GB682859A - Improvements in or relating to the assembling of elastic articles in rigid apertures - Google Patents

Abstract

682,859. Assembling rubber bush mountings. BRITISH DIELECTRIC RESEARCH, Ltd. May 21, 1951 [May 22, 1950], No. 12801/50. Class 108 (iii). A method of securing a body of insulating material having " elastic memory '' in an aperture in a rigid conducting member, the transverse dimensions of the body being greater than those of the aperture, consists in compressing the body to reduce its transverse dimensions to a value less than those of the aperture, and inserting it into the aperture after removing the forces of compression before the part inserted regains its original dimensions. Suitable materials for the method are polytetrafluorethylene, plasticized polyvinyl chloride, polychlortrifluorethylene, copolymers of tetrafluorethylene, ethylene vinyl chloride and chlortrifluorethylene with minor amounts of other polymerizable monomers, and mixtures of the polymers or copolymers with minor amounts of other materials. The materials must have a smooth surface of low frictional coefficient. The invention is described as applied to the insertion of a bushing 11, Fig. 2, of polytetrafluorethylene in a plate 22. The purpose of the bushing is to carry a conductor 23 within a central aperture which may be formed either before or after insertion of the bushing. The diameter of the aperture is <4>/5 of the initial diameter of the bushing. Compression of the bushing is effected within a tapered section 6, Fig. 1, of a bore formed in a barrel 1, under the action of a plunger 2. A non-tapered section 5 of the bore has a diameter equal to that of the bushing. This section may be made long enough to accommodate a number of bushings so that insertion may be effected successively. For bushings of 0.25 inch diameter, the diameter of the bore at the lower end of the section 5 is 0.003 inch less than that of the aperture. The bushings need not be cylindrical, and the crosssectional shape of the bore section 6 may vary from the top to the bottom. The bushings are formed by moulding polytetrafluorethylene powder with a compression ratio of 4 : 1, sintering at 350-380‹ C. for 20 minutes, and allowing to cool overnight in the oven. Another bushing described, was made from 65 parts of polyvinyl chloride and 35 parts of dioctyl phthalate. According to the Provisional Specification plasticized polystyrene, and copolymers of styrene, with minor amounts of other materials, may be used.