GB507843A - Improvements in means for electric welding - Google Patents

Abstract

507,843. Control systems for welding arcs. ENGLISH ELECTRIC CO. Ltd., CHADWICK, A. T., BERTLES, E. J., and WHITE, J. S. Dec. 17, 1937, No. 34975. [Class 38 (iv)] In electric welding apparatus of the kind wherein the potential of an electrode holder or equivalent part is reduced when welding is not actually in progress and is raised automatically in response to welding contact, a contactor operating coil 3 in parallel with the electrode 4 is substantially short circuited and de-energized whereby it closes its contacts 3a when the welding circuit is completed through the work 5. Welding current is drawn from one end of the secondary 1a of a transformer 1 the other end of which is earthed, the low potential for the welding electrode 4 being taken from a tapping 1b. The high potential end of the secondary and the tapping 1b are connected by a circuit including a current limiting resistance 2, the usual regulating choke 6 and the contactor contacts 3a which are closed when th coil 3 is de-energized. In the example the electrode 4 and one end of coil 3 are connected to the high potential end of resistance 2, the work and the other end of coil 3 being earthed. When the supply is switched on, coil 3 is energized and contacts 3a open immediately, but the coil remains energized due to the connection to the lower voltage tapping 1b, so that the contacts remain open. The electrode 4 is at low potential until brought into contact with the work 5, whereupon the coil 3 is short-circuited and the contacts 3a close. The full voltage of the secondary 1a is then available for welding. The contactor may be biassed to the closed position by a spring or gravity, and is preferably provided with a time-lag device for delaying the opening of its contacts after the breaking of the arc. The contactor may be operated by a D.C. coil fed through rectifiers, the time lag then being produced, at least in part, by shortcircuited secondary coils on the contactor for increasing artificially the time constant of the operating-coil.