Apparatus for forming foam-skin insulation on telephone wires

Claim 1

Extruder apparatus for forming a foam-skin insulation on a wire, the foam-skin insulation comprising an inner layer of foamed plastic insulation and an outer layer of solid plastic insulation, the apparatus comprising: an extruder tool having a passage through which the wire is drawn, the tool also including-- an inner annular channel surrounding said passage for feeding the material for forming said inner layer of foamed insulation, and an outer annular channel surrounding both said passage and said inner annular channel for feeding the material for forming said outer layer of solid insulation; and an extruder head adapted to be connected to the discharge end of an extruder and to said extruder tool, the head including-- a portion defining an annular mixing space and having mixing means therein, means for injecting a foaming agent into said mixing space, said mixing space leading to said inner annular channel for forming said inner insulating layer, and a bypass channel extending from a position upstream of said means for injecting a foaming agent to said outer annular channel for forming the outer insulation layer on the inner layer.