Patent GB-644690-A (GB)
Title: Improvements in the sheathing of electric cables
IPC: H01B13/24
Filed: 1948-07-26
Abstract: 644,690. Sheathing electric cables. BRITISH INSULATED CALLENDER'S CABLES, Ltd., FAIRFIELD, R. M., ALDRIDGE, D. W., and TRAVIS, W. July 26, 1948, No. 19973. [Classes 83 (ii) and 83 (iv)] Extruding; drawing.-In a method of applying a sheath of aluminium or other metal having a substantially higher extrusion temperature than lead to an electric cable body, an oversize sheath is extruded on to the cable body by a discontinuous extrusion process, and after cooling said sheath to a safe temperature it is operated upon to effect a reduction in its crosssectional area, reduce its internal diameter, and elongate it, during the interval between two successive periods of extrusion. The sheath 8, extruded from the press 3 around the cable body 1, is cooled by jets 11 or a cooling tube 60, Fig. 10, and drawn through a die 15 by a capstan 16. A guide tube 7 is connected to a source of gaseous fluid under pressure or alternatively to a vacuum plant which maintains a high degree of vacuum in the space between the body and the sheath. A loop 18, the weight of which may be taken by a counterweighted frame 22, or which may be formed horizontally on a roller table, is formed during the extrusion process and taken up by continuing the drawing during the period when the extrusion press is being recharged. This permits the relative movement between the body and sheath, due to the elongation of the sheath when drawn, to be maintained during the charging period and thus reduces the heating effect of the sheath upon the body while the sheath is stationary. In a modification, Fig. 6, instead of allowing a loop of slack to form, the drawing die 15 is mounted on a carriage 31 driven by a motor 39 through a rack and pinion and arranged to move towards the press during charging and away during extrusion. The cable on either side of the carriage is supported on rolls 33, each mounted in a carriage 34, said carriages being coupled to each other and to the die carriage by long flexible couplings 35. In a further modification, Figs. 8 (not shown) and 9, the die 15 is carried between and reciprocated by two hydraulic rams 46a, 46b, which may be telescopic to reduce the length of their stroke, or one ram only may be used. The speed of travel of the cable body through the press during charging is a maximum when the die moves forward at the speed of extrusion during the extrusion period, i.e. when drawing is confined to the charging period. In this event the capstan may be driven through a slip clutch during the extrusion period, serving only to overcome frictional resistance, and is positively driven during the return movement of the drawing die, when drawing is effected, by chains 49, Fig. 9, attached to the die block 50 and which pass over sprockets 51 driving the capstan 16 through a ratchet and gear train. When drawing is effected during both the extrusion and charging period, close coordination between the capstan and die speeds is necessary to avoid excess tension in the hot sheath, and is arranged, for example, by adjusting the speeds of both the carriage and capstan motors to a fixed ratio during charging and another during extrusion, change-over being effected by limit switches, or the capstan drive may be controlled by the measured tension in the cable. Two or more drawing dies may be used in tandem.