GB923149A - Improvements in or relating to apparatus for welding tubing or cable sheaths - Google Patents

Abstract

923,149. Making tubes and cable sheaths; drawing; welding by pressure. PIRELLI GENERAL CABLE WORKS Ltd. March 20, 1961 [May 9, 1960], No. 16319/60. Classes 83 (2) and 83 (4). Apparatus for the longitudinal welding of a tube or cable sheath made from metal strip, comprises means for bending the strip to form the tube and means for supplying high frequency current to the bent strip including contacts wiping the strip and forming part of or incorporated in forming or closure means for the strip. The strip is formed in roll stages until its edges nearly abut and it then passes into a tapered bore die 1, Fig. 1, of insulating refractory material having two conductive segments 6 set therein which supply current of 500 kc. per sec. to heat the edges which are pressed together and welded in a rear portion 3 of the die having a slot 8 for the weld bead. The welded tube emerges into a water-cooled extension 5. In a modification, a slotted metal cylinder 9, Fig. 2, having a tapered bore forms the closure die to which H.F. current is supplied at points near the end of the slot. The strip edges are heated by current supplied by the die and abut about a third of the way along the slot 10. A second slot 12 may be provided to allow the bore to be varied under transverse forces. In a further embodiment the last stage of the forming means comprises an insulating die plate 13, Fig. 3, having radial contact 6 separated by an insulating segment 7 forming an edge guide. After passing through the die, the edges converge and are welded at a point 11 and the welded tube passes between squeeze rolls 15. A die plate similar to the plate 13 but annular is pivoted about a diameter. According to the Provisional Specification the last forming stage may comprise four rollers, the top roll of which is formed of two outer conductive portions separated by an insulating portion and connected to the H.F. supply. The outer portions bear on the edge faces or on the strip adjacent the edges.