Patent GB-911602-A (GB)
Title: Improvements in or relating to the method of manufacture of abrading elements and tosuch elements
IPC: B24D18/00
Filed: 1958-10-13
Abstract: 911,602. Laminates. SIMPSON, H. A. Oct. 8, 1959 [Oct. 13, 1958], No. 32636/58. Class 140. [Also in Group XXIII] An abrasive material or element is produced by making a preform including abrasive grain, e.g. alumina or sand, and a partially polymerized thermosetting resin, the latter when fully polymerized being softer than the grain, applying the preform to a layer of backing material, and subjecting the assembly of the preform and backing layer to pressure and/or heat to polymerize the resin completely and bond the preform to the layer of backing material. The backing material may be of fibrous material, e.g. vulcanized fibre, paper, wire gauze, loosely or closely woven fabric formed of natural or synthetic fibres such as cotton, nylon, polyvinyl chloride or viscose, which may be impregnated with a thermosetting resin, preferably that present in the preform, or a laminate of two sheets of vulcanized fabric joined by an interlayer of paper impregnated with the thermosetting resin which is completely polymerized by said pressure and/or heat to bond the laminate together. The " preform " is defined as being a block comprising partially polymerized thermosetting resin and abrasive grain, or a plate-like article of said materials incorporating a paper lamination. The " preform " is made by (i) impregnating a strip or sheet of paper with partially polymerized thermosetting resin, partially drying the impregnated paper so as to leave a coating of resin on the surface of the paper, applying a loose coat of abrasive grain to the tacky surface, and drying to a non-tacky state; (ii) superposing and moulding together a number of the abrasive coated resin impregnated papers of (i); (iii) coldmoulding a mixture of abrasive grain and partially polymerized thermosetting resin in powder or liquid form to the desired shape; and (iv) placing a mixture of abrasive grain and partially polymerized thermosetting resin in powder or liquid form in a mould having the shape of the desired abrasive material or element, laying a layer of backing material over the mixture in the mould, and subjecting the whole to heat and pressure to polymerize the resin and bond the mixture to the layer of backing material. The preform mixture may also contain a filler consisting of ground or cut length reinforcement. The thermosetting resin may be a phenol-formaldehyde resin which is completely polymerised at about 130‹ C., and 550 lbs./sq. inch pressure, in ten minutes. The preform 2 and backing material 1 are subjected to pressure in a mould, the face of the mould which engages the surface of the preform being provided with a plurality of spaced ridges in a regular configuration so that when the assembly is subjected to pressure in the mould, corresponding channels, or cavities 15, 16 are formed in the face of the preform, adjacent which channels or cavities the preform material has a greater density than in other parts of the preform. A disc-shaped abrasive element, which may have a depressed centre (Figs. 1 and 2) may be formed in the mould 10 (Fig. 5) and said face of the mould comprises a plurality of equispaced radial ridges and a plurality of concentric ridges which produce radial channels 13 and concentric channels 14. The element may also take the form of a strip (Fig. 4) or cone (Fig. 3). The preform as shown in Fig. 5 is formed by impregnating sheets of paper 5 with partially polymerized thermosetting resin which is partially dried to leave resin coating 6 to which abrasive grain 7 is applied before drying the impregnated paper to a non-tacky state.