GB546805A - Improvements relating to abrasive articles and their manufacture - Google Patents

Abstract

546,805. Making abrasive laps. NORTON GRINDING WHEEL CO., Ltd. July 25, 1941, No. 9472. Convention date, Oct. 2, 1940. [Class 60] An abrasive lap particularly for grinding lenses comprises a part-spherical grooved metal backing 10 having an abrasive layer bounded by spherical surfaces of different radii so that the layer is thicker at the perimeter than at the centre of the lap. The backing may be made by pressing and may be of brass, copper, bronze, aluminium or steel. The grooves may be either concentric or spiral and are preferably undercut to improve the locking of the abrasive layer 20, which may consist of diamond abrasive mixed with a bond. The latter may be of sintered metal consisting of 20 per cent. of tin and 80 per cent. of copper, or the metal bonds described in U.S.A. Reissue Patent 21,165 may be used. Alternatively the bond may be of synthetic resin such as phenol formaldehyde, or one of the polyhydric alcohol-polybasic acid resins such as glycerol phthalate or aniline formaldehyde condensed in the presence of a strong acid with or without modifying ingredients or polymerized methyl methacrylate preferably hardened with an interpolymer thereof. The metal back 10 may be placed on a plate support 13 surrounded by a ring 12 and the abrasive mixture 20 shaped by rotating an arcuate-edged scraper 21. A top plate having an operative surface of different radius from the backing layer is then applied and the mixture pressed into the backing ring and the product placed in an oven to mature or sinter the bond. Finally a central hole 26 may be formed in the lap. A tool having a concave operative face may be formed in a similar way to the convex tool shown in Fig. 4, the abrasive layer being in this case also thicker at the edges than in the centre.