U.S. patent number 3,867,795 [Application Number 05/406,918] was granted by the patent office on 1975-02-25 for composite resinoid bonded abrasive wheels.
This patent grant is currently assigned to Norton Company. Invention is credited to William C. Howard.
United States Patent |
3,867,795 |
Howard |
February 25, 1975 |
Composite resinoid bonded abrasive wheels
Abstract
Reinforced resin bonded abrasive depressed and straight center
wheels for portable snagging grinders in which the thickness of
each wheel comprises a primary abrading portion containing a
superior, expensive, premium, fast cutting and durable cofused
alumina-zirconia abrasive particles and an adjoining secondary
abrading portion containing different, less costly, slower cutting
abrasive particles which, it has been discovered, does not
materially reduce the grinding performance of the wheel from one
made entirely with alumina-zirconia abrasive throughout the
thickness of the wheel.
Inventors: |
Howard; William C. (Worcester,
MA) |
Assignee: |
Norton Company (Worcester,
MA)
|
Family
ID: |
23609888 |
Appl.
No.: |
05/406,918 |
Filed: |
October 16, 1973 |
Current U.S.
Class: |
451/548; 451/544;
451/546 |
Current CPC
Class: |
B24D
7/04 (20130101); C09K 3/1409 (20130101) |
Current International
Class: |
B24D
7/04 (20060101); B24D 7/00 (20060101); C09K
3/14 (20060101); B24d 007/04 () |
Field of
Search: |
;51/26R,26NF,29R,207,358,376-379,401,204,29DL |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kelly; Donald G.
Attorney, Agent or Firm: Fred; Walter
Claims
What is claimed is:
1. A reinforced resin bonded abrasive grinding wheel of
predetermined thickness having a relatively narrow peripheral
grinding face usually presented and worn at an angle during
grinding, extending between a top and a bottom side, reinforcing
material bonded thereto and means for mounting the wheel for
rotstion about its axis, wherein the improvement comprises:
a primary abrading portion extending along the bottom side to the
peripheral grinding face and occupying a portion of the
predetermined thickness of the wheel, and having
resin bonded primary abrasive particles of co-fused
alumina-zirconia abrasive material containing from 10% to 60% by
weight of zirconia; and
a secondary abrading portion bonded to and extending from the
primary abrading portion to the top side and peripheral grinding
face of the wheel and having
resin bonded secondary abrasive particles of a secondary abrasive
material which differs from and of less durability than the
alumina-zirconia abrasive material.
2. A reinforced resin bonded abrasive grinding wheel according to
claim 1 wherein the primary abrading portion further comprises:
resin bonded diluent abrasive particles of an abrasive material
selected from a group consisting of garnet, aluminum oxide, silicon
carbide, emery, flint, silica, quartz and mixtures thereof mixed in
with the alumina-zirconia particles and comprising up to 25% by
volume of the abrasive particles in the primary abrading
portion.
3. A reinforced resin bonded abrasive grinding wheel according to
claim 2 wherein the diluent abrasive particles are made of
garnet.
4. A reinforced resin bonded abrasive grinding wheel according to
claim 1 wherein the secondary abrasive particles are made of an
abrasive material selected from a group consisting of aluminum
oxide, silicon carbide, garnet, silica, quartz, emery, flint and
mixtures thereof and wherein the primary abrading portion occupies
at least about one-half the thickness of the wheel.
5. A reinforced resin bonded abrasive grinding wheel according to
claim 1 wherein the secondary abrasive particles are no larger than
16 grit size and wherein the alumina-zirconia particles are from 16
to 60 grit size.
6. A reinforced resin bonded abrasive grinding wheel according to
claim 1 wherein the alumina-zirconia particles are of larger and
coarser grit size than the secondary abrasive particles.
7. A reinforced resin bonded abrasive grinding wheel according to
claim 4 wherein the secondary abrasive material is aluminum
oxide.
8. A reinforced resin bonded abrasive grinding wheel according to
claim 1 wherein the reinforcing material comprises:
a first disc of open mesh fiber glass cloth situated substantially
between and bonded to the primary and secondary abrading portions
of the wheel.
9. A reinforced resin bonded abrasive grinding wheel according to
claim 8 wherein the reinforcing material further comprises:
a second disc of fiber glass cloth bonded to the bottom side and
primary abrading portion of the wheel; and
a third backing disc of fiber glass cloth bonded to the top side
and secondary abrading portion of the wheel.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to resin bonded abrasive grinding wheels and
particularly to relatively thin reinforced raised hub or depressed
center and straight center snagging wheels for portable
grinders.
2. Description of the Prior Art
Heretofore grinding wheels have been made with inner and outer
layers, sides and zones varying either in density, hardness, type
of abrasive, bond, and in the grit size of the abrasive particles
as disclosed in the following publications U.S. Pat. Nos.
1,403,416, 1,616,531, 2,479,078, 2,877,105 and German
Gebrauchsmuster No. 7,306,787 dated May 24, 1973. In use straight
and depressed center or raised hub wheels of various shapes are
usually attached and driven by hand operated portable grinders, and
held at a slight angle to grind welding beads, flash, gates and
risers off castings. During grinding the peripheral grinding face
or edge of the wheel wears at an angle to the axis of rotation and
the opposite sides of the wheel. As a result a sharp and relatively
thin fragile peripheral edge is formed at the junction of the
grinding face and the back or top side of the wheel. The fragile
edge has a tendency to break away and contributes very little to
removing the unwanted material. Also known, are wheels having
various types of backing materials for reinforcing the fragile edge
and for supporting the primary cutting or abrading portion of the
wheel.
For many years and up to the present time depressed center also
known as raised hub grinding wheels have been made in the United
States with a backing layer of bonded abrasive particles of
relatively fine grit size bonded between a layer of coarser primary
abrasive particles of substantially uniform grit size and a fiber
glass backing. The finer abrasive being of the same type as the
coarser and usually include what are known in the art as abrasive
fines which vary in grit size. When mixed and bonded together the
fines tend to occupy the spaces between the larger particles and
thereby densify and strengthen the backing layer of finer abrasive
particles.
The Applicant's invention differs from the prior art in that
abrasive particles of a tough, superior, more durable, faster
cutting and more expensive alumina-zirconia abrasive material such
as disclosed in U.S. Pat. No. 3,181,939 and a commonly owned prior
copending application Ser. No. 386,718 filed Aug. 8, 1973 and to
which reference may be had for details not disclosed herein, is
used in the primary abrading portion and differs from the abrasive
used in the secondary abrading portion of the wheel. U.S. Pat. No.
3,181,939 discloses rapidly cooled co-fused alumina-zirconia
containing 10 to 60% zirconia. The preferred abrasive for this
invention is the 35 to 50% zirconia, very rapidly cooled material
of Ser. No. 386,718.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional veiw through the center of a typical
depressed center or raised hub wheel made according to the
invention;
FIG. 2 is a sectional view through the center of a straight center
wheel made according to the invention; and
FIG. 3 is a partial sectional view through a peripheral portion of
a wheel showing the wheel inclined and the grinding edge thereof
worn at an angle during grinding.
SUMMARY OF THE INVENTION
Depressed and straight center reinforced resin bonded abrasive
grinding wheels comprising a primary abrading portion or layer
containing tough, durable, fast cutting and relatively expensive
bonded alumina-zirconia abrasive particles occupying a portion of
the thickness of the wheel situated on the working or bottom side
of the wheel. A secondary abrading portion or layer containing
different, less expensive, less durable abrasive particles is
bonded to the primary abrading portion and situated on the back or
top side of the wheel. If desired and preferably there is a backing
consisting of at least one layer of reinforcing material molded in
and bonded to the back or top side of the secondary abrading
portion of the wheel.
The reinforced wheel may have one or more additional layers or
discs of fiber glass reinforcing material integrally molded and
bonded therein. One layer of reinforcement is preferably bonded to
and situated in between the secondary and primary abrading layers
of the wheel. The central hub portion of the wheel is preferably
further reinforced with a disc of fiber glass cloth molded in and
bonded to the bottom side of the primary abrading layer or
portion.
Therefore it is the primary object of the invention to provide
reinforced resin bonded abrasive grinding wheels having a primary
abrading portion comprising particles of co-fused alumina-zirconia
abrasive material and a secondary abrading portion containing
particles of different abrasive material.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Referring to the drawings wherein there is shown a depressed center
or raised hub grinding wheel 10 and a straight center or hub wheel
10'. The wheels are shown in only one of the many possible
conventional shapes to which they may be made and known to those
skilled in the art. For example, they may be molded to the shape of
a shallow dish or saucer with curved or straight flaring sides and
still have either a straight or depressed center portion about the
mounting hole. As used herein the term straight center is meant to
include wheels other than depressed center or raised hub and those
having top and bottom surfaces which continue without any deviation
or sharp bends to the center mounting hole. The construction of
each of the wheels 10 and 10' being substantially the same except
for the configuration of the central hub mounting portion around
the center mounting hole which may be adapted to receive any
suitable mounting, such as shown in FIG. 3, for attaching the wheel
to the drive spindle or shaft of a portable grinder. In U.S. Pat.
Nos. 3,081,584; 3,136,100; 3,500,592; and 3,596,415 there are
disclosed wheel mountings which may be attached to the wheels
disclosed herein and to which reference may be had for details not
disclosed herein. Obviously, there are many other types of suitable
mountings known to those skilled in the art which may be attached
in various ways to the wheels. The mounting forms no part of the
invention and therefor is not shown but merely incorporated by
reference herein.
As shown both of the wheels 10 and 10' have a bottom or working
side 12, a top or back side 14, a peripheral grinding edge or face
16 and a center hole 18 for mounting the wheel. Adjacent the bottom
side 12 is a primary abrading portion or layer 20 containing resin
bonded primary abrasive particles of a premium co-fused
alumina-zirconia abrasive material of the type disclosed in U.S.
Pat. No. 3,181,939 and the copending application disclosed above to
which reference may be had for details not disclosed herein and
which preferably occupies about one-half the thickness of the wheel
and at least two particles deep. Embedded in and bonded to the
bottom side of the primary abrading layer in the central hub
portion of the wheel about center hole 18 is a layer or disc 22 of
reinforcing material. The disc or layer 22 of reinforcing material
is preferably a disc 4 inches in diameter of resin coated, open 14
.times. 14 mesh, plain woven, fiber glass cloth having
approximately 14 openings to the inch and commercially available as
number 196 from Eli Sandman Company, Worcester, Mass. Molded within
the wheel and bonded to the inner side of the primary abrading
portion 20 is another disc 24 of reinforcing material which extends
radially out from the center hole to the peripheral grinding edge
16 of the wheel. The disc 24 is preferably made of resin coated,
open 7 .times. 7 mesh, plain woven fiber glass cloth having
approximately 7 openings to the inch and commercially available as
number RC717 from Eli Sandman Company, Worcester, Mass.
Adjacent to and resin bonded to both the reinforcement 24 and the
primary abrading layer 20 is a secondary abrading portion or layer
26 of resin bonded secondary abrasive particles which differ from
and are preferably less costly than the co-fused alumina-zirconia
abrasive particles in the primary abrading layer 20. The secondary
abrading layer 26 extends axially to the back or top side 14 and
occupies approximately the upper half or remaining portion of the
thickness of the wheel.
Integrally bonded to and molded into the secondary abrading layer
26 at the back or top side 14 of the wheel is a third or composite
disc or layer 28 of backing material extending to the peripheral
edge 16 of the wheel. The disc 28 of backing material is preferably
a composite disc consisting of a thin layer of paper adhered to a
layer of fiber glass cloth and designated as a number 955 paper
stick resin coated 5 .times. 5 open mesh, low twist woven fiber
glass cloth with approximately five openings per inch available
from Eli Sandman Company, Worcester, Mass.
The secondary abrasive may be any of the well known abrasive
materials selected from a group consisting of aluminum oxide,
garnet, silicon carbide, silica, emery, flint and quartz and
mixtures thereof which are less costly, not as durable and less
efficient than the primary co-fused alumina-zirconia abrasive
material. Preferably, for most grinding applications, the secondary
abrasive material comprises particles of aluminum oxide of either
24 or 46 grit size. However, for other applications the size of the
secondary abrasive particles may be in a range of 16 to 60 grit
size and if desired no larger than 16 grit size and include what is
known as abrasive fines. When bonded together both the fines and
smaller grit size particles provide a denser and stronger secondary
abrading portion which backs up and supports the primary abrading
portion.
The primary co-fused alumina-zirconia abrasive particles are
preferably rolls crushed elongated particles of substantially
uniform grit size of from 16 to 60, of high purity fine crystalline
structure containing 10 - 60 percent by weight of zirconium oxide.
However, in the grinding wheels of this invention elongated
particles of co-fused alumina-zirconia of 24 grit size having about
43% of zirconia by weight, a specific gravity of 4.66 and a bulk
density of 129 to 137 pounds per cubic feet are preferred for most
foundry snagging operations while in other operations particles
having a content of 25% zirconia and a specific gravity of 4.35
will suffice.
The alumina-zirconia abrasive particles are preferably of the type
disclosed in a prior copending application Ser. No. 386,718 filed
Aug. 8, 1973 to which reference may be had for details not
disclosed herein. It is made by rapidly crystallizing and
solidifying a eutectic or near eutectic molten mixture of aluminum
oxide and 35 to 50%, but preferably around 40%, by weight of
zirconium oxide. One of the various methods of rapidly
crystallizing the molten mixture is to pour it between a plurality
of three-fourths inch thick plates spaced about three-sixteenths of
an inch apart which quickly cool and solidify the mixture into a
product with a microcrystalline structure having the following
typical analysis of ingredients by weight percent.
______________________________________ SiO.sub.2 0.21% Fe.sub.2
O.sub.3 0.15% TiO.sub.2 0.15% Na.sub.2 O 0.04% ZrO.sub.2 40.56%
Al.sub.2 O.sub.3 58.89 (by difference)
______________________________________
No analysis was made for the small amounts of lime or magnesia
which were present. However, the analysis shows that the fine
crystalline alumina-zirconia abrasive product was of high purity
with less than 1% by weight of impurities therein.
The solidified alumina-zirconia product has very high strength
combined with high desirable microfracture properties. Also, the
zirconia is in the form of rods (or platelets) which average less
than 3,000 angstroms in diameter and preferably at least 25% by
weight of the zirconia is in the tetragonal crystal form. The
solidified product is made up of eutectic cells or colonies
typically 40 microns or less in width. Groups of cells having
idential orientation of microstructure, form grains each of which
typically include from 2 to 100 or more cells or colonies. During
crushing, the material fractures along grain boundaries and cell
boundaries and is first jaws crushed and then rolls crushed to form
elongated abrasive particles which are separated and screened to
obtain the desired grit size particles thereof. As used above, the
term "grain" is not synonymous with the word "grit. " Typically an
abrasive grit will contain a large number of grains, in the sense
used above.
The wheels 10 and 10'to may be molded either by hot or cold
pressing in any suitable manner well known to those skilled in the
art. A mold having a center hole forming arbor surrounded by a
circular cavity in which the center is depressed can be used to
mold the depressed center or raised hub wheel 10 and a mold also
having a hole arbor but a straight cylindrical cavity may be used
to mold the straight hub or center wheel 10'. The wheels may be
molded by first placing the paper side of the paper stick fiber
glass disc 28 of composite backing material with a center hole
around the arbor and in contact with the bottom of the mold. Then,
spreading a uniform layer of a prepared abrasive mixture containing
a suitable resin bond and the secondary abrasive particles on top
of the fiber glass backing disc 28. Thereafter, placing the disc 24
of fiber glass reinforcing material with a center hole about the
arbor and onto the layer of secondary abrasive mix followed by
spreading a uniform layer of a prepared mixture comprising a
suitable and compatible resin bond and the primary abrasive
containing particles of alumina-zirconia abrasive material thereon.
Lastly, laying the hub reinforcing disc 22 with a center hole
therein around the arbor and onto the layer of primary abrasive and
placing a top mold plate of the desired shape to either produce the
depressed center or the straight center hub portion of the wheels,
on top of the layers. The mold assembly is then placed between the
platens of either a conventional cold or hot press. Then the press
is actuated to force the mold plate downwardly and compress the
discs and abrasive mixtures together, at a pressure of 1 to 4 tons
per square inch, into a self supporting structure of predetermined
thickness, diameter and density. After molding the wheel is
stripped from the mold and placed in an oven heated to a
temperature of approximately 175.degree.C for approximately 6 hours
to fully cure the resin bond.
The resin bond may comprise any one of a number of the conventional
and well known thermosetting or infusible resins, such as,
phenol-aldehyde, epoxy, polyester, polyimides, and
polybenzimadazole in either liquid for powder form. Preferably the
resin bond comprises a phenolic (phenol-aldehyde) resin in powder
form which is premixed with other fillers and coloring materials
and then mixed with predetermined amounts of the secondary and
primary abrasive particles.
A suitable primary abrasive mixture of primary abrasive particles
and resin bond for a snagging operation may comprise the following
percentage of ingredients by weight:
% by Ingredients Weight ______________________________________
Abrasive-24 grit alumina-zirconia abrasive 78.54 particles Resin
Bond % by Weight 21.46 100.00 VARCUM Chemical Co. No. 29-345 40.9
powdered phenolic resin Wallastonite - (Grade C-6 53.0 Interface
Corp., Willsboro, New York) Calcium Oxide (CaO) 5.1 Carbon Black
1.0 100.0 ______________________________________
The secondary abrasive mixture of secondary abrasive and resin bond
may comprise the following percentage of ingredients by weight:
% by Ingredients Weight ______________________________________
Abrasive-24 grit aluminum oxide abrasive 75.62 particles Resin Bond
% by Weight 24.38 100.00 VARCUM Chemical Co. No. 29-345 40.9
powdered phenolic resin Wallastonite - (Grade C-6 53.0 Interface
Corp.) Calcium Oxide (CaO) 5.1 Carbon Black 1.0 100.00
______________________________________
In addition there was added to each of the primary and secondary
abrasive mixtures of abrasive and resin bond 45 cc of furfural
plasticizer and 25 cc of CARBOSOTA (creosote oil) for each pound of
powdered phenolic resin. The CARBOSOTA being mixed separately with
the resin bond and the furfural being mixed with and wetting the
abrasive particles prior to mixing the wetted abrasive particle
with the resin bond. Thereafter, to the entire mixture of wetted
abrasive and resin bond there is added and mixed therewith 4 cc of
a mixture of 60% by weight of furfural and 40% by weight of castor
oil and lastly, 0.0005 of a pound (lb.) or 0.23 grams of dry
colloidal silica (CAB-O-SIL) for each pound (lb.) of the entire
abrasive mixture.
Referring to FIG. 3 there is shown a sectional view through a
portion of a grinding wheel of the invention mounted on a shaft and
positioned at an angle to the surface of the workpiece W being
worked upon to show how in normal use the initial grinding face or
edge 16 is worn at an angle to the back or top side 14 and bottom
or working side 12. It can be seen that when the wheel is used at
an angle that the length of the grinding face 16 is increased and
that the thinnest, weakest and most fragile part of the wheel is at
and adjacent the outer tip or edge 16a located at the junction of
the grinding face 16 and the back side 14. When grinding pressure
is applied, the edge 16a and the adjacent tapered portions of the
secondary abrading portion have a tendency to break away because
they are only supported by the fiber glass backing layer 28. As a
result, the secondary abrading portion 26 does much less grinding
or cutting of unwanted material. In contrast, the primary abrading
portion 20 does not have as fragile an edge or corner as the edge
16a and is more rigidly supported and backed up by the secondary
abrading portion of the wheel. Therefore, the primary abrading
portion 20 with the more durable faster cutting and more efficient
alumina-zirconia abrasive therein does most of the grinding or
cutting away of material without the tendency to break away.
Wheels 7 inches in diameter, one-quarter of an inch thick each with
a seven-eighths inch diameter center hole were made according to
the invention with the 24 grit size alumina-zirconia abrasive resin
mixtures, and 24 grit aluminum oxide abrasive resin mixtures
disclosed above. The wheels were tested and compared with a variety
of other wheels all of comparable size and shape, 24 grit size
particles and resin bond disclosed above but with variations in the
type, amount by volume and location of abrasive particles in the
wheel. Some of the wheels were made with aluminum oxide or the
alumina-zirconia throughout, with the alumina-zirconia abrasive in
the secondary portion and alumina in the primary portion, and with
a mixture containing by volume 50% of alumina-zirconia and 50%
alumina in both portions of the wheel. Another wheel had a mixture
containing by volume 75% of alumina-zirconia and 25% garnet in the
primary portion and alumina in the secondary portion. The
alumina-zirconia abrasive used in all the wheels tested contained
about 43% zirconia by weight.
The grinding tests were performed by mounting each wheel on an
automated apparatus adapted to transverse and manipulate a Chicago
Pneumatic 360 cycle right angle portable grinder rotatable at 5,200
RPM and inclined so the bottom side of the wheel was at an angle of
25.degree. from a horizontal plane to simulate the position,
applied force and movements of a hand operated portable
grinder.
Each wheel tested was run four times during each of which the
grinding wheels ground into the annular edge of a 12 inch O.D.
.times. 103/4 inch I.D. ring of cast steel, mounted on a reversible
rotary table rotated at 15 RPM in reversed directions every
one-half minute. Each run lasted for a period of 15 minutes while a
constant downward force of 20 pounds was applied to the wheel
reciprocated 13/8 inches across the annular edge. After each run
the ring of cast steel was weighed and the wheel measured to
determine the number of pounds of metal removed per hour and the
number of cubic inches of wheel wear per hour. The "grinding ratio"
of the wheel is the ratio of metal removed to wheel wear.
In the following Tables I and II, RGR refers to the "Relative
Grinding Ratio" in percent which is determined by dividing the
grinding ratio .times. 100 of the wheel being tested by the
grinding ratio of a conventional standard wheel with 24 grit
aluminum oxide abrasive throughout the wheel given an RGR rating of
100%. The "Relative Rate of Cut" in percent is indicated by RRC in
the table and is determined by dividing the rate of cut .times. 100
of the wheel being tested with that of a comparable conventional
standard wheel rated at 100% and made with aluminum oxide abrasive
throughout. The results of one of the tests are shown in Table I
below.
TABLE I
__________________________________________________________________________
TYPE AND LOCATION OF 24 GRIT SIZE ABRASIVE PARTICLES WHEEL METAL
TYPE OF PRIMARY SECONDARY WEAR REMOVED RGR RRC WHEEL PORTION
PORTION IN..sup.3 /HR. LBS./HR. IN. % IN. %
__________________________________________________________________________
STANDARD aluminum aluminum 3.43 2.91 100 100 PRIOR ART oxide oxide
WHEEL VARIATION alumina- alumina- 1.46 3.00 243 103 OF zirconia
zirconia WHEELS 50% alumina- 50% alumina- 2.32 3.13 159 108
zirconia zirconia % BY VOLUME mixed with mixed with 50% aluminum
50% aluminum oxide oxide aluminum alumina- 3.58 3.08 102 106 oxide
zirconia WHEELS alumina- aluminum 1.34 2.82 2.47 97 OF zirconia
oxide INVENTION 75% alumina- aluminum 1.78 2.91 193 100 % BY VOLUME
zirconia oxide 25% garnet
__________________________________________________________________________
As can be seen from the test data, the wheel with alumina-zirconia
in both the primary and secondary portions with a 243% RGR and 103%
RRC was far superior to the standard wheel with aluminum oxide in
both the primary and secondary portions. The wheel having a mixture
of one-half (50%) alumina-zirconia and one-half (50 %) aluminum
oxide by volume in both the primary and secondary portions gave as
expected a 159% RGR and 108% RRC which is an improvement over the
standard wheel with aluminum oxide throughout but not equal to the
wheel with alumina-zirconia in both portions of the wheel. However,
the wheel of the invention with all of alumina-zirconia in the
primary abrading portion of the wheel and aluminum oxide in the
secondary portion gave a result of 247% RGR and 97% RRC which is
very nearly equal to the wheel with alumina-zirconia throughout the
wheel. In contrast, the wheel with the aluminum oxide in the
primary portion and alumina-zirconia in the secondary portion gave
a result of 102% RGR and 106% RRC which shows a performance equal
to that of the standard wheel with aluminum oxide throughout the
wheel. The data shows that the wheels made according to the
invention with approximately one-half as much of the more costly
alumina-zirconia located in the primary portion of the wheel and a
less costly abrasive in the secondary portion performs very nearly
as well as the wheel with alumina-zirconia throughout the wheel.
Hence, only one-half as much of the premium abrasive is required
with no apparent loss in performance.
In another embodiment of the invention the primary abrading portion
may contain a primary abrasive mixture consisting of the superior
co-fused primary alumina-zirconia abrasive particles and up to
one-fourth or 25% by volume of the primary abrasive particles
therein of a different, less costly, less efficient and less
durable diluent or filler abrasive particles of material such as,
garnet, flint, silica, emery, silicon, carbide, alumina and quartz
and mixtures thereof which it has been discovered does not
materially reduce the performance of the wheel below one without
the 25% of diluent abrasive therein. As shown in Table I wheels
were made and tested in which the primary and secondary abrading
portions were comprised of abrasive and resin bond mixtures
consisting of the following percentage of ingredients by
weights.
______________________________________ Primary Abrading Portion
______________________________________ % by Ingredients Weight
______________________________________ Primary Abrasive Mixture %
by Volume 78.54 24 grit size particles of 75 alumina-zirconia 12
thru 28 grit size particles 25 of garnet 100 Resin Bond % by Weight
21.46 100.00 VARCUM Chemical Co. No. 29-345 40.9 powdered phenolic
resin Wallastonite - (Grade C-6 53.0 Interface Corp.) Calcium Oxide
(CaO) 5.1 Carbon Black 1.0 100.0 Secondary Abrading Portion
______________________________________ % by Ingredients Weight
______________________________________ Abrasive-24 grit aluminum
oxide abrasive 75.62 particles Resin Bond % by Weight 24.38 100.00
VARCUM Chemical Co. No. 29-345 40.9 powdered phenolic resin
Wallastonite (Grade C-6 53.0 Interface Corp.) Calcium Oxide (CaO)
5.1 Carbon Black 1.0 100.0
______________________________________
The 25% mixture of garnet particles in the primary abrading portion
had a particle grit size break down which was the sizing as
prepared by the manufacture of the garnet, as follows:
Screen Size Percent ______________________________________ thru 12
on 16 1/2- 3 thru 16 on 18 8 - 30 thru 18 on 24 50 - 65 thru 24 on
28 12 - 25 ______________________________________
In addition there was added to each of the primary and secondary
abrasive mixtures of abrasive and resin bond 45 cc of furfural
plasticizer and 25 cc of CARBOSOTA (creosote oil) for each pound of
powdered phenolic resin. The CARBOSOTA being mixed separately with
the resin bond and the furfural being mixed with and wetting the
abrasive particles prior to mixing the wetted abrasive particle
with the resin bond. Thereafter, to the entire mixture of wetted
abrasive and resin bond there is added and mixed therewith 4 cc of
a mixture of 60% by weight of furfural and 40% by weight of castor
oil and lastly, 0.0005 of a pound (lb.) or 0.23 grams of dry
colloidal silica (CAB-O-SIL) for each pound (lb.) of the entire
abrasive mixture.
The data in Table I discloses that the wheel with alumina-zirconia
abrasive blended with 25% garnet abrasive particles in the primary
abrading portion and 24 grit size aluminum oxide in the secondary
portion gave a RGR of 193% and RRC of 100% and a performance nearly
equal to the wheels with alumina-zirconia in only the primary
portion and throughout the wheel.
In another embodiment a wheel of comparable size and shape was made
according to the invention with finer 46 grit size alumina
particles in the secondary portion and with a mixture of
alumina-zirconia and 25% garnet in the primary portion. The wheel
consisted of the following percentages by weight of
ingredients.
______________________________________ Primary Abrading Portion
______________________________________ % by Ingredients Weight
______________________________________ Primary Abrasive Mixture %
by Volume 79.6 20 thru 30 grit size alumina- 75 zirconia 12 thru 28
grit size garnet 25 100 Resin Bond % by Weight 20.4 100.0 Union
Carbide BRP5417 phenolic 42 resin powder VARCUM 29-390 liquid resin
14 (plasticizer) Wallastonite (Grade C-6 42.9 Interface Corp.)
Carbon Black 1.1 100.0 Secondary Abrading Portion
______________________________________ % by Ingredients Weight
______________________________________ Abrasive-46 grit size
aluminum oxide 77.8 Resin Bond % by Weight 22.2 100.0 Union Carbide
BRP5417 phenolic 42 powdered resin VARCUM 29-390 liquid resin 14
(plasticizer). Wallastonite (Grade C-6 42.9 Interface Corp.) Carbon
Black 1.1 100.0 ______________________________________
Of the total volume of the 20 thru 30 grit alumina-zirconia
abrasive particles, one-third (331/3 %) were 20 grit, 1/3 were 24
grit and 1/3were 30 grit size particles. The garnet of 12 thru 28
grit size was of the same sizes disclosed before in the table
above.
In addition there was added to each of the primary and secondary
resin bonds 25 cc of CARBOSOTA (creosote oil) for each pound of dry
powdered phenolic resin. The CARBOSOTA being mixed separately with
the resin bond prior to mixing the abrasive particles therewith.
Then, to each of the primary and secondary abrasive mixtures of
abrasive and resin bond is added 4 cc of a mixture containing by
weight 60% of furfural and 40% castor oil and lastly, 0.0005 pounds
or 0.23 grams of colloidal silica (CAB-O-SIL) for each pound of the
entire abrasive mixture.
The grinding wheel was tested and compared with a comparable
standard wheel. The grinding test was performed on the annular edge
of a rotating ring of cast steel of the same type, in the same
manner and with the same apparatus disclosed above except that the
wheel was reciprocated and traversed 31/8inches across the edge
instead of 11/8 inches disclosed above. Results of the test are
shown for comparison in Table II below.
TABLE II
__________________________________________________________________________
TYPE AND LOCATION OF ABRASIVE PARTICLES WHEEL METAL TYPE OF PRIMARY
SECONDARY WEAR REMOVED RGR RRC WHEEL PORTION PORTION IN..sup.3 /HR.
LBS./HR. IN. % IN. %
__________________________________________________________________________
STANDARD aluminum aluminum 9.75 4.70 100 100 PRIOR ART oxide oxide
WHEEL 24 grit 46 grit WHEEL OF 75% alumina- aluminum 5.12 5.28 214
113 INVENTION zirconia oxide 20 thru 30 46 grit grit % BY VOLUME
25% garnet 12 thru 28 grit
__________________________________________________________________________
As can be seen the standard comparable wheel in Table II has a
higher wheel wear and metal removal rate than the standard wheel
shown in Table I above. This is due to the fact that the wheel
forced downwardly by the 20 pounds of force had a longer transverse
across the annular edge than those recited in Table I. As a result
it cut more severely into the ring of cast steel. However,
comparing the relative grinding ratio (RGR) and the relative rate
of cut (RRC) discloses that the wheel with three-fourths (75%)
alumina-zirconia, one-fourth (25%) garnet, and 46 grit aluminum
oxide gave an RGR twice as good and an RRC slightly better than the
100 given the standard wheel and substantially equal to the 2.47
RGR and 97 RRC for the other wheel of the invention with all
alumina-zirconia in the primary portion and 24 grit aluminum oxide
in the secondary portion.
All of the wheels tested, including those of the invention, had
substantially a volume percent composition of about 46% abrasive,
34% resin bond and 20% pores and a density of about 2.7.
It will thus be seen that there has been provided by the invention
raised hub or depressed center and straight center portable
grinding wheels in which the object hereinabove set forth together
with the many thoroughly practical advantages are successfully
achieved. As many possible embodiments may be made of the invention
and as many changes might be made in the embodiments set forth
above, it is to be understood that all matter hereinbefore set
forth is to be interpreted as illustrative only and includes all
embodiments and modifications coming within the scope of the
appended claims.
* * * * *