GB774813A - Molded abrasive articles and method for producing them - Google Patents

Abstract

In making a moulded abrasive product, such as a grinding-wheel or disc, an abrasive grit is wetted with a liquid heat-hardenable phenol-aldehyde resin by mixing it therewith, the wetted grit is then mixed with a chopped rag filler and, as bonding resin, a heat-hardenable synthetic resin precondensate or with a chopped rag filler impregnated with the precondensate, and the mixture is subjected to a hot pressing operation in a mould cavity. Liquid condensates specified are the A-stage condensates of phenol or cresol with formaldehyde or acetaldehyde. Bonding resins specified are the above liquid-condensates, condensates of furfural per se, furfural with phenol, urea and/or thiourea with formaldehyde, glycerol with phthalic acid unmodified or modified with amine-aldehyde resins; cresylic acid-modified phenol-formaldehyde and aniline-formaldehyde resins; condensates of melamine, 2,4,6-triethyl- and triphenyl-triamino 1,3,5-triazines, 2,4,6-trihydrazo-1,3,5-triazine, melam, and melam with formaldehyde; and any mixture of the above resins. The filler is preferably cellulosic, e.g. cotton or regenerated cellulose. Other fillers, e.g. clay, asbestos fibres, glass particles or fibres, mica, mineral wool, cotton fibres or other natural or vegetable fibres, may be added. Abrasive grits specified are alumina, emery, corundum, dense regular fused alumina, porous white alumina, silicon carbide, quartz, glass, garnet and diamonds, or any mixture thereof. The bonding resin and filler may be added separately in any order or simultaneously to the wetted grit; preferably the rag filler is impregnated with the resin, dried and disintegrated. In general the product may contain 50 to 85 per cent grit, 12 1/2 to 25 per cent of heat-hardened resin, 1/5 of which is the phenolic resin used for wetting the grit, and 2 1/2 to 25 per cent filler, at least 9/10 of which is the chopped rag filler. Mould lubricants, dyes, pigments and inorganic cements may also be added in amount up to 10 parts per 100 parts of the moulded product. The moulding may be faced with layers of fabric, e.g. heavy canvas or duck and/or be reinforced with one or more such layers disposed within the body of the moulding so as to produce a laminated product. In a disc or wheel used for grinding weld beads, the back is faced with an aminotriazine-impregnated fabric and the front with a phenol-aldehyde-impregnated fabric, whereas in the cutting type of wheel both fabric facings are impregnated with phenol-aldehyde resins. The fabric used for facings or reinforcement may be made of glass, cotton, nylon or burlap. Examples are given.