GB456130A - Improvements in and relating to methods of and apparatus for electric welding - Google Patents

Abstract

456,130. Supply systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. June 29, 1936, No. 18011. Convention date, June 27, 1935. [Class 38 (iv)] In spot or seam welding in which a part of one or more cycles is utilized for each timed weld, grid-controlled rectifiers being blocked to terminate the welding period when a timing or control condenser is sufficiently charged by current impulses dependent upon the alternating grid potential applied to the rectifiers, the non-welding period is also timed by a second control condenser which when sufficiently charged brings about the discharge of the first condenser and starts another weld. 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 grid 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 supplied at positive potential from the battery 14 through resistances. When the control switch 12 is moved to position b, current from the battery charges the adjustable control condenser C1 and the potential on the grid of the valve 11 drops rendering the valve non-conductive so that the grid potential peak of 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 16 in series with the primary of the grid transformer 9. The secondary 161 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 C1. 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 shortcircuiting secondary 10<1> and blocking the pilot valve 4. Secondary 16<11> of control transformer 16 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. The switch 19 being closed, the discharge lamp 8 when rendered conducting discharges the first control condenser C1 and starts another welding period, the potential applied to the grid being dependent upon the second control condenser C2. The charging of this condenser is effected through the adjustable resistance R2, rectifier G2 and transformer 26 connected across resistance 20. When a welding period is completed by auxiliary valve 11 becoming conductive, the increased potential difference across resistance 20 starts the charging of condenser C2 which when sufficiently charged terminates the non- welding period.