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1480632 Extrudate lubrication DAINICHI NIHON DENSEN KK and MITSUBISHI PETROCHEMICAL CO Ltd 22 Aug 1974 [22 Aug 1973] 36918/74 Heading B5A [Also in Division H1] An electric cable conductor 11 is sheathed with an extruded cross-linked polyolefin during passage through the constant section circular outlet bore of a heated extrusion die 3a, which effects curing of the polyolefin, and degradation of the polyolefin in the outlet bore is prevented by a lubricant continuously introduced along a tapering inlet 3c to the outlet bore, to the surface 3c of which lubricant is continuously supplied at a location upstream of the downstream end of the tapering inlet 3c. The lubricant may be supplied to the inlet 3c through a porous sintered metal surface, or through an annular slit 8, e.g. of 0À005 to 1 mm. thickness, which is located between 10 mm. downstream of the upstream end of inlet 3c, and 2 mm. upstream of its downstream end. The slit 8 is defined between die members 3a, 3b, clamped together by a member 4, at a seal 5. The inlet 3c is of 50 to 200 mm. length and the circular bore of die 3a is of 1 to 50 m. length, and preferably 5 to 30 m. length, and may be defined by a plurality of assembled shorter die pieces. The die 3a is heated electrically, or by a hot oil jacket, e.g. to 200‹ to 300‹ C., and the cured sheathing issues from the die directly into a pressurized water cooling device (not shown). Various polyolefins and curing agents are specified, and the lubricants are of specified properties and may be these described in Specification 1,380,942. The example relates to the simultaneous extrusion of an insulating sheathing of polyethylene, between inner and outer semiconducting layers of ethylene-vinyl acetate copolymer containing carbon black.
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