GB450750A - Improvements in and relating to systems of electric resistance welding - Google Patents

Abstract

450,750. Control systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Jan. 22, 1936, No. 2061. Convention date, Jan. 22, 1935. [Class 38 (iv)] A welding period of one or more A.C. cycles or half cycles is obtained by grid-controlled discharge vessels in the welding circuit controlled by the secondary of a transformer, the secondary being short circuited as required, by a grid-controlled auxiliary valve to prevent ignition of the main discharge vessels. The welding electrodes 3 are supplied through the welding transformer 2 in circuit with the grid-controlled discharge vessel 4. The grid is biassed by battery 10 and is connected to the secondary of the control transformer 9 which is supplied from the mains through a phase shifting resistance 7 and condenser 6. Ignition of the discharge vessel 4 is prevented when the secondary of the transformer 9 is short circuited by ignition of the auxiliary valve 11, which is rendered non-conducting for one or more cycles as required, when the switch 12 is moved from contact c to contact b in conjunction with some adjustment of the electrodes 3. With the switch as shown against contact c, a positive bias is given by the battery 14 through resistance R1 to the grid, thus rendering the valve conducting; but when the switch moves to contact b, condenser c1 is charged, the resistance R1 having such a value that the grid voltage is rendered negative relatively to the cathode voltage for a sufficient period to allow energization of the discharge vessel 4 during several cycles. The rate of charging of condenser c1 is accelerated, so as to limit the welding period to one cycle, by means of a transformer 15, rectifier 16 and resistance R2, which is smaller than resistance R1. By switching in condensers c2, c3, c4, the charging interval may be increased so that the welding period includes two or more cycles. A second discharge vessel opposedly connected in parallel with the vessel 4 may be controlled in dependence thereon as described in Specification 448,833, to enable both the positive and negative parts of the cycle to be utilized.