GB707732A - Improvements relating to grinding wheels - Google Patents

Abstract

707,732. Abrasive wheels. TEAGUE, E.D., and NORTON GRINDING WHEEL CO., Ltd. Sept. 29, 1950 [Sept. 29, 1949], No. 24999/49. Class 60 A coping wheel for cutting granite, marble or like stone and other hard non-metallic materials, such as porcelain, glass and concrete comprises a steel centre 10, an annular abrasive portion 20 of abrasive grain bonded with thermo-irreversible resin extending over the periphery and both faces of the peripheral portion of the steel centre, and an unvulcanised layer 21a of thermoplastic resin in a hard state but which becomes slightly plastic when heated and selected from the group consisting of polymerised shellac, alkyl and vinyl resins or mixtures of these resins, between and bonding the abrasive portion to the steel centre. The peripheral portion of the steel centre may have dovetail slots 12 and holes 13. The abrasive may be silicon carbide, aluminium oxide or natural corundum or emery. The bond in the annular portion 20 is a phenol formaldehyde resin (phenol being used broadly to include phenolic bodies such as cresol and xylenol). Furfural may be used as a plasticizer, and hexamethylenetetramine may be added to speed the curing. The layer 21a which may have granular, refractory or abrasive material distributed therein, consists of (1) polymerized shellac or (2) alkyd resins, i.e. condensation products of polyhydric alcohols and polycarboxylic acids, e.g. the condensation product of glycerol and phthalic anhydride; other suitable polyhydric alcohols are penta erythritol, penta glycerol, ethylene glycol, propylene glycol, butylene glycol, trimethylolmethane and 2-ethyl hexane diol, and other suitable acids are maleic anhydride, succinic anhydride, glutaric acid, adipic acid and tricarballylic acid, or (3) vinyl resins including polymers of styrene which can be termed vinyl benzene, vinyl acetate and the methacrylates, e.g methyl methacrylate and allyl methacrylate, ethylene glycol dimethacrylate, glycerol trimethacrylate, penta glycerol trimethacrylate and trimethylene glycol dimethacrylate; also copolymers of any of the above with each other or with acrylic acid, acrylic anhydride, methacrylic acid, and methacrylic anhydride can be used. In the manufacture of the wheel grease is removed from the steel centre by a solvent, e.g. petrol. The rim is then coated by means of a brush with a solution of the thermoplastic resin; the solvent may be acetone, methyl alcohol or ethyl alcohol. The coat is allowed to dry at room temperature, and another coating applied, the process being repeated until a layer of thermoplastic resin of desired thickness has been obtained. A layer of a mixture of uncured phenol-formaldehyde resin and abrasive grain is placed in a mould, the centre 10 is placed on the layer, a further layer of uncured resin and abrasive grain is added to the mould and levelled off, the top plate of the mould is placed in position and the contents of the mould pressed in a hydraulic press; just prior to inserting the centre 10 into the mould, the last brushing on of the solution of thermoplastic resin is done without any subsequent drying step, thus promoting adhesion of the layer 21a and the annular portion 20. After pressing, the wheel is stripped from the mould and heated in an oven to cure the formaldehyde resin, to drive off the remainder of any solvent in the thermoplastic resin, and to convert the thermoplastic resin to a hard state. If the thermoplastic layer is to include granular material such as quartz sand, aluminuim oxide or silicon carbide, the grains of this material are coated with thermoplastic resin by mixing the granular material with a solution of the resin and subsequently drying to evaporate the solvent, the steps being repeated if necessary. A first coating of thermoplastic resin solution is applied to the steel centre and dried; a second coating is applied and while it is still tacky the centre is rolled in the coated granular material. The process is repeated until the layer is of desired thickness. Specification 562,815 is referred to.