GB1475292A - Heat-recoverable articles and their use for splicing cables - Google Patents

Abstract

1475292 Cable joints RAYCHEM CORP 29 March 1972 [31 March 1971] 14804/72 Heading H2E In a cable joint of the kind in which polymeric inner sleeves 4 are heat-shrunk over individual conductor splices 14, and subsequently a larger polymeric outer sleeve 1 is heat-shrunk over the whole joint region, at least parts of the inner surfaces of the sleeves 1, 4 are provided with adhesive to seal the sleeves to the ends of cable sheaths 7 and conductor sheaths 8, 9, 10 respectively; moreover, each sleeve 1, 4 has a tensile strength of at least 1200 p.s.i., and a maximum stiffness of 10,000 p.s.i.; and sleeve 1 has a dielectric strength of at least 200 volts/ mil. while the sleeves 4 have a dielectric breakdown voltage of at least 6000 volts. Preferably, inner sleeves 4 exhibit specified values of flameretardancy and resistance to water, lubricating oils and non-inflammable hydraulic fluids, while outer sleeve 1 exhibits specified values of flammability, and resistance to water &c., and to heat. Further desiderata for both inner and outer sleeves are specified values of ultimate elongation, brittleness temperature, corrosive effect, volume resistivity, and water absorption. The material of the sleeves 1, 4 may be a cross-linked copolymer of ethylene-ethylacrylate or of ethylenevinyl acetate, and preferably contains a flame retardant; a suitable composition comprises 40 -50% (e.g. 45%) ethylene vinyl acetate; up to 10% (e.g. 7%) ethylene ethyl acrylate; 10- 20% (e.g. 15%) carbon black; up to 25% flame retardant, e.g. 18% halogenated bisimide; up to 10% (e.g. 6%) antimony oxide; remainder antioxidants and cross-linking agents, e.g. a peroxide. The adhesive may be a curable epoxy, but is preferably a hot melt adhesive, e.g. a low molecular weight polyamide posessing specified values of tensile yield strength, dielectric constant, dissipation factor, and volume resistivity. The heat to recover the sleeves may be produced by torch, hot air or catalytic heater, or the reaction of an exothermic material coated on to the sleeves; and a coating of thermochromic paint or other such material may indicate the degree of heat applied. Preferred characteristics of the completed joint include specified values of insulation resistance, flex life, bond strength, voltage withstand, and flame resistance. The Specification gives details of the tests used to determine the values of the characteristics specified, many by reference to the appropriate ASTM. The conductors splices 14 may be welded or mechanically formed, e.g. by beat rings or parallel or butt crimp connectors. The invention is of particular use in jointing cables in coal mines.