Patent GB-881091-A (GB)
Title: Lapped welding of metal portions
IPC: B23K13/04
Filed: 1959-04-16
Abstract: 881,091. Welding by pressure. MAGNETIC HEATING CORPORATION. April 16, 1959 [Aug. 11, 1958 ; Feb. 20, 1959], No. 13018/59. Addition to 748,528. Class 83 (4). In lap welding the edge regions of two sheet metal portions, the portions are advanced to bring the regions into overlapping relation while causing bands on the opposed faces of the regions to come into contact at a weld point where the bands are pressed together, the bands are heated by applying thereto highfrequency current by electrodes which engage the edge regions in advance of the weld point, the current being at a frequency not less than 100 kc. per second and following the bands to the weld point and the portions are advanced at such speed that the metal of each portion behind the band thereon remains below welding temperature. In an embodiment thin aluminium or steel sheet formed by rollers into tubing 10, Fig. 1, is advanced at e.g. 300- 2000 ft. per minute by rollers 11 with the edges 13, 14 overlapped and spaced, so that the gap 12 rapidly closes in advance of the weld point w. A pair of fluid-cooled electrodes 15, 16 connected to a source of current at a frequency of 100 kc. per second to 500 kc. per second slidably engage the upper surface of the edges and current to and from the contact 15 flows over the edge 13 and then along the underside of the edge portion to the weld point. The current flows on the upper side of the edge portion 14 and due to mutual inductance the heating is concentrated in the surfaces on which the current flows leaving the opposite surfaces at lower temperature. To obtain equal heating the contact 16 is placed closer the weld point than the contact 15. The overlapping portions are pressed together between an outer spring &c. urged roller 22 and an inner roller 21 mounted in an insulated water-cooled carriage 30 on rollers 31 engaging the tube inner surface. Elements 33, 33<SP>1</SP>, Fig. 2, e.g. of sintered magnetic oxide may be arranged in the carriage to increase the inductance to circumferential current flow in the tubing. In another embodiment two sheets 10a, 10b, Fig. 5, which may be of different metals are welded using blocks 38, 39 of magnetic material above and below the overlapped portions to increase the impedance of current paths spaced from the overlapped portions. Spacers of synthetic resin or ceramic may be mounted ahead of the electrodes to engage the edge portions. A photomicrograph (100x) of an etched transverse section of a weld in tin-plated sheet steel made with sufficient pressure to compress the overlapped portions to the thickness of one sheet and resulting in a weld extending diagonally of the sheet surfaces, shows the exact line of the weld to be unobservable. The molten tin is squeezed out to form pools at each end of the weld line. The edges of the portions may have oppositely bevelled surfaces or one or both may be slightly crimped. Iron or steel, zinc coated, sheets may be welded as may be tubing for can manufactue although the metal is lithographed with conductive or insulating material. Specifications 772,279 and 811,251 also are referred to.