Two=stage cable sheathing process - uses initial thermally insulating sheath to protect core during subsequent extrusion

摘要

The process comprises a first stage during which a thermally insulating sheath (3') is applied and a second stage during which an electrically insulating sheath (4) is extruded around the first sheath. The first sheath (3) is provided by a longitudinally split tube wrapped around the cable core and with the split edges subsequently thermally welded together. One of the sheaths (3,4) pref. has ribs (5) or corrugations to obtain a number of spaces between the two sheaths (3,4) extending longitudinally along the cable length. The first sheath (3') is applied at room temp. while the extrusion is carried out at a temp. of between 200 and 300 deg.C, the first sheath providing sufficient thermal insulation to prevent the cable core temp. rising above about 30 deg.C. The process is used for coaxial cables or fibre optic cables.