GB547532A - Improvements in or relating to vitreous coatings - Google Patents

Abstract

547,532. Transformers. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. April 4, 1941, No. 4518. Convention date, April 10, 1940. Drawings to Specification. [Class 38 (ii)] [Also in Groups XXIII and XXXVI] A method of applying a vitreous coating to an article consists in using a polymerized resin as a carrier for a vitreous frit, the resin being of such a nature that it depolymerizes and evaporates at the temperature to which the coated article is heated to fuse the frit into a glass. Polystyrene and methyl methacrylate resins are suitable and they are mixed with a suitable solvent such as toluene or benzene, a plasticizer being added if necessary. A frit suitable for application to copper consists of 3.5 per cent of K 2 O, 1.5 per cent of Na 2 0, 38 per cent of Sc0 2 , 51.4 per cent of P 3 O, 0.4 per cent Ca 0, and 5.5 per cent of AS 2 O 3 . Other frit compositions are given in the Specification. The mixture may be applied as a coating to an electric conductor and dried at a relatively low temperature to form a varnish-like film. The conductor may then be shaped to any desired configuration and heated to drive off the resin and fuse the frit into a vitreous coating. A conductor shaped and coated in this way may be used as a heating resistance, or for building a dry-type transformer which has no liquid dielectric and is operated at high temperature. In such cases, graded particles of refractory material, such as silicon carbide or zirconium oxide, may be mixed with the composition. The particles do not fuse and serve as spacing members for preventing neighbouring turns of a coiled conductor from touching one another during the fusion of the frit.