Examination of mechanical stresses frozen into extruded cable insulation during the fabrication process

The insulated cores within a polymeric insulated power cable are produced by extruding the insulation onto the metallic conductor. In this process the polymeric material is melted in the barrel of the extruder and forced through a tapered die down onto the surface of the conductor, as the conductor is being pulled through the die. The drawing down of the insulation onto the moving conductor is liable to produce a mechanical stress in a longitudinal direction. Further mechanical stresses can also be introduced into the insulation during cooling of the extrudate. These stresses are caused by differential cooling and polymer adhering to the conductor so that it is not free to contract. Here, the author describes an experimental examination of these mechanical stresses.