GB553864A - Improvements in or relating to laminated magnetic core structures - Google Patents

Abstract

553,864. Synthetic resin compositions. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. April 9, 1941, No. 4724. Convention date, April 26, 1940. Drawings to Specification. [Class 2 (iii)] [Also in Group XXXV] Laminated core structures for transformers &c. such as described in Specification 540,662, [Group XXXV], comprise laminations of magnetic material bonded into a solid core by a heat-treated insulating composition composed of 20-80 per cent. of a polyvinyl acetal together with either or both polyvinyl acetate as plasticizer and a phenol-aldehyde heat-hardening resin up to a maximum of 20 per cent. The preferred acetal is that obtained by the reaction of acetaldehyde upon 70 per cent. hydrolyzed polyvinyl acetate ; other acetals are those derived from partially hydrolyzed polyvinyl acetates, propionates, butyrates or mixtures and formaldehyde, propionaldehyde and butyraldehyde. A solution of the resin in a mixture of alcohol and either toluene, xylene or solvent naphtha may be applied to the laminations, the solvent flashed off and the assembled laminations consolidated under beat and pressure; alternatively a wound core may be vacuum impregnated. Magnetic steel of very high permeability, obtained by cold rolling silicon steel and annealing under such conditions that the grains lie in the direction of easiest magnetization, may be employed for the whole or part of the core structure. The metal laminations may be chemically treated to form an adherent insulating scale, e.g. magnesium silicate, before applying the bonding material. Specific compositions are (1) the preferred acetal with 20 per cent. by weight of a cresylic acid-formaldehyde resin, (2) 42¢ per cent. of the acetal, 42¢ per cent. of polyvinyl acetate and 15 per cent. of cresylic acid-formaldehyde resin.