GB448342A - Improvements in methods of coating abrasive grains - Google Patents

Abstract

448,342. Abrasive articles. CARBORUNDUM CO., Niagara Falls, New York, U.S.A. Dec. 5, 1934, No. 34989. Convention date, Dec. 16, 1933. [Class 60] Abrasive grains for use in the manufacture of abrasive articles, such as sheet abrasives and wheels, are coated with a film of bonding material and dispersed in a fluid medium until the outer surface at least of the coating has hardened, the coated grains being thus rendered non-adherent so that they can be stored in the same way as uncoated grains until required for use. The coating materials may be of any kind which will harden or set under suitable conditions so that the grains will be non- adherent when stored or handled, but which can be subsequently rendered adherent when the abrasive article is to be formed from them ; for example, glues, varnishes, lacquers, synthetic resins, cellulose compounds, drying oils and other known bonding materials. The hardening may occur by evaporation of solvents, as in the case of lacquers, glues, cellulose solutions, &c. ; by heat, as in synthetic resins ; by the use of thermoplastic materials, such as shellac ; or by oxidation, as in materials having a base of tung or linseed oil. The mixed granular abrasive and bonding material may be sprayed from a nozzle into a gaseous medium, or one or more gaseous streams may be directed on to the mixture as it is extruded from an orifice so as to separate the coated grains. Another method consists in directing a stream of liquid bonding material into a stream of abrasive grains which are thus coated and dispersed. In a still further method, the coated grains are dispersed in a liquid; for example, grains coated with a liquid thermoplastic bond may be dropped into a cooled non-reactive and non- solvent liquid, and grains coated with a heathardenable bond into a heated and similarly inert liquid. Where the bond is hardened by evaporation of solvents, the mixture may be sprayed into a warm atmosphere, the air being subsequently passed to a recovery system and then to the spraying device to prevent the loss of solvent not recovered from it. Materials hardened by heat may be cured only sufficiently to harden the outer surface, and in any case are not cured sufficiently to render the bond infusible. An atmosphere rich in oxygen or ozone may be used for hardening bonding material which hardens by oxidation. Magnetic material may be added to the bonding material when it is desired to render the grains magnetic. Specification 431,062 is referred to.