GB444113A - Improvements in and relating to electric welding apparatus - Google Patents

Abstract

444,113. Supply systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Sept. 19, 1934, No. 26933. Convention date, Sept. 19, 1933. [Class 38 (iv)] Switching control.-In resistance - welding apparatus in which the current supplied to the welding electrodes passes through grid-controlled discharge tubes and the grid voltage is changed so as to render the tubes conductive during an interval dependent upon a time element con. sisting of a, condenser and a resistance, the switch controlling the time element is coupled to the mechanism operating the welding electrodes. The welding electrodes E, Fig. 1, are supplied with A.C. from a source W1 through a transformer T3 and reversed discharge tubes F1, F2 having incandescent cathodes K1, K2, whenever the voltage in the grids G1, G2 is suitable. The grid voltage is changed during the desired interval of time by A.C. from a source W2 supplied from the same network as the source W1. Before welding is commenced, the switches S1, S2 are in the positions shown and the condensers are then charged from the source W1 through a transformer and rectifiers V co-operating with condensers C1, C2 and potential dividers P1, P2. When the electrodes F approach one another, the switches S1, S2 are changed over and each condenser is connected to its grid G1, G2, the voltage of which is thus changed during an interval of time which depends upon the rate of discharge through variable resistances W1, W2. In a modification, Fig. 2, the discharge tubes are operative when the grids receive, through the transformer T2, a positive voltage, the phaso of which is displaced slowly backwards until, at the end of the predetermined interval, the welding current ceases. The primary of the transformer T2 is connected to a circuit which includes the resistance W, the auto-transformer T1 and the secondary of a transformer T supplied with current from a source W2 in phase with the source W1. Before welding commences, the switch S is in the position shown and the condenser C is short-circuited. When the electrodes E are brought together, the switch S is changed over so that the condenser C is charged through the rectifiers G and the adjustable resistance WZ. The autotransformer T1 is thus loaded so that its impedance is small as compared with the resistance W, and the phase of the positive grid voltage is displaced backwards during an interval dependent upon the rate at which the condenser C is charged through the adjustable resistance W2 which thus determines the number of welding half waves. Reference has been directed by the Comptroller to Specification 420,100.