Patent GB-777845-A (GB)
Title: Improvements in or relating to the metal sheathing of electric cables
Inventor: MILLER HERBERT JOHN
IPC: B21C29/00
Filed: 1954-07-02
Abstract: 777,845. Extruding. BRITISH INSULATED CALLENDER'S CABLES, Ltd. July 1, 1955 [July 2, 1954; Aug. 12, 1954], Nos. 19465/54 and 23467/54. Class 83 (4). [Also in Group XXIX] In a metal sheathing of electric cable core in a metal extrusion press, the risk of over-heating the core is reduced by permitting flash evaporation in proximity to the extrusion orifice or to the incoming cable core, of at least part of a supply of a solid or liquid evaporative cooling medium which at normal atmospheric temperatures and pressures is gaseous. The cooling medium may be liquid nitrogen, liquid carbon dioxide or solid carbon dioxide in particulate form carried by compressed nitrogen gas. In one embodiment, Fig. 1, the outer die 4 has an annular cavity 6 into which the cooling medium admitted through inlet passages 8 is allowed to expand and from which it is released to the atmosphere through passages 9 and 10, the latter passages being directed on to the sheathing 5. The inner die 3 also has a cavity 13 to which the coolant is admitted through passages 12 and released to the atmosphere through passages 15, 14. In another embodiment, Fig. 2 (not shown), the outlet passages 9, 15 are omitted and nozzles are provided at the ends of the inlet passages to direct the coolant towards the cable. In another embodiment, Fig. 3, the coolant is supplied to a manifold 21 from which it is directed as an annulus into the outer die 4 by means of nozzles 20; the inner die is cooled by the coolant issuing from nozzles 22. Further nozzles 63, Fig. 4 (not shown), are provided adjacent the entry end of the core tube or mandrel 1 for cooling the cable as it enters the press. During normal running conditions the cable may be cooled solely by the nozzles at the entry end of the press, and cooling of the dies may only be effected during temporary stoppage. Different cooling medium may be used for the inner and outer dies. The cooling of the dies may be continuous and the rate of cooling may be controlled manually or preferably automatically by a spring-loaded piston valve 42, Fig. 6, which is controlled by the reduced pressure in a venturi 46 through which the coolant flows to the dies. Alternatively the rate of flow of coolant may be controlled by a cam-operated lift valve 53, Fig. 7, in which the cam 56 is driven from the spindle of the take-up reel on to which the extruded sheath is wound. The control valve may alternatively be actuated under manual control by a solenoid, Fig. 8 (not shown). When the coolant is solid carbon dioxide 33, Fig. 5, it is reduced to powder form by a rotary chipper 34 and the powder passes through a non-return valve 35 into a cylinder 36. Compressed nitrogen gas is directed into the cylinder through port 37 to blow the powder through tubes 38 and nozzles 39, 40 towards the cable core 2. The supply of coolant issuing from the nozzles creates a pressure within the core tube 1, Fig. 1, which prevents ingress of air thereto and thus reduces the amount of oxygen coming into contact with the paper wrapping and impregnating oil on the core. The gas in the core tube may permeate the dielectric and therefore if necessary this gas may be removed. Alternatively, the core may be enclosed in a gas-impermeable envelope.