GB881036A - Improvements relating to insulated electrical conductors - Google Patents

Abstract

881,036. Insulation of dynamo-electric machine windings. McGRAW-EDISON CO. Jan. 28, 1958 [Feb. 27, 1957], No. 2881/58. Class 35. A slot conductor is insulated with a wrapping comprising two layers of backing material, e.g. glass or cotton cloth, between which is sandwiched a layer of mica, the composite wrapper being stuck together during wrapping by a fugitive binder consisting of water or other volatile liquid which is subsequently driven off and replaced by a polymerizable resin. A surface-treating material compatible with the resin is applied to both surfaces before impregnation, for instance, water may contain in solution a surface treating substance e.g. methacrylate chromic chloride with or without ammonia. A plant for producing the composite wrapper is shown in Fig. 1, in which strips of backing material 21, 21A from rolls 20, 38 pass through optional ovens 25, 25A and are then wetted with the water in baths 23 before being placed under and over a strip of mica paper 30 at rolls 28, 29 and 36, 37 respectively, additional water being added at 33. The composite tape may now be stored wet for immediate use, or dried in an oven 42 to set the surface treating chromium complex to the tape materials, washed in a bath 45, and then dried in an oven 44 if it is desired to store in a dry condition. A modification is described in which mica flakes are used instead of, or as well as, the mica paper. The fugutive binder bath may include various surface treating materials, e.g. a solution of a vinyl silane and xylol, e.g. vinyl chlorosilane in carbon tetrachloride, or this may be applied in its vapour phase. After wrapping and shaping, the coil is dried by heat and then vacuum impregnated with a setting resin under pressure. During curing, the coil is wrapped in an impervious material and clamped in a jig, Fig. 5A, comprising portions 80, 82 and 81, 83 accommodating the slot part of the coil and having steam heating chambers S, further portions 90, 91 for the end turns and support blocks 93, 94 for the coil knuckles. Electric heating is also used. Suitable polymerizable monomers are mentioned as having two unsaturated C = C groups capable of vinyl-type addition polymerization, and mixtures, e.g. 95% monostyrene and 5% divinyl benzene, may be used. Numerous alternatives are mentioned.