GB459346A - Improvements in and relating to electric welding apparatus - Google Patents

Abstract

459,346. Supply systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. June 2, 1936, No. 15403. Convention date, June 1, 1935. [Class 38 (iv)] In A.C. spot or seam welding in which a part of one or more cycles is utilized for each timed weld, and in which rectifiers controlled by phase variable A.C. grid potential are blocked to terminate the weld when a timing or control condenser is sufficiently charged, the condenser is charged by impulses produced in dependence upon the phase .variable grid potential applied to the rectifiers. The primary of the welding transformer 2 is supplied from the mains 1 through opposed rectifiers 4, 5 in parallel, the follower valve 5 being controlled in dependence upon the pilot valve 4. The control potential for the grids of the rectifiers is taken from the mains 1 through a phase shifter 6 and transformer 9. The secondary winding 10<1> in the circuit of the control grid of the pilot valve 4 is short-circuited between welds by the auxiliary valve 11, the grid of which is connected to the positive pole of the battery 14 through resistances. When the control switch 12 is actuated to connect contacts a, b, current from the battery charges the adjustable control condenser C and the potential on the grid of the valve 11 drops so that a positive grid potential from the transformer 9 ignites the pilot valve 4. This potential simultaneously is applied to the grid of the valve 7, to complete a circuit through the primary of control transformer 15 in parallel with the primary 10 of the grid transformer 9. The secondary 16<1> of the control transformer thereby applies through the rectifier 17 an impulse dependent upon the main grid potential to complete the charging of the control condenser C. When the condenser is sufficiently charged, the potential applied by the battery 14 to the grid of the auxiliary valve 11 renders it conducting, thus short-circuiting secondary 101 and blocking the pivot valve 4. Secondary 16<11> of control transformer 15 charges condenser 22 which is associated with resistance 23 and rectifier 24 so as to co-operate with secondary 10<11> of grid transformer 9 to start and stop follower valve 5 to deal with the negative part of each cycle in dependence upon pilot valve 4. Valve 5 may be cut out by switch 21. By operating switch 13, valve 11 may be cut out, the ratios of current and pause for seam welding being then regulated by a rotating switch drum 25.