Patent GB-1014326-A (GB)
Title: Grinding of materials with hard abrasives
IPC: B24D7/10
Filed: 1962-06-25
Abstract: 1,014,326. Grinding. ENGLEHARD HANOVIA Inc. June 25, 1962 [June 26, 1961], No. 24404/62. Heading B3D. A method of grinding a material comprises grinding the material with an initial grinding surface having a predetermined concentration of hard abrasive particles of a predetermined grit size, and finally grinding the material with a final grinding surface having an appreciably lower concentration of hard abraside particles of smaller grit size than the initial grinding surface. The material may be first ground with  a preliminary grinding surface having a lower concentration of hard abrasive particles of larger grit size than the initial grinding surface. The method may be used for grinding surfaces of glass, stone, ceramic, cemented carbides and ferrous metals and for sharppening the edges of metal cutting blades. As described, the method is applied to the grinding of glass which is supplied from a melting furnace and annealing chamber. From the latter, the glass passes through a plurality of preliminary grinding stations, a plurality of initial stations, a plurality of final grinding stations and finally an iron oxide polishing station. The glass is then turned over and the process repeated to grind the other side of the glass. The glass may be carried on a supporting surface for passage through the grinding stations, each of which has rollers 17 . . . 19, Fig. 3, for transporting the glass beneath a grinding wheel 21 carried by the shaft 22 of a motor 24 supported by a frame 25, 26. Each grinding-wheel consists of a disc having a plurality of segment holders 30, Fig. 4, secured to its periphery by screws 35, 36, each holder having a grinding segment 38 brazed thereto. The segments may form a continuous or substantially continuous narrow circular grinding face, or, alternatively, small spaces may be provided between the segments. For grinding- wheels of large diameter, e.g. 30 inches, the discs are provided with orifices 50, Fig. 12, for coolant which is directed through the orifices from chambers 46, 47 supplied with coolant from pipes 45 and a pump 44. For smaller diameter wheels, the coolant is supplied to the grinding segments through a hollow spindle supporting the grinding disc. The coolant consists of an oil in water emulsion. The grinding segments comprise natural or synthetic diamonds which are bonded by metal, for example, a copperbased alloy which may include one or more of zinc, tin, silver, aluminium, beryllium, manganese and iron. Instead of diamond, the abrasive particles may be of any material having a hardness number of at least 8 on the Extension of Moh's Scale or Metal Equivalent, for example, quartz, topaz, garnet, fused zirconia, fused alumina, silicon carbide, boron carbide, cubic boron nitride, stellite, tantalum carbide or tungsten carbide. The preliminary grinding is effected at, for example, three stations, the grinding-wheel at each station having a diamond concentration of less than 20, preferably 9, carats per cubic inch of segment matrix, and a grit size of 50-60, the feed of the glass being 200 inch/minute and the cut 0À004 inch. The initial grinding is effected at, for example, four additional stations in which each grinding disc has a diamond concentration of 20 or higher carats per cubic inch and a grit size of 100-120, the feed of the glass being 200 inches per minute and the cut 0À002 inch. The final grinding is effected at, for example, seven stations, the grinding-wheel at each of these stations having a diamond concentration lower than 9, and preferably lower than one, carat per cubic inch and a grid size of between 200 and 2,500. The Specification includes data for determining the concentration of diamonds at the leading edge of the grinding segments, the plane surface of the segments, and the trailing edge of the segments which is defined as the first edge of the second half of the annular surface engaging the glass. A large grinding disc of 12 feet diameter may have its segments 3 inches wide and the diamond concentrations at the leading and trailing edges in <SP>1</SP>/ 32 , inch wide strips at these edges.