Note: Descriptions are shown in the official language in which they were submitted.
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RESIN BONDED GRINDING WHEEL
BACKGROUND
Polycrystalline diamond compacts (PDC) include a polycrystalline diamond layer
bonded to a tungsten carbide substrate. The polycrystalline diamond layer
provides high
hardness and abrasion resistance, while the tungsten carbide layer improves
the toughness
of the composite. PDC's are often employed as the cutting tips for boring bits
used to drill
into the earth for natural resources.
Resin bond grinding wheels with diamond abrasive particles can be used to
grind
and finish PDC to its final specified dimensions. PDC is extremely difficult
to grind
because of the interface of the two dissimilar hardness materials. Because of
the extreme
hardness of the polycrystalline diamond layer, the diamond abrasive in the
resin bonded
grinding wheel dulls very quickly. In addition, the tungsten carbide substrate
loads the
grinding wheel reducing the ability of the abrasive wheel to further grind the
polycrystalline diamond layer. As a result, the resin bonded grinding wheel
must be
constantly dressed with a carborundum stone to reduce or eliminate the
tungsten carbide
loading of the grinding wheel and to expose fresh diamond cutting points.
SUMMARY
To improve the grinding of PDC with resin bonded grinding wheels, it is
desirable
to reduce or eliminate the need to constantly dress the resin bonded grinding
wheel with a
carborundum stone. Reducing or eliminating the need to dress the resin bonded
grinding
wheel, while still achieving an acceptable cut rate on the polycrystalline
diamond layer of
PDC, improves the safety and efficiency of the grinding operation. A grinding
wheel
operator can run more than one grinding machine if the resin bonded grinding
wheel does
not require constant dressing while finish grinding a PDC.
In one aspect, the invention resides in a method of grinding comprising:
contacting a polycrystalline diamond compact with a grinding wheel; the
grinding wheel
comprising diamonds, a resin binder, and a mixture of hard filler particles
and soft filler
particles; and wherein the diamonds comprise a diamond concentration from 175
to
225 based on volume, the resin binder comprises 30 percent to 40 percent based
1
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on volume, a ratio of hard filler particles to soft filler particles in the
mixture is from 85:15 to
15:85, and the mixture of hard filler particles and soft filler particles
comprises 5 percent to 30
percent based on volume.
In another aspect, the invention resides in an abrasive article comprising: a
grinding
wheel, the grinding wheel comprising diamonds, a resin binder, and a mixture
of hard filler
particles and soft filler particles; and wherein the diamonds comprise a
diamond concentration
from 175 to 225 based on volume, the resin binder comprises 30 percent to 40
percent based
on volume, a ratio of hard filler particles to soft filler particles in the
mixture is from 85:15 to
15:85, and the mixture of hard filler particles and soft filler particles
comprises 5 percent to 30
percent based on volume.
According to one aspect of the present invention, there is provided a method
of grinding
comprising: contacting a polycrystalline diamond compact with a high
concentration
diamond portion of a grinding wheel, the high concentration diamond portion of
the grinding
wheel comprising diamonds, a resin binder, and a mixture of hard filler
particles, wherein the
hard filler particles comprise ceramic alpha alumina and a blend of soft
filler particles,
wherein the soft filler particles comprise petroleum coke, a first portion of
the blend of soft
filler particles having a first mesh size and a second portion of the soft
filler particles having
a second mesh size different than the first mesh size; wherein the diamonds
are metal bond
diamonds and have a mesh size ranging from 60/80 to 200/230 and a diamond
concentration
in the high concentration diamond portion of the grinding wheel of 175 to 225
based on
volume of the high concentration diamond portion, about 30 vol% to about 40
vol% of the
high concentration diamond portion is the resin binder, the hard filler
particles comprise a
major portion of a ratio of hard filler particles to soft filler particles,
and 5 vol% to about 30
vol% of the high concentration diamond portion of the grinding wheel is the
mixture of hard
filler particles and soft filler particles, and after being dressed, a rate of
decrease of cut rate of
the polycrystalline diamond compact by the grinding wheel per pass without
further dressing
is less than a rate of decrease of cut rate of the polycrystalline diamond
compact by a
corresponding grinding wheel having a diamond concentration in the high
concentration
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diamond portion thereof of less than 175 per pass without further dressing
tested under the
same conditions.
According to another aspect of the present invention, there is provided an
abrasive
article comprising: a grinding wheel comprising a high concentration diamond
portion
comprising diamonds, a resin binder, and a mixture of hard filler particles,
wherein the hard
filler particles comprise ceramic alpha alumina and a blend of soft filler
particles, wherein the
soft filler particles comprise petroleum coke, a first portion of the blend of
soft filler particles
having a first mesh size and a second portion of the soft filler particles
having a second mesh
size different than the first mesh size; wherein the diamonds are metal bond
diamonds and
have a mesh size ranging from 60/80 to 200/230 and a diamond concentration in
the high
concentration diamond portion of 175 to 225 based on volume of the high
concentration
diamond portion, about 30 vol% to about 40 vol% of the high concentration
diamond portion
is the resin binder, the hard filler particles comprise a major portion of a
ratio of hard filler
particles to soft filler particles, and 5 vol% to about 30 vol% of the high
concentration
diamond portion of the grinding wheel is the mixture of hard filler particles
and soft filler
particles, and after being dressed, a rate of decrease of cut rate of a
polycrystalline diamond
compact by the grinding wheel per pass without further dressing is less than a
rate of decrease
of cut rate of the polycrystalline diamond compact by a corresponding grinding
wheel having
a diamond concentration in the high concentration diamond portion thereof of
less than 175
per pass without further dressing tested under the same conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
Repeated use of reference characters in the specification and drawings is
intended to
represent the same or analogous features or elements of the disclosure.
FIG. 1 shows a centerless grinding process with a resin bonded grinding wheel
operating to grind a PDC to its final diameter.
FIG. 2 shows the grinding results for the inventive resin bonded grinding
wheel
versus the comparative resin bonded grinding wheel with different dressing
frequency.
2a
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DEFINITIONS
As used herein, variations of the words "comprise", "have", and "include" are
legally
equivalent and open-ended. Therefore, additional non-recited elements,
functions, steps or
limitations may be present in addition to the recited elements, functions,
steps, or limitations.
DETAILED DESCRIPTION
Referring to FIG. 1 a centerless grinder 10 is illustrated. The centerless
grinder
includes a resin bonded grinding wheel 12, a regulating wheel 14, and a
support 16 for
holding a PDC 18 between the two wheels. The PDC includes a polycrystalline
diamond layer
20 bonded to a tungsten carbide substrate 22. The speed at which the PDC will
traverse
through the grinding interface between the two wheels is controlled by the
helix
2b
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angle a between the axis of the resin bonded grinding wheel 12 and the axis of
the
regulating wheel 14 in combination with the rotational speed of the regulating
wheel.
Prior art resin bonded grinding wheels require constant dressing of the outer
surface 26
with a carborundum stone to maintain the ability of the resin bonded grinding
wheel to
grind the polycrystalline diamond layer.
In order to reduce or eliminate dressing of the outer surface while grinding
PDC, it
is desirable to make the resin bonded grinding wheel behave similar to a
vitrified bonded
grinding wheel. Such an effect can be achieved by using a very high diamond
concentration while including both hard filler particles and soft filler
particles to control
the breakdown rate of the resin bonded abrasive wheel. Such a resin bonded
grinding
wheel will ensure the exposure of fresh diamonds particles in the wheel while
reducing or
eliminating glazing of the outer surface during use. The high concentration
diamond
portion can be an outer annulus of the grinding wheel, a segmented portion
thereof, or the
entire grinding wheel.
Suitable diamonds for use in the abrasive wheel include, for example, natural
diamond, synthetic diamond, resin bond diamonds, metal bond diamonds, diamond
abrasive powder, resin bonded or vitrified bonded diamond agglomerates of the
foregoing,
and combinations of all of the foregoing. To achieve the necessary hardness of
the resin
bonded abrasive wheel, the diamond concentration is very high. In particular,
the
diamond concentration as a volume percent of the total volume of the high
concentration
diamond portion of the grinding wheel is from 175 to 225 or from 180 to 200.
Diamond concentrations less than 175 do not reduce the need for dressing and
concentrations greater than 225 become difficult to bond with sufficient
integrity. The
coated diamonds are used, the coating weight percent should be less than 40%,
or less
than or equal to 30%. Excessive coating amounts reduces the diamond
concentration to too
low of a level and does not result in reduced dressing of the resin bonded
grinding wheel
during use. The size of the diamonds, if not agglomerated, should be between
60/80 mesh
size to 200/230 mesh size. Ranges above and below these limits do not provide
the
requisite packing density to achieve the desired diamond concentration.
While resin bond diamonds may be suitable, especially if agglomerated, the
diamonds are preferred to be metal bond diamonds. Resin bond diamonds are
generally
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too weak and friable to be used in a resin bonded grinding wheel to grind PDC.
Metal
bond diamonds are available in strengths from friable (weaker) to less friable
(stronger).
Such strength rating is qualified by various suppliers using different
designations. In order
to expose fresh diamonds more effectively, weaker metal bond diamonds are
preferred.
For example, if using diamonds from ABC Superabrasives, the strength is rated
on a scale
from ABS 2 (weak) to ABS 9 (strong). When using ABC Superabrasive diamonds,
the
diamonds are desirably ABS 2 or ABS 3. From Worldwide Superabrasives strength
ratings from WSG 200 to WSG 900 are available. Suitable strength diamonds can
include
WSG 200, WSG300, WSG400, and WSG500. LANDS Superabrasives has strengths
designated as LS200, LS230, LS250, LS260, LS270, and LS290. Suitable strength
diamonds can include LS200, LS230, and LS240. In general, the bottom 50% of
the
strength scale for a given supplier's metal bond diamonds are suitable.
Suitable resin binders for use with the diamond abrasive particles include
formaldehyde-containing resins, such as phenol formaldehyde, novolac phenolics
and
especially those with added crosslinking agent (e.g., hexamethylenetetramine),
phenoplasts, and aminoplasts; unsaturated polyester resins; vinyl ester
resins; alkyd resins,
allyl resins; furan resins; epoxies; polyurethanes; cyanate esters; and
polyimides. The
amount of binder resin used in the resin bonded grinding wheel is from about
30% to
about 40% by volume such as approximately 35% by volume of the high
concentration
diamond portion. In general, the amount of resin should be sufficient to fully
wet the
surfaces of all the individual particles during manufacturing such that a
continuous resin
structure, substantially devoid of porosity, is formed with the inorganic
components
discretely bonded throughout, which comprises the mechanical structure of the
grinding
wheel.
Suitable filler additives can include reinforcing particles, grinding aids,
dessicants,
colorants, and lubricants. As mentioned, both hard and soft filler particles
are used in
addition to the diamonds to reinforce and control the breakdown rate of the
grinding
wheel. Hard filler particles (excluding diamonds) are those having a Mohs
hardness of 7
or greater. Suitable hard filler particles include aluminum oxide, silicon
carbide, zirconia,
ceramic alpha alumina particles typically derived from boehmite sol gels, or
other abrasive
particles having the requisite Mohs hardness. Soft filler particles have a
Mohs hardness of
5 or less. Suitable soft fillers include petroleum coke, pyrophyllite,
cryolite, lime,
4
<,
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graphite, refractory grog, ball clay, copper, or talc. The volume ratio of the
hard to soft
filler particles is from (can be)15:85 to 85:15, or from 30:70 to 70:30, or
from 40:60 to
60:40. Suitable hard filler particle sizes include sizes equal to or less than
about 30
microns, such as 600, 800, or 1000 ANSI mesh equivalents. Suitable soft filler
particles
sizes include 100 mesh or finer. The soft particles can have a fine fraction
and coarse
fraction if desired. The fine fraction can be finer than 280 mesh and the
coarse fraction
can be from 100 to 180 mesh. If two sizes of soft filler particles are used
the volume
fraction of the coarse to fine particles can be 50:50 to 70:30. Too large a
volume fraction
of hard filler particles impedes breakdown leading to heat buildup and glazing
of the
grinding wheel, and too large a volume fraction of soft filler particles
undesirably increase
the wear rate of the grinding wheel. The volume percent of a mixture of hard
filler
particles and soft filler particles used in the resin bonded grinding wheel is
from 5% to
30%, or from 8% to 20% of the high concentration diamond portion.
Other fillers can include fibrous and plate-like materials such as carbon or
glass
whiskers and mica. Grinding aids such as cryolite, potassium tetrafluoroborate
(KBF4),
polyvinyl chloride, lignosulfonates, and blends thereof. Colorants such as
organic or
inorganic pigments or dies may be incorporated into the grinding wheel.
EXAMPLES
Advantages of this disclosure are further illustrated by the following
non-limiting examples. 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. Unless otherwise noted, all parts, percentages, ratios, etc.
in the Examples
are by weight.
The following materials were used to prepare the inventive and comparative
grinding wheels.
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Table 1: Components
Symbol Description
NP1 Phenolic Resin Powder from Hexion Speciality Chemicals Inc., Augusta,
GA
as Durite AD-3237
NP2 Phenolic Resin Powder from Hexion Speciality Chemicals Inc., Augusta,
GA
as DuriteR) AD-5575
NP3 Phenolic Resin Powder from Hexion Speciality Chemicals Inc., Augusta,
GA
as Durite AD-3235
SC 1000 grit Green Silicon Carbide from Washington Mills Electro Minerals
Corp.,
Niagara Falls, NY as "CGW-3" Green Silicon Carbide, Wheel Grade, Grade
1000
BC Boron Carbide, Grade 1000 from Electro Abrasives Corporation, Buffalo,
NY
as ElectroborTM B4C grade 1000
CU Untreated Copper Powder from ACuPowder International LCC, Union, NJ as
Copper Powder EL-100 untreated
MO Magnesium Oxide from Atlantic Equipment Engineers, Bergenfield, NJ as
Magnesium Oxide MG-601
PC1 Calcined Petroleum Coke from Asbury Graphite Mills Inc., Asbury, NJ as
Calcined Petroleum Coke (4082)
PC2 Calcined Petroleum Coke from Asbury Graphite Mills Inc., Asbury, NJ as
Calcined Petroleum Coke (4372)
CO Calcium Oxide from Mississippi Lime, Alton, IL as PolycalTM 0F325
Calcium
Oxide
321 Ceramic abrasive from 3M Company, St. Paul, MN as 321 Cubitronim JIS800
321B Ceramic abrasive from 3M Company, St. Paul, MN as 321 CubitronTM JB800
D1 Metal Bond Synthetic Diamond Powder, 30% Nickel Coated, 100/120 mesh
from WorldWide Superabrasives, Ft. Lauderdale, FL as MB-100 N30 100/120
D2 Metal Bond Synthetic Diamond Powder, 30% Nickel Coated, 140/170 mesh
from WorldWide Superabrasives, Ft. Lauderdale, FL as MB-100 N30 140/170
D3 LSMBO Synthetic Metal Bond Diamond Powder, Uncoated, 200/230 mesh from
LANDS Superabrasives Co., New York, NY
D4 LSMBO Synthetic Metal Bond Diamond Powder, Uncoated, 325/400 mesh from
LANDS Superabrasives Co., New York, NY
D5 LS-MAO Synthetic Metal Bond Diamond Powder, Uncoated, 100/120 mesh
from LANDS Superabrasives Co., New York, NY
D6 LS-MAO Synthetic Metal Bond Diamond Powder, Uncoated, 120/140 mesh
from LANDS Superabrasives Co., New York, NY
D7 LS-MAO Synthetic Metal Bond Diamond Powder, Uncoated, 140/170 mesh
from LANDS Superabrasives Co., New York, NY
D8 Resin Bond Synthetic Diamond Powder, Uncoated, 140/170 mesh from
WorldWide Superabrasives, Ft. Lauderdale, FL as RB-150 140/170
D9 Resin Bond Synthetic Diamond Powder, 50% Copper Coated, 120/140 mesh
from WorldWide Superabrasives, Ft. Lauderdale, FL as RB-150 C50 120/140
NP4 Resin Powder from Bitrez Ltd., Standish Wigan, Lancashire, United
Kingdom
as Dialok AR939P Resin Powder
6
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Symbol Description
CK Synthetic Cryolite from Washington Mills, Tonawanda, NY as SODIUM
HEXAFLUOROALUMINATE, CRYOLITE K
D 10 Resin Bond Synthetic Diamond Powder, 30% Nickel Coated, 140/170 mesh
from WorldWide Superabrasives, Ft. Lauderdale, FL as RB-150 N30 140/170
Dll Resin Bond Synthetic Diamond Powder, 56% Nickel Coated, 100/120
mesh
from WorldWide Superabrasives, Ft. Lauderdale, FL as RB-150 N56 100/120
Graphite/Carbon 4539 Powder from Asbury Graphite Mills Inc., Asbury, NJ
D12 Metal Bond Synthetic Diamond Powder, 30% Nickel Coated, 60/80 mesh
from
WorldWide Superabrasives, Ft. Lauderdale, FL as MB-100 N30 60/80
D13 Metal Bond Synthetic Diamond Powder, 30% Nickel Coated, 80/100
mesh from
WorldWide Superabrasives, Ft. Lauderdale, FL as MB-100 N30 80/100
D14 LSMBO Synthetic Metal Bond Diamond Powder, Uncoated, 60/80 mesh
from
LANDS Superabrasives Co., New York, NY
D15 LSMBO Synthetic Metal Bond Diamond Powder, Uncoated, 80/100 mesh
from
LANDS Superabrasives Co., New York, NY
D16 LSMBO Synthetic Metal Bond Diamond Powder, Uncoated, 100/120 mesh
from
LANDS Superabrasives Co., New York, NY
D17 LS-MAO Synthetic Metal Bond Diamond Powder, Uncoated, 80/100 mesh
from
LANDS Superabrasives Co., New York, NY
D18 LSOO Synthetic Metal Bond Diamond Powder, Uncoated, 200/230 mesh
from
LANDS Superabrasive Co., New York, NY
The grinding wheels of Examples 1, 7, 9 to 14 and Comparative Examples lA to
6A were prepared and tested to evaluate their grinding performance on PDC.
Examples 1
and Comparative Example lA were evaluated under different grinding wheel
dressing
procedures. The weight percentage compositions of the various grinding wheels
are
shown in Table 2.
General Procedure for Forming Grinding Wheel Section
Each composition listed in Table 2 was thoroughly mixed for 4 hours in a 1000
ml
polyethylene mixing jar and a roller mill stand (2-Bar Tumbler Base, C&M
Toplinc Inc.,
Goleta CA) set at approximately 180 rpm. The abrasive wheels were direct-
pressed onto
preformed phenolic cores to yield type 1A1 abrasive wheel sections 8" OD x
1.25" TK x
1.25" ID, with diamond depth x = 0.375. The die cavity in the five-piece, ring-
punch
double-compaction steel mold was filled with the mixed abrasive composition by
rotating
the die assembly on a circular table while pouring the abrasive powder mixture
into the
annular cavity around the core. The powder was then smoothed and leveled with
a plastic
straightedge tool, and the filled mold was closed with the upper ring punch.
7
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The filled mold was placed in a 200-ton heated-platen hydraulic press with the
platen set point temperature set at 350 degrees F. The press platens were
closed to bring
the ring-punch surfaces flush against the mold shell. A magnetic thermometer
was
attached to the side of the mold shell and the mold temperature was monitored.
When the
mold shell reached 350 degree F, the mold was held closed under pressure for
20 minutes.
After 20 minutes at 350 degree F, the mold assembly was removed from the
heated-platen press and placed on a water-cooled steel table and allowed to
cool to room
temperature. The mold shell was stripped from the formed wheel section using a
50-ton
hydraulic press and steel spacers. The formed wheel sections were cured in air
according
the following schedule. One hour ramp to 150 degree F, one hour soak at 150
degree F, 4
hour ramp to 350 degree F, seven hour soak at 350 degree F, followed by 3 hour
cool to
room temperature.
The wheel sections were surface ground to thickness and then two sections were
bonded together using epoxy adhesive. The bonded structure was then trued and
dressed
using a 40/60 grit SiC grinding wheel on a 3M E228 truing and dressing machine
to make
the final test grinding wheels
8
Table 2: Grinding Wheel Compositions
Percent by Weight
0
Component Example 1 Comp. Comp. Comp. Comp. Comp.
Example 7 Example 9 Example Example Example 12 Example
Example INJ
Example lA Example 2A Example 3A Example 4A
Example 6A 10 II 13 14 C
1-L
tµ..)
NP 1 0 19.5
.6.
NP2 8.4 0 19.4 18.4 16.5 18.2
8.4 8.3 16.2 16.3
t...)
NP3 8.4 0 8.4
8.3 oe
4..
SC 0 10.6 14.6 11.1
BC 0 1.7
5.0
Cu 0 18.5
MO 0 1.5
PCI 3.9 0 4.5 4.3 2.1 3.5 3.9
3.8 3.8
PC2 3.9 0 3.9
1.9
CO 0.7 0 0.6 1.1 0.9 0.7 0.6 0.5 0.7
0.7 0.7 0.7 a
321 12.2 0 14.0 13.3 7.7 11.3
12.2 8.0
o
321B
8.0 19.5 11.8 ro
CD
(A
Dl 0 34.5 38.8 16.5 21
La
La
D2 0 8.1 9.1
.i.
ts..)
D3 0 2.8 3.2
Iv
D4 0 2.8 3.2
0
I-.
W
D5 23.6 0 25.2
23.5 20.4 20.0 1
i-
D6 23.6 0 25.2
23.5 20.4 20.0 20.2 o
1
D7 15.3 0
23.5 i-
cri
D8 11.6
D9 48.7
NP4 14.1 12.1 16.1
CK 10.4 6.9 6.5
5.8
D10 13.5
Dll 55.3
*I:
G 6.9
n
D12 16.5 21
.....
CA
D13 23.8 41.4
is.)
c
D14 18.8
t..)
D15 33.9
--C-
c....)
D16 20.4
oe
D17 16.6
oe
c
D18
20.2 19.8 20.0
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Grinding Test
Cylindrical diamond cutter inserts (PDCs), obtained from US Synthetic
Corporation, Orem, Utah, were ground using a centerless grinder (Acme Model 47
Centerless Grinder, Acme Manufacturing Company, Auburn Hills, Michigan) using
the 8"
diameter x 2.5" wide resin bond diamond wheels of Example 1 and Comparative
Example
A. The PDCs were mounted in a spring-loaded fixture to hold them during the
grinding
process. The grinding wheel speed was about 4000 SFPM and the regulating wheel
speed
was about 55 SFPM and the helix angle of the regulating wheel was set to about
3 degrees.
This provided a grinding contact time of about 5.5 seconds per load of PDC. A
coolant
flood of 5% "Shell Metalina Y-850" (Shell Lubricants, Houston, Texas) in water
was
used. Depending on the size of the PDCs, testing was performed using either 2
PDCs per
load or 3 PDCs per load as noted below:
Test Format PDC Diameter Diamond Depth Carbide Depth per
per PDC PDC
2 PDCs Nominal 0.63" 0.085" 0.4365"
3 PDCs Nominal 0.63" 0.062" 0.257"
Testing was performed with Comparative Example lA that verified the 2 PDC
format gave a similar polycrystalline diamond volume removal rate as the 3 PDC
format.
The motor load during grinding was controlled to about 2.5 ¨ 3.1 amps over the
idle load
via in feed control of the regulating wheel. Test grinding wheels were dressed
after every
pass for the high frequency dressing test. For the low frequency dressing
test, each
grinding wheel was dressed after every 10th pass. Dressing was accomplished by
manually contacting a 220 grit, 1" x 1" x 6" white dressing stick ("3M
Dressing Stick
200TH", 3M Company, St. Paul, Minnesota) with the wheel and traversing it
across the
wheel a total of 6 passes.
Comparative Example lA is a prior art resin bonded grinding wheel sold by 3M
having part number MMMRBDW26435-R. Comparative Examples 2A and 3A utilized
non-agglomerated resin bond diamonds, which were too friable and sheared off
on the
outer surface of the grinding wheels when grinding PDC leading to excessive
glazing and
poor cut. Comparative Example 4A used the same diamond concentration of
CA 02833342 2013-11-15
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Comparative Example IA of approximately 125 and brittle soft filler particles
instead
of ductile soft filler particles. The need for dressing was reduced, but not
significantly.
Comparative Example 6A used the same 125 diamond concentration but the fine
grade
diamonds were replaced with courser grades. No significant performance
difference was
noted. Example 1(185), Example 7 (225), Example 9 (200), and Example 10(200)
used
significantly higher diamond concentrations with a mixture of hard and soft
filler particles
as described above. During test grinding on PDC, the need for dressing was
significantly
reduced.
Referring now to FIG. 2, the cut rate of the inventive grinding wheel was
significantly greater than that of the comparative grinding wheel when
dressing was
employed every pass (0.0027 cubic inches versus 0.0023 cubic inches), and the
inventive
wheel had a good level of cut rate when dressing was employed only every 10th
pass
(0.0013 cubic inches versus 0.0008 cubic inches). The cut rate of the
inventive wheel with
only every 10111 path dressing was approximately 48% of the single pass cut
rate versus
approximately 35% for the comparative wheel 1A.
Example 1 was evaluated at a customer who produces PDC's using centerless
grinding. The centerless grinding application reduced the outside diameter of
the PDC's
to the final required diameter/tolerance and was conducted under a coolant
flood. The
existing grinding wheel that was previously used by the customer required
frequent or
substantially continuous abrasive media dressing to maintain stock removal
with the
existing diamond abrasive grinding wheel. When the Example 1 grinding wheel
was
installed on the centerless grinder, the PDC's were processed using the same
previous
grinding conditions of the prior existing diamond abrasive grinding wheel. No
external
abrasive dressing media was used on the Example 1 grinding wheel during the
centerless
grinding of the PDC's. The centerless grinding operations were able to
continue to
produce PDC's to the required finished size using the existing process
parameters while
achieving the same production rates without the use of abrasive wheel dressing
or
conditioning media on the surface of the Example 1 grinding wheel during the
production
of the PDC's. The total absence of dressing media while grinding PDC's had not
been
previously possible under the existing process conditions for any prior
grinding wheel
used. Furthermore, the Example 1 grinding wheels were fully consumed to the
core while
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grinding the PDC's and did not become glazed over or inoperative at any point
in the grinding
process.
Other modifications and variations to the present disclosure may be practiced
by those of ordinary skill in the art, without departing from the scope of the
present
disclosure, which is more particularly set forth in the appended claims. It is
understood that
aspects of the various embodiments may be interchanged in whole or part or
combined with
other aspects of the various embodiments. In the event of inconsistencies or
contradictions
between portions of any references mentioned herein and this application, the
information in
the preceding description shall control. The preceding description, given in
order to enable
one of ordinary skill in the art to practice the claimed disclosure, is not to
be construed as
limiting the scope of the disclosure, which is defined by the claims and all
equivalents thereto.
12
