Chilled twin screw extruded for continuously coating cables - enables high throughputs without premature crosslinking or thermal damage to non halogenated coatings

摘要

Extrusion coating of an electric cable (85) is effected using a twin-screw extruder (10) provided with external cooling jackets throughout the length of the barrel (24) except where openings are provided for a hopper neck (58) at one end of the barrel and vacuum assisted vent or degassing parts (64) at an intermediate point along the line of each extruder. The melt flow passage (86) between the screw tips (28) and the crosshead coating passage (94) is kept relatively short. USE/ADVANTAGE - Esp. for coating cables with non-halogenated thermplastic materials, such as ethylene-vinyl acylonitrile blends containing fire retardant additives such as alumina trihydrate. Allows melt temp. to be kept below about 160 deg.C to 165 deg.C, to avoid premature crosslinking or degradation. Offers higher outputs than a conventional single screw extrusion unit, e.g. about 250 kg/h instead of 30 to 50 kg/h for an extruder with a barrel bore dia. of 90 mm.