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摘要

1461648 Cross-linking extruded thermoplastics tubing N LUNDBERGS FABRIKS AB 15 Oct 1974 [18 Oct 1973] 44713/74 Heading B5A A tube R, Fig. 3, of circular or other section, which is extruded from a die 10 comprises polyethylene containing a peroxide cross-linking agent, and is cured by a heated fluid admitted within its interior during its passage from the extruder die 10 along a region in which it is externally supported between the co-operating mould halves 13, 14 of a pair of endless chains 12 of mould halves, which are either driven to move with, or are moved by the extruding tube R. Either a single tube, or a pair of tubes inparallel may be extruded and supported by the chains of mould halves which are each supported by a guide rail (16), Fig. 1 (not shown), over their path of co-operation, which may be vertical, or downwardly inclined from the die as shown. The die is provided with a sealing projection 22 between the co-operating mould halves and, in the Fig. 3 embodiment, the medium comprises superheated steam which is admitted, from a pipe 17 extending through a die 10, to the upstream part 24 of a region which has a downstream part 25 through which cooling water is circulated, via die pipes 18, 19, and which is closed at its downstream end by a plug 20 having a polytetrafluoroethylene seal 21. The tube issuing from between the moulds 13, 14 is further cooled by water sprays. In the Fig. 5 embodiment the medium comprises either steam or hot oil, circulated within the region 24, with cooling and sizing of the tube being effected during its further passage through a vacuum chamber 32, containing sizing dies 33, and cooling sprays. Between the co-operating mould halves and the chamber 32, the tube is supported interiorly, when the medium comprises steam, by steam pressure in a region 31 defined between the plug 20 and a further plug 29, and to which region 31 the steam is admitted by leakage past the plug 20, or when the medium comprises oil, is supported by a separately introduced vapour or gas.