U.S. patent number 3,650,715 [Application Number 04/813,754] was granted by the patent office on 1972-03-21 for abrasive compositions.
This patent grant is currently assigned to E. I. du Pont de Nemours and Company. Invention is credited to Dieter Klaus Brushek, Frank Clyde Starr, Jr..
United States Patent |
3,650,715 |
Brushek , et al. |
March 21, 1972 |
ABRASIVE COMPOSITIONS
Abstract
Abrasive compositions and articles such as grinding wheels and
hones formed therefrom which abrasive compositions contain from 6
to 35 volume percent of diamonds from 5 to 65 volume per cent of a
dendritic form of a metal such as copper, or silver or alloys
thereof, from 10 to 75 volume percent of a coalesced aromatic
polyimide and up to 80 volume percent (but retaining the 10 volume
percent minimum of polyimide) of the polyimide phase of a filler or
a metal coating on the diamonds.
Inventors: |
Brushek; Dieter Klaus
(Wilmington, DE), Starr, Jr.; Frank Clyde (Wilmington,
DE) |
Assignee: |
E. I. du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
25213291 |
Appl.
No.: |
04/813,754 |
Filed: |
April 4, 1969 |
Current U.S.
Class: |
51/298; 51/309;
75/231; 75/247; 51/295; 75/230; 75/243; 428/932 |
Current CPC
Class: |
C08L
79/08 (20130101); Y10S 428/932 (20130101) |
Current International
Class: |
C08L
79/00 (20060101); C08L 79/08 (20060101); C08g
051/12 (); C09c 001/68 () |
Field of
Search: |
;51/298,295,309 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Arnold; Donald J.
Claims
We claim:
1. An abrasive article comprising from between about 6 and about 35
volume percent of diamonds, from between about 10 and about 75
volume percent of poly-N,N'(4,4'-oxydiphenylene) pyromellitimide,
and from between about 5 and about 65 volume percent of compacted
dendritic copper.
2. An abrasive article comprising from between about 6 and about 35
volume percent of diamonds from between about 10 and about 75
volume percent of an aromatic polyimide derived from
3,3',4,4'-benzophenone tetracarboxylic dianhydride and
4,4'-oxydianiline, and from between about 5 and about 65 volume
percent of compacted dendritic copper.
3. The article of claim 2 wherein said compacted dendritic metal is
derived from clustered dendritic particles wherein said clusters
are of between about 50 and about 600 U.S. Standard mesh size.
4. An abrasive composition comprising diamonds, coalesceable
aromatic polyimide of poly-N,N'(4,4'-oxydiphenylene)
pyromellitimide and dendritic copper having in molded form from
about 6 to about 35 volume percent of diamonds, from about 10 to
about 75 volume percent of said aromatic polyimide, and from about
5 to about 65 volume percent of compacted dendritic copper.
5. An abrasive composition comprising diamonds, coalesceable
aromatic polyimide derived from 3,3',4,4'-benzophenone
tetracarboxylic dianhydride and 4,4'-oxydianiline and dendritic
copper having in molded form from about 6 to about 35 volume
percent of diamonds, from about 10 to about 75 volume percent of
said aromatic polyimide, and from about 5 to about 65 volume
percent of compacted dendritic copper.
6. The article of claim 1 wherein said compacted dendritic copper
is derived from clustered dendritic particles wherein said clusters
are of between about 50 and about 600 U.S. Standard mesh size.
7. The article of claim 1 in the form of a grinding wheel.
8. The article of claim 1 in the form of a hone.
9. The article of claim 2 in the form of a grinding wheel.
10. The article of claim 2 in the form of a hone.
11. The composition of claim 4 wherein said dendritic copper is in
the form of clustered dendritic particles wherein said clusters are
of between about 50 and about 600 U.S. Standard mesh size.
Description
BACKGROUND OF THE INVENTION
In the past polyimide bonded diamond grinding wheels have been
produced containing various combinations of diamond fillers and
polyimide fillers. Generally, these grinding wheels have exhibited
grinding properties superior to other diamond grinding wheels for
wet grinding materials such as tungsten carbide and the various
cemented carbides but not for dry grinding these materials. It is
believed that these high loadings of metal filler serve among other
functions to conduct away heat as it is generated by the grinding
operation. Previously the problems involved in fabricating
polyimide resin powders made high loadings of metal difficult to
achieve while still maintaining adequate strength in the final
product.
SUMMARY OF THE INVENTION
It has now been found that when a particulate dendritic metal
filler is incorporated in aromatic polyimide bonded abrasive
articles such as grinding wheels or hones an unexpected sharp
increase in the dry grinding efficiency or dry grinding ratio of
the grinding wheel is obtained. This increase is particularly large
when high loadings such as over 40 volume percent of the
non-diamond phase of such dendritic metal as compared with other
fillers are used.
Dendritic metal as used herein refers to an arborescent, branched,
tree-like-shaped form which can be prepared electrolytically.
Typically, the clusters of dendritic metal particles are from 50 to
600 U.S. Standard mesh size. The individual dendrites within a
cluster typically resemble small diameter cylindrical rods, the
surface of which is closely covered with branches about 3 microns
long and 1 micron in diameter as seen in scanning electron
micrographs. The metals which are suitable for use in the present
invention are those structural metals which can be electrodeposited
in dendritic form and include nickel, iron, zinc, nickel alloys,
copper, silver and copper alloys such as bronze and brass. The
nature of these dendritic metal particles appears to aid in
producing a strong molded object by permitting interlocking of the
particles with each other and around the diamonds and resin. The
malleability of a metal such as copper permits deformation during
the pressing and molding of the resin such that strong molded
objects can be produced with relatively low levels of resin binder,
a result which is in striking contrast to that obtained with low
levers of resin and similar levels of hard or relatively smooth
surfaced filler. Thus, diamond abrasive composition made with the
dendritic metal-polyimide system at high metal loading can
withstand the high forces involved in dry grinding and at the same
time easily remove the heat generated by the grinding process from
the area surrounding the diamond. The latter permits greater
retention of the diamonds with consequent increases in grinding
efficiency.
The polyimides used herein are powders of the aromatic polyimides.
Generally, these aromatic polyimides have the fomula ##SPC1##
where R, R.sup.1 and R.sup.2 are organic radicals selected from the
group consisting of aromatic, aromatic heterocyclic, bridged
aromatic and substituted groups thereof. Preferred R's include
##SPC2##
wherein the bonds to the carbonyl groups are arranged in pairs with
the carbonyl groups of each pair on adjacent or peri carbon atoms.
Preferred R.sup.1 's include ##SPC3##
When pyromellitic dianhydride is used at least 14 mole percent of
the diamine used should contain two aromatic rings. Preferred
R.sup.2 's include ##SPC4##
wherein the bonds to the carbonyl groups are arranged in pairs on
adjacent or peri carbon atoms.
R.sup.3 is selected from the group consisting of carbon in an
alkylene group or perfluorinated alkylene group of from one to
three carbon atoms, oxygen, silicon in ##SPC5##
hydrogen. The polyimide powder may be prepared in accordance with
the teachings of U.S. Pat. No. 3,249,588 issued May 3, 1966 to
Walter George Gall and should have a surface area of at least 0.1
square meter/gram and preferably greater than 2 square meters/gram,
as measured by adsorption of nitrogen from a gas stream of nitrogen
and helium at liquid nitrogen temperature, using the technique
described by F. M. Nelsen and F. T. Eggertson (Anal. Chem. 30, 1387
(1958) ). Sample weights are in the order of 0.1-3.5 g. The thermal
conductivity detector is maintained at 40.degree. C. and the flow
rate is approximately 50 ml./min. The gas mixture used is 10 parts
by weight nitrogen and 90 parts by weight helium.
The polyimide should have an inherent viscosity of at least 0.1 and
preferably from 0.3 to 5, as measured at 35.degree. C from a 0.5
percent by weight solution in 96 percent sulfuric acid. If the
polyimide is not soluble to the extent of 0.5 percent in 96 percent
sulfuric acid at 35.degree. C. and a strong article can be
coalesced therefrom it is assumed to have an inherent viscosity of
greater than 0.1.
The molded abrasive composition generally contains from 6 to 35
volume percent diamonds, from 5 to 65 volume percent dendritic
metal, and from 10 to 75 volume percent aromatic polyimide.
Optionally, part of the resin phase can be replaced with up to 80
volume percent of another abrasive such as silicon carbide, or
aluminum oxide, or a filler such as glass, or a metal in the form
of metal coating on the diamonds, powder or metal fibers provided
that at least 10 volume percent of the composition is aromatic
polyimide. As used herein volume percent is based on the as-molded
composition. Generally, the diamonds are from 50 to 300 U.S.
Standard screen series size for grinding wheels while diamonds as
fine as 1,200 sieve size are suitable for hones.
Generally, when fabricating grinding wheels, the diamond-containing
composition is made up as a rim with the diamonds embedded in a
coalesced polyimide matrix which rim is then mounted on a core. The
core preferably is aluminum, but other materials such as aluminum
filled phenolic resin may be used. Hones of various shapes can be
molded by similar techniques.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Grinding Ratio Test - I
A D11V9 (American Standards Association) flaring cup wheel is
mounted on the spindle of a Cincinnati No. 2 grinder and rotated at
4,000 r.p.m. The work consists of 16 blocks of cemented carbide,
grade C-3 or C-5, mounted and evenly spaced on a rotatable head and
each having an exposed rectangular surface 1/4 inch .times. 3/4
inch. The blocks are ground sequentially by passing the work across
the face of the grinding wheel at a table speed of 6 ft./min.,
returning the work in a spark-out pass and then rotating the head
to expose the next block to action of the wheel. When each block
has been ground in turn, the work is fed into the wheel 0.002 inch
and the grinding cycle is repeated. The whole operation is carried
out automatically under dry grinding conditions to remove carbide
at a rate of 0.232 in..sup.3 /hr. The grinding ratio (GR) is the
ratio of the volume of carbide removed to the volume of wheel
removed.
Grinding Ratio Test - II
A D11V9 flaring cup wheel is mounted on the spindle of a Gallmeyer
and Livingstone No. 28 grinder and rotated at 4,000 r.p.m. The work
consists of a row of 6 blocks of cemented carbide, C-2 grade, and 6
blocks of cemented carbide, C-5 grade, each 1/4 inch .times. 3/4
inch and spaced alternately 1 inch apart. The table speed is either
2 or 5 ft./min. and the infeed is 0.002 inch. The grinding
operation consists of a cutting pass during which each block is
ground followed by a spark-out pass prior to the next infeed. The
grinding operation is continued at carbide removal rate of 0.14
in..sup.3 /hr. and 0.35 in..sup.3 /hr. at table speed of 2 ft./min.
and 5 ft./min., respectively. The grinding ratio (GR) is the ratio
of the volume of carbide removed to the volume of wheel
removed.
EXAMPLES 1-3
Examples 1-3 employed 33/4 inches D11V9 flaring cup wheels made
from synthetic diamonds, poly-N,N'(4,4'-oxydiphenylene)
pyromellitimide binder, and selected fillers. The diamonds were 180
grit, metal clad diamonds present at a 100 concentration (72
carats/in..sup.3) in rims 1/8 inch wide. Grinding ratio test I was
used to evaluate the wheels and the results are shown in Table I.
The results show that the presence of metal fillers is beneficial
with the results using dendritic copper filler unexpectedly good.
##SPC6##
EXAMPLES 4-9
Examples 4-9 employed 5 inch D11V9 flaring cup wheels made from
synthetic diamonds, poly-N,N'(4,4'-oxydiphenylene)-pyromellitimide
binder and selected fillers. The diamonds were 150 or 180 grit,
optionally metal clad, present at a concentration of 100, 75 or 50
in rims 1/8 inch wide. Grinding ratio test II was used to evaluate
the wheels and the results are shown in Table II. The results again
show the superiority of dendritic copper filler. ##SPC7##
EXAMPLE 10
A 3-3/4-inch D11V9 flaring cup wheel was made with the composition
of Example 8 except the resin binder used was the polyimide from
4,4'-oxydianiline and 3,3',4,4'-benzophenone tetracarboxylic
dianhydride. Under Grinding Test I conditions using cemented grade
C-5, the wheel had a grinding ratio of 49.
EXAMPLES 11-14
Examples 11-14 employed 3-3/4 -inch D11V9 flaring cup wheels
identical to that used in Example 3 except the amounts of resin
binder and dendritic copper filler were varied to provide bonds of
different degrees of hardness. The results, shown in Table III were
obtained using grinding ratio test I.
---------------------------------------------------------------------------
TABLE III
Rim Composition (Vol.
%) Grinding Metal Resin Dendritic Ratio Example Diamond cladding
binder copper C-5 C-3
__________________________________________________________________________
11 25 12 53 10 8 65 12 25 12 43 20 11 .apprxeq.202 13 25 12 23 40
16 521 14 25 12 33 30 39 832
__________________________________________________________________________
EXAMPLES 15- 20
Examples 15- 20 indicate the remarkable increase in the strength of
compositions containing dendritic metal filler compared with usual
copper and silicon carbide fillers (Table IV), when using the
polyimide of Example 1. ##SPC8##
EXAMPLE 21
Two compositions were prepared by dry blending (a) 40.3 g. nickel
clad diamonds (60-80 grit U.S. mesh), 92.0 g. dendritic copper
powder and 3.8 g. poly-N,N'(4,4'-oxydiphenylene) pyromellitimide
resin, and (b) 72.9 g. dendritic copper powder and 30.1 g.
poly-N,N'(4,4'-oxydiphenylene) pyromellitimide resin. Composition
(a) was placed and leveled in the cavity of a 3.5-inch diameter
cylindrical mold and preformed at ambient temperature and 6,000
p.s.i. Composition (b) was placed and leveled on top of the
preformed composition (a) and also preformed at 6,000 p.s.i. The
mold and contents were then heated at low contact pressure to
450.degree. C. and the preform was molded at this temperature for
20 minutes under a pressure of 55,000 p.s.i. The mold was cooled to
below 200.degree. C. The pressure was released and the molded
cylinder was ejected. The composition of the abrasive layer, as
expressed in volume percent, was 25 percent diamond (100
concentration), 50 percent dendritic copper, 13 percent polyimide
resin, and 12 percent nickel (cladding on diamonds), while that of
the nonabrasive layer was 79.5 percent dendritic copper and 20.5
percent polyimide resin. Hones were cut from the molding 11/8
inches .times. 3/4 inch and the surface of the abrasive layer, 1/8
inch in depth was machined to a 2 -inch radius of curvature in the
direction of the short dimension. The yield was 6 hones per
cylinder. The bases of 8 hones were shaped to fit the holders of a
two-turret honing machine manufactured by Micromatic Hone Corp. for
honing cast iron brake drums. After mounting the hones,
semi-finished drums of 12 inches I.D. and 2.8 inches width were
then honed, during which operation the turrets were rotated at
about 170 r.p.m. At equilibrium, the wear ratio, expressed as
number of drums honed per gram of diamond consumed was about 1.900.
Phenolic bonded stones with the same diamond grit size and
concentration exhibited a wear ratio of about 450 drums per gram of
diamond used, while the metal bonded stones normally used to hone
cast iron brake drums had ratios about the same as that of the
composition of this Example.
EXAMPLE 22
An abrasive composition was prepared by dry blending 1.18 g. nickel
clad diamonds (60-80 grit, U.S. mesh), 0.10 g.
poly-N,N'(4,4'-oxydiphenylene) pyromellitimide, 1.3 g. dendritic
copper powder, 0.69 g. fine zinc powder and 0.22 g. silicon carbide
(400 grit U.S. mesh), and the mixture was compacted in a 11/4 -inch
diameter cylindrical mold at ambient temperature and 6,000 p.s.i.
Dendritic copper powder (17.1 g.) was then compacted on top of the
abrasive-containing preform at 6,000 p.s.i. and the mold and its
contents were heated to 450.degree. C. under low contact pressure.
The preform was molded at this temperature for 20 minutes at 30,000
p.s.i. and cooled under pressure to below 200.degree. C. The
resultant disc had an abrasive layer 0.030 inch thick and its
composition by volume was 25 percent diamond (100 concentration),
12 percent nickel (cladding on the diamonds), 11.5 percent
polyimide resin, 24 percent dendritic copper, 16 percent zinc and
11.5 percent silicon carbide. The high volume loading of fillers
with corresponding low volume of resin was made possible by the
dendritic nature of the copper filler. The molded composition was
shown to be strong and useful by the following test.
The 11/4 -inch diameter disc was center drilled to form a 9/32 inch
hole and it was mounted on a variable speed, vertical spindle in
such a way that the abrasive surface was in contact with a 1/4 inch
thick cast iron, wear plate having a ring shape whose inside
diameter of about 1 inch and outside diameter of about 11/4 inches
resulted in an area of contact of 0.4 inch.sup.2. The surface of
the wear plate was lapped with a 600 G SiC finish. The flat
surfaces of both the test specimen and the wear plate were parallel
and in the same plane. The wear plate was thermally insulated from
its holder and was connected to a strain gage through a lever arm.
A force sufficient to produce a load of 18 pounds on the nominal
area of contact of 0.40 inch.sup.2 was applied through the lever
arm to the test specimen. The spindle was rotated at a speed such
that the velocity of the surface of the test specimen in contact
with the wear plate was 600 ft./min., thus giving a PV value
(pressure in lbs./in..sup.2 .times. velocity in ft./min.) of about
27,000. After a short break-in period, a wear ratio was calculated
following a test of about 1 minute duration using the losses in
weight of the wear plate and of the specimen. The result, expressed
as grams of cast iron removed per gram of hone material consumed,
was 24.0 and the removal rate of the cast iron was 0.012 g./min.
The load was increased to give a pressure of 250 p.s.i. at the same
velocity (PV=150,000) and the test was carried out for about 1/2
minute. The wear ratio was again 24.0 but the removal rate had
increased about 80-fold to 0.93 g./min. When the same composition
was tested by honing cast iron brake drums, as described in Example
21, the wear ration was 1,950 drums honed per gram of diamond
consumed.
* * * * *