Resin-bonded Abrasive Tools With Metal Fillers

Abstract

High ratios of metal removed to abrasive tool wear are achieved when resin-bonded diamond or cubic boron nitride abrasive tools include in the bond from 10 to 60 percent by volume of silver, silver coated copper, or copper powder in the presence of from 5 to 30 percent by volume of a solid lubricant. Other fillers such as finely divided metal oxides or carbide such as silicon carbide may be present in an amount of from 0 to 40 percent by volume, depending upon the total content of metal and lubricant. The diamond wheels or tools of this invention are particularly suitable for the dry grinding of carbide tools. The cubic boron nitride wheels employ metal clad boron nitride abrasive particles and are particularly suitable for the dry grinding of hard steel tools, that is, high speed steels such as T15, M2, M3, and M4. Solid lubricants useful in this invention include organic polymers such as polytetrafluoroethylene, fluorinated ethylene polymers, chlorinated hydrocarbon, fluorinated ethylene propylene polyethylene styrene-butadiene, acrylonitrile-butadiene-styrene, polyurethane, polyforaldehyde, polycarbonate, and nylon and inorganic crystalline solids such as boron nitride, tungsten disulfide, graphite, metal coated graphite, molybdenum disulfide, niobium diselenide tungsten diselenide, and fluorinated graphite.

Parent Case Text

This application is a continuation-in-part of U.S. Pat. application Ser. No. 61,905, filed Aug. 7, 1970, now abandoned.

Description

FIELD OF THE INVENTION

This invention relates to abrasive tools, in particular grinding wheels and coated abrasive belts, containing the hardest known abrasives, diamond and cubic boron nitride which, when metal coated diamond grit is the primary abrasive are particularly suitable for the dry grinding of cemented carbide tool material, e.g., cemented tungsten carbide, and when metal coated boron nitride grit is the primary abrasive are particularly suitable for grinding hard tool steels such as T15, M2, M3, and M4.

BACKGROUND OF THE INVENTION

Improvement of resinoid bonded diamond (or cubic boron nitride) abrasive tools has been recently achieved by the use of metal clad diamond grit or by the use of metal-clad cubic boron nitride grit. The present inventors have disclosed the use of finely divided graphite in such tools in U. S. application Ser. No. 876,655, filed Nov. 14, 1969, to improve, significantly the performance in dry grinding. The present invention provides further improvement in performance through the use of particular combinations of particulate solid film lubricant fillers and silver or copper fillers.

SUMMARY OF THE INVENTION

The present invention involves modifying the bond of resinoid bonded abrasive tools, containing metal clad diamond or cubic boron nitride, by inclusion of from 10 to 60 percent by volume, preferably 30 to 50 percent by volume of the total of bond and fillers (exclusive of the metal clad abrasive) of silver or copper (or a combination such as silver coated copper), and from 5 to 30 percent, preferably 10 to 20 percent of a solid dry film lubricant, hereinafter defined.

The components of the grinding elements or tools of the present invention will now be discussed in detail.

THE DRAWINGS

FIG. 1 shows a perspective view of a grinding element such as produced according to the present invention.

FIG. 2 shows a perspective view of the grinding element of FIG. 1 mounted for use.

THE BOND

Any of the known synthetic resins useful in making coated or bonded abrasives may be employed in the present invention. Obviously, strength and heat resistance are necessary properties. The well-known cross linked resins such as phenol-aldehyde resins, melamine-aldehyde resins, urea-aldehyde resins, polyester resins, and epoxy resins, including the epoxy novolacs, may all be used and conventional modifiers and plasticizers may be used. Part of the filler content may consist of conventional particulate fillers such as silicon carbide. Fairly recently, new essentially linear polymers as well as thermoset polymers (such as thermoset polymers disclosed in French Patent No. 1,455,514) have been introduced which have utility in bonding abrasive grains. These resins, like the crosslinked resins discussed above, are infusible, as opposed to the more common thermoplastic linear polymers having definite softening ranges and which are reversibly softenable. Examples of such resins, having utility in making abrasive tools, are given in U. S. Pat. No. 3,329,489 (polybenzimidazole), and U. S. Pat. No. 3,295,940 and 3,385,684 (polymides). Polysulfide resins such as disclosed in U. S. Pat. No. 3,303,170 and polypyrrones may also be employed. For use in making coated abrasive discs or belts liquid resin systems may be preferred, while for bonded abrasives solid powdered resins can be used.

THE ABRASIVE

One of the preferred features of the present invention is that the abrasive, diamond grit, or cubic boron nitride, have a metal coating encapsulating the abrasive grit such that the metal is present in the coated particle in an amount between 10 and 70 percent, by volume. Uncoated diamonds can be used, however, and tools employing them are considered part of the present invention. Metal coated diamonds are disclosed in Soulard French Patent No. 1,142,688, Belgian Patent Nos. 683,508 and 698,428, and French Patent No. 1,522,735. Suitable metal coatings are copper, silver, nickel, cobalt, molybdenum and, in general, any metal melting above about 500.degree.F which is chemically stable in the grinding tool. Although, for wet grinding the volume percent of metal coating can be higher, for dry grinding, to which the tool of the present invention is particularly directed, the volume percent of metal coating should be between 10 to 60 percent, by volume.

Coated diamonds are commercially available which have nickel coatings within the above range of 10 to 50 percent, by volume, and copper coatings, within the same range. These coatings can be produced by electrodeposition on a thin, silver coating produced by chemical deposition on the grits. Thus the coatings need not be a single metal, only, and a wide variety of metal coatings are possible and useful in the present invention. Alloys of the metals are also useful.

The grit size of the abrasive is not relevant to the present invention, but grit sizes of 60 through 320 (based on the uncoated grit) are commonly used in diamond wheels.

THE GRINDING TOOL

Grinding elements according to the present invention may be formed by pressing the mixture in a mold of the desired shape. The mold may be heated and the resin may be completely or partially cured in the mold.

FIG. 1 shows a typical grinding element 10. FIG. 2 shows the grinding element mounted on a core 20 to produce a straight grinding wheel. FIG. 3 shows the element 10 mounted on a cup shaped support to form a grinding wheel commonly referred to as a "cup wheel." A suitable material for making the support member is an aluminum-filled resin as disclosed in U. S. Pat. No. 2,150,886. The tool may be molded directly onto the support, the support may be molded onto the tool, or the tool may be cemented onto the support after fabrication.

For the production of coated abrasive discs or belts, a liquid phenol-formaldehyde resin can be used. A size coat of liquid resin should be employed after the maker coat, and at least the size coat should contain the fillers of this invention. The size should be "high," that is, it should extend from the maker coat to close to the tips of the abrasive so that the fillers in the coat contact the work during grinding.

THE FILLERS

The required fillers of the present invention are:

1. silver or copper or a combination such as silver coated copper, present in the bond in the amount of from 10 to 60 percent by volume, preferably 30 to 50 percent, and

2. a solid dry-film lubricant present in the bond in the amount of from 5 to 30 percent, by volume, and preferably from 10 to 20 percent.

Silver is significantly better than copper, and silver coated copper is better than copper. Although the exact particle size range is not critical, the finer metal powders are more effective. Typical powders are 325 mesh and finer and may measure 1 to 10 microns in size, by conventional microscopic examination. When copper is employed, deoxidized powders should be used.

The lubricant filler may be one of the known inorganic materials such as graphite, fluorinated graphite, metal coated graphite (U. S. Pat. No. 3,402,035) hexagonal boron nitride, tungsten disulfide, molybdenum disulfide, niobium diselenide, and tungsten diselenide, all of which have been effective in the present invention to give a grinding efficiency at least 200 percent of a standard test wheel containing a silicon carbide filler only. All of these materials are crystalline and have a layer-lattice structure in which the bonding between layers is by relatively weak Van der Waal's forces.

Organic dry-film lubricants are finely divided solid polymeric materials. Suitable materials are extrusion grades of acrylonitrile-butadiene-styrene terpolymers, acetal copolymers (polyformaldehyde), chlorinated polyethers, polytetrafluoroethylene, polychlorotrifluoroethylene, fluorinated ethylene propylene, polyvinylidene fluoride, ionomers, nylons, polyphenylene oxides, polyvinyl chloride, polyvinylidene chloride, polycarbonates, thermoplastic polyesters, flexible polyesters, polyethylene, polysulfones, styrene butadiene copolymers, and urethanes.

In addition to the metal and dry-film lubricant powder fillers, inert fillers such as silicon carbide may be added to improve the strength of the bond or otherwise control its physical properties. Where lower diamond concentrations are employed it may be desirable to add such fillers to reduce the overall bond content of the tool or grinding element.

SPECIFIC EMBODIMENTS OF THE INVENTION

Normal process steps, conventional in the art, are used to fabricate the wheels, discs, or belts according to the present invention.

A preferred example of a bond mix for making a bonded abrasive ring for mounting on a backing element, such as shown in the drawing is as follows:

PHENOLIC BOND EXAMPLE

Parts Parts by by weight volume Powdered phenol-aldehyde pre-polymer (BRP 5980 available from Union Carbide Corporation) 17.3 45.2 which includes 9% hexamethylene tetramine and to which 10% by weight of lime is added Silver powder (Metz Refining 58.6 20 Co. No. C-18) polytetrafluoroethylene powder (Liquid Nitrogen Processing Co. 6.0 10 No. TL-115) Silicon Carbide (800 grit) 15.8 17.7 Furfural 2.3 7.1

In making a bonded abrasive tool employing the above mix, the abrasive is wet with the furfural and the mixture of bond and fillers is added and mixing continued to form a homogeneous batch. Sufficient of the mix is then placed in a mold of the desired shape and the mix is hot-pressed to shape. Normally, using the above bond, the tool is then removed from the mold and further cured in an oven. Typical molding conditions are a pressure of 5 tons per square inch, a temperature of 160.degree.C, and a molding time of 20 minutes. The final cure can be carried out in an air atmosphere oven for 24 hours at 175.degree.C. Control of the temperature of the final cure is effective, as is well known in the art, in controlling the hardness or grade of the bond which may differ depending upon the specific application.

The cured abrasive element is attached to a core or holder, as in conventional in the art, to produce a grinding tool such as shown in FIGS. 2 and 3 of the drawing. In the tabulated examples below, cup type wheels were employed of the dimensions and standard indicated. All the tests were run dry (no liquid coolant).

Where other resin systems are employed than the phenolic bond given above, it is known in the art that different curing or processing temperatures may be required. For example, in the case of the polymide resins, typical fabrication conditions would be a pressure of 10 tons per square inch, and a hold at 270.degree.C for 15 minutes. No post cure is required. A commercial polymide available from Rhone-Poulenc, identified as P.I.-M33A, cured under these conditions, and containing 50 percent silver filler and 10 percent polytetrafluorethylene as fillers, gave a grinding efficiency of 202 percent, or 102 percent above the control wheel, in a test similar to that of Table I. A second test with a different polymide identified as P.I.-M33B, gave a grinding efficiency of 293 percent under identical conditions where 40 percent silver and 10 percent TFE fillers were used.

The following test was made on wheels made according to the Phenolic Bond Example given above, the amounts of fillers and resin, however, being varied as indicated. The wheels were cup wheels, 6A9 type, 4" .times. 1-3/4" .times. 1-1/4". The diamond was coated with 56 weight percent nickel and was 150 grit (uncoated), and the wheels contained 17 percent diamond by volume. The work ground on a modified surface grinder was a cemented tungsten carbide, the unit infeed was 2.5 mils. Grinding conditions and the work piece were the same for all the wheels. The first wheel listed was a standard commercial wheel containing 35 percent by volume of silicon carbide in the bond. Table I gives the results. The "wheel no." is for identification purposes, G is the grinding ratio or grinding efficiency expressed as a ratio of the volume of carbide removed from the workpiece to the volume of wheel worn away, P is the average power drawn by the wheel in watts, and %G and %P give the %'s in terms of the standard comparison wheel. TFE stands for polytetrafluoroethylene.

TABLE I

(% of Wheel Filler Level bond) No. G P %G %P SiC Ag TFE 18617 36.2 1390 100 100 35 0 0 18577 33.0 950 91 68 25 0 10 18578 36.9 1085 102 78 37.7 0 10 18580 74.5 1215 205 87 5 20 10 18641 96.6 1180 266 85 17.7 20 10 18583 47.2 1350 130 97 20 10 5 18584 46.7 1095 129 78 10 15 10 18593 36.4 1380 100 99 20 15 0

the above results show that the lubricant filler alone, at the 10 percent level, does not significantly improve the grinding efficiency, although the power is substantially reduced. Similarly the metal, alone, at the 15 percent level produces no significant improvement. But combined, at these levels, the efficiency is significantly improved and the power is significantly reduced. Best results, in this test, were shown with 20 percent silver and 10 percent polytetrafluoroethylene. The results thus show a synergistic effect when the two fillers are employed together in the bond, which would not be expected from the results obtained when only silver or only polytetrafluoroethylene are employed.

The test results given in Table II compare the results for wheels of various levels of fillers with a standard wheel like that of Table I, but containing a slightly higher level of silicon carbide filler. The diamond was 150 grit, nickel coated, except for the diamond in the last two wheels which was copper coated in the amount of 50 weight percent. The infeed was 2.5 mils on cemented tungsten carbide workpieces. The carbide material and the grinding conditions were the same for all wheels.

TABLE II

Wheel Filler Level No. G P %G %P SiC Ag TFE 18664 47.6 1425 100 100 40 0 0 18665 78.5 1120 165 79 10 20 10 18666 89.6 975 188 68 5 20 15 18667 87.7 1180 184 83 5 25 10 18668 95.2 1020 200 72 0 25 15 18669 147.5 1280 312 90 0 30 15 18670 108.5 1090 228 76 0 30 15 18671 91 1120 191 79 10 20 10 18672 75.3 960 158 67 5 20 15

the conclusions drawn from this test are that the optimum silver content is over 30 percent, 15 percent TFE is better than 10 percent from the standpoint of power drawn, and nickel and copper coated diamond are similar in performance when 20 percent silver filler is employed.

The following results were performed on a different, somewhat more rigid machine than the previous tests. Otherwise the test conditions were essentially the same, but a different cemented tungsten carbide sample was employed in the workpieces. This test evaluated silver contents of 10 to 20 percent with no lubricants and silver contents of 10 to 20 percent combined with 15 to 25 percent graphite.

TABLE III

Wheel Filler Level No. G P %G %P %SiC %Ag %Gra- phite 18713 (Control) 26 1075 100 100 40 0 0 18714 38 750 146 70 15 10 15 18715 39 625 150 58 5 10 25 18716 32 775 123 72 10 15 15 18721 29 775 112 72 0 20 25 18722 23 1075 89 100 30 10 0 18723 19 975 73 68 25 15 0 18724 22 1000 85 93 20 20 0

Table IV gives the results of a test wherein silver contents of 30 to 50 percent, with a solid film lubricant filler, were compared to a standard wheel and to a wheel containing graphite only. As in the previous tests, the wheels were all run on the same sample of carbide and under the same test conditions. The infeed was 2.0 mil. The diamond was present in the amount of 11 percent by volume in the wheels, instead of 17 percent as in the previous tests, and was nickel clad, except for the diamond in wheel 84 which was copper clad.

TABLE IV

Wheel Filler Levels No. G P %G %P Ag TFE Gra- Sic phite 47 (Control) 17.4 1025 100 100 0 0 0 35 51 22.6 765 130 75 0 10 20 15 82 63.6 1135 365 111 40 10 0 0 83 79.8 1190 459 116 50 10 0 0 84 67.8 925 390 90 50 10 0 0 85 44.0 840 253 82 30 0 20 0 86 43.1 840 248 82 40 0 20 0

At 2.5 mil. infeed the relative results were similar except that wheels 84 and 86 were unsatisfactory under the higher infeed in that they loaded, chipped, and drew high power. Wheel 82 appeared best for general use.

In the following test silver filler was compared with silver coated copper. The wheels all contained 11 percent by volume of diamond, and the diamond was nickel clad. The unit infeed was 2.0 mils. The results were as follows:

TABLE V

Wheel Ag No. G P %G %P Ag TFE on SiC Cu Control 17.8 875 100 100 0 0 0 35 950 28.9 825 162 94 50 15 0 0 951 29.6 800 166 91 45 15 0 0 956 29.2 750 164 86 0 15 45 0

Although this test showed that Ag and Ag coated Cu are equivalent, more sensitive testing has indicated the superiority of Ag over Ag coated Cu.

In the grinding of high-speed steels, wheels employing metal clad 150 grit cubic boron nitride were compared with various filler contents. The unit infeed was 2.0 mils. and the wheels were the same shape and dimensions as in the tests reported above.

The filler content of the wheels was as follows:

TABLE VI

Wheel No. SiC Al.sub.2 O.sub.3 Ag TFE Gra- phite 80B 20 20 0 0 0 81B 35 0 0 0 0 82B 15 0 0 0 20 83B 28 0 0 0 20 85B 0 0 40 0 15

the test results on M3, M43, and T15 high-speed steel workpieces were as follows: ##SPC1##

Based on the most reproduceable testing methods, gained from the above tests, a variety of metal and solid lubricant combinations were employed. Grinding efficiencies of at least 40 percent above the standard were achieved with the metal silver, copper, or silver coated copper with various fillers, as listed below in Table VIII and grinding efficiencies lower than the standard control wheel were achieved with nickel, molybdenum, iron, tin, and aluminum fillers.

TABLE VIII

Wheel No. G %G P %P Metal Lubri- cant 19083 42 410 1200 120 Ag BN 19076 39.5 383 1150 115 Ag TFE 19086 35.9 348 1250 125 Ag WS.sub.2 19229 30.8 299 1350 135 Ag BN Nickel Coated 19089 30.5 296 1400 140 Ag Graphite 19085 27.9 271 1150 115 Ag MoS.sub.2 19088 27.8 270 1150 115 Ag Polyethylene 19084 26.3 255 1350 135 Ag NbSe.sub.2 19087 20.2 196 1100 110 Ag WSe.sub.2 19090 15.1 147 1050 105 Mo MoS.sub.2 19077 14.4 140 1150 115 Cu TFE 19231 11.9 116 1000 100 Mo MoS.sub.2 19257 10.7 104 850 85 -- Graphite 19252 10.3 104 1000 100 Control Wheel 35% SiC 19078 9.3 90 950 95 Ni TFE 19082 7.5 73 800 80 Mo TFE 19228 6.4 62 850 85 Mo TFE 19081 5.8 56 850 85 Fe TFE 19079 5.4 52 900 90 Al TFE 19080 4.4 43 800 80 Sn TFE 19230 3.2 31 750 75 Al TFE

a large variety of organic fillers, in the form of a finely divided powder were prepared and tested at the 10 and 15 percent levels in the bond, in combination with 40 percent of fine silver in the bond. The following gave improvement in G of from 2 1/2 to 5 or more times that of a similar wheel omitting the organic filler, but including 40 percent silver:

styrene butadiene ("56B" Pliolite from Goodyear Company, from 85 percent styrene by weight and 15 percent butadiene); acrylonitrile-but-adiene-styrene (Lustran 1-410-1000 supplied by Monsanto) styrene-acrylonitrile (Lustran A-21-2020 from Monsanto, 71 percent styrene, 21 percent acrylonitrile); polyurethane (Estane Type 58105 from Goodrich); polyvinyl chloride (Geon 92 from Goodrich) acetal (Delrin from DuPont); polysulfone (Union Carbide TXRP 2044); polyurethane (made from 83 percent Adiprene L-167, and 17 percent by weight of 4-4' methylenebis (2 chloroaniline), Adiprene being a liquid diisocyanate reaction product with a polyalkylene ether glycol, available from DuPont); nylon (DuPont Zytel), and polycarbonate (General Electric Lexan).

To show the improvement obtained using non-metal clad diamond phenolic bonded wheels were compared in dry carbide grinding as follows, employing uncoated diamond:

Filler G Power Control Wheel 35% SiC 21 1200 watts Test Wheel 40% Ag, 10% PTFE 97 1100 watts

Thus, in comparing with wheels employing uncoated diamond the invention wheel is almost 5 times as efficient, with a lower power draw.

Although instances have been found of solid powdered organic polymers, which do not improve wheel performance, that is do not function as solid lubricants, when employed according to this invention, the selection of an operative polymer from one of those disclosed generically or specifically herein, or an obvious equivalent, is a simple matter for one skilled in the art, involving at most, in the case of equivalent materials, the manufacture and testing of a wheel containing such material.

Throughout the specification the volume percent of fillers in the bond means the parts of filler per hundred parts of total bond solids, including fillers, but not including abrasive particles and not including the metal cladding on the abrasive.

Claims

What is claimed is:

1. An abrasive tool having a surface at which abrasive grits are bonded, said abrasive grits being selected from diamond and metal clad cubic boron nitride particles, said bond being an infusible organic polymer containing from 10 to 60 percent, by volume, of finely divided silver, silver coated copper, or copper, or a combination thereof, in the presence of from 5 to 30 percent of a particulate dry film lubricant filler selected from the group consisting of MoS.sub.2, WS.sub.2, WSe.sub.2, NbSe.sub.2, graphite, fluorinated graphite, hexagonal boron nitride, polytetrafluoroethylene, polyethylene, polychlortrifluoroethylene, fluorinated ethylene-propylene, nylon, polycarbonate, polysulfone, styrene-butadiene, acrylonitrile-butadiene-styrene, styrene-acrylonitrile, polyurethane, polyvinylchloride, polyformaldehyde, and polyester polymers.

2. An abrasive tool as in claim 1 in which the metal filler is present in an amount of from 30 to 50 percent, by volume, and the dry film lubricant filler is present in an amount of from 10 to 20 percent, by volume.

3. An abrasive tool as in claim 1 in the form of a bonded abrasive annulus.

4. An abrasive tool as in claim 1 in the form of a coated abrasive belt.

5. A tool as in claim 1 in the form of an abrasive disc.