wherein the abrasive particles have an average tip radius
and the average tip radius is less than 75 microns. [0436] 80. The
article according to any of items 1 to 79, wherein the shaped
abrasive particles each have a cross-sectional shape along a
longitudinal axis of the shaped abrasive particles, the
cross-sectional shape comprising a non-circular cross-sectional
plane, and the shaped abrasive particles comprise an Average
Roundness Factor of between about 15% to 0%. [0437] 81. The article
according to any of items 1 to 80 having a three-dimensional shape
selected from the shape of a wheel, honing stone, grinding segment,
mounted points or other shapes. [0438] 82. The article according to
any of items 1 to 81, wherein the article comprises a wheel.
[0439] 83. The article according to any of items 1 to 82, wherein
the article is a wheel. [0440] 84. The article according to any of
items 82 or 83, wherein the wheel is selected from grinding wheels
for cylindrical grinding, centerless grinding, surface and profile
grinding, reciprocating grinding, creep-feed grinding, grinding in
generating methods of gears, threads, tools, camshafts, crankshafts
bearings, and guard rails. [0441] 85. The article according to any
of items 1 to 84, wherein the shaped abrasive particles are
homogeneously distributed in the abrasive article. [0442] 86. The
article according to any of items 1 to 84, wherein the shaped
abrasive particles are non-homogeneously distributed in the
abrasive article. [0443] 87. The article according to item 86,
which is or comprises a bonded abrasive wheel, the wheel comprising
an outer zone and an inner zone, wherein the compositions of the
inner and outer zone differ in one or more aspects selected from
the composition of the bond, the shape of abrasive particles, the
grit size of abrasive particle, and the amount of abrasive
particles. [0444] 88. Use of an article according to any of items 1
to 87 in high performance grinding applications. [0445] 89. Use
according to claim 88 for outer diameter grinding with a Q'.sub.w
of at least 1.5 mm.sup.3/mm/sec, inner diameter grinding with a Q',
of at least 1 mm.sup.3/mm/sec, surface grinding with a Q'.sub.w of
at least 1.5 mm.sup.3/mm/sec, profile grinding with a Q'.sub.w of
at least 3 mm.sup.3/mm/sec, profile grinding with generating method
with a Q'.sub.w of at least 8 mm.sup.3/mm/sec, creep-feed grinding
with a Q'.sub.w of at least 4 mm.sup.3/mm/sec, and camshaft
grinding with a Q'.sub.w of at least 8 mm.sup.3/mm/sec. [0446] 90.
Use of an article according to any of claims 1 to 87 for abrading a
workpiece material selected from steels, non-ferrous metals,
alloys, hard metals, ceramics and glasses. [0447] 91. Method for
abrading a workpiece, the method comprising frictionally contacting
at least a portion of the abrasive article according to any of
items 1 to 87 with a surface of a workpiece; and moving at least
one of the workpiece or the abrasive article to abrade at least a
portion of the surface of the workpiece. [0448] 92. A method of
grinding characterized by using a bonded abrasive article according
to any of items 1 to 87, wherein the specific chip volume V'.sub.w
is at least 20% higher, than the specific chip volume achieved when
using a comparable bonded abrasive article at the same specific
material removal rate Q'.sub.w.
[0449] In particularly preferred embodiments, the present invention
relates to the following items: [0450] 1. A bonded abrasive article
comprising shaped abrasive particles and a bonding medium
comprising a vitreous bond, said shaped abrasive particles each
comprising a first side and a second side separated by a thickness
t, wherein said first side comprises (or preferably is) a first
face having a perimeter of a first geometric shape, wherein the
thickness t is equal to or smaller than the length of the shortest
side-related dimension of the particle, wherein said second side
comprises (or preferably is) a second face having a perimeter of a
second geometric shape, said second side being separated from said
first side by thickness t and at least one sidewall connecting said
second face and said first face, said first geometric shape and
said second geometric shapes having substantially identical
geometric shapes which may or may not be different in size, wherein
said identical geometric shapes are both selected either from
triangular shapes or from quadrilateral shapes. [0451] 2. The
article according to item 1, wherein said identical geometric
shapes are both selected from triangular shapes. [0452] 3. The
article according to any of items 1 or 2, wherein the first face
and the second face are substantially parallel or non-parallel to
each other. [0453] 4. The article according to any of items 1 to 3,
wherein the first and/or the second face are substantially planar.
[0454] 5. The article according to any of items 1 to 4, wherein at
least one of the first and second face is a non-planar face. [0455]
6. The article according to item 5, wherein at least one of the
first and the second face is shaped inwardly. [0456] 7. The article
according to item 6, wherein the first face is shaped inwardly and
the second face is substantially planar or the first face is shaped
outwardly and the second face is shaped inwardly or the first face
is shaped inwardly and the second face is shaped inwardly. [0457]
8. The article according to any of items 1 to 7, wherein the second
side comprises a second face and four facets intersecting the
second face at a draft angle alpha forming a truncated pyramid.
[0458] 9. The article according to any of items 1 to 8, wherein the
shaped abrasive particles are ceramic shaped abrasive particles.
[0459] 10. The article according to any of items 1 to 9, wherein
the shaped abrasive particles comprise alpha alumina. [0460] 11.
The article according to any of items 1 to 10, wherein the shaped
abrasive particles comprise seeded or non-seeded sol-gel derived
alpha alumina. [0461] 12. The article according to any of items 1
to 7, wherein said shaped abrasive particles comprise a major
portion of aluminum oxide. [0462] 13. The article according to item
12, wherein said aluminum oxide is fused aluminum oxide. [0463] 14.
The article according to any of items 1 to 13, further comprising
secondary abrasive particles. [0464] 15. The article according to
item 14, wherein the shaped and secondary abrasive particles are
independently selected from particles of fused aluminum oxide
materials, heat treated aluminum oxide materials, ceramic aluminum
oxide materials, sintered aluminum oxide materials, silicon carbide
materials, titanium diboride, boron carbide, tungsten carbide,
titanium carbide, diamond, cubic boron nitride, garnet, fused
alumina-zirconia, sol-gel derived abrasive particles, cerium oxide,
zirconium oxide, titanium oxide or a combination thereof. [0465]
16. The article according to item 14 or 15, wherein the secondary
abrasive particles are selected from crushed abrasive particles
having a specified nominal grade. [0466] 17. The article according
to item 16, wherein the crushed abrasive particles are of a smaller
size than the shaped abrasive particles. [0467] 18. The article
according to any of items 14 to 17 wherein said secondary abrasive
particles are selected from particles of fused aluminum oxide
materials, particles of superabrasive materials or particles of
silicon carbide materials. [0468] 19. The article according to any
of items 1 to 18 comprising 10 to 80% by volume of said shaped
abrasive particles and 1 to 60% by volume of said bonding medium.
[0469] 20. The article according to any of items 1 to 19, wherein
said vitreous bond comprises, based on the total weight of the
vitreous bond, 25 to 90% by weight of SiO.sub.2; 0 to 40% by weight
of B.sub.2O.sub.3; 0 to 40% by weight of Al.sub.2O.sub.3; 0 to 5%
by weight of Fe.sub.2O.sub.3, 0 to 5% by weight of TiO.sub.2, 0 to
20% by weight of CaO; 0 to 20% by weight of MgO; 0 to 20% by weight
of K.sub.2O; 0 to 25% by weight of Na.sub.2O; 0 to 20% by weight of
Li.sub.2O; 0 to 10% by weight of ZnO; 0 to 10% by weight of BaO;
and 0 to 5% by weight of metallic oxides. [0470] 21. The article
according to any of items 1 to 21, wherein the vitreous bond is
obtainable from a vitreous bond precursor composition comprising
frit. [0471] 22. The article according to any of items 1 to 22,
comprising porosity. [0472] 23. The article according to any of
items 14 to 22 wherein the shaped abrasive particles and the
secondary abrasive particles are comprised in a blend, wherein the
content of the secondary abrasive particles is up to 95% by weight
based on the total amount of abrasive particles present in the
blend. [0473] 24. The article according to item 1, wherein the at
least one sidewall is a sloping sidewall. [0474] 25. The article
according to any of items 1 to 24, wherein said shaped abrasive
particles each comprise at least one shape feature selected from:
an opening, at least one recessed (or concave) face; at least one
face which is shaped outwardly (or convex); at least one side
having a plurality of grooves or ridges; at least one fractured
surface; a low roundness factor; a perimeter of the first face
comprising one or more corner points having a sharp tip; a second
side comprising a second face having a perimeter comprising one or
more corner points having a sharp tip; or a combination of one or
more of said shape features. [0475] 26. The article according to
any of items 1 to 25, wherein the shaped abrasive particles each
have an opening. [0476] 27. The article according to any of items 1
to 26, wherein the shaped abrasive particles further comprise a
plurality of grooves and/or ridges on the second side. [0477] 28.
The article according to any of items 1 to 27 having a
three-dimensional shape selected from the shape of a wheel, honing
stone, grinding segment, mounted points, or other shapes. [0478]
29. The article according to any of items 1 to 28, wherein the
article comprises a wheel. [0479] 30. The article according to any
of item 29, wherein the wheel is selected from grinding wheels for
cylindrical grinding, centerless grinding, surface and profile
grinding, reciprocating grinding, creep-feed grinding, grinding in
generating methods of gears, threads, tools, camshafts, crankshafts
bearings, and guard rails. [0480] 31. The article according to any
of items 1 to 30, wherein the shaped abrasive particles are
homogeneously distributed in the abrasive article. [0481] 32. The
article according to any of items 1 to 31, wherein the shaped
abrasive particles are non-homogeneously distributed in the
abrasive article. [0482] 33. The article according to item 32,
which is or comprises a bonded abrasive wheel, the wheel comprising
an outer zone and an inner zone, wherein the compositions of the
inner and outer zone differ in one or more aspects selected from
the composition of the bond, the shape of abrasive particles, the
grit size of abrasive particle, and the amount of abrasive
particles. [0483] 34. Use of an article according to any of items 1
to 32 in high performance grinding applications. [0484] 35. Use
according to item 34 for outer diameter grinding with a Q'.sub.w of
at least 1.5 mm.sup.3/mm/sec, inner diameter grinding with a
Q'.sub.w of at least 1 mm.sup.3/mm/sec, surface grinding with a
Q'.sub.w of at least 1.5 mm.sup.3/mm/sec, profile grinding with a
Q'.sub.w of at least 3 mm.sup.3/mm/sec, profile grinding with
generating method with a Q'.sub.w of at least 8 mm.sup.3/mm/sec,
creep-feed grinding with a Q'.sub.w of at least 4 mm.sup.3/mm/sec,
and camshaft grinding with a Q'.sub.w of at least 8
mm.sup.3/mm/sec. [0485] 36. Use of an article according to any of
items 1 to 32 for abrading a workpiece material selected from
steels, non-ferrous metals, alloys, hard metals, ceramics and
glasses. [0486] 37. Method for abrading a workpiece, the method
comprising frictionally contacting at least a portion of the
abrasive article according to any of items 1 to 32 with a surface
of a workpiece; and moving at least one of the workpiece or the
abrasive article to abrade at least a portion of the surface of the
workpiece. [0487] 38. Method of gear grinding characterized by
using a bonded abrasive article according to any of items 1 to 32.
[0488] 39. Method of creep-feed grinding characterized by using a
bonded abrasive article according to any of items 1 to 32. [0489]
40. Method of surface grinding characterized by using a bonded
abrasive article according to any of items 1 to 32. [0490] 41.
Method of cylindrical grinding characterized by using a bonded
abrasive article according to any of items 1 to 32. [0491] 42. A
method of grinding characterized by using a bonded abrasive article
according to any of items 1 to 32, wherein the specific chip volume
V'.sub.w is at least 20% higher, than the specific chip volume
achieved when using a comparable bonded abrasive article at the
same specific material removal rate Q'.sub.w.
Determination of Particle Dimensions
[0492] The dimensions of the shaped abrasive particle (such as
length, width and thickness) can be determined using methods known
in the art, for example, by using conventional measuring tools such
as rulers, vernier calipers, micrometers, or microscopy measurement
techniques and typically calculating the average of a suitable
number of measurements.
[0493] For example, a measuring microscope such as a Nikon MM-40
obtained from Nikon Americas Inc. in Melville, N.Y. according to
the following test method can be used: One or more shaped abrasive
particles are supported on a glass slide preferably by its largest
substantially planar surface (if it has one) in contact with the
glass slide (dished or concave surface up if the particle has one.)
The glass slide is then placed on the Nikon MM-40 microscope stage.
The stage has the ability to move in the X and Y direction and it
is also equipped with counters for the X-Y distance travelled. The
crosshair is aligned with one of the exterior vertices of the
shaped abrasive particle. For example, a thin triangular particle
would use one of the three vertices; a rectangular base pyramid
would use one of the four rectangular base vertices of the pyramid.
The X and Y counters are then reset to zero. The crosshair is then
moved clockwise to the next exterior vertex of the geometry being
measured and the X and Y readings are recorded. The remaining
exterior vertices moving in a clockwise direction are then
sequentially measured. The X and Y coordinates of each exterior
vertex can then be placed into a spreadsheet and the maximum
dimension between any two of the vertices calculated using
Pythagoras' theorem.
[0494] For a triangle the length is maximum distance between any
two adjacent vertices of the three vertices. For a rectangle, the
length is the maximum dimension between adjacent vertices. For an
elongated parallelogram, the length is the maximum dimension
between adjacent vertices. For a kite or a rhombus, the length is
the maximum dimension between opposing vertices. The maximum
dimension to determine length for alternative geometries can be
determined by those of skill in the art when looking at the
geometry in the microscope. The width can then be determined
perpendicular to the length by using the coordinates of selected
vertices or by rotating the stage or slide such that the length
dimension is parallel to the X-axis. For a triangle the width is
the maximum distance between the side with the longest adjacent
vertices and the opposing vertex. For a rectangle, the width is the
largest dimension between the two pairs of shorter opposing
vertices. For an elongated parallelogram, the width is the maximum
dimension between the side with the longest adjacent vertices and
the opposing side. For a kite or a rhombus, the width is the
shorter dimension between opposing vertices. The maximum dimension
to determine width for alternative geometries can be determined by
those of skill in the art when looking at the geometry in the
microscope.
[0495] The Nikon MM-40 microscope is also equipped with a Z-axis
scale with a counter. To measure thickness, t, (height from glass
slide) the viewfield is first focused on the upper surface of the
glass slide using the 100.times. objective for maximum accuracy.
The Z counter is then reset to zero. The viewfield is then moved to
the highest possible point of the shaped abrasive particle that can
be observed (a lower magnification may be needed to find the
highest point) and the microscope refocused at that the highest
point at the 100.times. magnification. The particle's thickness is
determined by the Z reading after refocusing.
[0496] At least 20 shaped abrasive particles are measured for the
dimension of interest (individual length, individual width,
individual thickness). The averages of the dimension of interest
(individual lengths, widths, thickness dimensions) are determined
to define the dimension (length, width, thickness) for the measured
shaped abrasive particles respectively.
[0497] For the purposes of this measurement, the thickness of a
particle having an opening is measured at the site of the actual
maximum thickness of the particle (i.e. typically not within the
opening). The shortest side related dimension, the width and the
length of a particle having an opening are typically measured
without subtracting the length of overlap of the opening with any
one of these dimensions (if any). For example, the width and length
of an equitrilateral, prismatic particle having an opening
extending between the first and the second side of uniform
thickness t can be measured based on the perimeter of the first
face (or the second face) without taking into account the
opening.
[0498] The volumetric aspect ratio can be determined using methods
known in the art, for example by using the actual maximum and
minimum cross sectional areas of the particle, and/or exterior
dimensions determined by microscopy measurement techniques as
previously described and calculating the average of a suitable
number (for example 20 or more) of individual particle
determinations. For an equilateral triangular shaped abrasive
particle, the thickness and side length can be measured by
microscopic techniques discussed above and the volumetric aspect
ratio determined.
[0499] The radius of curvature can be measured by using image
analysis for example, using a CLEMEX VISION PE image analysis
program available from Clemex Technologies, Inc. of Longueuil,
Quebec, Canada, interfaced with an inverted light microscope, or
other suitable image analysis software/equipment. Using a suitable
polished cross-section taken between the first face and the second
face may help in microscopic examination of the edge or corner
point of a sidewall. The radius of curvature of each point of the
shaped abrasive article can be determined by defining three points
at the tip of each point (when viewed e.g. at 100.times.
magnification). A point is placed at the start of the tip's curve
where there is a transition from the straight edge to the start of
a curve, at the apex of the tip, and at the transition from the
curved tip back to a straight edge. The image analysis software
then draws an arc defined by the three points (start, middle, and
end of the curve) and calculates a radius of curvature. The radius
of curvature for at least 30 apexes are measured and averaged to
determine the average tip radius.
[0500] The Average Roundness Factor can be determined as described
in [0029] to [0033] of US Patent Application Publication No.
2010/0319269 by using a transverse cut C, as defined in of said
patent application publication.
[0501] Objectives and advantages of this disclosure are further
illustrated by the following non-limiting examples, but the
particular materials and amounts thereof recited in these examples,
as well as other conditions and details, should not be construed to
unduly limit this disclosure.
EXAMPLES
[0502] Unless otherwise noted, all parts, percentages, ratios, etc.
in the Examples and the rest of the specification are by weight.
Unless otherwise noted, grinding was performed wet using lubricants
common for the grinding application, such as a 3 to 5% emulsion
(v/v) of oil or synthetic lubricant (for example Castrol Syntilo 81
E, available from Castrol LTd. or Castrol Group, or Cimtech.RTM.
D18, available from Cimcool.RTM. Fluid Technology, LLC) in
water.
Materials Used in the Examples
TABLE-US-00001 [0503] 80+ Shaped abrasive particles with the
composition of 3M .TM. Ceramic Abrasive Grain 321 with each
abrasive particle shaped as a triangular prism with sloping side
walls (side wall draft angle 98 degrees) with two substantially
parallel faces, wherein the first face comprises an equilateral
triangle with a median dimension of 0.49 mm and the second face
also comprises an equilateral triangle of median edge length of
0.415 mm. The average distance between the faces was 0.095 mm. 60+
Shaped abrasive particles with the composition of 3M .TM. Ceramic
Abrasive Grain 321 with each abrasive particle shaped as a
triangular prism with sloping side walls (side wall draft angle 98
degrees) with two substantially parallel faces, wherein the first
face comprises an equilateral triangle with a median dimension of
0.63 mm and the second face also comprises an equilateral triangle
of median edge length of 0.540 mm. The average distance between the
faces was 0.120 mm T Shaped abrasive particles with the composition
of 3M .TM. Ceramic Abrasive Grain 321 with each abrasive particle
shaped as a tetrahedron with a median edge length of 0.510 mm White
fused aluminium available as Alodur .RTM. WSK from Treibacher
Schleifmittel oxide AG, Austria in grit size F24, F30, F40, F46,
F54, F60, F70, F80, and F100 according to FEPA-Standard 44-1: 2006
Monocrystalline available as Alodur .RTM. SCTSK from Treibacher
Schleifmittel aluminium oxide AG, Austria in grit size F80
according to FEPA-Standard 44-1: 2006 3M .TM. Ceramic Abrasive
crushed non-seeded sol-gel derived ceramic alpha alumina Grain 321
based abrasive particles having the same chemical composition:
Al.sub.20.sub.3 94-96% MgO 1.2% +/- 0.3% Y.sub.20.sub.3 1.2% +/-
0.3% La.sub.20.sub.3 + Nd.sub.20.sub.3 2.4% +/- 0.5% Traces of:
Ti0.sub.2, Si0.sub.2, CaO, and CoO and Fe and having grit size ANSI
46, ANSI 60, ANSI 80 and ANSI 90, available from 3M, USA Cerpass
TGE .RTM., Code Extruded abrasive rods composed of seeded gel
product; TGE-0557 containing .gtoreq.99.6% alpha aluminium oxide in
grit size grit size 36 with an aspect ratio [the ratio of the
length to the greatest cross-sectional dimension (the greatest
dimension perpendicular to the length)] in the range of 2.9-4.5 and
a side dimension of the cross-sectional area of 474-546 .mu.m, and
in grit size 100 with an aspect ratio [the ratio of the length to
the greatest cross-sectional dimension (the greatest dimension
perpendicular to the length)] in the range of 3.3-5.1 and a side
dimension of the cross-sectional area of 140-152 .mu.m,
Saint-Gobain Grains & Powders, Worcester, USA Cerpass XTL
.RTM., Code Crushed seeded gel product, containing .gtoreq.99.6%
alpha XTL-0560 aluminium oxide in grit size 90 according to ANSI
available from Saint-Gobain Grains & Powders Mix 1 -
Comparative 100% by weight white fused aluminium oxide based on the
Example Ref. 1A-2 total weight of abrasive grain, consisting of 20%
by weight of FEPA grade F70, 50% by weight of FEPA grade F80, and
30% by weight of FEPA grade F100 Mix 2 - Comparative 30% by weight
3M .TM. Ceramic Abrasive Grain 321 and 70% Example Ref. 2A-1, by
weight of white fused aluminium oxide based on the total
Comparative Example weight of abrasive grain Ref. IX-3 The 3M .TM.
Ceramic Abrasive Grain 321 portion consists of each 50% by weight
of ANSI grade 80 and ANSI grade 90. The portion of white fused
aluminium oxide consists of each 28.6% by weight of FEPA grade F70
and F100, and 42.8% by weight of FEPA grade F80. Mix 3 - Examples
1A-1, 30% by weight 80+ and 70% by weight white fused alumina and
1B-1, Example V-4, by weight based on the total weight of abrasive
grain Example IX-1 The portion of white fused aluminium oxide
consists of each 28.6% by weight of FEPA grade F70 and F100, and
42.8% by weight of FEPA grade F80 Mix 4 - Examples 2A-1, 30% by
weight 60+ and 70% by weight of white fused and 2B-1 alumina based
on the total weight of abrasive grain The portion of white fused
aluminium oxide consists of each 28.6% by weight of FEPA grade F70
and F100, and 42.8% by weight of FEPA grade F80 Mix 5 - Examples
3A-1, 30% by weight T and 70% by weight of white fused and 3B-1
aluminium oxide based on the total weight of abrasive grain The
portion of white fused aluminium oxide consists of each 28.6% by
weight of FEPA grade F70 and F100, and 42.8% by weight of FEPA
grade F80 Mix 6 - Examples 1A-2, 100% by weight 80+ based on the
total weight of abrasive and 1B-2, II-1, IV-1, V-3, grain IX-2 Mix
7 - Comparative 30% by weight Cerpass TGE .RTM., code TGE-0557,
grit size Example Ref. 3A-1 100 and 70% by weight of white fused
aluminium oxide based on the total weight of abrasive grain The
portion of white fused aluminium oxide consists of each 28.6% by
weight of FEPA grade F70 Mix 8 - Comparative 100% by weight Cerpass
TGE .RTM., code TGE-0557, grit size Example Ref. 3A-2 100 based on
the total weight of abrasive grain Mix 9 - Example II-1, 100% by
weight white fused aluminium oxide based on the Comparative Example
total weight of abrasive grain, consisting of 20% by weight Ref.
II-2, Example IV-1, of FEPA grade F54, 50% by weight of FEPA grade
F60, and Comparative Example IV- 30% by weight of FEPA grade F70 2,
Comparative Example Ref. V-5 Mix 10 - Comparative 30% by weight 3M
.TM. Ceramic Abrasive Grain 321 and 70% Example Ref. II-2, by
weight of white fused aluminium oxide based on the total
Comparative Example weight of abrasive grain Ref. V-5 The 3M .TM.
Ceramic Abrasive Grain 321 portion consists of 100% by weight of
ANSI grade 60. The portion of white fused aluminium oxide consists
of each 28.6% by weight of FEPA grade F54 and F60, and 42.8% by
weight of FEPA grade F70. Mix 11 - Example III-1, 100% by weight
60+ based on the total weight of abrasive VI-1, VII-1, VIII-1 grain
Mix 12 - Comparative 30% by weight 3M .TM. Ceramic Abrasive Grain
321 and 70% Example Ref. III-2, by weight of white fused aluminium
oxide based on the total Comparative Example weight of abrasive
grain Ref. VIII-2 The 3M .TM. Ceramic Abrasive Grain 321 portion
consists of 100% by weight of ANSI grade 46. The portion of white
fused aluminium oxide consists of each 42.9% by weight of FEPA
grade F40 and F54, and 14.2% by weight of FEPA grade F46. Mix 13 -
Comparative 20% by weight 3M .TM. Ceramic Abrasive Grain 321 and
80% Example IV-2 by weight of white fused aluminium oxide based on
the total weight of abrasive grain The 3M .TM. Ceramic Abrasive
Grain 321 portion consists of 100% by weight of ANSI grade 60. The
portion of white fused aluminium oxide consists of 25% by weight of
FEPA grade F54, and of each 37.5% by weight of FEPA grade F60 and
F70. Mix 14 - Example V-1 30% by weight 80+ and 70% by weight white
fused alumina by weight based on the total weight of abrasive grain
The portion of white fused aluminium oxide consists of each 50% by
weight of FEPA grade F46 and F60 Mix 15 - Example V-1, 100% by
weight white fused aluminium oxide based on the Example V-2,
Example V-3 total weight of abrasive grain, consisting of each 35%
by weight of FEPA grade F46 and F60, and 30% by weight of FEPA
grade F54. Mix 16 - Example V-2 50% by weight 80+ and 50% by weight
white fused alumina by weight based on the total weight of abrasive
grain The portion of white fused aluminium oxide consists of 40% by
weight of FEPA grade F46, and 60% by weight of FEPA grade F60 Mix
17 - Example V-4, 100% by weight white fused aluminium oxide based
on the Comparative Example total weight of abrasive grain,
consisting of each 20% by Ref. V-6, Example IX-1, weight of FEPA
grade F70 and F100, and 60% by weight of Example IX-2, FEPA grade
F80. Comparative Example Ref. IX-3 Mix 18 - Comparative 30% by
weight 3M .TM. Ceramic Abrasive Grain 321 and 70% Example Ref. V-6
by weight of white fused aluminium oxide based on the total weight
of abrasive grain The 3M .TM. Ceramic Abrasive Grain 321 portion
consists of 100% by weight of ANSI grade 80. The portion of white
fused aluminium oxide consists of each 28.6% by weight of FEPA
grade F70 and F100, and 42.8% by weight of FEPA grade F80. Mix 19 -
Comparative 5% by weight 3M .TM. Ceramic Abrasive Grain 321, 25% by
Example Ref. VI-2 weight of Cerpass XTL .RTM. code XTL-0560, 50% by
weight of monocrystalline aluminium oxide, and 20% by weight of
white fused aluminium oxide based on the total weight of abrasive
grain The 3M .TM. Ceramic Abrasive Grain 321 portion consists of
100% by weight of ANSI grade 90. The Cerpass XTL .RTM. code
XTL-0560 portion consists of 100% by weight of ANSI grade 90. The
monocrystalline aluminium oxide portion consists of 100% by weight
of FEPA grade F80. The white fused aluminium oxide portion consists
of 100% by weight of FEPA grade F70. Mix 20 - Example VII-2 30% by
weight 60+ and 70% by weight white fused alumina by weight based on
the total weight of abrasive grain The portion of white fused
aluminium oxide consists of 42.9% by weight of FEPA grade F24, and
57.1% by weight of FEPA grade F30 Mix 21 - Comparative 30% by
weight Cerpass TGE .RTM., code TGE-0557, grit size 36 Example VII-3
and 70% by weight white fused alumina by weight based on the total
weight of abrasive grain The portion of white fused aluminium oxide
consists of 42.9% by weight of FEPA grade F24, and 57.1% by weight
of FEPA grade F30 Mix 22 - Example VIII-1, 100% by weight white
fused aluminium oxide based on the Comparative Example total weight
of abrasive grain, consisting of each 30% by Ref. VIII-2 weight of
FEPA grade F40 and F54, and 40% by weight of FEPA grade F46.
Vitrified bond precursor Mix of 98.5% by weight vitrified bond
having a grain size of mix 97% <63 .mu.m and a composition
consisting of Na.sub.2O, Al.sub.2O.sub.3, B.sub.2O.sub.3, and
SiO.sub.2, commercially available as vitrified bond VO 82069 from
Reimbold & Strick, Germany and 1.5% by weight of blue pigment,
cobalt blue colour stain for glazes consisting of
CoAl.sub.2O.sub.4, commercially available as K90084 from Reimbold
& Strick, Germany Temporary binder Consisting of Liquid
temporary binder mix and solid temporary binder Liquid temporary
binder Urea formaldehyde resin.sup..cndot., for example PA1175G
available mix from PA resins AB, Sweden, now Chemoplastica AB,
Sweden Solid temporary binder Potato starch.sup..cndot., for
example Dextrin 20.912 available from Agrana Starke GmbH, Austria
Pore inducing agent Naphthalene.sup..cndot., for example available
from Sinta SA, Belgium, in crystalline and sifted form; depending
on the grain size distribution herein later referred to as Type A
(212-500 .mu.m) and Type B (300-1190 .mu.m) .sup..cndot.not present
in the final product
Example I
Outer Diameter (OD) Grinding
[0504] a. Manufacturing Process of Abrasive Grinding Wheels
[0505] Vitrified bonded abrasive grinding wheels having the same
bond and wheel dimension of 500.times.25.times.304.8 mm (wheel
diameter.times.thickness.times.bore diameter) and Ti shape
(according to DIN:ISO 603:1999), i.e. a straight grinding wheel,
were prepared according to the following manufacturing process:
(i) Mixing
[0506] The abrasive grain/grain mix as specified with respect to
the examples was put into a mixing aggregate and the liquid
temporary binder was poured onto it while mixing. After stirring
for about 3-5 minutes, a mixture consisting of the vitrified bond
precursor mix and the solid temporary binder was added and the
mixing was continued thoroughly for about 10 minutes.
(ii) Sieving
[0507] With reference to the examples given, the mixture obtained
in step (i) is screened with a sieve 16 mesh (mesh size 1.18
mm).
(iii) Moulding
[0508] The mixture obtained in step (ii) is put into a mould and
formed by pressing to give green bodies. Typical forming pressures
were 126-150 kg/cm.sup.2 for green bodies with an abrasive mix
containing 100% 80+ and 21-51 kg/cm.sup.2 for green bodies with an
abrasive mix containing 30% 80, 60+ or T shaped abrasive grain.
(iv) Heat Treatment
[0509] With reference to the examples given, the achieved green
bodies are dried at a temperature of 130.degree. C. and sintered at
a temperature of 930.degree. C.
(vii) Finishing
[0510] The finishing operation comprises the grinding of the bore,
the lateral surfaces, and the peripheral surface.
TABLE-US-00002 TABLE 1 Characteristics of the test wheels of
Example I Amounts [wt. %]* Comparative Comparative Comparative
Comparative Example 1A- Example 2A- Example 3A- Example 1A- Example
Ref. Example Ref. Example Ref. Example Ref. 1 1 1 2 1A-2 2A-1 3A-1
3A-2 Green Structure Abrasive Mix 3 Mix 4 Mix 5 Mix 6 Mix 1 Mix 2
Mix 7 Mix 8 Grain shaped 26.55 80+ 26.55 60+ 26.55 T 88.50 80+
abrasive grain 3M .TM. 26.55 Ceramic grit 80, 90 Abrasive Grain 321
Cerpass 26.55 88.50 TGE .RTM., grit 100 grit 100 code TGE- 0557
White fused 61.95 61.95 61.95 -- 88.50 61.95 61.95 -- aluminium
F70, 80, 100 F70, 80, 100 F70, 80, 100 F70, 80, 100 F70, 80, 100
F70, 80, 100 oxide Vitreous 11.50 11.50 11.50 11.50 11.50 11.50
11.50 11.50 bond Temporary binder Starch 0.50 0.50 0.50 0.50 0.50
0.50 0.50 .0.50 Liquid 4.20 4.20 4.20 4.20 4.20 4.20 4.20 4.20
temporary binder mix Moulding 2.110 2.110 2.110 2.110 2.110 2.110
2.110 2.110 density [g/cm.sup.3] Wheel Type** Type III Type III
Type III Type III Type III Type III Type III Type III Shape T1 T1
T1 T1 T1 T1 T1 T1 Dimension 500 .times. 25 .times. 500 .times. 25
.times. 500 .times. 25 .times. 500 .times. 25 .times. 500 .times.
25 .times. 500 .times. 25 .times. 500 .times. 25.times. 500 .times.
25 .times. 304.8 304.8 304.8 304.8 304.8 304.8 304.8 304.8 Amounts
[wt. %]* Example 1B- Example 2B- Example 3B- Example 1B- 1 1 1 2
Green Structure Abrasive Mix 3 Mix 4 Mix 5 Mix 6 Grain shaped 25.97
80+ 25.97 60+ 25.97 T 86.58 80+ abrasive grain 3M .TM. Ceramic
Abrasive Grain 321 White fused 60.61 60.61 60.61 aluminium F70, 80,
100 F70, 80, 100 F70, 80, 100 oxide Vitreous bond 13.42 13.42 13.42
13.42 Temporary binder Starch 0.85 0.85 0.85 0.85 Liquid 3.30 3.30
3.30 3.30 temporary binder mix Moulding 2.150 2.150 2.150 2.150
density [g/cm.sup.3] Wheel Type** Type VII Type VII Type VII Type
VII Shape T1 T1 T1 T1 Dimension 500 .times. 25 .times. 500 .times.
25 .times. 500 .times. 25 .times. 500 .times. 25 .times. 304.8
304.8 304.8 304.8 **Here and in the following the Wheel Type (or
the abrasive article or tool type) relates to the
hardness/structure of the test abrasive tools and had been
classified as a type ranging from Type I (lower volume percentage
of bond and abrasive grain, and higher volume percentage of
porosity) to Type XI (higher volume percentage of bond and abrasive
grain, and lower volume percentage of porosity) based on the
percentage of bond and porosity in the abrasive tools (for example
wheels or segments), with a higher volume percentage of bond
corresponding to a higher type and a more rigid or hard abrasive
tool. For example with specific reference to Example 1, i.e. Type
III or Type VII, test wheels of Type VII can be considered as
acting harder or more rigid under the grinding conditions used as
compared to test wheels of Type III because of the higher volume
percentage of bond and less porosity present in wheels of Type VII.
*weight amounts of the green wheels before firing
B. Testing Procedure
[0511] The grinding wheels prepared as in Example I were tested in
a cylindrical grinding application in order to establish the
grinding performance of the wheels. The grinding tests were
performed using the following grinding conditions: [0512] Grinding
Process: outer diameter (OD-) grinding [0513] Machine: UVA
Johansson 10MD; 18.5 kW, year of construction 1979 (rebuilt) [0514]
Workpiece: bearing steel; Ovako 824, Ovako Hofors AB, Sweden 1.3537
(100CrMo7) according to EN ISO 683-17:1999, 62-64 HRc, diameter 100
mm, length 20 mm [0515] Parameters: operating speed of grinding
wheel: 45 m/s; wet grinding using Cimtech D18 (3%) as a
lubricant/coolant [0516] Dressing: Multi-point diamond dresser,
V448-0,8x4-4 bars, Kucher GmbH, Germany, synthetic diamond, width
15 mm, length 28 mm, traverse speed 350 mm/min
[0517] Using the grinding wheels of Example I, three sets of
grinding tests were performed.
[0518] Test Series (I) used a specific material removal rate of
Q'.sub.W 2.5 min.sup.3/mm/s (infeed: 0.006 mm/turn of work piece;
peripheral speed of work piece: 25 m/min).
[0519] Test Series (II) used more severe grinding conditions by
applying a specific material removal rate of Q'.sub.W 5
mm.sup.3/mm/s (infeed: 0.010 mm/turn of work piece; peripheral
speed of work piece: 30 m/min).
[0520] Test series (III), using a specific material removal rate of
Q'.sub.W 2.5 mm.sup.3/mm/s (infeed: 0.006 mm/turn of work piece;
peripheral speed of work piece: 25 m/min) to remove 1.2 mm of work
piece in radius following by 5 s of outspark was chosen to
characterise the surface quality of the work piece.
[0521] The power drawn was recorded as a function of the grinding
time. The results of Test Series (I) are shown in FIG. 1 and FIG.
2. The results of Test Series (II) are shown in FIG. 3 and FIG.
4.
[0522] Typically grinding curves of this type are cyclical: The
power drawn (kilowatts) increases over time as the grinding forces
increase. When the forces get high enough the wheel breaks down,
breaking and ejecting grit particles and then the grinding power
consumption (grinding force) decreases. At this point dressing of
the grinding wheel has to be set up in order to avoid defects at
the workpiece to be abraded and in order to provide for constant
abrading performance of the grinding wheel. Then the grinding cycle
has to be started again. What is desired is a grinding wheel having
a long cycle period (in terms of constant power drawn), indicating
good form holding and long total service life of the wheel.
[0523] For each wheel the grinding test was operated until the
power consumption fell below the power consumption at the initial
grinding level. This was considered the test endpoint. Due to their
long service life the tests of Test Series (I) using the wheels of
all examples excluding Example Ref. 1A-2 and Ref. 2A-1, and the
tests of Test Series (II) using the grinding wheels of Examples
1A-2 and 1B-2 (100% 80+) were ended before reaching this point.
[0524] In addition, the mean value of surface roughness R.sub.a of
the workpiece after the grinding according to Test Series III has
been determined with a device of type SURFTEST SJ-210 of Mitutojo.
The results of the Type III-wheels are summarized in FIG. 5.
C. Results
[0525] A comparison of the results obtained under Test Series I and
II shows the higher grinding performance of the examples given by
increasing the specific material removal rate (FIG. 1-4). While in
Test Series I (Q'.sub.w 2.5 mm.sup.3/mm/s) all variants comprising
non-seeded sol-gel derived aluminium oxide refer to a long service
life (FIG. 1 and FIG. 2, examples excluding the Comparative
Examples Ref. 1A-2, Ref. 2A-1, Ref 3A-1, and Ref. 3A-2),
differences in the power drawn can be seen in FIG. 3 and FIG. 4
when applying the grinding conditions of Test Series II comprising
a specific material removal rate Q'.sub.W of 5 mm.sup.3/mm/s.
[0526] FIG. 3 and FIG. 4 illustrate a marked increase in the period
of the grinding cycle when using grinding wheels containing shaped
abrasive particles in accordance with the present invention in
comparison to the variants comprising white fused aluminium oxide
or 3M.TM. Ceramic Abrasive Grain 321 or extruded Cerpass TGE.RTM.
(Comparative Examples Ref. 1A-2 or Ref. 2A-1, or Ref. 3A-1)
respectively, and confirm the increase in the service life. For
example, the period for the grinding cycle of Example 1A-1 in
comparison to Ref. 2A-1 is nearly doubled, thus resulting in a
longer dressing interval. Considering grinding wheels with abrasive
mixes consisting of 100% shaped abrasive particles in accordance
with the present invention (Example 1A-2) as well as 100% extruded
Cerpass TGE.RTM. (Comparative Example Ref. 3A-2) Example 1A-2 shows
a marked increase in service life. The testing of Example 1A-2 was
terminated artificially because of the constant power drawn during
a certain grinding duration.
[0527] With reference to the examples comprising shaped abrasive
particles in accordance with the present invention an influence of
the abrasive grain size and the amount of the abrasive grain
portion can be seen. Increasing the abrasive grain portion effects
longer service life. This can be seen from Examples 1A-2 and 1B-2
in comparison to examples 1A-1 and 1B-1, each containing shaped
abrasive particles 80+. Using the same portion of the shaped
abrasive particle of the invention, examples 2A-1 and 2B-1,
containing shaped abrasive particles 60+, show the influence of the
grain size and an increase of the service life by reducing the wear
of the shaped abrasive particles in comparison to the Examples 1A-1
and 1B-1, comprising shaped abrasive particles 80+.
[0528] In sum, the use of shaped abrasive grains in a vitrified
bond can provide abrasive grinding wheels exhibiting a long and
stable grinding curve in grinding applications, particularly under
more severe grinding conditions, as for example shown in Test
Series II. Surprisingly, the service life of the wheels increased
when tested using a higher specific removal rate (Q'.sub.w=5.0
mm.sup.3/mm/s). Increasing the amount of shaped abrasive particles
according to the present invention can provide an extremely long
grinding cycle.
[0529] In addition, the use of shaped abrasive grains has been
found to provide improved surface finish as evident from a
comparison of the examples for wheels of Type III given and shown
in FIG. 5. With respect to the grinding practice, it has to be
stated that deviation of the results is low. Because of its narrow
range the results of the mean value of surface roughness R.sub.a
are not described in detail.
[0530] With respect to the results obtained it is also to be noted
that the grinding tests involved a specific grinding machine built
in 1979. The use of a more recently constructed machine is expected
to provide even better results since higher values for Q'w could be
accomplished.
Example II
Outer Diameter (OD) Grinding
A. Manufacturing Process of Abrasive Grinding Tools
[0531] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 2 were prepared as described in Example I.
TABLE-US-00003 TABLE 2 Characteristics of Grinding Wheels used in
Example II Comparative Example II-1 Example Ref. II-2 Green
Structure Rim Center Rim Center Abrasive Grain Mix 6 Mix 9 Mix 10
Mix 9 Shaped abrasive 88.50 grain 80+ 3M .TM. Ceramic 26.55
Abrasive Grain Grit 60 321 White fused 88.50 61.95 88.50 alumina
F54, 60, 70 F54, 60, 70 F54, 60, 70 Vitreous bond 11.50 11.50 11.50
11.50 Starch 1.50 1.50 1.00 1.00 Liquid temporary 4.24 4.24 3.89
3.89 binder mix Pore inducing 13.27 13.27 13.27 13.27 agent (Type
A) (Type A) (Type A) (Type A) Moulding density 2.100 2.100 2.010
2.010 [g/cm.sup.3] Wheel Wheel Type** Type IV Type V Shape T5 T5
Dimension 750 .times. 100 .times. 750 .times. 100 .times.
304.8-1-420 .times. 30 304.8-1-420 .times. 30 **(see Table 1)
B. Testing Procedure
[0532] The grinding wheels prepared as in Example II were tested in
an outer diameter (OD) grinding application in order to establish
the grinding performance of the wheels.
[0533] Using the grinding wheels of Example II, grinding tests were
performed using the following grinding conditions: [0534] Grinding
Process: outer diameter (OD-) grinding [0535] Machine: HOL-MONTA
2000CNC (22 kW) [0536] Workpiece: pressure cylinder, diameter 620
mm, length 1110 mm, hard-chrome plated; required surface roughness
R.sub.z<4 .mu.m (R.sub.z describing the average roughness depth)
[0537] Parameters: Roughing via plunge grinding; 10 plunges, speed
ratio q.sub.s 67 and finishing via traverse grinding, speed ratio
q.sub.s 67, speed of flunge speed rate v.sub.f 700 mm/min [0538]
Dressing: Multi-point diamond dresser MKD4x0,8
C. Results
TABLE-US-00004 [0539] TABLE 3 Results of Exampe II Q'.sub.w
grinding Q'.sub.w Semi- Q'.sub.w stock v.sub.w v.sub.c Roughing
roughing Finishing [mm] [rpm/min] [m/s] [mm.sup.3/mm/s]
[mm.sup.3/mm/s] [mm.sup.3/mm/s] Dressing Comparative Example
Roughing 0.5 11 25 1.8 0.9 0.25 after each Ref. II-2 plunge, 4
.times. 0.02 mm Finishing 0.04 11 25 2 2 0.2 1.times. before
grinding, 4 .times. 0.02 mm Example II-1: Test 1 Roughing 0.5 I 1
25 1.8 0.9 0.25 after each plunge, 4 .times. 0.02 mm Finishing 0.04
11 25 2 2 0.2 1.times. before grinding, 4 .times. 0.02 mm Example
II-1: Test 2 Roughing 0.5 12 27 2.3 1.3 0.6 after each 2.sup.nd
plunge 4 .times. 0.01 mm Finishing 0.04 11 25 2 2 0.2 1.times.
before grinding 4 .times. 0.01 mm Example II-1: Test 3 Roughing 0.9
12 27 2.9 1.5 0.8 after each 2.sup.nd plunge 4 .times. 0.01 mm
Finishing 0.04 11 25 2 2 0.2 l.times. before grinding 4 .times.
0.01 mm
[0540] The grinding tests were performed in test series using three
different parameter sets for the roughing and the same parameter
sets for the finishing process. The parameter sets are summarized
in Table 3. The results show an increase in the performance thus
reflected by the specific material removal rate Q'.sub.W and the
total grinding time for the test wheel as well as an improvement in
the dressing process by reducing the dressing amounts by 50%.
Considering the total grinding time the reference wheel as well as
the test wheel using the parameter set of Test 1 show total
grinding times of 270 minutes. Using parameter set of Test 2
enables to reduce the grinding time to 190 minutes (-30%) and to
increase the infeed by 29% in comparison to the reference wheel and
Test 1. Test 3 comprised a 80% higher grinding stock and a 40%
higher infeed. Even with these more severe conditions present the
grinding time was increased by only 10% (210 minutes) than in. Test
2 and still was ca. 20% shorter than in Test 1. In all test series
the test wheel met the required surface quality and gained a
silk-mat surface quality.
Example III
Outer Diameter (OD) Grinding
A. Manufacturing Process of Abrasive Grinding Tools
[0541] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 4 were prepared as described in Example I.
TABLE-US-00005 TABLE 4 Characteristics of Grinding Wheels used in
Example III Comparative Example Ref. Green Structure Example III-1
III-2 Abrasive Grain Mix 11 Mix 12 Shaped abrasive grain 85.10 60+
3M .TM. Ceramic Abrasive Grain 25.53 321 Grit 46 White fused
alumina 59.57 F40, 46, 54 Vitreous bond 14.90 14.90 Starch 1.50
1.50 Liquid temporary binder mix 4.92 4.92 Pore inducing agent
12.77 12.77 (Type A) (Type A) Wheel Moulding density [g/cm.sup.3]
2.450 2.360 Wheel Type** Type X Type XI Shape T1 T1 Dimension
250.times.9.times.85 250.times.9.times.85 **(see Table 1)
B. Testing Procedure
[0542] The grinding wheels prepared as in Example III were tested
in an outer diameter (OD) grinding application in order to
establish the grinding performance of the wheels.
[0543] Using the wheels of Example III, grinding tests were
performed using the following grinding conditions: [0544] Grinding
Process: outer diameter (OD-) grinding; semi-finish sidegrinding of
chrome plated slots [0545] Machine: Chris Marie, adopted to
customer needs [0546] Workpiece: vessel engine piston with diameter
460 mm, 4 slots per piston [0547] Parameters: semi finish
side-grinding of chrome plated slots, 4 slots per piston; stock
removal: 0.3-0.5 mm per side [0548] Dressing: Multi-point diamond
dresser MKD4x0,8
C. Results
TABLE-US-00006 [0549] TABLE 5 Results of Example III Comparative
Example Ref. III-2 Example III-1 Total infeed [mm] 0.43 0.30
Effective take of material per 0.23 0.25 slot [mm] Dressing 9 times
0.01 mm 2 times 0.01 mm Dressing without infeed, to 6 times 4 times
open the wheel again Grinding time per side [min] 20 11
[0550] Using the same parameter sets the test wheel gains
improvements with regard to the grinding time as well as to the
dressing process as follows:
[0551] The grinding time was reduced by 9 minutes per side, each
slot showing two sides this results in a 72 minutes decrease of the
grinding time per piston (4 slots per piston). In comparison to the
reference wheel the grinding time can be reduced almost by 50%.
[0552] Considering the dressing process 7 dressing cycles less were
necessary for the test wheel. Calculating the total dressing amount
for both sides of all slots (2 sides each slot, 4 slots) leads to
0.56 rum less wheel usage.
Example IV
Outer Diameter (OD) Grinding
A. Manufacturing Process of Abrasive Grinding Tools
[0553] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 6 were prepared as described in Example I.
TABLE-US-00007 TABLE 6 Characteristics of Grinding Wheels used in
Example IV Comparative Green Example IV-1 Example Ref. IV-2
Structure Rim Center Rim Center Abrasive Mix 6 Mix 9 Mix 13 Mix 9
Grain Shaped 87.72 abrasive grain 80+ 3M .TM. Ceramic 17.54
Abrasive Grit 60 Grain 321 White fused 87.72 70.18 87.72 alumina
F54, 60, F54, 60, 70 F54, 60, 70 70 Vitreous bond 12.28 12.28 12.28
12.28 Starch 0.80 0.80 0.80 0.80 Liquid 3.12 3.12 3.12 3.12
temporary binder mix Moulding 2.300 2.300 2.190 2.190 density
[g/cm.sup.3] Wheel Wheel Type** Type IX Type VII Shape T5N T5N
Dimension 610 .times. 100 .times. 610 .times. 100 .times.
304.8-1-390 .times. 50 304.8-1-390 .times. 50 **(see Table 1)
B. Testing Procedure
[0554] The grinding wheels prepared as in Example IV were tested in
an outer diameter (OD) grinding application in order to establish
the grinding performance of the wheels.
[0555] Using the wheels of Example IV, grinding tests were
performed using the following grinding conditions: [0556] Grinding
Process: outer diameter (OD-) grinding [0557] Machine: Schaudt
FlexGrind M [0558] Workpiece: drive shaft showing diameter 170 mm,
140 mm, and 160 mm, case hardened to 60-62 HRc; material:
17CrNiMo6; required surface quality R.sub.a 0.8 .mu.m [0559]
Parameters: see Table 7; grinding stock 1 mm; dressing every 2
parts one stroke [0560] Dressing: Diamond dresser CVD
1.0.times.1.0.times.4 D (one rod)
C. Results
TABLE-US-00008 [0561] TABLE 7 Results of Example IV Infeed Grinding
Infeed semi- Infeed time v.sub.c roughing roughing finishing Speed
roughing Q'.sub.w [m/s] [mm/min] [mm/min] [mm/min] ratio q.sub.s
[min:sec] [mm.sup.3/mm/s] R.sub.a [.mu.m] Comparative Example Ref.
O170 k6 45 0.2584 0.0861 0.0215 92 05:08 2.2 0.647 Ref. IV-2 Mix f2
Ref. O140 k6 45 0.3137 0.1046 0.0261 95 2.3 Mix f2 Ref. O160 h11 45
0.2628 0.1314 0.0788 90 2.3 Mix f2 Example IV-1: Test 1 Mix f1 O170
k6 45 0.2584 0.0861 0.0215 92 05:08 2.2 0.602 Mix f1 O140 k6 45
0.3137 0.1046 0.0261 95 2.3 Mix f1 O160 h11 45 0.2628 0.1314 0.0788
90 2.3 Example IV-1: Test 2 Mix f1 O170 k6 63 0.5610 0.1350 0.0330
60 01:32 5 0.466 Mix f1 O140 k6 63 0.6820 0.1600 0.0400 60 5 0.38
Mix f1 0160 h11 63 0.5960 0.1430 0.0788 60 5 0.337 Example IV-1:
Test 3 Mix f1 O170 k6 63 0.8988 0.1350 0.0330 60 8 Mix f1 O140 k6
63 1.0913 0.1600 0.0400 60 8 Mix f1 O160 h11 63 0.9549 0.1430
0.0788 60 8
[0562] The tests were performed in three test series using
different parameter sets. Test 1 applying the same parameter set as
for the reference results in a better surface quality represented
by the mean value of surface roughness R.sub.a. The results of Test
2 and Test 3 show that the test wheel enables an increase in the
operating speed v.sub.c, as well as higher infeed rates for each
machining step thus resulting in a marked increase in the specific
material removal rate Q'.sub.W and in ca. 70% shorter grinding
times as described for the roughing. The surface quality generally
improves using the test specification and results in a reduction of
the mean surface roughness R.sub.a by 50%.
Example V
Single Rib Gear Grinding
A. Manufacturing Process of Abrasive Grinding Wheels
[0563] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 8 were prepared as described in Example I:
B. Testing Procedure
[0564] The grinding wheels prepared as in Example V were tested in
a single rib gear grinding application in order to establish the
grinding performance of the wheels.
[0565] Using the wheels of Example V, two sets of grinding tests
were performed using the following grinding conditions:
Test 1:
[0566] Grinding Process: single rib gear grinding [0567] Grinding
tool: T1ESP 400.times.60.times.127 V=50.degree., U=15 [0568]
Machine: Hofler Rapid 2500 (37 kW) [0569] Workpiece: Planet gear,
normal module 13.5 mm, pressure angle: 20.degree., helix angle:
7.25.degree., number of teeth: 50, face width 380 mm; Material:
18CrNiMo7-6 case hardened to 62 HRc [0570] Parameters: operating
speed v.sub.c of grinding wheel: 30 m/s
Test 2:
[0570] [0571] Grinding Process: single rib gear grinding [0572]
Grinding Tool: T1ESP 400.times.50.times.127 V=65.degree. U=12
[0573] Machine used: Hofler Rapid 1250 (24 kW) [0574] Workpiece:
Planet gear, normal module 13.5 min, pressure angle: 20.degree.,
helix angle: 7.degree., number of teeth: 43, face width 250 mm;
Material: 17CrNiMo6 Planet gear, normal module 16 mm, pressure
angle: 20.degree., helix angle: 6.25.degree., number of teeth: 31,
face width 371.2 mm; Material: 18CrNiMo7-6 case hardened to 62 HRc,
required mean value of surface roughness R.sub.a 0.4 .mu.m (both
workpieces) [0575] Parameters: operating speed v.sub.c of grinding
wheel: 30 m/s
TABLE-US-00009 [0575] TABLE 8 Characteristics of the test wheels of
Example V Example V-1 Example V-2 Example V-3 Green Structure Rim
Center Rim Center Rim Center Abrasive Grain Mix 14 Mix 15 Mix 16
Mix 15 Mix 6 Mix 15 Shaped 27.52 45.87 91.74 abrasive 80+ 80+ 80+
grain 3M .TM. Ceramic Abrasive Grain 321 White fused 64.22 91.74
45.87 91.74 91.74 alumina F46, 60 F46, F46, 60 F46, F46, 54, 54, 60
54, 60 60 Vitreous bond 8.26 8.26 8.26 8.26 8.26 8.26 Starch 2.10
2.10 2.10 2.10 2.10 2.10 Liquid 3.37 3.37 3.37 3.37 3.37 3.37
temporary binder mix Pore 9.17 9.17 9.17 9.17 9.17 9.17 inducing
(Type A) (Type A) (Type A) (Type A) (Type A) (Type A) agent
Moulding 2.090 2.090 2.090 2.090 2.090 2.090 density [g/cm.sup.3]
Wheel Wheel Type Type IV Type IV Type IV ** Shape T1ESP T1ESP T1ESP
Dimension 400 .times. 50 .times. 127 V 400 .times. 50 .times. 127 V
400 .times. 50 .times. 127 V 65.degree., 65.degree., U = 12
65.degree., U = 12 U = 12 (Test 2) (Test 2) (Test 2) 400 .times. 60
.times. 127 V 50.degree., U = 15 (Test 1) Comparative Comparative
Example V-4 Example Ref. V-5 Example Ref. V-6 Green Structure Rim
Center Rim Center Rim Center Abrasive Grain Mix 3 Mix 17 Mix 10 Mix
9 Mix 18 Mix 17 Shaped 27.40 abrasive 80+ grain 3M .TM. 27.52 27.3
Ceramic Grit 60 Grit 80 Abrasive Grain 321 White fused 63.92 91.32
64.22 91.74 63.92 91.32 alumina F70, F70, F54, 60, F54, F70, 80,
F70, 80, F80, 80, 100 70 60, 70 100 100 F100 Vitreous bond 8.68
8.68 8.26 8.26 8.68 8.68 Starch 1.62 1.62 1.60 1.60 1.62 1.62
Liquid 3.01 3.01 3.49 3.49 3.01 3.01 temporary binder mix Pore
18.26 18.26 18.35 18.35 18.26 18.26 inducing (Type B) (Type B)
(Type B) (Type B) (Type B) (Type B) agent Moulding 1.980 1.980
2.020 2.020 1.980 1.980 density [g/cm.sup.3] Wheel Wheel Type Type
IV Type IV Type IV ** Shape T1ESP T1ESP T1ESP Dimension 400 .times.
50 .times. 127 V 50.degree., 400 .times. 50 .times. 127 V
50.degree., 400 .times. 50 .times. 127 V 65.degree., U = 15 (Test
1) U = 12 (Test 2) U = 12 (Test 2) **(see Table 1)
C. Results
TABLE-US-00010 [0576] TABLE 9A Results of Test 1 - Test series A
Comparative Example Ref. V-5 Example V-4 Example V-3 Specific
material removal 16 24 30 rate Q'.sub.W [mm.sup.3/mm/s] Specific
chip volume V'.sub.W 10.000 15.000 18.000 [mm.sup.3/mm] Mean value
of surface 0.40 0.30 0.30 roughness R.sub.a [.mu.m]
TABLE-US-00011 TABLE 9B Results of Test 1 - Test series B showing a
specific material removal rate Q'.sub.W of 16 mm.sup.3/mm/s
Comparative Example Ref. V-5 Example V-4 Example V-3 Specific
material removal 16 16 16 rate Q'.sub.W [mm.sup.3/mm/s] Specific
chip volume V'.sub.W 10.000 18.000 30.000 [mm.sup.3/mm]
TABLE-US-00012 TABLE 9C Results of Test 2 Comparative Example Ref.
Example Example Example V- V-6 V-1 V-2 3 Specific material 14 24 30
30 removal rate Q'.sub.W [mm.sup.3/mm/s] Specific chip 800 1500
2500 2500 volume V'.sub.W [mm.sup.3/mm] Comment: Too less machine
power
[0577] The test series show an increase in the specific material
removal rate Q'.sub.W as well as in the specific chip volume
V'.sub.W for the test wheels in comparison to the reference wheels
independent from the workpiece material type and dimensions. In
Test 2 the machine used had too less machine power to increase both
parameters for Example V-3. In general it can be seen that the
increase depends on the amount of shaped abrasive particles
resulting in the highest values for an abrasive fraction entirely
consisting of shaped abrasive particles (Example V-3). Using an
amount of 30% of shaped abrasive grain (Example V-1 and Example
V-4) results in an increase in the specific chip volume V'.sub.W in
the range of 50-90% and an increase of the specific material
removal rate Q'.sub.W in the range of 50-70%. Increasing the amount
of shaped abrasive grain to 50% (Example V-2) gains an increase by
ca. 210% for the specific chip volume and ca. 1.15% for the
specific material removal rate. Keeping the specific material
removal rate Q'.sub.W constant, in comparison to the reference
grinding wheel Comparative Example Ref. V-5 Test Series B of Test 1
shows an increase in the specific chip removal of 80% for Example
V-4 and of 200% for Example V-3, thus resulting in longer dressing
cycles, less redressing and proving the excellent form and profile
holding of the test grinding wheels. Even under these severe
grinding conditions no workpiece burning or discoloration was
observed. Considering the surface quality of the workpieces an
improvement can be seen related to the test wheels of Test 1 (Test
Series A) thus reflected by the mean value of the surface roughness
R.sub.a and its decrease by 25% with regard to the reference wheel.
The test series document the beneficial effects of abrasive tools
consisting of shaped abrasive grain referring to high performance
grinding and combined with highly efficient process and tool
economics.
Example VI
Generating Gear Grinding
A. Manufacturing Process of Abrasive Grinding Tools
[0578] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 10 were prepared as described in Example I.
TABLE-US-00013 TABLE 10 Characteristics of Grinding Wheels used in
Example VI Comparative Example Ref. Green Structure Example VI-1
VI-2 Abrasive Grain Mix 11 Mix 19 Shaped abrasive grain 86.58 60+
3M .TM. Ceramic 4.45 Abrasive Grain 321 grit 90 Cerpass XTL .RTM.,
22.25 code 0560 Grit 90 Single crystal alumina 44.5 F80 White fused
alumina 17.8 F70 Vitreous bond 13.42 11.00 Starch 1.20 0.96 Liquid
temporary 4.56 3.29 binder mix Pore inducing agent 12.99 6.05 (Type
A) (Type A) Moulding density 2.040 2.125 [g/cm.sup.3] Wheel Wheel
Type** Type IX Type VII Shape T1SP T1SP Dimension 320 .times. 230
.times. 110 mm 320 .times. 230 .times. 110 mm modulus 9.0 mm,
modulus 9.0 mm, pressure angle 20.degree., 2 pressure angle
20.degree., 2 starts starts **(see Table 1)
B. Testing Procedure
[0579] The grinding wheels prepared as in Example VI were tested in
a generating gear grinding application in order to establish the
grinding performance of the wheels. Using the wheels of Example VI,
grinding tests were performed using the following grinding
conditions [0580] Grinding Process: Generating gear grinding using
so-called grinding worms [0581] Machine used: Liebherr LCS1200 (35
kW) [0582] Work piece: Helical gear, normal module 9 mm, pressure
angle: 20.degree., helix angle: 10.degree., number of teeth: 65,
face width 153 mm; Material: 18CrNiMo6-7, case hardened to 58 HRc
[0583] Parameters: operating speed v.sub.c of grinding wheel: 59
m/s
C. Results
TABLE-US-00014 [0584] TABLE 11 Results of Example VI Specific
material Material removal removal rate Infeed Feed rate rate Q'W
roughing roughing Q.sub.max [mm.sup.3/ radial [mm] [mm/rpm]
Shifting [mm.sup.3/s] mm/s] Comparative 0.34 0.45 diagonal 267 6.5
Example Ref. VI-2 Example 0.34 0.45 diagonal 269 6.5 VI-1: Test 1
Example 0.34 0.75 diagonal 475 10.2 VI-1: Test 2 Example 0.34 1.00
diagonal 502 13.6 VI-1; Test 3 Example 0.34 1.30 diagonal 772 17.7
VI-1: Test 4 Example 0.45 1.20 diagonal 883 21.0 VI-1: Test 5
[0585] The tests were performed in five test series using different
grinding parameters thus described by the infeed and the feed rate
for the roughing process. Varying the feed rate shows an increase
in the specific material removal rate Q'.sub.W in the range of
55-170%. Increasing the feed rate as well as the infeed results in
a marked increase in the specific material removal rate Q'.sub.W
with regard to the reference wheel thereby reducing the process
consisting of three roughing steps by one roughing step thus
effecting the total grinding time. Even under these severe
conditions the test wheel showed no clogging.
Example VII
Surface Grinding with Segments
A. Manufacturing Process of Abrasive Grinding Tools
[0586] Vitrified bonded abrasive grinding segments having
composition, type, dimension (segment width B.times.thickness
C.times.length L), shape and bond as described in Table 12 were
prepared as described in Example I.
TABLE-US-00015 TABLE 12 Characteristics of Grinding Segments used
in Example VII Comparative Green Structure Example VII-1 Example
VII-2 Example Ref. VII-3 Abrasive Grain Mix 11 Mix 20 Mix 21 Shaped
abrasive 91.74 27.52 grain 60+ 60+ Cerpass TGE .RTM., 27.3 code
0557 Grit 36 White fused 64.22 63.7 alumina F24, F30 F24, F30
Vitreous bond 8.26 8.26 9.00 Starch 1.50 1.50 1.74 Liquid temporary
3.85 3.85 3.67 binder mix Pore inducing 13.76 13.76 15.00 agent
(Type B) (Type B) (Type B) Moulding density 2.080 2.080 2.070
[g/cm.sup.3] Segments Abrasive tool Type II Type Il Type II Type**
Shape T3101 T3101 T3101 Dimension 120 .times. 40 .times. 200 120
.times. 40 .times. 200 120 .times. 40 .times. 200 **(see Table
1)
B. Testing Procedure
[0587] The segments prepared as in Example VII were tested in
surface grinding application in order to establish the grinding
performance of the segments. Using the segments of Example VII,
grinding tests were performed using the following grinding
conditions: [0588] Grinding Process: surface grinding [0589]
Machine: Kehren D15CNC (110 kW), Table diameter 1500 mm, grinding
head diameter 800 mm (applying 14 segments
T3101-120.times.40.times.200) [0590] Workpiece: Die plate,
546.times.696.times.66.95 mm, Material: 1.2085 (soft, high chrome
content 16-17%) [0591] Parameters: operating speed v.sub.c 800 rpm,
feed rate v.sub.w 15 rpm, grinding stock, 0.3 mm, traverse speed of
(see Table 13) [0592] Dressing: Multipoint diamond dresser, 16
mm
C. Results
TABLE-US-00016 [0593] TABLE 13 Results of Example VII Total
Grinding v.sub.f1 v.sub.f2 v.sub.f3 Wear time [mm/min] [mm/min]
[mm/min] R.sub.a [.mu.m] [mm] [min:sec] Example VII-1 Test 1 0.15
0.15 0.10 0.97 0.28 07:10 Test 2 0.30 0.30 0.10 1.1 0.33 05:45 Test
3 0.30 0.30 0.10 1.0 0.39 06:15 Test 4 0.50 0.50 0.10 0.97 0.36
06:05 Example VII-2 Test 1 0.15 0.15 0.10 1.9 0.35 07:45 Test 2
0.30 0.30 0.10 1.4 0.50 07:30 Test 3 0.15 0.15 0.10 1.3 0.28 07:30
Test 4 0.15 0.15 0.10 0.25 08:00
[0594] The tests were performed in comparison to a reference
segment comprising extruded abrasive rods using different parameter
sets. For the reference conditions as in Test 1 were chosen. In
general the traverse speed was increased from 0.15 to 0.30, and
0.50 mm/min, respectively. With the machine table present the
reference set of segments was able to grind two die plates
simultaneously in a total grinding time of 10-12 minutes.
Considering the corresponding set of test segments four die plates
could be ground simultaneously in ca. 6 minutes (Mix f1, ca. -50%)
and ca. 7.5-8 minutes (Mix f2, ca. -30%). The wear of the tests
segments was reduced to 0.3-0.4 mm (ca. -35%) in comparison to the
reference segments showing a wear of 0.4-0.7 mm. In comparison to
the reference segments no clogging of the test segments was
observed. The workpiece showed silk-mat surface quality. In general
the test series resulted in a marked improvement with regard to the
efficiency of the entire grinding process.
Example VIII
Surface Grinding--Reciprocating Method
A. Manufacturing Process of Abrasive Grinding Tools
[0595] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 14 were prepared as described in Example I.
TABLE-US-00017 TABLE 14 Characteristics of Grinding Wheels used in
Example VIII Comparative Example VIII-1 Example Ref. VIII-2 Green
Structure Rim Center Rim Center Abrasive Mix 11 Mix 22 Mix 12 Mix
22 Grain Shaped 92.17 abrasive 60+ grain 3M .TM. 26.79 Ceramic grit
46 Abrasive Grain 321 White fused 92.17 62.51 89.30 alumina F40,
46, 54 F40, 46, 54 F40, 46, 54 Vitreous 7.83 7.83 10.70 10.70 bond
Starch 2.10 2.10 1.25 1.25 Liquid 3.57 3.57 3.86 3.86 temporary
binder mix Pore 13.82 13.82 17.86 17.86 inducing (Type A) (Type A)
(Type B) (Type B) agent Moulding 2.240 2.240 2.050 2.050 density
[g/cm.sup.3] Wheel Wheel Type** Type I Type IV Shape T26 T26
Dimension 400 .times. 100/6 .times. 400 .times. 100/6 .times.
127-2-200 .times. 25/11 A = 2 127-2-200 .times. 25/11 A = 2 **(see
Table 1)
B. Testing Procedure
[0596] The grinding wheels prepared as in Example VIII were tested
in a reciprocating grinding application in order to establish the
grinding performance of the wheels. Using the wheels of Example
VIII, grinding tests were performed using the following grinding
conditions [0597] Grinding Process: reciprocating grinding [0598]
Machine: Rosa Linea Avion 13.7 P (17 kW) [0599] Workpiece:
customer-specific component; type of material: GGG60; required mean
value of surface roughness R.sub.a 1.8 mm [0600] Parameters:
Roughing via plunge grinding and finishing via reciprocating
grinding; operating speed v.sub.c and other grinding parameters
(see Table 14) [0601] Dressing: multipoint diamond dresser
C. Results
TABLE-US-00018 [0602] TABLE 15 Results for Example VIII Counts
Grinding Infeed/ Speed Specific material Surface of v.sub.c Infeed
stock pass ratio removal rate Q'.sub.w Roughness Process passes
[m/s] [mm/min] [mm] [mm] q.sub.s [mm.sup.3/mm/s] R.sub.z [.mu.m]
Comparative Roughing 3.times. 32 16000 0.8 0.007 120 2 Example Ref.
VIII-2 Finishing 1.times. 32 16000 0.03 0.005 120 1.4 6.33 Example
VIII-1: Roughing 3.times. 32 16000 0.8 0.007 100 2 Test 1 Finishing
1.times. 32 16000 0.03 0.005 100 1.4 3.94 Example VIII-1: Roughing
3.times. 32 16000 0.8 0.014 100 4 Test 2 Finishing 1.times. 27
16000 0.03 0.005 100 1.4 3.33 Example VIII-1: Roughing 3.times. 27
16000 0.8 0.020 100 5.3 Test 3 Finishing 1.times. 27 16000 0.03
0.005 100 1.4 5.64
[0603] The results are shown for the roughing as well as for the
finishing process. The roughing process was investigated by three
test series using different grinding parameters. The parameter set
for the finishing process was kept as for the reference wheel.
Performing the tests with the same parameter set as for the
reference wheel gains a higher surface quality as for the
reference, represented by a lower value for the average roughness
depth R.sub.z which means a mean value for the surface roughness of
0.64 .mu.m for Test 1. In Test 2 and Test 3 the infeed per pass was
increased by 100-185% resulting in 100-165% higher specific
material removal rates Q' w and for Test 2 in a further improvement
of the surface quality of the workpiece (R.sub.a 0.49 .mu.m) in
comparison to the reference test. Even under the grinding
conditions of Test 3a better surface quality (R.sub.a 0.88 .mu.m)
was obtained than with the reference wheel. Additionally it was
observed that the reference wheel showed clogging and the workpiece
became unusually warm during grinding. Considering all test series
the test wheel does not show this behavior. The dressing after each
plunge of the roughing process was reduced to dressing after the
third plunge thus leading to an increase in efficiency of the
entire grinding process.
Example IX
Surface Grinding--Creep-Feed Grinding
A. Manufacturing Process of Abrasive Grinding Tools
[0604] Vitrified bonded abrasive grinding wheels having
composition, type, dimension (wheel
diameter.times.thickness.times.bore diameter), shape and bond as
described in Table 16 were prepared as described in Example I.
TABLE-US-00019 TABLE 16 Characteristics of Grinding Wheels used in
Example IX Example 1X-1 Example 1X-2 Comparative Example Ref. IX-3
Green Structure Rim Center Rim Center Rim Center Abrasive Grain Mix
3 Mix 17 Mix 6 Mix 17 Mix 2 Mix 17 Shaped abrasive grain 26.32
87.72 80+ 80+ 3M .TM. Ceramic Abrasive 26.32 Grain 321 Grit 80, 90
White fused alumina 61.40 87.72 87.72 61.40 87.72 F70, 80, 100 F70,
80, 100 F70, 80,100 F70, 80, 100 F70, 80, 100 Vitreous bond 12.28
12.28 12.28 12.28 12.28 12.28 Starch 1.10 1.10 1.50 1.50 1.10 1.10
Liquid temporary binder mix 3.93 3.93 4.74 4.74 3.93 3.93 Pore
inducing agent 21.93 21.93 13.82 13.82 21.93 21.93 (Type A) (Type
A) (Type B) (Type B) (Type A) (Type A) Moulding density
[g/cm.sup.3] 1.870 1.870 2.020 2.020 1.870 1.870 Wheel Wheel Type *
Type VI Type IV Type VI Shape T1MSP T1MSP T1MSP Dimension 600
.times. 65 .times. 203, 600 .times. 65 .times. 203, 600 .times. 65
.times. 203, 2 V = 20.degree. U = 1 2 V = 20.degree. U = 1 2 V =
20.degree. U = 1 **(see Table 1)
B. Testing Procedure
[0605] The grinding wheels prepared as in Example IX were tested in
a creep-feed grinding application in order to establish the
grinding performance of the wheels. Using the wheels of Example IX,
grinding tests were performed using the following grinding
conditions [0606] Grinding Process: creep-feed grinding [0607]
Machine: Magerle MGC [0608] Workpiece: saw blades, to be ground:
2.times.100.times.110 mm, tooth depth 3 mm [0609] Parameters: see
Table 17, two wheels in a set for grinding both sides of workpiece
[0610] Dressing: diamond rotary dressing tool, synchronous
dressing, ratio of surface speeds of grinding wheel and dressing
roll 0.75
C. Results
TABLE-US-00020 [0611] TABLE 17 Results for Example IX Comparative
Example Example Ref. IX-3 Example IX-1 IX-2- Operating speed
v.sub.c 45 49 40 [m/s] Feed rate 550 1200 800 v.sub.W[mm/min]
Dressing 2 .times. 0.03 mm 1 .times. 0.03 mm 1 .times. 0.02 mm
[0612] The main improvements of the test specifications can be
referred to an increase in the feed rate and to the dressing
process. The dressing process was improved by reducing the number
of dressing cycles by 50%. For Example IX-1 the dressing amount was
kept constant but in total was reduced by 50% (0.03 mm instead of
0.06 mm). For Example IX-2 the dressing amount was decreased to
0.02 mm this in total reflecting an improvement by ca. 65%. Due to
the machine settings no further variation of the grinding
parameters could not be tested. Even with this restriction an
increase of the feed rate by 45-120% was obtained. Additionally
considering the dressing process the efficiency of the entire
grinding process was improved.
* * * * *
References