Plastics insulated esp. coaxial cable with inner insulating layer - compacted by shrinkage of outer insulation having higher fusion point

摘要

A plastics-insulated electric cable is intended esp. for medium and high voltages; the inner conductor (1) and its surrounding, conducting layer (2) are covered with an insulation (3) of partly crystalline polymer, typically (not claimed) a low density polyethylene having a fusion range of 110-120 deg.C. This is followed by one or more further concentric insulation layers of partly crystalline polymer having a higher fusion range than the first, typically (not claimed) high density polyethylene with a fusion range of 150-160 deg.C or a polypropylene. During cooling after extrusion, the outer layer (4) first crystallises, thus shrinking and applying pressure onto the layers below and causing compaction of the inner insulating layer (3). This arrangement provides a simple method of eliminating or reducing the inhomogeneities resulting from cavities in the insulation.