Patent GB-851530-A (GB)
Title: Improvements relating to seam welding
IPC: B23K13/04
Filed: 1957-03-13
Abstract: 851,530. Welding by pressure. MAGNETIC HEATING CORPORATION. March 13, 1957 [Feb. 6, 1957], No. 38815/59. Divided out of 851,528. Class 83 (4). In welding opposed edges of elongated metal portions by advancing the portions, maintaining the edges together at least in the region of a weld point, applying conductively to the portions current having a frequency of at least 100,000 cycles per second to flow in or adjacent the edges in advance of the weld point to heat the edges to welding temperature, the impedance to current flow in at least one of the portions in a selected region adjacent to the desired current flow path is raised by positioning an element of magnetic material of high volume resistivity adjacent to the selected region of the portion. In an embodiment in which the element or elements of magnetic material are not shown a gapped metal tube 10, Fig. 1, is advanced by rollers 11, 12 which press the gap edges together at the weld point w and the edges are heated by current, e.g. of 300 or 400 kc. per second applied to a contact 14 slidable on the upper surface of the tubing and the gap edges and to a grooved contact 20 slidable on the tubing upper surface before, at, or beyond the weld point. The current flows from the contact 14 in parallel paths along the edges to the contact 20 and returns along a conduit 27 above the edges to concentrate the current in the edges. Cooling water &c. is supplied through the hollow supply conduits. The contact 14 may engage only the upper surface, only the edges or only the inrier surface of the tubing, the contacts may be rollers and the gap may be closed before the contact 14 is reached. In a modification in which the gap is closed before the contact 14a, the further contact 20a, Fig. 4, engages the top of the rollers 11a, 12a, so that current in parallel paths diverges at the weld point and passes through the rollers into contact 20a. The conductor 27a may be non-circular in this case. In a further embodiment strips 35, 36, Fig. 9, of the magnetic material, e.g. sintered magnetic oxide and insulation material or sintered iron carbonyl and synthetic resin are secured to the contact 14a alongside the conductor 27a and another strip is provided beneath the seam. Two strip edges may be welded and if they are of different metals the magnetic material may be differently spaced from the seam. In a further embodiment a pair of strips 50, 51, Fig. 12, are heated by current supplied by contacts carried by supports 55, 56 to flow along the gap edges around the weld point. Blocks of the magnetic material are adjustably mounted in holders 63, 64 and are cooled by jets of fluid from conduits 70, 71. An arrangement similar to that of Fig. 12 but with a single block of magnetic material above the seam is employed for welding tubing and a rod of magnetic material is mounted within the tubing. One of the magnetic elements may be replaced by a non-magnetic conductive element, e.g. of copper, which lowers the impedance of a current path adjacent thereto. Specifications 748,528, 772,279, 851,528 and 851,529 also are referred to.