GB615671A - Improvements in and relating to the manufacture of electric insulating bushings, tubes, and the like - Google Patents

Abstract

615,671. Coating webs. DUNTON, A. R., CARTWRIGHT, R. P., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. May 6, 1946, No. 13704. [Class 140] [Also in Group XXVIII] In the manufacture of electrical insulating bushings, tubes and the like by winding strip material on a mandrel, the strip is first impregnated with a liquid comprising a copolymerizable homogenous mixture of an allyl ester and an unsaturated alkyd resin. One such mixture consists of 66.6 per cent of dyallyl ester, 33.3 per cent of diethylene glycol maleate and .1 per cent of a catalysing agent such as benzoyl-peroxide. Fig. 1 shows an apparatus for carrying out the process, consisting of a V-shaped tank 1, which contains the liquid and which carries a fixed cylinder 2 and metal (preferably steel) blocks 6 and mandrels 3, 4. Dried paper strip 5 is fed from the mandrel 3, between the cylinder 2 and the blocks 6 on to the mandrel 4 which is rotated at a moderately low speed (e.g. 40 r.p.m.). The process is preferably carried out in a vacuum chamber. If the mandrel 4 is submerged in the impregnant this condition is unnecessary. In this latter case, the cylinder 2 may constitute the mandrel. Fig. 2 shows a modified apparatus, the cylinder 2 being hollow, perforated on its underside and connected by a pipe 9 with a vacuum pump 10. This allows the impregnant to be sucked through the strip 5 as it passes under the cylinder, and thus ensures complete impregnation. A receptacle 11 traps any impregnant carried over by the pipe 9. Fig. 2 also shows the strip being dried before entering the tank by being drawn across a smooth metal sheet guide plate 7 heated by electric heaters 8. An alternative method is to wind the strip dry and then impregnate it under pressure. In each case, the wound tube is finally heated in an oven to convert the resin to a solid state.