GB758878A - Improvements in and relating to electric cable - Google Patents

Abstract

758,878. Making coaxial electric cable. BRITISH INSULATED CALLENDER'S CABLES, Ltd. May 18, 1955 [May 19, 1954], No. 14734/54. Addition to 716,826. Class 87(2) An open-turn winding 6a, Fig. 2, of thermoplastic strip, which is to form the whole or part of the insulation between the two conductors of a coaxial cable, is applied to a continuously-travelling inner conductor 1 by (a) drawing the-strip from a rotating source of supply and preforming it, in the cold state, into helical form in a forming guide 28; (b) presenting the helical strip under low tension or without tension to a rotating helical mould 28a that is concentric with and opens into a passage through which the conductor is drawn; (c) softening the strip by heating it in the mould; and (d) cooling the winding as it is drawn from the mould by the conductor. As shown, the forming guide 28 and the mould 28a are integral parts of a mandrel having a continuous helical radial slot 30 which begins at 31 and ends at 32 where it emerges into the end face of the mandrel. The mandrel has an axial bore 29 for passage of the conductor, is supported by bearings 36, 53, and is surrounded at its centre by a steam-heating jacket 40 and at its discharge end by a cold-water jacket 35a. The bearing 36 is water-cooled to prevent transmission of heat from the heated part of the mandrel to the preforming part 28. The conductor 1 is drawn from a spool 3, Fig. 1, travels straight through the mandrel, and is wound, with the helical strip thereon, onto a capstan 2. The mandrel is fixed to a shaft 22 rotated by an electric motor 9 via chain 10, shaft 11, chain 12 and gears 13, 14. A strip supply reel 21 is loosely mounted on shaft 22 and is rotated, under the control of a friction brake, by the pull of the strip 6 as the latter is being wound into the slot 30. The strip passes from the reel to the slot via rollers 25, 27, 26. The cold water supply comprises a manifold 38 having branch pipes 37, 51, and the steam supply comprises a manifold 45, 44 having branch pipes 42, 43 and an exhaust 54. Steam pipe 45 leads into cold water pipe 44, and to ensure that steam and cold water will not be led simultaneously into the heating jacket 40 a mechanical linkage 57 may be provided between valves 46, 47. Another linkage 56 having a similar function is provided between valves 46, 55. The capstan 2 is rotated by the motor 9, and relative speed control as between the capstan and the mandrel is obtained by gear boxes 19, 20.