Patent GB-888242-A (GB)
Title: Improvements relating to the welding of metal portions to one another
IPC: B23K11/04
Filed: 1959-03-03
Abstract: 888,242. Welding by pressure. MAGNETIC HEATING CORPORATION. March 3, 1959 [March 20, 1958 (2)], No. 7390/59. Class 83 (4). In welding the elongated edge regions of two metal portions the portions are located with those surfaces to be welded juxtaposed in spaced-apart relation, current of frequency not less than 50 kc. per second is conductively applied at corresponding ends of the edge regions, to flow, at any instant, in opposite directions along the edge regions while the impedance of the current paths in the edge regions is controlled so as to cause such a concentration of current flowing in the surfaces as will bring about a substantially uniform degree of heating of the surfaces and then the heated surfaces are brought into contact under pressure. Conductive elements may be positioned in contact with the metal portions and/or an element of magnetic material of high volume resistivity is positioned adjacent the edge regions. In an embodiment, two sheetsteel strips 10, 11, Fig. 1, have spaced edges 12, 13 which are contacted with an held on to a support surface by a pair of rigid conductive bars 14, 15, e.g. of aluminium or copper or other material of higher conductivity than that of the strips. The support may be an insulating surface or another pair of rigid bars. A highfrequency current source 18 is connected to one end of the bars 14, 15 at 19, 20 and the other ends are joined by a conductor 21. Some of the current is transferred to the members 10, 11 and is concentrated in the edges due to proximity effect. The edges of the bars may be straight and parallel or may be formed with recesses 27, 28 or with projections 31, 32 to modify the heating effect on the edges. In a modification the bars 14, 15, Fig. 2, are pressed by power cylinders on to the strip ends and the current is applied to the bars by fluidcooled sliding contacts, the interconnecting member at the other end of the bars being also fluid-cooled and slidingly contacting the bars. To modify the heating of the edges narrow slits 45 terminating in circular apertures 46 are cut in the facing bevelled edges of the bars. The frequency of the current may be 100,000 or 450,000 or more cycles per second. When the strip edges are at welding temperature the current is cut off and the edges are butted by a power cylinder. Bars similar to bars 14, 15 may be provided beneath the strips. If the strips to be welded are of different metals the edges of the bars are provided with different contours to obtain the required temperature in each strip and a member of high conductivity, e.g. copper, which may be wedge-shaped may be arranged beneath the edges to be welded to reduce the impedance to current flow in the edges. In a further embodiment a strip of sheet-steel 110, Fig. 4 and 6, to be welded to the end of a strip 110<SP>1</SP> which is rolled up each time a further strip is welded thereto, is clamped between jaws 113, 114, operated by a cylinder 115 with its edge spaced 1/ 16 -1/ 4  inch from the edge of strip 110<SP>1</SP> clamped between jaws 116, 117, operated by a cylinder 118. A high-frequency current source is connected to contacts 125, 126, moved by a cylinder 127 into engagement with the side edges of the strips and a U- shaped contact 128 is moved by a cylinder 129 to engage the other side edges. Bars 130, 131, 132, 133 of magnetic material of low-loss factor and high-volume resistivity, e.g. sintered magnetic oxide or iron carbonyl powder and insulation material are arranged adjacent the edges of the strips, but may extend along only the mid-portion of the edges, to increase the impedance of paths spaced from the edges to force the current to flow along the edges. A pair of clamping jaws 119, 120, operated by cylinder 121 are arranged above and below the edges. The magnetic bars may be mounted on adjustable brackets 140, Fig. 6, on cross-bars 141 and are provided with cooling fluid conduits 142. The jaws 113, 114 may be mounted on a bracket 143 connected to a cylinder 112. In operation, the current is connected and applied to the strips and when the edges are heated to welding temperature the current is switched-off and cylinder 122 is operated to bring the edges together just as the jaws 119, 120 are actuated to bring them into engagement with the upper and lower sides of the seam. If the strips are substantially thinner than <SP>1</SP>/ 16  inch their ends are overlapped and spaced for heating and are then pressed together by the jaws 119, 120. The strips to be welded may be of iron, aluminium copper or of different metals and the Specification refers to the welding of the strips in steel mills, rolling mills and when making strip to be formed into tubing.