U.S. patent application number 16/077120 was filed with the patent office on 2019-01-31 for depressed center grinding wheel.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Thu A. Nguyen, Loc X. Van.
Application Number | 20190030684 16/077120 |
Document ID | / |
Family ID | 58264644 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190030684 |
Kind Code |
A1 |
Van; Loc X. ; et
al. |
January 31, 2019 |
DEPRESSED CENTER GRINDING WHEEL
Abstract
A depressed center grinding wheel comprises an abrasive disc.
The abrasive disc comprises a working layer, an intermediate layer,
a back layer, and at least two reinforcing scrims. The working
layer comprises first abrasive particles retained in a first binder
material. The first abrasive particles include from 40 to 100
weight percent of first shaped abrasive particles. The back layer
comprises second abrasive particles retained in a second binder
material. The second abrasive particles include first crushed
abrasive particles and are essentially free of shaped abrasive
particles. The intermediate layer is disposed between the working
layer and the back layer. The intermediate layer comprises third
abrasive particles retained in a third binder material. The third
abrasive particles include 25 to 75 weight percent of second shaped
abrasive particles.
Inventors: |
Van; Loc X.; (Woodbury,
MN) ; Nguyen; Thu A.; (Woodbury, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
58264644 |
Appl. No.: |
16/077120 |
Filed: |
February 27, 2017 |
PCT Filed: |
February 27, 2017 |
PCT NO: |
PCT/US2017/019670 |
371 Date: |
August 10, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62302977 |
Mar 3, 2016 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24D 5/14 20130101; B24D
7/14 20130101 |
International
Class: |
B24D 7/14 20060101
B24D007/14 |
Claims
1-13. (canceled)
14. A depressed center grinding wheel comprising an abrasive disc
having a working surface and a back surface opposite the working
surface, wherein the working surface has a depressed center
portion, and wherein the abrasive disc comprises: a working layer
comprising first abrasive particles retained in a first binder
material, the first abrasive particles comprising first shaped
abrasive particles, wherein the first shaped abrasive particles
comprise from 40 to 100 weight percent of the first abrasive
particles; a back layer comprising second abrasive particles
retained in a second binder material comprising first crushed
abrasive particles and essentially free of shaped abrasive
particles; an intermediate layer disposed between the working layer
and the back layer, the intermediate layer comprising third
abrasive particles retained in a third binder material, the
intermediate layer comprising second shaped abrasive particles and
second crushed abrasive particles, wherein the second shaped
abrasive particles comprise 25 to 75 weight percent of the second
abrasive particles; a first reinforcing scrim sandwiched between
the back layer and the intermediate layer; and a second reinforcing
scrim adjacent one of: the back layer opposite the intermediate
layer; the intermediate layer opposite the back layer; or the
working layer opposite the intermediate layer.
15. The depressed center grinding wheel of claim 14, wherein the
second reinforcing scrim is sandwiched between the working layer
and the intermediate layer.
16. The depressed center grinding wheel of claim 15, further
comprising a third reinforcing scrim bonded to the working layer
opposite the intermediate layer.
17. The depressed center grinding wheel of claim 14, wherein the
second reinforcing scrim is secured to the back layer opposite the
intermediate layer.
18. The depressed center grinding wheel of claim 17, further
comprising a third reinforcing scrim sandwiched between the
intermediate layer and the working layer.
19. The depressed center grinding wheel of claim 17, further
comprising a fourth reinforcing scrim bonded to the working layer
opposite the intermediate layer.
20. The depressed center grinding wheel of claim 14, wherein the
first shaped abrasive particles comprise triangular shaped abrasive
particles.
21. The depressed center grinding wheel of claim 14, wherein the
second shaped abrasive particles comprise triangular shaped
abrasive particles.
22. The depressed center grinding wheel of claim 14, wherein the
ratio of the weight percent of the first shaped abrasive particles
in the first abrasive particles to the weight percent of the second
shaped abrasive particles in the second abrasive particles is from
40:60 to 60:40.
23. The depressed center grinding wheel of claim 14, wherein the
ratio of the weight percent of the first shaped abrasive particles
in the first abrasive particles to the weight percent of the second
shaped abrasive particles in the second abrasive particles is from
45:55 to 55:45.
24. The depressed center grinding wheel of claim 14, wherein the
first and second shaped abrasive particles comprise alpha
alumina.
25. The depressed center grinding wheel of claim 14, further
comprising a centrally disposed arbor hole extending through the
abrasive disc.
26. The depressed center grinding wheel of claim 14, further
comprising an attachment member centrally disposed on the back
surface of the abrasive disc.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to depressed center grinding
wheels.
BACKGROUND
[0002] Depressed center grinding wheels are often used in
combination with a handheld portable grinder held by an operator,
either at an angle of 90 degrees (e.g., when used as a cut of
wheel) or at an angle of up to about 30 degrees (e.g., when used
for grinding welding beads, flash, gate, and risers off of
castings), more typically about 15 degrees, relative to the surface
of the workpiece being abraded. Depressed center wheels may also be
referred to in the abrasive art as raised hub wheels or by their
shape designation of "Type" (e.g., Types 27, 28, and 29), with Type
27 being the most popular.
[0003] The depressed center design allows a flange/lock nut to
recess within the wheel so that it can be used for various grinding
and cutting applications. Bonded abrasive articles have abrasive
particles bonded together by a bonding medium. The bonding medium
is typically an organic resin, but may also be an inorganic
material such as a ceramic or glass (i.e., vitreous bonds).
Examples of bonded abrasive articles include stones, hones, and
abrasive wheels such as, for example, grinding wheels and cut-off
wheels.
[0004] Grinding wheels are of various shapes may be, for example,
driven by a stationary-mounted motor such as, for example, a bench
grinder, or attached and driven by a hand-operated portable
grinder. Hand-operated portable grinders are typically held at a
slight angle relative to the workpiece surface, and may be used to
grind, for example, welding beads, flash, gates, and risers off
castings.
SUMMARY
[0005] In recent years there have efforts to include shaped
abrasive particles in various grinding wheels (e.g., depressed
center grinding wheels); however, the relatively high cost of such
abrasive particles remains an obstacle to their widespread
acceptance in the industry. It would be desirable to have
alternative constructions that can reduce cost of grinding wheels
by reducing the amount of shaped abrasive particles while achieving
comparable abrading performance.
[0006] Advantageously, the present disclosure solves this technical
problem in the case of depressed center grinding wheels by
providing a depressed center grinding wheel comprising an abrasive
disc having a working surface and a back surface opposite the
working surface, wherein the working surface has a depressed center
portion, and wherein the abrasive disc comprises:
[0007] a working layer comprising first abrasive particles retained
in a first binder material, the first abrasive particles comprising
first shaped abrasive particles, wherein the first shaped abrasive
particles comprise from 40 to 100 weight percent of the first
abrasive particles;
[0008] a back layer comprising second abrasive particles retained
in a second binder material comprising first crushed abrasive
particles and essentially free of shaped abrasive particles;
[0009] an intermediate layer disposed between the working layer and
the back layer, the intermediate layer comprising third abrasive
particles retained in a third binder material, the intermediate
layer comprising second shaped abrasive particles and second
crushed abrasive particles, wherein the second shaped abrasive
particles comprise 25 to 75 weight percent of the second abrasive
particles;
[0010] a first reinforcing scrim sandwiched between the back layer
and the intermediate layer; and
[0011] a second reinforcing scrim adjacent one of: [0012] the back
layer opposite the intermediate layer; [0013] the intermediate
layer opposite the back layer; or [0014] the working layer opposite
the intermediate layer.
[0015] Depressed center grinding wheels according to the present
disclosure are useful; for example, for abrading a surface of a
workpiece.
[0016] Accordingly, in another aspect, the present disclosure
provides a method of abrading a workpiece, the method comprising
contacting a workpiece with the working surface of a depressed
center grinding wheel according to the present disclosure and
moving the working surface relative to the workpiece to abrade the
workpiece.
[0017] As used herein, the term "nominal" means: of, being, or
relating to a designated or theoretical size and/or shape that may
vary somewhat from the actual (e.g., within a manufacturing process
tolerance). As used herein, the term "shaped abrasive particle"
refers to an abrasive particle (e.g., a ceramic abrasive particle)
with at least a portion of the abrasive particle having a nominal
predetermined shape corresponding to a mold cavity used to form a
precursor shaped abrasive particle, which is then calcined and
sintered to form the shaped abrasive particle. Shaped abrasive
particle as used herein excludes abrasive particles shaped solely
by a mechanical crushing process.
[0018] As used herein, the term "crushed abrasive particle" refers
to an abrasive particle shaped solely by a mechanical crushing
process.
[0019] As used herein, the term "essentially free of" means
containing less than 5 weight percent of (preferably less than 1
weight percent of, or even free of).
[0020] Features and advantages of the present disclosure will be
further understood upon consideration of the detailed description
as well as the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic side view of an exemplary depressed
center grinding wheel 100 according to the present disclosure.
[0022] FIGS. 2A-2F are schematic cross-sectional representations
showing various exemplary configurations of scrim placement in
exemplary depressed center grinding wheels 100a-100f.
[0023] FIG. 3 is a schematic perspective view of exemplary shaped
abrasive particle 300.
[0024] FIG. 4 is a schematic side view showing a depressed center
grinding wheel 100 abrading a workpiece 400 according to the
present disclosure.
[0025] Repeated use of reference characters in the specification
and drawings is intended to represent the same or analogous
features or elements of the disclosure. It should be understood
that numerous other modifications and embodiments can be devised by
those skilled in the art, which fall within the scope and spirit of
the principles of the disclosure. The figures may not be drawn to
scale.
DETAILED DESCRIPTION
[0026] Referring now to FIG. 1, depressed center grinding wheel 100
comprises an abrasive disc 110 having a working surface 122 and a
back surface 142 opposite the working surface 122. Working surface
112 has a depressed center portion 114. Abrasive disc 110 comprises
working layer 120, intermediate layer 130, and back layer 140.
[0027] Working layer 120 comprises first abrasive particles 124
retained in a first binder material 126. The first abrasive
particles 124 comprise first shaped abrasive particles 125. The
first shaped abrasive particles 125 comprise from 40 to 100 weight
percent of the first abrasive particles 124. The first abrasive
particles 124 may also comprise crushed abrasive particles, if
desired, in amounts of up to about 60 percent by weight (e.g., 5 to
60 percent by weight, 20 to 60 percent by weight, or 40 to 60
percent by weight), based on the total weight of the first abrasive
particles. The first shaped abrasive particles 125 may all be of
the same size and shape or they may be a mixture of various shaped
abrasive particles with different sizes, shapes, and/or
compositions. In some preferred embodiments, the first abrasive
particles are all shaped abrasive particles having the same nominal
size and shape. The first shaped abrasive particles 125 may all be
of the same size and shape or they may be a mixture of various
shaped abrasive particles with different sizes and/or shapes.
Likewise, any optional crushed abrasive particles included in the
first abrasive particles may have any size distribution and/or
compositional distribution.
[0028] Back layer 140 comprises second abrasive particles 144
retained in a second binder material 146 comprises first crushed
abrasive particles 148, and is essentially free of shaped abrasive
particles (e.g., first shaped abrasive particles, second shaped
abrasive particles, or other shaped abrasive particles).
[0029] The second abrasive particles 144 comprise at least 95
percent by weight of first crushed abrasive particles, preferably
at least 99 percent by weight, and more preferably about 100
percent by weight of first crushed abrasive particles, based on the
total weight of second abrasive particles. Accordingly, the back
layer is essentially free of shaped abrasive particles. The second
abrasive particles 144 may be of any size. The second abrasive
particles 144 may have any size distribution and/or compositional
distribution.
[0030] Intermediate layer 130 is disposed between the working layer
120 and the back layer 140. The intermediate layer 130 comprises
third abrasive particles 134 retained in a third binder material
136. The intermediate layer 130 comprises second shaped abrasive
particles 135 and second crushed abrasive particles 138. The second
shaped abrasive particles 135 comprise 25 to 75 weight percent
(e.g., 30 to 60 weight percent, or 40 to 60 percent) of the second
abrasive particles. The second shaped abrasive particles 135 may
all be of the same size and shape or they may be a mixture of
various shaped abrasive particles with different sizes, shapes,
and/or compositions. In some preferred embodiments, the second
abrasive particles include second shaped abrasive particles having
the same nominal size and shape. The second shaped abrasive
particles 135 may all be of the same size and shape or they may be
a mixture of various shaped abrasive particles with different sizes
and/or shapes. Likewise, the second crushed abrasive particles may
have any size distribution and/or compositional distribution.
[0031] Preferably, the first and second shaped abrasive particles
are the same (i.e., same compositional, shape, and size
distribution); however, they may be different in other embodiments,
if desired. Likewise, the first and second crushed abrasive
particles are preferably the same (i.e., same compositional and
size distribution); however, they may be different in other
embodiments, if desired.
[0032] While shaped abrasive particles in FIG. 1 are shown as
vertically aligned triangles, this is for illustration purposes
only, and the shaped abrasive particles may have any orientation
(e.g., randomly aligned or aligned parallel to the backing).
[0033] Referring again to FIG. 1, depressed center grinding wheels
include at least two reinforcing scrims deployed at various
locations throughout the grinding wheel. First reinforcing scrim
150 is sandwiched between back layer 140 and intermediate layer
130. Second reinforcing scrim 152 (not shown) is positioned
adjacent to one of: a) back layer 140 opposite intermediate layer
130; b) intermediate layer 130 opposite back layer 140; or c)
working layer 120 opposite intermediate layer 130.
[0034] Optional centrally disposed arbor hole 170 extends through
abrasive disc 110. Optional attachment member 175 is centrally
disposed, and optionally secured by nut 180, to back surface 142 of
abrasive disc 110, although this is not a requirement.
[0035] In some embodiments, the second reinforcing scrim 152 is
sandwiched between the working layer 120 and the intermediate layer
130. Examples include the embodiments shown in FIG. 2B (shown as
152b), FIG. 2D (shown as 152d), and FIG. 2F (shown as 152f). In
some of these embodiments, a third reinforcing scrim 156 is bonded
to the working layer 110 opposite the intermediate layer (e.g., see
156b in FIG. 2B).
[0036] In some embodiments, second reinforcing scrim 152 is secured
to the back layer opposite the intermediate layer. Examples are
shown in FIG. 2A (shown as 152a), FIG. 2C (shown as 152c), and FIG.
2E (shown as 152e). In some of these embodiments, third reinforcing
scrim 156 is sandwiched between the intermediate layer and the
working layer (e.g., shown as 156e in FIG. 2E). In some of these
embodiments, an optional fourth reinforcing scrim 169 is bonded to
working layer 120 opposite intermediate layer 130 (e.g., shown as
169e in FIG. 2E).
[0037] In FIG. 2C, optional third scrim 156c is secured to working
layer 120 opposite the intermediate layer 130. Likewise, in FIG.
2F, optional third scrim 156f is secured to working layer 120
opposite the intermediate layer 130.
[0038] Depressed center grinding wheels according to the present
disclosure are generally made by compression molding, injection
molding, transfer molding, or the like. The molding can be done
either by hot or cold pressing or any suitable manner known to
those skilled in the art. During the manufacturing, the individual
components (e.g., working layer, intermediate layer, back layer,
and scrims) are typically layered up into a green body that is then
subjected to curing conditions. The green body typically contains
one or more binder material precursors, either liquid organic,
powdered inorganic, powdered organic, or a combination of thereof,
mixed with abrasive particles (i.e., shaped abrasive particles and
crushed abrasive particles selected and positioned as described
herein), and reinforcing scrims (positioned at desired locations in
the wheel). In some instances, a liquid medium (either resin or a
solvent) is first applied to the abrasive particles to wet their
outer surface, and then the wetted particles are mixed with a
powdered medium.
[0039] The various binder materials in the working layer,
intermediate layer, and back layer (which may be the same or
different, preferably the same) typically comprise a glassy
inorganic material (e.g., as in the case of vitrified abrasive
wheels), metal, or an organic resin (e.g., as in the case of
resin-depressed center grinding wheels).
[0040] Glassy vitreous binders may be made from a mixture of
different metal oxides. Examples of these metal oxide vitreous
binders include silica, alumina, calcia, iron oxide, titania,
magnesia, sodium oxide, potassium oxide, lithium oxide, manganese
oxide, boron oxide, phosphorous oxide, and the like. Specific
examples of vitreous binders based upon weight include, for
example, 47.61 percent SiO.sub.2, 16.65 percent Al.sub.2O.sub.3,
0.38 percent Fe.sub.2O.sub.3, 0.35 percent TiO.sub.2, 1.58 percent
CaO, 0.10 percent MgO, 9.63 percent Na.sub.2O, 2.86 percent
K.sub.2O, 1.77 percent Li.sub.2O, 19.03 percent B.sub.2O.sub.3,
0.02 percent MnO.sub.2, and 0.22 percent P.sub.2O.sub.5; and 63
percent SiO.sub.2, 12 percent Al.sub.2O.sub.3, 1.2 percent CaO, 6.3
percent Na.sub.2O, 7.5 percent K.sub.2O, and 10 percent
B.sub.2O.sub.3. During manufacture of a vitreous bonded depressed
center grinding wheel, vitreous binder in powder form, may be mixed
with a temporary binder, typically an organic temporary binder. The
vitrified binders may also be formed from a frit, for example
anywhere from about one to 100 percent frit, but generally 20 to
100 percent frit. Some examples of common materials used in frit
binders include feldspar, borax, quartz, soda ash, zinc oxide,
whiting, antimony trioxide, titanium dioxide, sodium
silicofluoride, flint, cryolite, boric acid, and combinations
thereof. These materials 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 very fine powder to
then be used as a frit vitreous binder precursor. The temperature
at which the frit vitreous binder precursor is matured to form a
vitreous binder is dependent upon its chemistry, but typically
ranges from about 600.degree. C. to about 1800.degree. C., although
this is not a requirement.
[0041] Examples of metal binders include tin, copper, aluminum,
nickel, and combinations thereof. Metal binder materials can be
formed by sintering metal powders, optionally containing a
temporary organic binder material that burns off during
sintering.
[0042] Organic binder materials are typically included in an amount
of from 5 to 30 percent, more typically 10 to 25, and more
typically 15 to 24 percent by weight, based of the total weight of
the depressed center grinding wheel. Phenolic resin is the most
commonly used organic binder material, and may be used in both the
powder form and liquid state. Although phenolic resins are widely
used, it is within the scope of this disclosure to use other
organic binder materials including, for example, epoxy resins,
urea-formaldehyde resins, rubbers, shellacs, and acrylic binders.
The organic binder material may also be modified with other binder
materials to improve or alter the properties of the binder
material.
[0043] Useful phenolic resins include novolac and resole phenolic
resins. Novolac phenolic resins are characterized by being
acid-catalyzed and having a ratio of formaldehyde to phenol of less
than one, typically between 0.5:1 and 0.8:1. Resole phenolic resins
are characterized by being alkaline catalyzed and having a ratio of
formaldehyde to phenol of greater than or equal to one, typically
from 1:1 to 3:1. Novolac and resole phenolic resins may be
chemically modified (e.g., by reaction with epoxy compounds), or
they may be unmodified. Exemplary acidic catalysts suitable for
curing phenolic resins include sulfuric, hydrochloric, phosphoric,
oxalic, and p-toluenesulfonic acids. Alkaline catalysts suitable
for curing phenolic resins include sodium hydroxide, barium
hydroxide, potassium hydroxide, calcium hydroxide, organic amines,
or sodium carbonate.
[0044] Phenolic resins are well-known and readily available from
commercial sources. Examples of commercially available novolac
resins include DUREZ 1364, a two-step, powdered phenolic resin
(marketed by Durez Corporation of Addison, Tex. under the trade
designation VARCUM (e.g., 29302), or HEXION AD5534 RESIN (marketed
by Hexion Specialty Chemicals, Inc. of Louisville, Ky.). Examples
of commercially available resole phenolic resins useful in practice
of the present disclosure include those marketed by Durez
Corporation under the trade designation VARCUM (e.g., 29217, 29306,
29318, 29338, 29353); those marketed by Ashland Chemical Co. of
Bartow, Fla. under the trade designation AEROFENE (e.g., AEROFENE
295); and those marketed by Kangnam Chemical Company Ltd. of Seoul,
South Korea under the trade designation "PHENOLITE" (e.g.,
PHENOLITE TD-2207).
[0045] Curing temperatures of organic binder material precursors
will generally vary with the material chosen and wheel design.
Selection of suitable conditions is within the capability of one of
ordinary skill in the art. Exemplary conditions for a phenolic
binder may include an applied pressure of about 20 tons per 4
inches diameter (224 kg/cm.sup.2) at room temperature followed by
heating at temperatures up to about 185.degree. C. (degrees
Celsius) for sufficient time to cure the organic binder material
precursor.
[0046] In some embodiments, the depressed center grinding wheels
include from about 10 to 60 percent by weight of abrasive
particles; typically 30 to 60 percent by weight, and more typically
40 to 60 percent by weight, based on the total weight of the binder
material(s) and abrasive particles.
[0047] Shaped abrasive particles composed of crystallites of alpha
alumina, magnesium alumina spinel, and a rare earth hexagonal
aluminate 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.).
[0048] In some embodiments, alpha-alumina-based shaped abrasive
particles can be made according to a multistep process. Briefly,
the method comprises the steps of making 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 sol-gel, drying the sol-gel to form precursor shaped abrasive
particles; removing the precursor shaped abrasive particles from
the mold cavities; calcining the precursor shaped abrasive
particles to form calcined, precursor shaped abrasive particles,
and then sintering the calcined, precursor shaped abrasive
particles to form shaped abrasive particles. The process will now
be described in greater detail.
[0049] The first process step 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.
[0050] 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.
[0051] The physical properties of the resulting 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.
[0052] 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. 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.
[0053] 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 disclosure 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).
[0054] 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.
[0055] 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.
[0056] 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).
[0057] 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, poly(vinyl chloride), 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.
[0058] 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.).
[0059] 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.
[0060] The cavities have a specified three-dimensional shape to
make the 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.
[0061] 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.
[0062] 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 shaped abrasive
particles.
[0063] 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.
[0064] The fifth process step involves removing resultant precursor
shaped abrasive particles with from the mold cavities. The
precursor 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.
[0065] 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 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.
[0066] The sixth process step involves calcining the precursor
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 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 shaped abrasive particles. Then the
precursor shaped abrasive particles are pre-fired again. This
option is further described in U.S. Pat. No. 5,164,348 (Wood).
[0067] The seventh process step involves sintering the calcined,
precursor shaped abrasive particles to form alpha alumina
particles. Prior to sintering, the calcined, precursor shaped
abrasive particles are not completely densified and thus lack the
desired hardness to be used as shaped abrasive particles. Sintering
takes place by heating the calcined, precursor shaped abrasive
particles to a temperature of from 1,000.degree. C. to
1,650.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 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.
[0068] In another embodiment, the duration for the sintering step
ranges from one minute to 90 minutes. After sintering, the shaped
abrasive particles can have a Vickers hardness of 10 GPa, 16 GPa,
18 GPa, 20 GPa, or greater.
[0069] 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).
[0070] Shaped abrasive particles used in the present disclosure may
comprise plates, rods, or a combination thereof, for example. In
preferred embodiments, the shaped abrasive particles have shapes
that can be characterized as thin bodies having triangular,
rectangular (including square), or other geometric shapes with
sharp points. Such shaped abrasive particles have a front face and
a back face, both of which faces have substantially the same
geometric shape. The faces are separated by the thickness of the
particle. The ratio of the length of the shortest facial dimension
of an abrasive particle to its thickness is at least 1 to 1,
preferably at least 2 to 1, more preferably at least 5 to 1, and
most preferably at least 6 to 1.
[0071] Preferred shaped abrasive particles are shaped as
rectangular (including square), or triangular plates, preferably
having a sloping sidewall; for example, triangular particles having
a sloping sidewall as described in U.S. Pat. No. 8,142,531 (Adefris
et al.). FIG. 3 shows an exemplary such shaped abrasive particle
300 having the shape of a truncated triangular pyramid.
[0072] Further details concerning methods for making shaped
abrasive particles are described in U.S. U.S. Pat. No. 8,764,865
(Adefris et al.), U.S. Pat. No. 8,142,532 (Adefris et al.), U.S.
Pat. No. 8,123,828 (Adefris et al.), U.S. Pat. No. 8,142,891
(Culler et al.), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), and
U.S. Pat. No. 5,204,916 (Berg et al.), and in U.S. Publ. Patent
Appln. No. 2009/0165394 A1 (Culler et al.) and 2013/0040537 A1
(Erickson et al.).
[0073] The shaped abrasive particles used in the present disclosure
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.
[0074] 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 depressed center
grinding wheel in which it is contained. For example, the shaped
abrasive particle may have a length greater than half the thickness
of the depressed center grinding wheel. In some embodiments, the
length may be greater than the thickness of the depressed center
grinding wheel.
[0075] 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 lengths
may also be used.
[0076] The shaped abrasive particles are typically selected to have
a thickness in a range of from 0.005 mm to 1.6 mm, more typically,
from 0.2 to 1.2 mm.
[0077] In some embodiments, the shaped abrasive particles may have
an aspect ratio (length to thickness) of at least 2, 3, 4, 5, 6, or
more.
[0078] The first abrasive particles (i.e., in the working layer)
may contain solely of first shaped abrasive particles, or first
shaped abrasive particles in combination with an amount of third
crushed abrasive particles. Likewise, the second abrasive particles
(i.e., in the intermediate layer) may contain solely of second
shaped abrasive particles, or second shaped abrasive particles in
combination with an amount of second crushed abrasive particles. In
any event, the ratio of the weight percent of the first shaped
abrasive particles in the first abrasive particles to the weight
percent of the second shaped abrasive particles in the second
abrasive particles is from 40:60 to 60:40, preferably from 45:55 to
55:45.
[0079] The first and/or second abrasive particles may comprise more
than one size or shape of shaped abrasive particles, although a
single size and shape is typically preferred. The first and second
abrasive particles may be the same or different, preferably the
same, with regard to shape, size, and/or composition.
[0080] 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 of skill
in the art.
[0081] Useful crushed abrasive particles include, for example,
crushed particles of fused aluminum oxide, heat treated aluminum
oxide, white fused 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., black
silicon carbide, green silicon carbide, titanium diboride, boron
carbide, tungsten carbide, titanium carbide, diamond, cubic boron
nitride, garnet, fused alumina zirconia, sol-gel derived abrasive
particles, iron oxide, chromia, ceria, zirconia, titania,
silicates, tin oxide, silica (such as quartz, glass beads, glass
bubbles and glass fibers) silicates (such as talc, clays (e.g.,
montmorillonite), feldspar, mica, calcium silicate, calcium
metasilicate, sodium aluminosilicate, sodium silicate), flint, and
emery. 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.). It is also contemplated that the
abrasive particles could comprise abrasive agglomerates such, for
example, as those described in U.S. Pat. No. 4,652,275 (Bloecher et
al.) or U.S. Pat. No. 4,799,939 (Bloecher et al.).
[0082] Typically, conventional crushed abrasive particles are
independently sized according to an abrasives industry recognized
specified nominal grade. Exemplary abrasive industry recognized
grading standards include those promulgated by ANSI (American
National Standards Institute), FEPA (Federation of European
Producers of Abrasives), and JIS (Japanese Industrial Standard).
Such industry accepted grading standards include, for example: ANSI
4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 30, ANSI 36, ANSI 40,
ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI 120, ANSI 150, ANSI 180,
ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, and
ANSI 600; FEPA P8, FEPA P12, FEPA P16, FEPA P24, FEPA P30, FEPA
P36, FEPA P40, FEPA P50, FEPA P60, FEPA P80, FEPA P100, FEPA P120,
FEPA P150, FEPA P180, FEPA P220, FEPA P320, FEPA P400, FEPA P500,
FEPA P600, FEPA P800, FEPA P1000, FEPA P1200; FEPA F8, FEPA F12,
FEPA F16, and FEPA F24; and JIS 8, JIS 12, JIS 16, JIS 24, JIS 36,
JIS 46, JIS 54, JIS 60, JIS 80, JIS 100, JIS 150, JIS 180, JIS 220,
JIS 240, JIS 280, JIS 320, JIS 360, JIS 400, JIS 400, JIS 600, JIS
800, JIS 1000, JIS 1500, JIS 2500, JIS 4000, JIS 6000, JIS 8000,
and JIS 10,000. More typically, the crushed aluminum oxide
particles and the non-seeded sol-gel derived alumina-based abrasive
particles are independently sized to ANSI 60 and 80, or FEPA F36,
F46, F54 and F60 or FEPA P60 and P80 grading standards.
[0083] Alternatively, 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 prescribes 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, 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. Alternatively, a custom
mesh size could be used such as -90+100.
[0084] In some embodiments, some or all of the abrasive particles
(shaped and/or crushed) are treated with a coupling agent (e.g., an
organosilane coupling agent) to enhance adhesion of the abrasive
particles to the binder. Coupling agents are well-known to those of
skill in the abrasive arts. Examples of coupling agents include
trialkoxysilanes (e.g., gamma-aminopropyltriethoxysilane),
titanates, and zirconates. The abrasive particles may be treated
before combining them with the binder material, or they may be
surface treated in situ by including a coupling agent to the binder
material.
[0085] In some embodiments, depressed center grinding wheels
according to the present disclosure contain additional grinding
aids such as, for example, polytetrafluoroethylene particles,
cryolite, sodium chloride, FeS.sub.2 (iron disulfide), or
KBF.sub.4; typically in amounts of from 1 to 25 percent by weight,
more typically 10 to 20 percent by weight, subject to weight range
requirements of the other constituents being met. Grinding aids are
added to improve the cutting characteristics of the cut-off wheel,
generally by reducing the temperature of the cutting interface. The
grinding aid may be in the form of single particles or an
agglomerate of grinding aid particles. Examples of precisely shaped
grinding aid particles are taught in U.S. Patent Publ. No.
2002/0026752 A1 (Culler et al.).
[0086] In some embodiments, the organic binder materials may
contain plasticizer such as, for example, that available as
SANTICIZER 154 PLASTICIZER from UNIVAR USA, Inc. of Chicago,
Ill.
[0087] Depressed center grinding wheels according to the present
disclosure may contain additional components such as, for example,
filler particles, subject to weight range requirements of the other
constituents being met. Filler particles may be added to occupy
space and/or provide porosity. Porosity enables the depressed
center grinding wheel to shed used or worn abrasive particles to
expose new or fresh abrasive particles.
[0088] Depressed center grinding wheels according to the present
disclosure have any range of porosity; for example, from about 1
percent to 50 percent, typically 1 percent to 40 percent by volume.
Examples of fillers include bubbles and beads (e.g., glass, ceramic
(alumina), clay, polymeric, metal), cork, gypsum, marble,
limestone, flint, silica, aluminum silicate, and combinations
thereof.
[0089] Depressed center grinding wheels according to the present
disclosure are useful, for example, as Type 27 (e.g., as in
American National Standards Institute standard ANSI B7.1-2000
(2000) in section 1.4.14) depressed-center grinding wheels.
[0090] Depressed center grinding wheels according to the present
disclosure are typically 0.80 millimeter (mm) to 16 mm in
thickness, more typically 1 mm to 8 mm, and typically have a
diameter between 2.5 cm and 100 cm (40 inches), more typically
between about 7 cm and 13 cm, although other dimensions may also be
used (e.g., wheels as large as 100 cm in diameter are known). An
optional center hole may be used to attaching the depressed center
grinding wheel to a power driven tool. If present, the center hole
is typically 0.5 cm to 2.5 cm in diameter, although other sizes may
be used. The optional center hole may be reinforced; for example,
by a metal flange. Alternatively, a mechanical fastener may be
axially secured to one surface of the cut-off wheel. Examples
include threaded posts, threaded nuts, Tinnerman nuts, and bayonet
mount posts.
[0091] As discussed previously, depressed center grinding wheels
according to the present disclosure include at least two scrims
that reinforce the depressed center grinding wheel. Examples of
scrims include woven or knitted cloth, mesh, and screens. The scrim
may comprise glass fibers (e.g., fiberglass), organic fibers such
as polyamide, polyester, or polyimide. The scrim may comprise an
open mesh selected from the group consisting of woven, nonwoven, or
knitted fiber mesh; synthetic fiber mesh; natural fiber mesh; metal
fiber mesh; molded thermoplastic polymer mesh; molded thermoset
polymer mesh; perforated sheet materials; slit and stretched sheet
materials; and combinations thereof. The scrim need not be woven in
a uniform pattern but may also include a nonwoven random pattern.
Thus, the openings may either be in a pattern or randomly spaced.
The scrim network openings may be rectangular or they may have
other shapes including a diamond shape, a triangular shape, an
octagonal shape or a combination of shapes.
[0092] In some instances, it may be desirable to include
reinforcing staple fibers within the bonding medium, so that the
fibers are homogeneously dispersed throughout the grinding
wheel.
[0093] Depressed center grinding wheels according to the present
disclosure are useful, for example, for abrading a workpiece.
During use, the depressed center grinding wheel can be used dry or
wet. During wet grinding, the wheel is used in conjunction with
water, oil-based lubricants, or water-based lubricants. Depressed
center grinding wheels according to the present disclosure may be
particularly useful on various workpiece materials such as, for
example, carbon steel sheet or bar stock and more exotic metals
(e.g., stainless steel or titanium), or on softer more ferrous
metals (e.g., mild steel, low alloy steels, or cast irons).
[0094] Depressed center grinding wheels according to the present
disclosure are useful for grinding a workpiece at an acute angle
with the workpiece. Such an abrading process is shown in FIG. 4,
wherein depressed center grinding wheel 100 abrades workpiece 400.
During grinding, the working, intermediate, and back layers
experience wear and participate in the abrading of the
workpiece.
SELECT EMBODIMENTS OF THE PRESENT DISCLOSURE
[0095] In a first embodiment, the present disclosure provides a
depressed center grinding wheel comprising an abrasive disc having
a working surface and a back surface opposite the working surface,
wherein the working surface has a depressed center portion, and
wherein the abrasive disc comprises: a working layer comprising
first abrasive particles retained in a first binder material, the
first abrasive particles comprising first shaped abrasive
particles, wherein the first shaped abrasive particles comprise
from 40 to 100 weight percent of the first abrasive particles;
[0096] a back layer comprising second abrasive particles retained
in a second binder material comprising first crushed abrasive
particles and essentially free of shaped abrasive particles;
[0097] an intermediate layer disposed between the working layer and
the back layer, the intermediate layer comprising third abrasive
particles retained in a third binder material, the intermediate
layer comprising second shaped abrasive particles and second
crushed abrasive particles, wherein the second shaped abrasive
particles comprise 25 to 75 weight percent of the second abrasive
particles;
[0098] a first reinforcing scrim sandwiched between the back layer
and the intermediate layer; and
[0099] a second reinforcing scrim adjacent one of: [0100] the back
layer opposite the intermediate layer; [0101] the intermediate
layer opposite the back layer; or [0102] the working layer opposite
the intermediate layer.
[0103] In a second embodiment, the present disclosure provides a
depressed center grinding wheel according to the first embodiment,
wherein the second reinforcing scrim is sandwiched between the
working layer and the intermediate layer.
[0104] In a third embodiment, the present disclosure provides a
depressed center grinding wheel according to the second embodiment,
further comprising a third reinforcing scrim bonded to the working
layer opposite the intermediate layer.
[0105] In a fourth embodiment, the present disclosure provides a
depressed center grinding wheel according to the first embodiment,
wherein the second reinforcing scrim is secured to the back layer
opposite the intermediate layer.
[0106] In a fifth embodiment, the present disclosure provides a
depressed center grinding wheel according to the fourth embodiment,
further comprising a third reinforcing scrim sandwiched between the
intermediate layer and the working layer.
[0107] In a sixth embodiment, the present disclosure provides a
depressed center grinding wheel according to the fourth or fifth
embodiment, further comprising a fourth reinforcing scrim bonded to
the working layer opposite the intermediate layer.
[0108] In a seventh embodiment, the present disclosure provides a
depressed center grinding wheel according to any one of the first
to sixth embodiments, wherein the first shaped abrasive particles
comprise triangular shaped abrasive particles.
[0109] In an eighth embodiment, the present disclosure provides a
depressed center grinding wheel according to any one of the first
to seventh embodiments, wherein the second shaped abrasive
particles comprise triangular shaped abrasive particles.
[0110] In a ninth embodiment, the present disclosure provides a
depressed center grinding wheel according to any one of the first
to eighth embodiments, wherein the ratio of the weight percent of
the first shaped abrasive particles in the first abrasive particles
to the weight percent of the second shaped abrasive particles in
the second abrasive particles is from 40:60 to 60:40.
[0111] In a tenth embodiment, the present disclosure provides a
depressed center grinding wheel according to any one of the first
to eighth embodiments, wherein the ratio of the weight percent of
the first shaped abrasive particles in the first abrasive particles
to the weight percent of the second shaped abrasive particles in
the second abrasive particles is from 45:55 to 55:45.
[0112] In an eleventh embodiment, the present disclosure provides a
depressed center grinding wheel according to any one of the first
to tenth embodiments, wherein the first and second shaped abrasive
particles comprise alpha alumina.
[0113] In a twelfth embodiment, the present disclosure provides a
depressed center grinding wheel according to any one of the first
to eleventh embodiments, further comprising a centrally disposed
arbor hole extending through the abrasive disc.
[0114] In a thirteenth embodiment, the present disclosure provides
a depressed center grinding wheel according to any one of the first
to twelfth embodiments, further comprising an attachment member
centrally disposed on the back surface of the abrasive disc.
[0115] Objects 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
[0116] Unless otherwise noted, all parts, percentages, ratios, etc.
in the Examples and the rest of the specification are by
weight.
[0117] The following abbreviations are used for materials in the
examples.
TABLE-US-00001 TABLE OF ABBREVIATIONS ABBREVIATION DESCRIPTION AP1
grade 36 aluminum oxide abrasive particles, obtained under trade
designation "36 BFRPL" from Treibacher Schleifmittel AG, Villach,
Austria. AP2 a grade 36+ precision-shaped ceramic alumina abrasive
particle prepared according to the procedure described hereinbelow.
AP3 grade 24 aluminum oxide abrasive particles, obtained under
trade designation "24 BFRPL" from Treibacher Schleifmittel AG,
Villach, Austria. PR1 liquid phenolic resin, obtained under trade
designation "PREFERE 825136G1" from Dynea Oy Corporation, Helsinki,
Finland. PR2 phenolic resin powder (a solid phenolic resin),
obtained under trade designation "VARCUM 29302" from Durez
Corporation, Dallas, Texas. CRY Sodium hexafluoroaluminate,
obtained under trade designation "CRYOLITE" from Freebee,
Ullerslev, Denmark. SCRIM1 fiberglass mesh having the trade
designation "STYLE 4400" from Industrial Polymer and Chemicals,
Inc., Shrewsbury, Massachusetts. SCRIM2 fiberglass mesh having the
trade designation "STYLE 184" from Industrial Polymer and
Chemicals, Inc.. HC5 0.7 micron aluminum trihydroxide particles
available as HYDRAL COAT 7 from Almatis, Inc., Leetsdale,
Pennsylvania.
Preparation of AP2
[0118] Shaped abrasive particles were prepared according to the
disclosure of U.S. Pat. No. 8,142,531 (Adefris et al.). The shaped
abrasive particles were prepared by molding alumina sol gel in
equilateral triangle-shaped polypropylene mold cavities of 0.028
inch (0.71 millimeter) depth and 0.11 inch (0.28 millimeter) on
each side. The draft angle .alpha. between the sidewall and bottom
of the mold was 98 degrees. After drying and firing, the shaped
particles were calcined at approximately 650.degree. C., and then
saturated with a magnesium nitrate solution (10.5 percent by weight
as magnesium oxide, and having 0.02 percent by weight of HC5
dispersed therein). Excess nitrate solution was removed, and the
saturated shaped particles were allowed to dry after which the
particles were again calcined at 650.degree. C. and sintered at
approximately 1400.degree. C. resulting in shaped ceramic abrasive
particles. Both the calcining and sintering were accomplished using
rotary tube kilns.
Grinding Test
[0119] Abrasive wheels were tested by grinding a rectangular mild
steel bar (0.25 inch (0.6 cm).times.18 inches (45.7 cm).times.3
inches (7.6 cm)) over a 0.25 inch (0.6 cm).times.18 inches (45.7
cm) area of the surface while mounted on a 12000 rpm air driven
grinder that oscillated back and forth (one cycle=18 inches (45.7
cm) each way for a total of 36 inches (91 cm)) for ten one-minute
cycles. The applied load was the grinder weight of 9 pounds (4.1
kg) and the abrasive wheel was held at an angle of 15 degrees
relative to the surface (i.e., 0 degrees). The steel bar was
weighed before and after each cycle, and the weight loss (i.e.,
cut) was recorded. The steel bar was traversed 16 times from end to
end per cycle. Weight loss from the grinding disc (i.e., disc wear)
was recorded after each 10-cycle test.
Example 1 and Comparative Examples a-b
[0120] Mixes were prepared according to the amounts and components
listed in Table 1. Mix 1, Mix 2 and Mix 4 were prepared by
combining the indicated components using a paddle-type mixer
(obtained as "CUISINART SM-70" from Conair Corporation, East
Windsor, N.J., operated at speed 1) for 10 minutes. Mix 3 was
prepared by combining Mix 1 and Mix 2 using a paddle-type mixer for
10 minutes. Mix 5 was prepared by combining Mix 4 and Mix 2 using a
paddle-type mixer for 10 minutes. Mix 6 was prepared by combining
50% Mix 1 and 50% Mix 4 using a paddle-type mixer for 10
minutes.
TABLE-US-00002 TABLE 1 AMOUNT IN GRAMS COMPONENT Mix 1 Mix 2 Mix 3
Mix 4 Mix 5 Mix 6 AP1 1000 -- 1000 -- -- 500 AP2 -- -- -- 1000 1000
500 PR1 105 -- 105 105 105 105 PR2 -- 194 194 -- 194 -- CRY -- 200
200 -- 200 --
Example 1
[0121] A Type 27 depressed-center composite grinding wheel was
prepared as follows. A 4.5-inch (11.4 centimeters) diameter disc of
SCRIM' was placed into a 4.5-inch (11.4 centimeters) diameter
cavity die. Mix 3 (50 grams) was spread out evenly. A second 4-inch
(10.2 centimeters) diameter of SCRIM2 was placed on top of Mix 3.
Mix 6 (50 grams) of was spread out evenly and a third 4-inch (10.2
centimeters) diameter of SCRIM2 was placed on top of Mix 6. Then
Mix 5 (50 grams) of was spread out evenly. The filled cavity mold
was then pressed at a pressure of 40 tons/38 square inches (14.5
megapascals).
[0122] The resulting wheel was removed from the cavity mold and
placed on a spindle between depressed center aluminum plates in
order to be pressed into a Type 27 depressed-center grinding wheel.
The wheel was compressed at 5 ton/38 square inches (1.8
megapascals) to shape the disc. The wheel was then placed in an
oven to cure for 7 hours at 79.degree. C., 3 hours at 107.degree.
C., 18 hours at 185.degree. C., and a temperature ramp-down over 4
hours to 27.degree. C. The dimensions of the final grinding wheel
were 180 millimeter diameter.times.7 millimeter thickness. The
center hole was 7/8 inch (2.2 centimeters) in diameter. The
resultant depressed-center composite grinding wheel was configured
such that a layer of Mix 5 was the working layer.
Comparative Example A
[0123] Comparative Example A was a Type 27 depressed-center
grinding wheel prepared according to the procedure of Example 1,
except that Mix 5 was used instead of Mix 6 in middle layer (so
that Mix 5 was used in both middle and top layers). The resultant
depressed-center composite grinding wheel was configured such that
a layer of Mix 5 was the working layer.
Comparative Example B
[0124] Comparative Example B was a Type 27 depressed-center
grinding wheel prepared according to the procedure of Example 1,
except that Mix 6 was used instead of Mix 5 in top layer (so that
Mix 6 was used in both middle and top layers). The resultant
depressed-center composite grinding wheel was configured such that
a layer of Mix 6 was the working layer.
[0125] Grinding test results of Example 1 and Comparative Examples
A and B are reported in Table 2 (below).
TABLE-US-00003 TABLE 2 COMPARATIVE COMPARATIVE EXAMPLE 1 EXAMPLE A
EXAMPLE B Total Cut 423.06 422.72 364.05 After 10 Cycles (grams)
Disc Wear 5.5 5.5 7 After 10 Cycles (grams)
Examples 2-7 and Comparative Examples C-E
[0126] Mixes were prepared according to the amounts and components
listed in Table 3. Mix 7, Mix 8 and Mix 10 were prepared by
combining the indicated components using a paddle-type mixer
(CUISINART SM-70 from Conair Corporation, East Windsor, N.J.,
operated at speed 1) for 10 minutes. Mix 9 was prepared by
combining Mix 7 and Mix 8 using a paddle-type mixer for 10 minutes.
Mix 11 was prepared by combining Mix 10 and Mix 8 using a
paddle-type mixer for 10 minutes. Mix 12 was prepared by combining
25% Mix 9 and 75% Mix 11 using a paddle-type mixer for 10 minutes.
Mix 13 was prepared by combining 50% Mix 9 and 50% Mix 11 using a
paddle-type mixer for 10 minutes. Mix 14 was prepared by combining
75% Mix 9 and 25% Mix 11 using a paddle-type mixer for 10
minutes.
TABLE-US-00004 TABLE 3 AMOUNT IN GRAMS COM- Mix Mix Mix Mix Mix Mix
Mix PONENT 7 8 Mix 9 10 11 12 13 14 AP3 1290 -- 1290 -- -- 322 645
968 AP2 -- -- -- 1290 1290 968 645 322 PR1 83 -- 83 83 83 83 83 83
PR2 -- 233 233 -- 233 233 233 233 CRY -- 233 233 -- 233 233 233
233
[0127] A Type 27 depressed-center composite grinding wheel was
prepared for each Example in Examples 2-7 and Comparative Examples
C-E as follows. Mixes used in each Example as bottom, middle and
top layers and their amounts are reported in Table 4. A 4.5-inch
(11.4-cm) diameter disc of SCRIM' was placed into a 4.5-inch
(11.4-cm) diameter cavity die. Bottom layer mix was spread out
evenly. A second 4.0-inch (10.2-cm) diameter of SCRIM2 was placed
on top of bottom layer mix. The middle layer mix was spread out
evenly and then top layer mix was spread out evenly. A third 3-inch
(7.6-cm) diameter of SCRIM2 was placed on top of top layer mix. The
filled cavity mold was then pressed at a pressure of 40 tons/38
square inches (14.5 mPa).
[0128] The resulting wheel was removed from the cavity mold and
placed on a spindle between depressed center aluminum plates in
order to be pressed into a Type 27 depressed-center grinding wheel.
The wheel was compressed at 5 ton/38 square inches (1.8 mPa) to
shape the disc. The wheel was then placed in an oven to cure for 7
hours at 79.degree. C., 3 hours at 107.degree. C., 18 hours at
185.degree. C., and a temperature ramp-down over 4 hours to
27.degree. C. The dimensions of the final grinding wheel were 180
millimeter diameter.times.7 millimeter thickness. The center hole
was 7/8 inch (2.2 cm) in diameter. The resultant depressed-center
composite grinding wheel was configured such that a top layer was
the working layer.
[0129] Grinding test results of Example 2-7 and Comparative
Examples C-E are reported in Table 4 (below).
TABLE-US-00005 TABLE 4 Comparative Comparative Comparative Example
2 Example 3 Example C Example 4 Example 5 Example D Example 6
Example 7 Example E Bottom Mix 9, Mix 9, Mix 9, Mix 9, Mix 9, Mix
9, Mix 9, Mix 9, Mix 9, Layer Mix 50 grams 50 grams 50 grams 50
grams 50 grams 50 grams 50 grams 50 grams 50 grams Middle Mix 13,
Mix 13, Mix 12, Mix 13, Mix 13, Mix 13, Mix 14, Mix 14, Mix 14,
Layer Mix 50 grams 70 grams 50 grams 50 grams 70 grams 50 grams 50
grams 70 grams 50 grams Top Layer Mix 11, Mix 11, Mix 12, Mix 12,
Mix 12, Mix 13, Mix 13, Mix 13, Mix 14, Mix 50 grams 30 grams 50
grams 50 grams 30 grams 50 grams 50 grams 30 grams 50 grams
Grinding Test Results Total Cut 350.90 317.58 287.57 319.31 323.40
242.84 275.19 266.81 200.36 After 10 Cycles, grams Disc Wear 3.67
3.11 3.45 3.36 3.58 3.91 3.34 3.16 2.59 After 10 Cycles, grams
[0130] Various modifications and alterations of this disclosure may
be made by those skilled in the art without departing from the
scope and spirit of this disclosure, and it should be understood
that this disclosure is not to be unduly limited to the
illustrative embodiments set forth herein.
* * * * *