Metal coated synthetic diamonds embedded in a synthetic resinous matrix bond

Abstract

A diamond abrasive device, such as a grinding wheel, comprising metal clad diamond particles embedded in a bonding matrix of resinous material, which is characterized in that the diamond particles comprise MD particles.

Parent Case Text

This application is a continuation of my application Ser. No. 761,171, filed Sept. 20, 1968, now abandoned.

Description

This invention relates to diamond abrasive grinding devices and, in particular, to diamond abrasive grinding wheels.

It is well known and indeed logical that the diamond, as the hardest and most wear-resistant material known, is extremely suitable for grinding hard and abrasive materials, such as tungsten carbide, glass, corundum and the like. It is, therefore, not surprising that production engineers look to a diamond abrasive grinding wheel as one of the most suitable tools for grinding such hard and abrasive materials. However, hitherto it was the accepted view that diamond is not suitable for the grinding of soft metals, particularly mild steel, and that the use of diamond abrasive devices is expensive.

Up to the present time, the art is familiar with the use of two principal types of diamond particles in abrasive devices. These types are generally known as resin bond diamond (RD) and metal diamond (MD). A third type, SD, refers to diamond used in saw applications. The RD, MD and SD classes of particles may be obtained today by both natural and synthetic means. The RD class of particles is typical of the particles employed in a bonding matrix of resinous material while the MD particles are used in metal bonds. In order to appreciate the nature of the present invention, it is necessary to outline the characteristics of these two classes of particles. The SD particles may also be used with great advantage in abrasive articles in metal bond form although in the art at the present time they are looked upon as being relatively expensive for this purpose. However, the Applicant envisages their use in the arrangement of the invention and for this reason specifies that the term MD is used herein to include SD particles.

MD particles have a higher impact resistance than RD particles which are friable and these two classes of particles lie within different, well-defined ranges of impact resistance. An RD particle is of an irregular nature and it exhibits the ability to splinter during the course of grinding operations before dulling of the cutting formation develops. In consequence it is continually generating new cutting formations so that a wheel tipped with RD particles is particularly suitable for grinding operations. MD particles, on the other hand, generally present a blocky crystal, but irregularly shaped MD crystals also exist. An important characteristic of all MD particles is that they do not tend to splinter and irrespective of whether they are of blocky or irregular shape, their grinding formations dull before any fracturing is likely to arise.

Until recent times RD particles had decided disadvantages. In normal operations where, say, the RD particles were embedded in a resin matrix of suitable quality, the splintering took place in such a manner that it became possible for whole particle bodies to loosen in the matrix and to be knocked out of the matrix by impact on the surface being ground. This is an aspect which hindered the use of resin-bonded wheels. The cause of the difficulty lay in the fact that once a splinter of a particle had broken away, a void might be developed into the heart of the particle into which the peripheral regions of the particle might be urged. This contributed to the particle freeing itself from the anchorage in the resin.

The problem outlined above was met by the novel concept of cladding RD diamond particles with a suitable metal coating. The metal-coated RD particles were then embedded in a bonding matrix of resinous material and the overall performance of such wheels was increased substantially. In particular, the tendency for particles to be pulled out of the bonding matrix as the particles splintered was materially reduced. An up-to-date statement on this development is to be found in British Pat. No. 1,154,598. The action of the metal cladding is to hold the particle rigidly as a unit despite the development of fracture lines and the splitting off of splinters which is characteristic of RD diamonds.

As far as the Applicant is aware, MD particles have never been used in a resin bond but only in a metal bond.

The art has generally developed to the stage where effective diamond abrading wheels are available for a variety of purposes but one area exists in which the use of these wheels has not been found to be commercially economical. This is in the abrading of metals of a soft nature, particularly mild steel. The use of, for example, a RD resin bond wheel on mild steel has the result that the steel literally holds on to the grit and tears it out of the bond, thus ruining the wheel surface as an economically useful unit for this purpose. In terms of money, the cost of removing a cubic centimeter of soft steel in the En 8/9 range with a resin bond RD wheel is about $1.28 as compared with 0.60 cents for an aluminum oxide wheel. This disparity is lessened fairly appreciably by metal cladding the RD particles but, in any event, the RD metal cald wheel is not looked upon as having any useful application in the grinding of soft metals. In fact, to date no diamond grit has been looked upon as useful for this purpose.

It is an object of the present invention to provide a general purpose diamond abrasive grinding device which can grind a wide range of materials with practically acceptable efficiency and economy, and which is particularly suitable for grinding soft metals.

According to the present invention, the Applicant has found that quite unexpectedly and contrary to the accepted view that diamond particles in general are not suitable for the grinding of soft metals, a substantial advance in diamond abrasive grinding of soft metals is achieved by substituting metal clad MD particles for RD particles in a bonding matrix of resinous material.

More particularly, according to one aspect of the invention, a diamond abrasive device incorporating metal clad diamond particles embedded in a bonding matrix of resinous material is characterized in that the diamond particles comprise MD particles.

According to another aspect of the invention, a method of grinding a workpiece, preferably a workpiece with a hardness lying in the range from VPN 95 to VPN 265, comprises the step of subjecting the workpiece to abrasion by metal clad MD diamond particles embedded in a bonding matrix of resinous material.

In reaching the present invention the Applicant investigated the grinding of various materials with resin-bonded diamond abrasive grinding wheels and during the course of the investigation, carried out a series of tests on soft steels in the En 9 range using metal clad RD particles and unclad RD particles. The results indicated that the metal clad RD particles were indeed capable of being used for cutting of such soft metals, but not to an extent that held out any high hopes for their general use in this field. Applicant also explored the position using metal clad MD grits in a resin bond and this part of the research was carried out with no high expectations in the light of past knowledge. Even the most modern literature does not envisage the possibility of these particles having any worthwhile use in the grinding of soft metals, and the language of the above-identified British patent supported this belief in its reference to particles splintering in use. MD particles do not splinter, while the effectiveness of RD in grinding operations is dependent mainly upon the particle breaking to present new grinding surfaces.

However, the tests unexpectedly showed that metal clad MD particles embedded in a bonding matrix of resinous material were indeed of great value in the grinding of soft steels and that their use in this field opens up unsuspected possibilities. Further tests showed that metal clad MD particles in a resin bond are also eminently suitable for the grinding of soft metals other than soft steels, and can grind virtually any material with practically acceptable efficiency and economy. A general purpose diamond abrasive grinding device can therefore be envisaged.

The reasons for the unexpected results achieved with metal clad MD particles in a resin bond are not yet fully understood, but it is clear that there is more to it than the simple explanation that the metal coating permits better retention of the diamond particles in the resin bond.

The MD particles may be metal coated and embedded in a resin matrix in any suitable manner as will be clear to a man skilled in the art. The methods disclosed in the above British patent may, for example, be used. The metal cladding preferably comprises 55% by weight of the metal clad diamond particles and the preferred metal coating comprises nickel. The resin matrix preferably comprises a synthetic thermosetting binder resin and may include suitable filler material.

The size of the MD particles may lie in the range 70 to 120 mesh. Preferably, the MD particles comprise 100 mesh or 100/120 mesh grit.

A grinding device according to the invention may comprise a wheel in which the resin-bonded metal clad MD particles form a peripheral skin about a hub.

It appears that when grinding soft metals such as mild steel, the grinding efficiency increases with the rigidity of the hub material. It has been found that for a general purpose grinding wheel according to the invention suitable for grinding virtually any material, good results are obtained with a hub wholly or partially composed of aluminum, such as an aluminum phenolic hub, and with a hub comprising bakelite, such as a fiber-filled phenolic hub.

Other objects, features and advantages of the invention will become apparent from the following more particular description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a graphical comparison of the grinding efficiencies of various types of diamond grit on similar material according to Example I.

FIG. 2 is a graphical comparison of the grinding efficiencies of two types of diamond grit on different materials according to Example II.

FIG. 3 is a graphical comparison of the grinding efficiencies of resin-bonded metal clad MD grit at different volumetric removal rates according to Example III.

FIG. 4 is a graphical representation of the relationship between grinding table traverse speed and total wheel cost for different cross-feeds according to Example III.

FIG. 5 is a graphical comparison of the grinding efficiencies of different types of diamond grit on a combination of tungsten carbide and steel at different down-feeds according to Example IV.

FIG. 6 is a graphical comparison of the total wheel cost of the different types of diamond grits of FIG. 5 when grinding a combination of tungsten carbide and steel at different down-feeds according to Example IV.

FIG. 7 is a graphical comparison of the grinding efficiencies of different types of diamond grit on tungsten carbide alone at different down-feeds according to Example IV.

FIG. 8 is a graphical comparison of the total wheel cost of the different types of diamond grits of FIG. 7 when grinding tunsten carbide alone at different down-feeds according to Example IV.

FIG. 9 is a perspective view of a flat grinding wheel according to the invention.

FIG. 10 is a cross-sectional view of the wheel of FIG. 9.

FIG. 11 is a perspective view of a cup-shaped grinding wheel according to the invention.

FIG. 12 is a cross-sectional view of the wheel of FIG. 11.

To illustrate the merits of the present invention, the following examples of tests conducted with resin-bond diamond abrasive grinding wheels are given:

EXAMPLE I

Tests were conducted on similar mild steel workpieces with grinding wheels carrying different diamond abrasive grits to determine the performance of the various grits under identical conditions.

______________________________________ Test Conditions: Workpieces 150 .times. 100 mm. EN 9 (55 carbon) mild steel Wheel Specification 175 mm .times. 10 mm .times. 11/4" D1A1 Peripheral Wheel on a Fiber-filled Phenolic Hub Diamond Types (1) 100/120 mesh metal clad RD grit (designated RDA-MC) (2) 100/120 mesh metal clad MD grit comprising a blend of blocky shaped and irregularly shaped MD crystals (designated MDA-MC-Blend) (3) 100 mesh metal clad MD grit comprising blocky shaped MD crystals blended with a pro- portion of specially selected irregularly shaped MD crystals (designated MDA-S-MC-Blend) Metal Cladding 55% by weight Nickel Diamond 100 (4.4 cts/cm.sup.3) Concentration Wheel Speed 35.6 meters/sec. Grinding Machine Jones & Shipman 540 Driving motor 2. h.p. Cross feed 1 mm. per table transverse reversal Downfeed 0.025 mm/pass Table Traverse Rate 12 meters/min. Coolant Bryto 5 (1% solution) Length of Tests 3 hours Volumetric Removal 300 mm.sup.3 /min. Rate ______________________________________

"DlAl" is the U.S. industry standard from USAS B 74.1-1963 and identifies a particular resinoid bond wheel made by practically all wheel makers. "RDA" means resinoid diamond abrasive, while "MDA" means metal-bond diamond abrasive. "MC" means metal clad, while "S" refers to the high strength of the specially selected MD crystals.

The grinding efficiencies obtained with the various types of diamond grit, expressed as the G ratio which is the ratio of the volume of workpiece removed to the volume of wheel worn away, are shown in Table I below and are compared graphically in FIG. 1 of the attached drawings.

TABLE I ______________________________________ Wheel No. Diamond G. Ratio ______________________________________ 1 RDA-MC 430 2 MDA-MC-Blend 660 3 MDA-S-MC-Blend 1250 ______________________________________

It will be seen that for the grinding of soft EN9 mild steels, considerably higher G ratios are obtained with metal clad MD particles than with metal clad RD particles.

EXAMPLE II

Tests were conducted on different materials with grinding wheels carrying grits nos. 1 and 2 of Example I under the same conditions as that of Example I with the exception that:

a. the downfeed for all the materials except the EN9 mild steel was 0.01 mm/pass, the downfeed for the EN9 mild steel remaining at 0.025 mm/pass.

b. the volumetric removal rate for all the different materials except the EN9 mild steel was 120 mm.sup.3 /min., the removal rate for the EN9 mild steel remaining at 300 mm.sup.3 /min. The G ratios and the power drawn are shown in Table II below.

The G ratios obtained with the two grits in question are compared graphically in FIG. 2 of the attached drawings. It is clear that for the softer metals, the MDA-MC-Blend grit is far superior to the RDA-MC grit. Although the performance of the MDA-MC-Blend is inferior to that of the RDA-MC on tungsten carbide, it is still within practically acceptable limits.

TABLE II __________________________________________________________________________ Workpiece Workpiece G. Ratio Power Drawn Kwh No. Material RDA-MC MDA-MC- RDA-MC MDA-MC- Blend Blend __________________________________________________________________________ A Cast Iron 384 1000 1.52 2.08 B Brass 332 785 2.04 2.37 C EN9 Mild Steel 430 660 2.72 2.99 D Copper 246 600 1.76 2.07 E Aluminum 176 250 1.68 1.53 F H.S.S. 98 110 3.13 3.15 G Tungsten Carbide 262 103 5.09 4.40 (P 20) __________________________________________________________________________

The surface finish, expressed as center line average in micro inches, is shown in Table III below.

TABLE III __________________________________________________________________________ Workpiece Workpiece Surface Finish-CLA(.mu.in.) Hardness No. Material RDA-MC MDA-MC-Blend __________________________________________________________________________ D Copper 70 63 VPN 95 B Brass 22 40 VPN 110 E Aluminum 24 30 VPN 114 A Cast Iron 22 30 VPN 160 C EN9 Mild Steel 16 16 VPN 265 F H.S.S. (Speedi- cut Leda) 9.5 10 Rc 65.1 G Tungsten Carbide 11 6 Ra 93.2 P 20 __________________________________________________________________________

EXAMPLE III

The following tests were conducted on cast steel to investigate the performance of resin-bonded metal clad MD grit with high volumetric removal rates when grinding large areas such as that experienced on press plattens, which could be as large as 10 .times. 3 meters. A tolerance of 0.025 mm cannot be achieved over such a large area with conventional grinding wheels which require frequent dressing and adjustment.

______________________________________ Test Conditions Machine Magerle F 10 Surface Grinder Workpiece BS 15 - 1964 800 .times. 200 mm. Wheel Type D1A1 Peripheral Wheel on an aluminum phenolic hub: (1) 254 mm .times. 12.5 mm .times. 127 mm (2) 254 mm .times. 25 mm .times. 127 mm Diamond Metal clad MD grit 100 mesh Resin Bond 100 concentration Metal Cladding 55% by weight Nickel Wheel Speed 27.4 meters/sec. Downfeed 0.02 mm per pass Crossfeed (1) 3.0 mm per traverse reversal (2) 4.5 and 6.0 mm per traverse reversal Table Traverse Speed 16, 23 and 30 meters/min. Coolant Bryto 5 (100:1) 9 liters/min. ______________________________________

The results obtained are shown in Table IV below and the G ratios are compared graphically in FIG. 3 of the accompanying drawings. The curves designated as A, B and C in FIG. 3 represent the results designated as A, B and C respectively in Table IV.

TABLE IV ______________________________________ Table Traverse Grinding Volume Removal Speed meters/min. Ratio G Rate cm.sup.3 /min. ______________________________________ A 12.5 mm wide wheel 3.0 mm crossfeed 16 416 .95 23 385 1.42 30 304 1.88 B. 25 mm wide wheel 4.5 mm crossfeed 16 360 1.42 23 288 2.12 30 178 2.83 C. 25 mm wide wheel 6.0 mm crossfeed 16 300 1.88 23 230 2.84 30 114 3.77 ______________________________________

Taking time cost comprising machine, labor, overhead costs, at $3.75 per hour and the cost of a diamond wheel at $25.00 per cubic centimeter of bond, which are average costs applicable in Germany, the results are shown in Table V below:

TABLE V __________________________________________________________________________ Table Traverse Time Cost Wheel Cost Total Cost Speed meters/min. cents/cm.sup.3 cents/cm.sup.3 cents/cm.sup.3 removed removed removed __________________________________________________________________________ A. 12.5 mm wide wheel 3.0 mm crossfeed 16 8.75 6.00 14.75 23 6.50 6.50 13.00 30 5.75 8.25 14.00 B. 25 mm wide wheel 4.5 mm crossfeed 16 5.75 7.00 12.75 23 4.75 8.75 13.50 30 4.00 14.00 18.00 C. 25 mm wide wheel 6.0 mm crossfeed 16 4.00 8.25 12.25 23 3.25 10.75 14.00 30 2.75 22.00 24.75 __________________________________________________________________________

Table V indicates that wheel cost must not be considered in isolation but must be considered in conjunction with time cost. Since time cost decreases and wheel cost increases with table speed, there is an optimum table speed at which the total cost is a minimum. The relationship between table traverse speed and total cost for different crossfeeds is indicated graphically in FIG. 4 of the accompanying drawings. The curves designated A, B and C in FIG. 4 represent the results designated A, B and C respectively in Table V. It will be seen that at a table traverse speed of 23 meters per minute, the sum of time cost and diamond abrasive wheel cost is between 13 and 14 cents per cubic centimeter of steel removed. The results indicate that the use of resin-bonded metal clad MD grit grinding wheels for the grinding of soft metals is economical.

EXAMPLE IV

The following tests were conducted to assess the performance of resin-bonded metal clad MD grit when grinding tungsten carbide on its own and when grinding a combination of tunsten carbide and steel shank material as is often encountered in industry.

__________________________________________________________________________ TEST PARAMETERS: Machine Jones & Shipman Model 1411 Semi-automatic surface grinder with 7.5 H.P. Spindle Drive Motor. Wheel type/size D1A1 Peripheral Wheel on a Fiber- filled Phenolic Hub -- 175 mm .times. 10 mm .times. 51 mm. Diamond (1) 55% Nickel clad RD grit 100/120 mesh Resin bond 100 Concentration (designated as RDA-MC) (2) 55% Nickel clad MD grit 100/120 mesh Resin bond 100 Concentration (designated as MDA-MC-Blend) Wheel speed 2,720 R.P.M. Wheel peripheral speed 25.4 meters per second Downfeed per pass .01, .025 and .05 mm Total downfeed per test 3.0 mm Crossfeed 1.5 mm per traverse reversal Table traverse speed 16 meters per minute Workpiece Series 1: 1/3rd Harmet G6 (94% WC, 6% Co) 2/3rds EN9 Steel (55 Carbon) 150 .times. 100 mm arranged in alternate pieces of 12.7 mm TC -- 25.4 mm steel, 4 times, in grinding direction. Series 2: P20 tungsten carbide (75% WC, 15% Tic/Tac, 10% Co.), 18 pieces with faces 5 mm .times. 12.7 mm arranged as a block 150 .times. 75 mm. Coolant Water + Bryto 5 (100 : 1) Coolant flow rate 9 liters per minute No. of tests per change At least 3 __________________________________________________________________________

Taking time cost comprising machine, labor and overhead costs, at $5.00 per hour and wheel cost at $20.00 per cm.sup.3, which are average costs applicable in South Africa, the results obtained are shown in Tables VI and VII below.

It will be noticed that 3 downfeed increments were used, namely 0.01, 0.025 and 0.05 mm. The reason for this is that a downfeed of 0.01 mm is generally used in Europe, whereas a standard downfeed of 0.025 mm (0.001 inch) is used in Britain, and the U.S.A. The 0.05 mm downfeed was investigated to determine the effect of an increase in downfeed and thus in production rate.

TABLE VI __________________________________________________________________________ Series 1. Grinding a combination of TC and Steel __________________________________________________________________________ Wheel Downfeed G ratio Removal per cm.sup.3 No. mm Time Mins. Time Wheel Total Cost Cost Cost Cents Cents Cents __________________________________________________________________________ (RDA-MC) .01 186.2 12.20 102.4 10.4 112.8 .025 126.3 4.50 37.7 15.3 53.0 .05 36.7 2.96 25.0 52.5 77.5 2 (MDA-MC- Blend) .01 169.0 12.40 104.2 11.5 115.7 .025 201.0 4.20 35.3 9.7 45.0 .05 63.3 2.78 23.4 30.5 53.9 __________________________________________________________________________

TABLE VII __________________________________________________________________________ Series 2. Grinding tungsten carbide alone __________________________________________________________________________ Wheel Downfeed G ratio Removal per cm.sup.3 No. mm Time Mins. Time Wheel Total Cost Cost Cost Cents Cents Cents __________________________________________________________________________ (RDA-MC) .01 292.0 11.00 92.4 6.6 99.0 .025 192.0 4.80 40.3 10.1 50.4 .05 96.0 2.40 20.2 20.3 40.5 (MDA-MC- Blend) .01 140.0 11.70 98.2 13.9 112.1 .025 96.0 4.90 41.2 20.2 61.4 .05 28.0 2.75 23.1 68.9 92.0 __________________________________________________________________________

Grinding efficiency (G ratio), which is often taken as the criterion as to whether a wheel is good or bad, is a misleading factor if the time taken on the grinding operation, the time cost and wheel cost for a given amount of material are not also taken into account. Grinding efficiency can only be considered as a dependable criterion if the wheels being compared are of the same size and cost the same, and if the tests are carried out under identical conditions.

FIG. 5 of the accompanying drawings compares the grinding efficiencies of Table VI for the combination of tungsten carbide and steel. FIG. 6 compares the total cost figures of Table VI. The curves designated 1 and 2 in FIGS. 5 and 6 represent the results for wheels Nos. 1 and 2 respectively in Table VI.

The grinding of a combination of tungsten carbide and steel is generally regarded as one of the more awkward jobs in the grinding world. It is therefore significant that as shown in FIG. 5, the G ratio obtained with metal clad MD grit is better than that obtained with metal clad RD grit over most of the range tested. Also, the total cost is generally lower with MDA-MC-Blend grit than with RDA-MC grit, except at low downfeed values. At a downfeed of 0.025 mm (0.001 inch), the MDA-MC-Blend grit is significantly better, whereas at a downfeed of 0.01, the RDA-MC grit is slightly better. The G ratio is lower for both grits at a downfeed of 0.05 mm. but the higher production rate has the effect of lowering the cost.

The grinding efficiencies of Table VII for tungsten carbide alone are compared graphically in FIG. 7 of the accompanying drawings. FIG. 8 compares the total cost figures of Table VII. The curves designated 1 and 2 in FIGS. 7 and 8 represent the results for wheels Nos. 1 and 2 respectively in Table VII.

It is clear from FIGS. 7 and 8 that when tungsten carbide on its own is to be ground, the RDA-MC grit is superior to MDA-MC-Blend both from the point of view of efficiency and total cost.

Although resin-bonded metal clad MD grit is less efficient than resin-bonded metal clad RD grit when tungsten carbide on its own is ground, the efficiency and economy of the metal clad MD grit is nevertheless of practically acceptable value. Considering the efficiencies and total cost obtained with metal clad MD grit when grinding a combination of tungsten carbide and steel and when grinding soft metals on their own, it is clear that a resin-bonded metal clad MD grit diamond abrasive grinding wheel can grind virtually any material efficiently and economically.

In consequence of the unexpected results achieved, the Applicant has determined that it is now possible to employ resin-bonded metal clad MD diamond abrasive wheels in a manner which could make them economic in the grinding of soft metals. It has previously been mentioned that in grinding a soft steel such as EN9 mild steel, aluminum oxide wheels may be used at a cost of about 0.60 cents per cubic centimeter of material removed. Resin-bonded metal clad MD grinding wheels in accordance with the invention appear to be able to do the same work for a figure in the region of 1.71 cents per cubic centimeter of material removed which, on first appearance, is not encouraging. However, by bringing the price down to 1.71 cents, it is possible to envisage a general purpose diamond abrasive grinding wheel which may be used for practically all purposes.

Instead of the operator having to replace the grinding wheel according to the material on which work is to be performed, he may now use a wheel of the invention for all purposes. The time lost in replacing a conventional diamond wheel with, say, an aluminum oxide wheel where a soft steel workpiece is to be treated subsequent to a hard metal workpiece can be avoided with a saving in time cost and the inconvenience of dressing the conventional abrasive wheel for the finishing cuts.

Another significant advantage of grinding wheels in accordance with the invention, as compared with a conventional aluminum oxide wheel, is that where high precision work is required to be done, the resin-bonded metal clad MD wheel can maintain accuracy within fine tolerances over extended working periods. Not only does this result in work of a superior quality, but the cost resulting from loss of wheel in dressing, dressing time and machine downtime for wheel replacement is minimized.

It will be appreciated that many variations are possible without departing from the scope of the appended claims. For example, the MD particles may be natural or synthetic diamond, but generally synthetic MD particles are preferred.

Any suitable metallic material may be used for cladding the MD particles. Apart from the preferred metal nickel, cobalt or any of the other metallic coating materials disclosed in the above British patent may be used, namely, platinum group metals, gold, silver, copper, molybdenum, titanium, aluminum, manganese, cadmium, tin, zinc, chromium, tungsten, iron, zirconium and alloys containing at least one of these metals.

The metal cladding may comprise 10 to 70% by weight of the total weight of the composite metal clad MD particles. More particularly, the metal cladding may comprise 50 to 60% by weight, preferably 55%, of the composite metal clad MD particles.

Any suitable resin matrix may be used, such as that disclosed in the above British patent, namely, phenolic, epoxy, polyimide, alkyd, unsaturated polyester, silicone, polybenzinimidazole and polyamidimide.

As shown in FIGS. 9 and 10, a flat grinding wheel according to the invention comprises an aluminum phenolic hub 1 carrying an abrasive peripheral skin 2 of resin-bonded metal clad MD diamond particles. Peripheral skin 2 is bonded to hub 1 under heat and pressure in well-known manner.

Instead of an aluminum phenolic hub, the wheel may be provided with a hub comprising bakelite, such as fiber-filled phenolic hub.

Referring now to FIGS. 11 and 12, the wheel comprises a cup-shaped hub 3 of suitable material carrying an annular skin 4 of resin-bonded metal clad MD diamond particles round the outer periphery of the cup on lip 5. As in the case of the flat wheel, annular skin 4 is bonded to lip 5 under heat and pressure in well-known manner.

Claims

I claim:

1. A diamond abrasive grinding wheel for grinding soft metal having a hardness lying in the range from VPN 95 to VPN 265, comprising a hub and an annular abrasive zone around the periphery of the hub, the abrasive zone comprising a bonding matrix of resinous material selected from the group consisting of phenolic, epoxy, polyimide, alkyd, unsaturated polyester, silicone, polybenzinimidazole and polyamidimide having embedded therein synthetic diamond particles coated with a metal selected from the group consisting of nickel, cobalt, silver, copper, molybdenum, titanium, aluminum, manganese, cadmium, tin, zinc, chromium, the platinum group metals, gold, tungsten, iron, zirconium and alloys containing at least one of said metals, the synthetic diamond particles being characterized in that they comprise synthetic MD particles and the metal coating comprising 10 to 70% by weight of the composite particles.

2. A diamond abrasive grinding wheel as claimed in claim 1, wherein the metal coating comprises approximately 55% by weight of the composite particles.

3. A diamond abrasive grinding wheel as claimed in claim 1, wherein the sizes of said synthetic MD particles lie in the range 70 to 120 mesh.

4. In a diamond abrasive grinding device for soft metal having a hardness lying in the range from VPN 95 to VPN 265, an abrasive surface comprising metal coated synthetic MD particles embedded in a bonding matrix of resinous material selected from the group consisting of phenolic, epoxy, polyimide, alkyd, unsaturated polyester, silicone, polybenzinimidazole and polyamidimide resin, the metal coating comprising 10 to 70% by weight of the composite particles and comprising a metal selected from the group consisting of nickel, cobalt, silver, copper, molybdenum, titanium, aluminum, manganese, cadmium, tin, zinc, chromium, the platinum group metals, gold, tungsten, iron, zirconium and alloys containing at least one of said metals.

5. A diamond abrasive grinding device as claimed in claim 4, wherein said metal coating comprises approximately 55% by weight of the composite particles.

6. A diamond abrasive grinding device as claimed in claim 4, in which the sizes of said particles lie in the range 70 to 120 mesh.

7. A method of grinding a workpiece having a hardness lying in the range from VPN 95 to VPN 265, comprising the step of subjecting the workpiece to abrasion by metal clad synthetic MD particles embedded in a bonding matrix of resinous material selected from the group consisting of phenolic, epoxy, polyimide, alkyd, unsaturated polyester, silicone, polybenzinimidazole and polyamidimide resin, the metal coating comprising 10 to 70% by weight of the composite particles and comprising a metal selected from the group consisting of nickel, cobalt, silver, copper, molybdenum, titanium, aluminum, manganese, cadmium, tin, zinc, chromium, the platinum group metals, gold, tungsten, iron, zirconium, and alloys containing at least one of said metals.