Abstract: An improved apparatus for extruding an expandable thermoplastic composition onto an elongated article is disclosed comprising an extruder housing; a cylindrical extruder screw axially positioned within an extruder barrel within the housing; a device for heating the expandable thermoplastic composition passing through the hollow chamber; a gas input for supplying an inert gas into the extruder barrel; and a die head attached to the output end of the extruder housing through which an elongated article is passed for the extrusion thereon of the expandable thermoplastic composition.

Abstract: Insulation is extruded onto a conductor and immediately quench-cooled to obtain solidification for retaining concentricity of conductor and envelope. The envelope is reheated under pressure to melt a surface zone, followed by gradual cooling whereby the melted zone migrates into the interior. Reheating under pressure and gradual cooling, possibly also under pressure, improves texture, and provides for a more ordered crystal structure and/or fuller crosslinking. Following extrusion, and on reheating, the cable is freely suspended and assumes catenoidal contour while advancing to avoid sliding contact of the outer surface until adequately stable solidification has taken place.