Two=stage extruder for high voltage cable insulation - has short initial cooling period above crystallisation temp. for stabilisation

The high-voltage cable insulation extrusion process is suitable for use with thermoplastic, elastomer or thermoplastic rubber combined with silane or a asilane cpd. The extruder is in two sections. The moulding material is introduced via a hopper to the first section where it is mixed, melted and compressed by a feed screw. The material passes into a second extruder in which a vacuum of 1-200 torr is established to provide out-gasing of the material. The material emerges at 200 degrees C to envelop the cable and undergoes a short period of cooling to stabilise the external dimensions of the cable and set the conductor inside the insulation. Further heating is applied to maintain the temp. above the crystallisation temp. and this is followed by passing the cable through an air-cooled.