GB793455A - Improvements relating to electrical contact brushes for high altitude electrical equipment - Google Patents

Abstract

793,455. Impregnated electric contact brushes. BRITISH THOMSON-HOUSTON CO., Ltd. March 28, 1956 [April 5, 1955], No. 9957/55. Class 140. An electrical contact-making brush for operation in environments of relatively low pressure and/or low water vapour content (e.g. at high altitudes) comprises a porous body of suitable brush material impregnated with an unsaturated polyester resin mixture as hereinafter defined, polymerized, after impregnation, into a substantially insoluble and infusible state. By an unsaturated polyester resin mixture is meant a mixture comprising a resin obtained by the esterification of an alpha-beta unsaturated dicarboxylic acid and a polyhydric alcohol together with one or more miscible co-polymerizable alpha-substituted ethylene compounds containing the group CH 2 =C<. Modifying reactants such as saturated carboxylic acids and monohydric alcohols may be included in the formulation of the polyester resin mixture which can be polymerized into a substantially insoluble and infusible state, usually with the aid of heat in the presence of a catalyst, for example an organic peroxy compound. The impregnation of the brush may be effected by progressive clipping in a catalysed unsaturated polyester resin mixture or by a vacuum or vacuum and pressure technique. In an example, a polyester resin mixture is prepared by heating a mixture of dipropylene glycol, maleic anhydride and tetrahydrofurfuryl alcohol in an atmosphere of nitrogen and then blending it with a mixture of styrene and quinone. The resin mixture is then catalysed with tertiary butyl perbenzoate. A graphite brush is first ignited and then immersed in the catalysed polyester resin mixture and impregnated by means of vacuum and pressure. The brush is thereafter baked.