GB523027A - Improvements in and relating to electric welding apparatus - Google Patents

Abstract

523,027. Control systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 22, 1938, No. 37313. Convention date, Dec. 24, 1937. Addition to 495,484. [Class 38 (iv)] In a resistance welding supply arrangement of the type in which the primary of a welding transformer is supplied with a modulated voltage obtained from alternating current mains by a pair of modulators as in the parent Specification, means are provided to start a driving motor for roller electrodes when the first weld of a stitch seam is made, thereby ensuring that this first weld lies near the edge of the work. In the Figure roller electrodes 1 and 2 of a resistance seam welding machine are connected to the low tension winding 9 of a welding transformer and are adapted to be driven by an electric motor 3 fed through a switch 6 from three-phase mains 7. The high tension winding 11 of the welding transformer is supplied from a modulator set 12 in series with alternating current mains 13. In parallel with the high tension winding 11 is a circuit which includes auxiliary contacts 14 which close when the electrode pressure is sufficient, auxiliary contacts 16 which are closed when switch 6 is open, a protective resistance 15, and the operating coil 17 of switch 6. When, therefore, high tension winding 11 is energized by the first voltage impulse to effect a weld, the simultaneous energization of coil 17 closes switch 6 against spring 8 to start motor 3. The closing of switch 6 makes auxiliary contacts 18 which connect operating coil 17 directly across the main supply thus preventing re-opening of switch 6 when the modulated voltage falls to zero. Auxiliary contacts 16 open after contacts 18 close and the protective resistance 15 prevents a short-circuit of modulator set 12.