Abstract: This invention is an improved insulation for electric cables and an improved method of making the insulation. Cross linked polyethylene insulation is too stiff, particularly in high voltage cables which require a thick layer of insulation. Copolymers of polypropylene have electrical properties substantially equal to those of polyethylene, but do not have the necessary physical strength and have to be filled with clay or other filler that provides the required strength but degrades the electrical characteristics. A novel feature of this method is the utilization of the screw of the extruder to effect a mixing of the ingredients in an improved polymer system for cable insulation.

Abstract: This invention is an improved method for dispersing antioxidant material in cross-linkable insulation for electric cables. The antioxidant, which has a high melting point, is dissolved in a carrier, preferably the cross-linking agent, to obtain a solution of low melting point that is dispersed through the pellets of insulation when the ingredients are mixed in a blender. Improvements in the blender cycle reduce the content of fines, improve dispersion of the antioxidant and shorten the blending cycle. The preferred ingredients used are 4,4'-thiobis (6 tert-butyl-m-cresol) as the antioxidant and dicumyl peroxide as the cross-linking agent.

Abstract: This invention makes extruded, vulcanized, high voltage cables insulated with thermosetting compounds at much higher rates of production and with superior insulation of reduced thickness and with reduced cavities or voids in the insulation. As the cable comes from an extruder, it passes into a curing chamber with a heat booster that quickly raises the insulation to a temperature at which it is cured much more quickly than with steam heating of the prior art. A high temperature liquid in contact with the insulation maintains the high temperature; and because of the greater curing heat, the cable can travel through the curing chamber at a faster rate and into a cooling tube where it contacts with a cooling liquid under high pressure. The insulation compound is treated to reduce the size of cavities; and the high pressure maintained by the curing and cooling mediums prevent expansion of cavities before the insulation is set.