Polishing plate

Abstract

A polishing plate wherein the arcs cut in the soft parts by a circle whose radius is equal to approximately half that of the disk and whose center is at a distance from that of the disk equal to half the radius of the disk have a length between 0.5 and 5 mm.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polishing or lapping plates, particularly those used in polishing machines comprising a plate driven to rotate about its axis, a work holder offset relative to the plate and driven, particularly by friction, to rotate about its own axis, and an abrasive suspension interposed between the workpieces being polished and the plate, the workpieces being applied against the plate, with the interposition of the suspension, with a certain pressure.

2. Prior Art

In U.S. Pat. No. 3,913,279 a polishing plate is described on whose plane surface appear flush soft parts in the form of islets regularly disseminated in a continuous hard part. In the present specification the expression "hard parts" is used to mean parts harder than the soft parts of the plate. The soft parts are distributed regularly in concentric circles on the plate. No importance is attached to the lengths of the gaps between the hard parts, which in the drawing, and in the corresponding plate on sale commercially, are very large.

In Swiss Patent No. 641,396 a polishing plate is described in which the soft parts are in the form of a continuous spiral. The width of the spiral is not specified. It is of the order of 10 mm in the corresponding product on sale commercially and also has that length in the drawing if it is assumed that the plate illustrated has the diameter usual in the art.

SUMMARY OF THE INVENTION

It has now unexpectedly been found that the lengths of the gaps between hard parts play a decisive part in respect of the polishing yield or amount of material removed per unit of time.

The invention therefore relates to a polishing plate giving an increased yield.

The plate according to the invention is characterized in that more than half of the arcs cut in the soft parts by an imaginary circle, whose radius is equal to 9/20ths of that of the disk and whose center is at a distance from that of the disk equal to half the radius of the disk, have a length between 0.5 and 8 mm.

Strictly speaking the curve in question on which the arcs are cut is the trace of the trajectory on the plate of a point on the workpiece which is to be polished or lapped. Such curves are shown in the drawings. However, for the sake of simplification they may be likened to the imaginary circle with sufficient approximation for the purpose of defining the invention.

80%, or better still 90%, of the arcs preferably have a length between 0.5 and 5 mm and, even better, between 1 and 4 mm.

There is an arc length, which is very short compared with the prior art, which gives optimum yield.

If, for the purpose of facilitating manufacture, it is desired to give identical shapes to the hard parts, the criterion laid down by the invention can be met only if the hard parts forms isolated islets in a soft matrix which is continuous, that is to say in a single piece. This form of construction is contrary to the form known in the prior art. It is also found that it enables the plate to be given greater flatness.

The islets are preferably rectangular, the ratio of the length of the longer sides to that of the shorter sides being between 1.5 and 3. The results are improved by depressions formed in the longer sides.

The prior art considered that the optimum yield was achieved with hard parts amounting to 70% and soft parts to 30%. However, when the arc length criterion is met, tests show that the best yield is obtained when the hard parts represent from 85 to 95% of the sum of the hard parts and soft parts.

The hard parts of the plate may be powders of cast iron, iron, copper, stainless steel, chromium, carbide, oxides, particularly aluminium oxide, preferably mixed with resins such as polyester resins, acrylic resins and phenolformaldehyde resins. The soft parts may be metallic powders, for example of copper, bronze, copper and lead alloys, brass, copper and aluminium alloys, aluminium, lead, antimony, tin, and zinc, preferably also mixed with resins, particularly polyester, acrylic and phenolformaldehyde resins. In these mixtures of resins and metallic powders, the resin advantageously represents from 20 to 40% of the total weight.

The abrasives used are products having on the Mohs scale a hardness of at least 9 and on the Knoop scale a hardness greater than 1,200. These abrasives, which are harder than the hard parts of the plate, are in particular corundum, fused alumina, silicon carbide, boron carbide and diamond, the latter being preferred. The abrasive is in the form of a suspension of the abrasive products mentioned above, in a binder, the particle size of the abrasives being between 1 micron and 200 microns, preferably between 10 microns and 40 microns, and the percentage of abrasives in the binder being between 0.2 and 5% by weight and preferably between 1 and 3% by weight. The binder may consist of a mixture of water and glycols, the glycols representing from 10 to 60% of the total weight of the binder and preferably from 20 to 50% of that weight. The binder may also consist of a mixture of water and kerosene, the latter representing from 40 to 60 % of the total weight of the binder.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawing, given solely by way of example, FIGS. 1 to 4 are plan views of plates according to the invention, which have a diameter of 230 mm, and

FIG. 5 is a graph illustrating the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lapping plate shown in FIG. 1 consists of a matrix 1 of a mixture of resin and copper, the resin representing 2/3 by weight of the mixture. The matrix 1 is continuous and constitutes the soft parts. The hard parts consist of islets 2, whose faces flush with the surface of the plate are circular, having a diameter of 25 mm.

The curve C1 is also shown, which is the trace on the polishing plate of a point of an object to be polished. On the soft matrix this curve C1 cuts arcs of which more than 50% have a length between 1 and 5 mm. This curve may also be likened to the imaginary circle C whose radius is equal to half that of the disk, and whose center is at a distance from that of the disk equal to half the radius of the disk. On the soft matrix this circle cuts the arcs 3 to 13, whose respective lengths are 8, 3, 6, 12, 2, 17, 10, 7, 8, 6, 2 and 12.

In FIG. 2 the islets 22 have substantially the shape of a rectangle whose longer sides are provided with depressions. The space between two shorter sides 23 of a rectangle is 2 mm. The space between the two depressed parts 24 of the longer sides of the rectangle is likewise 2 mm. The space between the longer side segments immediately adjacent to the shorter sides 23 is 2 mm. The space between the portions connecting the depressed parts to the remainder of the longer sides is only 1 mm.

In FIG. 3 the hard rectangular islets 32 are disseminated in a matrix 33. The distance separating two islets, measured along their sides, is 2 mm.

In FIG. 4 the hard islets 42 are disseminated in the soft matrix 41, the distance separating two islets being such that the arcs cut in the soft parts have lengths between 0.5 and 5 mm.

In order to determine the yield of the plates, six cylindrical workpieces of a diameter of 20 mm are lapped by applying a pressure of 265 g/cm.sup.2 in a lapping machine, the speed of rotation of the machine being 150 revolutions per minute and the speed of rotation of the workpiece holder being 175 revolutions per minute, which corresponds to a linear speed of the workpieces of 0.8 m/s. Six cycles lasting 5 minutes each are carried out. The abrasive used is brand MM 381 diamond liquid supplied by the applicants. The removal of material is measured in microns every five minutes on the six workpieces. The total removal of material is also measured on all the workpieces in all the cycles.

For a prior art plate of the Applicants, as described in the United States of America patent previously mentioned, the removal of material amounts to 615. This material removal value is taken as a base index equal to 100.

The results obtained are shown in Table I. In Table II the soft islets of the prior art plate have been replaced with hard islets in such a manner that these hard islets represents 71% of the plate surface, whereas the soft islets represented 70% of the prior art plate. The results obtained are shown in Table II.

TABLE I__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 19 20 20 20 242 16 20 20 16 223 16 21 17 19 214 19 22 19 21 225 20 20 25 21 236 22 20 22 24 24TOTAL 112 123 123 121 136 TOTAL REMOVAL OFREMOVAL OF MATERIAL/5 CYCLESMATERIALMEAN 3,73 4,1 4,1 4,03 4,53 615REMOVAL OFMATERIALDIVER- 6 6 8 8 3GENCE__________________________________________________________________________ TABLE II__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 31 26 31 31 292 27 27 28 24 263 27 27 28 26 234 33 30 26 28 295 36 27 32 33 356 34 28 36 26 38 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 193 167 178 168 180 886REMOVAL OFMATERIALMEAN 6,43 5,56 5,93 5,6 6REMOVAL OFMATERIALDIVER- 9 4 11 7 15GENCE__________________________________________________________________________

The yield is 144.

Table III gives the results for a plate of the same type as that in FIG. 1, but having islets of a diameter of 20 mm. The percentage of islets is 70%. The yield is 141. Table IV gives the results for a plate of the same type as that in FIG. 1, but with islets of a diameter of 13 mm. The percentage of islets is 72. The yield is 135.

Tables V to X give the results obtained with plates according to FIG. 2, but with spaces between the two shorter sides of the hard islets and the depressed parts of the longer sides of the hard islets equal respectively to 0.5, 1, 2, 4, 6 and 8 mm. The percentages of hard islets are 95, 91, 81, 69, 57 and 51 respectively. The yields are 126, 131, 148, 137, 122, 103. FIG. 5 plots the variation of removal of material with respect to the spaces between the hard parts. It can clearly be seen that maximum removal of material is obtained with a value close to 2 mm, the range extending from 0.5 to 6 mm corresponding to removals of material greater than 750. There is a close correlation between the length of the arcs cut in the soft parts and the lengths of the spaces between the hard parts.

In all these tables it has in addition been found that the smaller the difference in measurements (divergence) between the workpieces for the different passes, the better the yield.

Table XI gives the results obtained with a plate according to FIG. 3, and Table XII the results with a plate according to FIG. 4. The yields are 147 and 140.

TABLE III__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 27 23 34 32 292 24 27 29 30 243 22 29 30 24 224 28 27 28 26 255 30 33 32 32 316 32 35 32 36 32 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 163 174 185 180 163 865REMOVAL OFMATERIALMEAN 5,43 5,8 6,16 6 5,43REMOVAL OFMATERIALDIVER- 10 8 6 8 10GENCE__________________________________________________________________________ TABLE IV__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 22 26 30 28 312 20 22 28 28 293 21 23 25 27 304 23 23 35 26 325 31 24 34 35 296 24 28 34 36 29 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 141 146 186 180 180 833REMOVAL OFMATERIALMEAN 4,7 4,86 8,2 6 6REMOVAL OFMATERIALDIVER- 11 6 10 10 3GENCE__________________________________________________________________________ TABLE V__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 22 25 27 29 232 23 27 23 33 243 19 27 30 29 244 21 24 31 31 245 19 26 29 29 236 22 25 27 28 23 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 126 154 177 179 139 775REMOVAL OFMATERIALMEAN 4,2 5,13 5,9 5,96 4,6REMOVAL OFMATERIALDIVER- 4 3 8 5 1GENCE__________________________________________________________________________ TABLE VI__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 24 27 27 27 272 25 26 28 31 253 24 28 29 30 274 29 26 28 30 275 24 26 29 27 266 24 24 28 28 28 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 150 157 169 173 157 806REMOVAL OFMATERIALMEAN 5 5,23 5,63 5,76 5,2REMOVAL OFMATERIALDIVER- 5 5 2 4 3GENCE__________________________________________________________________________ TABLE VII__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 28 28 32 31 302 30 30 32 32 313 31 31 32 33 314 29 30 32 32 285 28 29 32 31 296 29 28 31 30 29 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 175 176 191 189 178 909REMOVAL OFMATERIALDIVER- 3 3 1 3 3GENCE__________________________________________________________________________ TABLE VIII__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 26 29 27 22 262 26 30 27 30 303 28 29 29 30 284 29 27 30 30 295 27 28 29 27 286 25 28 26 29 27 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 161 171 168 175 168 843REMOVAL OFMATERIALMEAN 5,36 5,7 5,6 5,83 5,6REMOVAL OFMATERIALDIVER- 4 4 4 8 4GENCE__________________________________________________________________________ TABLE IX__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 23 26 24 24 242 23 27 25 25 253 25 27 26 26 274 26 26 25 24 295 24 26 24 25 246 23 26 24 25 24 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 144 158 148 149 153 752REMOVAL OFMATERIALDIVER- 3 3 2 2 5GENCE__________________________________________________________________________ TABLE X__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 20 21 22 21 212 22 22 21 20 223 22 21 22 21 234 19 22 21 20 235 21 12 20 21 206 19 22 19 21 22 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 123 129 125 124 131 632REMOVAL OFMATERIALDIVER- 3 1 3 1 3GENCE__________________________________________________________________________ TABLE XI__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 26 32 30 31 312 31 29 30 32 313 30 29 31 33 314 32 27 33 33 295 29 28 31 31 286 27 31 28 30 29 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 175 176 183 190 179 903REMOVAL OFMATERIALDIVER- 6 5 5 3 3GENCE__________________________________________________________________________ TABLE XII__________________________________________________________________________ REMOVAL REMOVAL OF REMOVAL OF OF REMOVAL OF REMOVAL OFNo MATERIAL MATERIAL MATERIAL MATERIAL MATERIAL__________________________________________________________________________1 27 28 28 30 302 28 30 27 33 293 28 29 30 33 304 28 29 26 33 295 29 26 30 30 296 28 26 28 30 29 TOTAL REMOVAL OF MATERIAL/5 CYCLESTOTAL 168 168 169 189 167 861REMOVAL OFMATERIALDIVER- 2 4 4 3 1GENCE__________________________________________________________________________

Claims

1. A circular polishing plate for use in conjunction with an abrasive suspension and having a center a radius and a plane surface on which appear flush soft and hard parts, wherein more than half of arcs cut in the soft parts by any one of a plurality of imaginary circles, whose radii are equal to 9/20ths of the radius of the plate and whose centers are at a distance from that of the plate equal to half the radius of the plate, have a length between 0.5 and 8 mm and wherein the hard parts are not abrasive.

2. The plate of claim 1, wherein at least 80% of the arcs have a length between 0.5 and 5 mm.

3. The plate of claim 2, wherein at least 90% of the arcs have a length between 0.5 and 5 mm.

4. The plate of claim 1, wherein the length of the arcs is between 1 and 4 mm.

5. The plate of claim 2, wherein the length of the arcs is between 1 and 4 mm.

6. The plate of claim 3, wherein the length of arcs is between 1 and 4 mm.

7. The plate of claim 1, wherein the hard parts form isolated islets in a soft matrix, which is continuous.

8. The plate of claim 7, wherein the islets are rectangular, with longer sides and shorter sides, the ratio of the length of the longer sides to that of the shorter sides being between 1.5 and 3.

9. The plate of claim 8, wherein depressions are formed in the longer sides.

10. The plate of claim 1, wherein the hard parts represent from 85 to 95% of the sum of the hard parts and soft parts.

11. The plate of claim 2, wherein the hard parts represent from 85 to 95% of the sum of the hard parts and soft parts.

12. The plate of claim 3, wherein the hard parts represent from 85 to 95% of the sum of the hard parts and soft parts.

13. The circular polishing plate according to claim 1, wherein the non-abrasive hard parts have a hardness lower than 9 on a Mohs scale.

14. A circular polishing plate used in conjunction with an abrasive suspension, said polishing plate having a center, a radius and a plane surface on which appear flush soft and hard parts, said soft and hard parts being non-abrasive with respect to said abrasive suspension, wherein more than half of arcs cut in the soft parts by any one of a plurality of imaginary circles, whose radii are equal to 9/20ths of the radius of the plate and whose centers are at a distance from that of the plate equal to half the radius of the plate, have a length between 0.5 and 8 mm.

15. A circular polishing plate according to claim 14, in which the soft and hard parts have a hardness lower than 9 on a Mohs scale.