Electric esp. telephone cable has internal laminated sheath - with plastics lapped edges to contact extruded outer sheath

摘要

Cable mfr. involves sheathing it in a laminated metal-plastics band closed around the cable with a longitudinal joint, then extruding an outer casing onto this. A plastics band is first thermally bonded to a metal band, one or both edges of the plastics extending beyond the edges of the metal; secondly, differential tensions are applied at the edge(s) of the plastics to pull and fold the edge(s) over the metal and towards the centre-line, and simultaneously bond these laps to the metal; thirdly, the resultant laminated band is applied to the cable longitudinally, with a plastics-to-plastics joint. Finally the (conventional) external sheath or casing is extruded around this. There is no exposed metal (e.g. aluminium) at the longitudinal joint. Consequently an air-gap does not form between this joint and the extruded outer casing.