Resin bonded abrasive tool and method of making the tool

A resin bonded abrasive tool consists of abrasive grain and an organic bond comprising a thermosetting resin, such as epoxy resin, phenolic resin or rubber or blends thereof and a precursor filler system capable of forming in situ an active filler system by reacting under the heat generated during grinding. The organic bond optionally further comprises a filler system. A method of making the resin bonded abrasive tool consists of mixing the abrasive grain and the organic bond with the precursor filler system, pressing the resulting mixture into shape, and curing the abrasive tool at about 150 to 200.degree. C.

BACKGROUND OF THE INVENTION 
This invention relates to a resin bonded abrasive tool and method of making 
the same. 
A resin bonded abrasive tool comprises abrasive material such as fused 
aluminum oxide, sintered aluminum oxide, sintered sol gel microcrystalline 
alpha-alumina, silicon carbide, alumina zirconia, cubic boron nitride or 
diamond and an organic bond comprising a binder such as thermosetting 
resin such as epoxy resin, phenolic resin or rubber or blends thereof and 
a filler system. A resin bonded grinding wheel is made by mixing the 
abrasive material and organic bond comprising binder and filler system 
followed by pressing the resulting mixture into shape and typically curing 
the wheel at about 150 to 200.degree. C. 
A abrasive tool is used for a variety of grinding and finishing 
applications. The ground material may be metals such as carbon steel, low 
alloy steel or stainless steel or non-metals such as granite, ceramic or 
glass. Nearly 70 to 80% of the abrasive tools contain fused aluminum oxide 
abrasive and are used for grinding metals, while non-metals are ground 
using abrasive tools containing silicon carbide grain or diamond abrasive 
grain. 
A variety of filler systems, such as a complex salt of manganese and 
potassium chloride having stoichiometry of K.sub.2 MnCl.sub.6 and/or 
K.sub.4 MnCl.sub.6, cryolite, lithopone, iron pyrites, calcium carbonate, 
aluminum fluoride, iron oxide or barium sulfate or blends thereof are 
known to be used with resin bonded abrasive tools. Such filler systems are 
known to enhance the grinding performance of resin bonded abrasive tools. 
Examples of active fillers are described in U.S. Pat. Nos. 4,500,325, 
4,877,420, 4,475,926 and 4,609,381, the contents of which are hereby 
incorporated by reference. The filler systems undergo physical, chemical 
and mechanochemical reactions due to heat generated during grinding and 
increase the rate of grinding or cutting the workpiece and clear the chips 
faster thereby improving the performance of the abrasive tool and 
increasing the life of the abrasive tool. Such filler systems often have 
limitations in manufacturing and use due to chemical and/or physical 
instability at the operating conditions and/or handling problems. Such 
filler systems are also expensive. With particular reference to the 
complex salt of manganese and potassium chloride, it is highly 
hygroscopic. Therefore, abrasive tools comprising such complex salt must 
be kept out of contact with atmospheric air to prevent moisture formation 
thereon which will adversely affect the performance and life of the 
abrasive tools. This makes storage of such abrasive tools difficult and 
inconvenient. Other filler systems are also expensive or unstable, thereby 
rendering abrasive tools comprising the same very expensive. 
An object of the invention is to provide a resin bonded abrasive tool 
having improved performance and increased life. 
Another object of the invention is to provide a resin bonded abrasive tool 
which is commercially acceptable. 
Another object of the invention is to provide an efficient method of making 
a resin bonded abrasive tool. 
Another object of the invention is to provide a method of making a resin 
bonded abrasive tool having improved performance and increased life. 
Another object of the invention is to provide a method of making a resin 
bonded abrasive tool which is inexpensive. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a resin bonded abrasive tool 
consisting of abrasive material and an organic bond comprising a binder 
such as thermosetting resin such as epoxy resin, phenolic resin or rubber 
or blends thereof and a precursor filler system capable of reacting and 
forming in situ an active filler system under the heat generated during 
grinding, the organic bond optionally further comprising a filler system. 
According to the invention there is also provided a method of making a 
resin bonded abrasive tool under manufacturing conditions and temperatures 
selected to avoid causing a reaction among the complex salt precursors. 
The method consists of mixing abrasive material and organic bond 
comprising a binder such as thermosetting resin such as epoxy resin, 
phenolic resin or rubber or blends thereof and a precursor filler system 
capable of reacting and forming in situ an active filler system under the 
heat generated during grinding, the organic bond optionally further 
comprising a filler system, the method further comprising pressing the 
resulting mixture into shape and typically curing the abrasive tool at 
about 150 to 200.degree. C. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Abrasive tools of the invention include resin bonded grinding wheels, 
discs, segments and stones, as well as coated abrasive tools. 
Preferred abrasive materials according to the invention include, but are 
not limited to, fused aluminum oxide, sintered aluminum oxide, sintered 
sol gel microcrystalline alpha-alumina, silicon carbide, alumina zirconia, 
cubic boron nitride and diamond abrasive grains, and combinations thereof. 
Any abrasive grain known in the art may be used in the abrasive tools of 
the invention. 
For the active filler system, preferred precursor materials generally 
include those materials which are stable in the presence of the unreacted 
resin of the bond and in the presence of the abrasive and bond mixture 
during curing of the abrasive tool. Precursor materials are selected to 
yield an active filler system in the abrasive tool at the point of contact 
of the tool with the workpiece under temperature, pressure and 
environmental conditions existing during the grinding operation. 
A preferred precursor filler system for in situ creation of a complex 
manganese and potassium chloride salt filler comprises 60-70% by wt 
potassium chloride, 15-20% by wt manganese oxide and 15-20% by wt chlorine 
or hydrogen chloride generating compound, and preferably 65% by wt 
potassium chloride, 17.5% by wt manganese oxide and 17.5% by wt chlorine 
or hydrogen chloride generating compound. The chlorine or hydrogen 
chloride generating compound preferably contains decomposable chorine, is 
stable at ambient condition, and is in a form suitable for use in making 
an abrasive tool. Preferred compounds include polyvinyl chloride (PVC), 
polyvinylidene chloride (Saran.TM.) and perchloropentacyclooctene 
(Dechlorane Plus.TM.; 
1,2,3,4,7,8,9,10,13,13,14,14,-dodecachloro-1,4,4a,5,6,6a,7,10,10a,11,12,12 
a-dodecahydro-1,4:7,10-dimethanodibenzo(a,e)cyclooctene) and combinations 
thereof. 
Additional preferred active filler systems which may be made according to 
the invention include, but are not limited to, cryolite (Na.sub.3 
AlF.sub.6), iron sulfide (FeS.sub.2) and barium sulfide (BaS). 
For cryolite, aluminum fluoride (AlF.sub.3) and sodium fluoride (NaF) 
precursor materials are added to the abrasive tool and these precursors 
react under the heat and pressure of the grinding operation to form 
cryolite. Preferred quantities include 30-50 wt % aluminum fluoride and 
40-70 wt % sodium fluoride. Cryolite may be formed from other precursor 
materials, such as aluminum fluoride (AlF.sub.3), ammonium fluoride 
(NH.sub.4 F) and sodium chloride (NaCl); or sodium bifluoride and aluminum 
hydroxide (Al(OH).sub.3 ; or alkali metal fluosilicate (Na.sub.2 
SiF.sub.6), alumina hydrate (Al.sub.2 O.sub.3 --H.sub.2 O) and alkali 
metal hydroxide (NaOH); or sodium fluoride (NaF), ammonium fluoride 
(NH.sub.4 F) and sodium aluminum oxide (NaAlO.sub.2). 
Conditions found during grinding also will form iron sulfide from an iron 
oxide (Fe.sub.x O.sub.y, e.g., Fe.sub.3 O.sub.4) and an organic sulfur 
compound (R--S) precursors in the abrasive tool. While it is believed that 
iron sulfide is formed in situ, the organic sulfur compound may degrade 
under grinding conditions to release sulfur dioxide which is believed to 
be the active agent evolved when iron sulfide is added as an active 
filler. The organic sulfur compounds preferred for use in the invention 
are those which are stable under conditions found during mixing and curing 
of the abrasive tools. Suitable organic sulfur compounds include, but are 
not limited to, thiazoles, such as 2-mercaptobenzothiazole and 
2,2'-dibenzylthiazyl disulfide; sulfenamides, such as 
N-cyclohexylbenzothiazole-2-sulfenamide and 
morpholinylbenzothiazole-2-sulfenamide; thiurams, such as 
tetramethylthiuram disulfide and monosulfide, and tetraethylthylthiuram; 
and dithiocarbamates (or dithiocarbamic acids), such as zinc dimethyl- and 
zinc dibutyl-dithiocarbamate; and combinations thereof. Suitable iron 
oxides include, but are not limited to, ferrosoferric oxide, ferroferric 
oxide, hydrated ferric oxide and combinations thereof. Preferred amounts 
include 30-70 wt % iron oxide and 30-70 wt % organic sulfur compounds. 
Another reaction under the heat and pressure of grinding forms barium 
sulfide from barium sulfate (BaSO.sub.4) and a catalytic carbon material. 
Suitable catalytic carbon material includes, but is not limited to, carbon 
black, activated charcoal and graphite, and combinations thereof. 
In each instance, the reaction of the precursor materials and the active 
filler formation occurs at the grinding interface between the tool and the 
workpiece. Conditions encountered at this interface typically range from 
about 300.degree. to about 1000.degree. C., and from about 100 to about 
1000 p.s.i. (7.03 to 70.3 Kg/cm.sup.2). 
An additional benefit of the in situ formation of active filler is that the 
filler is formed only at the active site where it is needed. For fillers 
which act as a lubricant, no delivery mechanism is required because the 
active filler avoids thermal or mechanical damage to the workpiece and no 
other lubricant is needed. 
It is not necessary to supply the precursor materials in stoichiometric 
amounts as the reactions will proceed with non-stoichiometric amounts of 
reactants. The precursor materials may react to form active fillers in 
addition to those identified herein, depending upon the nature of the 
materials, the abrasive grain and the bond components. 
Each of these active filler precursor systems according to the invention 
may be present in the bond along with minor amounts of the other active 
filler systems or other secondary fillers as are known in the art. 
Suitable secondary fillers include, but are not limited to, bubble 
alumina, bubble mullite, glass bubbles, fluorspar, cryolite, lithophone, 
iron pyrites, calcium carbonate, aluminum fluoride and iron oxide, and 
blends thereof. 
For phenolic novolac resin bonds, the abrasive tool preferably is cured at 
150.degree. to 200.degree. C., most preferably at 175-185.degree. C. Other 
resin bonds, such as epoxy bonds, modified epoxy bonds and other types of 
phenolic bonds, may be cured as is known and customary in the art without 
loss of the benefits of the invention. 
Because complex salts are readily damaged by water and the like in 
conventional abrasive tools, these tools do not realize the full benefit 
of the active fillers in grinding performance. In contrast, water damage 
and other environmental hazards are avoided with the tools and method of 
the invention. Therefore, the active filler systems of abrasive tools made 
according to the invention perform to full capacity and the tools grind as 
well as, or better than, conventional tools. 
The invention also makes storage of abrasive tools comprising such 
precursor filler system easy and convenient. Precursor components may be 
stored in a manufacturing facility indefinitely without the necessity of 
special handling to avoid moisture absorption from the environment. This 
reduces the cost and complexity of manufacturing abrasive tools. Precursor 
components used in the complex salt filler system comprise potassium 
chloride, manganese oxide and chlorine and are relatively inexpensive 
compared to the complex salt, thereby rendering an abrasive tool 
comprising the same inexpensive.

The following experimental examples are illustrative of the invention but 
do not limit the scope thereof: 
EXAMPLE 1 
A abrasive tool composition was prepared by mixing 745 g of fused aluminum 
oxide abrasive (BRR of Orient Abrasives Ltd., Porbandar, Gujarat, India) 
with 35 g of liquid phenolic resin (PLGW-1 of Marvel Thermosets Pvt. Ltd., 
Mumbai, India) and 217 g of a blend prepared by blending of 488 g of 
powder phenolic resin of West Coast Polymers Pvt. Ltd., Kankole, Kerala, 
India), 310 g of iron pyrites powder (PYROXPAT 325 of Chemetall Gmbh, 
Frankfurt, Germany), 37 g of manganese oxide powder, 134 g of potassium 
chloride powder and 33 g of polyvinyl chloride powder. A conventional 
abrasive tool composition (control) was prepared by mixing 748 g of the 
same-fused aluminum oxide abrasive with 30 g of the same liquid phenolic 
resin and 222 g of a blend prepared by blending 477 g of the same powder 
phenolic resin, 303 g of the same iron pyrites powder and 220 g of complex 
salt of manganese and potassium chloride (MKC-S salt (described in U.S. 
Pat. No. 4,877,420) of BBU Chemie GMBH, Vienna, Austria). Both 
compositions were molded into Type 27 grinding wheels and cured in an oven 
at 180.degree. C. for about 20 hrs. The wheels had 48% by volume abrasive, 
46% by volume bond and 14% by volume porosity. The wheels were tested for 
grinding performance in a standard angle grinder under commercial test 
conditions. The overall grinding performance of both the wheels was 
comparable. 
EXAMPLE 2 
A grinding wheel composition was prepared by mixing 1520 g of fused 
aluminum oxide abrasive (BRR of Orient Abrasives Pvt. Ltd. Porbunder, 
Gujarat, India) with 79 g of liquid phenolic resin (PLGW-1 of Marvel 
Thermosets Pvt. Ltd., Mumbai, India) and 204 g of liquid phenolic resin of 
short flow (PLGW-1 of Marvel Thermosets Pvt. Ltd., Mumbai, India) and 305 
g of iron pyrites powder (PYROXPAT 325 of Chemetall Gmbh, Frankfurt, 
Germany), 37 g of manganese oxide powder, 133 g of potassium chloride 
powder and 33 g of polyvinyl chloride powder. A conventional grinding 
composition (control) was prepared by mixing 1495 g of the same fused 
aluminum oxide abrasive, 66 g of the same liquid phenolic resin and 200 g 
of the same liquid phenolic resin of short flow and 371 g of the same iron 
pyrites powder and 180 g of complex salt of manganese and potassium 
chloride (MKC-S salt of BBU, Chemie Gmbh, Vienna, Austria). Both 
compositions were molded into Type 1 grinding wheels with glass fibre 
reinforcement (350 mm diameter and 3.2 mm thickness). The wheels were 
cured in a oven at 180.degree. C. for about 24 hours. The wheels had 48% 
by volume abrasive, 46% by volume bond and 6% by volume porosity. The 
wheels were tested under laboratory condition in the cutting off mode in a 
standard cutting off machine and the results are given in the following 
Table I: 
TABLE 1 
__________________________________________________________________________ 
Material 
Wheel 
Work- Removal Rate 
Wear Rate 
Grinding 
piece 
Cutting 
No. of 
cm/min cm/min 
Power 
Grinding 
Wheel Type 
Material 
speed 
cuts 
(in./min) 
(in./min) 
kw Ratio 
__________________________________________________________________________ 
1) Control 
Steel 
3 50 1.303 0.606 
9-10 
2.15 
EN 9 sec/cut 
1.91 cm 
(3/4") 
diameter 
2) Invention 
Steel 
3 50 1.380 0.483 
10-11 
2.86 
EN 9 sec/cut 
1.91 cm 
(3/4") 
diameter 
__________________________________________________________________________ 
The Table 1 shows that the overall grinding performance of the grinding 
wheel of the invention was in the range of about 10 to 20% more than the 
conventional wheel under identical conditions. The quality of the cut 
pieces was comparable for both wheels. 
EXAMPLE 3 
Grinding wheels were made with the compositions of Example 2 as described 
therein but in the sizes of 400 mm diameter and 3.2 mm thickness. The 
wheels had the same percentage by volume abrasive, bond and porosity. The 
wheels were tested for cutting 38 mm diameter stainless steel bars and 
carbon steel bars under different cutting speeds and the results are given 
in the following Table II: 
TABLE II 
__________________________________________________________________________ 
Material 
Wheel 
Cutting Removal Rate 
Wear Rate 
Grinding 
Work-piece 
speed 
No. of 
cm/min cm/min 
Power 
Grinding 
Wheel Type 
Material 
Secs/Cut 
cuts 
(in./min) 
(in./min) 
kw Ratio 
__________________________________________________________________________ 
1) Control 
Stainless 
1.7 40 19.33 11.10 
20.1 
1.74 
Steel (7.61) (4.37) 
SS 304 
3.81 cm 
(1.5") dia. 
2) Invention 
Stainless 
1.7 40 18.85 8.38 19.1 
2.25 
Steel (7.42) (3.30) 
SS 304 
3.81 cm 
(1.5") dia. 
3) Control 
Stainless 
3.3 40 9.70 3.48 11.7 
2.80 
Steel (3.82) (1.37) 
SS 304 
3.81 cm 
(1.5") dia. 
4) Invention 
Stainless 
3.3 40 9.80 3.30 12.0 
2.95 
Steel (3.86) (1.30) 
SS 304 
3.81 cm 
(1.5") dia. 
5) Control 
Carbon 
1.7 34 18.54 15.65 
26.2 
1.18 
Steel (7.30) (6.16) 
C 1018 
3.81 cm 
(1.5") dia. 
6) Invention 
Carbon 
1.7 38 18.69 13.87 
27.2 
1.35 
Steel (7.36) (5.46) 
C 1018 
3.81 cm 
(1.5") dia. 
7) Control 
Carbon 
3.3 30 9.80 13.13 
18.1 
0.75 
Steel (3.89) (5.17) 
C 1018 
3.81 cm 
(1.5") dia. 
8) Invention 
Carbon 
3.3 30 10.29 10.44 
17.3 
0.99 
Steel (4.05) (4.11) 
C 1018 
3.81 cm 
(1.5") dia. 
__________________________________________________________________________ 
Table II shows that the G-ratio of the wheel of the invention was in the 
range of about 10-20% more compared to the conventional wheel under 
identical conditions. The quality of cut pieces was similar for both 
wheels. 
EXAMPLE 4 
A grinding wheel composition is prepared by mixing 33.7 kg of fused 
aluminum oxide abrasive with 1.12 kg of liquid phenolic resin and 10.5 kg 
of a preblend. The preblend is made by blending 4.79 kg of powder phenolic 
resin, 3.66 kg of iron pyrite powder, 0.82 kg of aluminum fluoride powder 
and 1.24 kg of sodium fluoride powder. A conventional grinding composition 
(control) is prepared from 32.8 kg of the same fused aluminum oxide 
abrasive, 1.12 kg of the same liquid phenolic resin and 10.6 kg of a 
preblend prepared by blending of 4.65 kg of powder phenolic resin, 3.65 kg 
of the same iron pyrites powder and 2.14 kg cryolite (Na.sub.3 AlF.sub.6). 
Both the compositions are molded into non-reinforced cut-off grinding 
wheels (508 mm diameter and 4.4 mm thickness). The wheels are cured in a 
oven at 180.degree. C. for about 24 hours. The wheels have 50% by volume 
abrasive, 36% by volume bond and 14% by volume porosity. The wheels are 
tested under laboratory condition in the cutting off mode in a standard 
cutting off machine. The wheels of the invention have a grinding 
performance at least equal to the grinding performance of the control 
wheels. 
EXAMPLE 5 
A grinding wheel composition is prepared by mixing 35.0 kg of fused 
aluminum oxide abrasive with 1.16 kg of liquid phenolic resin and 9.24 kg 
of a preblend. The preblend is made by blending 4.95 kg of powder phenolic 
resin, 2.22 kg of cryolite, 0.83 kg of iron oxide (Fe.sub.2 O.sub.3) 
powder and 1.22 kg of tetramethylthiuram disulfide. A conventional 
grinding composition (control) is prepared by mixing 32.8 kg of the same 
fused aluminum oxide abrasive, 1.12 kg of the same liquid phenolic resin 
and 10.6 kg of a blend prepared by blending of 4.65 kg of powder phenolic 
resin, 2.14 kg of the same cryolite powder and 3.65 kg iron sulfide 
(FeS.sub.2). Both of the compositions are molded into non-reinforced 
cut-off grinding wheels (508 mm diameter and 4.4 mm thickness). The wheels 
are cured in a oven at 180.degree. C. for about 24 hours. The wheels have 
50% by volume abrasive, 36% by volume bond and 14% by volume porosity. The 
wheels are tested under laboratory condition in the cutting off mode in a 
standard cutting off machine. The wheels of the invention have a grinding 
performance at least equal to the grinding performance of the control 
wheels. 
EXAMPLE 6 
A grinding wheel composition is prepared by mixing 34.0 kg of fused 
aluminum oxide abrasive with 1.13 kg of liquid phenolic resin and 10.2 kg 
of a preblend. The preblend is made by blending 4.82 kg of powder phenolic 
resin, 2.16 kg of cryolite, 3.04 kg of barium sulfate Ba(SO.sub.4)! 
powder and 0.15 kg carbon black. A conventional grinding composition 
(control) is prepared by mixing 34.0 kg of the same fused aluminum oxide 
abrasive, 1.13 kg of the same liquid phenolic resin and 10.3 kg of a blend 
prepared by blending of 4.82 kg of powder phenolic resin, 2.16 kg of the 
same cryolite powder and 3.29 kg barium sulfide (BaS). Both the 
compositions are molded into non-reinforced cut-off grinding wheels (508 
mm diameter and 4.4 mm thickness). The wheels are cured in a oven at 
180.degree. C. for about 24 hours. The wheels have 50% by volume abrasive, 
36% by volume bond and 14% by volume porosity. The wheels are tested under 
laboratory condition in the cutting off mode in a standard cutting off 
machine. The wheels of the invention have a grinding performance at least 
equal to the grinding performance of the control wheels.