GB420100A - Improvements in and relating to systems of electric welding - Google Patents

Abstract

420,100. Control systems for welding- apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and KNIGHT, H. DE B., 108, Eastlands Road, Rugby. May 26, 1933, No. 15276. [Class 38 (iv)] In an arrangement for " shot " welding in which the welding electrodes pass a heavy current for a predetermined short period of time an impedance S in series with the primary of the welding transformer W is short circuited by one or more grid controlled vapour discharge tubes TI whose grid circuits include a timing circuit in which a condenser C2 is charged through a resistance R3 and determines the period of the " shot ". The timing circuit may be supplied with A.C., or D.C. or through a rectifier T2 from the A.C. supply. A switch K2 controls the operation and in its position b short circuits the condenser C2, whilst in position a the welding operation is started and lasts until the condenser C2 is charged sufficiently to block the discharge tube T1. The period of the " shot " may be varied by (a) altering the position of the cathode tap A on the potentiometer R1, R2 from which the timing circuit is supplied, (b) adjusting the resistance R3, (c) varying the capacity C2 by an additional condenser or a series parallel arrangement of condensers. A variable resistance R4 in the primary circuit of the welding transformer may be used to control the welding current and a resistance R5 may be connected across the welding electrodes to minimize the effect of surges on the operation of the discharge tube T1. Specification 387,714 is referred to.