Patent GB-798934-A (GB)
Title: Improvements relating to metal sheathed cores
IPC: B21C37/08
Filed: 1954-12-22
Abstract: 798,934. Making electric conductors; bending; welding. CRAWFORD, T. J. Dec. 22, 1954 [April 20, 1954], No. 37077/54. Classes 83 (2) and 83 (4). [Also in Groups XXVIII and XXXVI] An elongated metal sheathed solid or hollow core assembly comprises a tubular metal sheath closely fitting a core and having a longitudinally extending butt-welded seam of interfused metal, the circumferential width of the seam being less than the tube wall thickness. In sheathing a cable C, a roller 13 grooved to accommodate the cable and a co-operating roller 12 advance a flat strip S of aluminium, copper, zinc, magnesium or lead with the cable centrally thereon between guides 7-10, past scarfing tools 4, 5 which clean the strip edges and beneath a grooved felt wiper W to clean the strip. The strip is formed about the cable by rollers, idle rollers 31, 32, to seat on the cable being provided over the first forming rollers 27-30. Insulating tape, e.g. of fibrous paper with or without an adhesive coating, glass fibre, &c., is introduced from a reel 81 into the sheath in front of the rollers 46, 47 above which a vertically adjustable finned roller 59 is arranged which enters the open sheath seam. Similar rollers 58, 60 above rollers 48-51 but with narrower fins also enter the seam, the fin of the roller 60 slightly compressing the cable. The cable recovers as the sheath approaches squeeze rollers 66, 67, 68, a seam guide 64 positioning the seam and spacing the edges before passage through a water-cooled induction coil 77 supplied with high-frequency current e.g. of 9600-500,000 cycles per second or higher. The inductor brings the edges to welding temperature in the manner described in Specification 732,780. The weld point is beyond the effective limit of the induction field and at this point the cable has recovered to fill the sheath and form a low and smooth internal weld bead on the sheath. The width of the welded seam may be less than 20 per cent of the sheath wall thickness. A scarfing tool 69 trims the external weld bead and two final roller sets 74-77 slightly reduce the welded sheath. The squeezing rolls 66-68 may be replaced by rolls including a small roll 89, Fig. 14, of ceramic or conductive material bearing, on the upper side of the sheath and having a groove 90 to receive the external weld bead. The cable may be formed of copper strands individually paper insulated, the entire cable being wrapped with insulating paper or a three-way conductor cable formed by three cables twisted together in a long helix, each cable comprising individually paper insulated copper strands 78, Fig. 8, enclosed in a copper foil shield may form the core. Strands of yarn 86 fill the space between the cables. Two, four, five, &c., cables may be used. Instead of a cable the core may be a bundle of small copper or steel tubes, e.g. hydraulic or pneumatic conduit, clusters of concentric cables, a rubber tube, a plastic tube, e.g. of silicone rubber, neoprene, polyvinyl chloride, cellulose esters or nylon or hard facing alloys for arc welding electrodes. Steel, stainless steel, brass, silicon, bonze, &c., may be employed for the sheath material.