| 摘要 |
1372587 Extrusion coating of cores BRITISH INSULATED CALLENDERS CABLES Ltd 20 June 1972 [21 June 1971] 28966/71 Addition to 1201528 Heading B5A [Also in Divisions G3 and H1] A further covering layer 22 of material is extruded from an annular die outlet around a covering layer 21 of a different material extruded around an electrical conductor 1, e.g. of sector shape, which is fed through the die along a core tube 15, and the modification of the parent Application comprises preventing the layer 22 from being forced back along the orifice from which the layer 21 extrudes, by maintaining by means of differential pressure control means, a predetermined pressure differential across the layer 22 between a treatment chamber 5 at the die outlet containing fluid medium at super-atmospheric pressure, and the space 17 between the extruding layers into which nitrogen under pressure is injected through a die passage 16. As in the parent Application, the layer 21 may be prevented from being forced back along the core tube 15, by maintaining a predetermined pressure differential of nitrogen, by differential pressure control means, across the layer 21 between the space 17 and the interior of the core tube 15. The layer 21 may be of a semi-conducting material, with the layer 22 being of insulating material, and being extruded with an exterior covering layer 23 material which may be the same as layer 21, or of a different material having a weaker bond to layer 22 to be readily strippable to facilitate joining or terminating. The treatment chamber 5 may contain water coolant for cooling the extruded covering but in the described embodiment, wherein the layers 21, 23 are of the same semiconducting polyethylene and the layer 22 is of insulating polyethylene, the chamber 5 contains steam to effect curing and is downwardly inclined from the die, Fig. 1 (not shown), and also contains cooling water at its lower end, the cable passing from the chamber 5 through further cooling fluid vessels and, via a haul-off unit, to a take-up drum. The differential pressure control means for monitoring the pressure differential across the layer 22, Fig. 3, comprises a differential pressure cell 31 which transmits to a controller 34, via a transducer (not shown), a signal proportional to the pressure difference across layer 22 and which is compared by the controller 34 with a pre-set level to effect, in accordance with the difference between the signal and the pre-set level, the automatic closing or opening of valves (not shown) to respectively effect either injection of nitrogen from a source 36 and through pipe 37 to the passage 16, or release of nitrogen from the passage 16. A vacuum pump 38 is also provided to establish and maintain the predetermined pressure level from the commencement of extrusion when the pressure inside the chamber 5 is atmospheric. |
