Patent GB-759142-A (GB)
Title: Improvements in or relating to electric welding apparatus
IPC: B23K11/24
Filed: 1952-10-13
Abstract: 759,142. Converting. IGRANIC ELECTRIC CO., Ltd. Oct. 13, 1952, No. 25574/52. Addition to 665,360, [Group XXII] Class 38 (2). [Also in Group XXII] Unidirectional pulses for welding are derived from a three-phase supply L1, L2, L3 through valves such as ignitrons 16, 17, 18 connected between the phases, each in series with one of the three primary windings 15b, 15c, 15d of the welding transformer 15, and a primary winding 19a, 20a, 21a of current transformers 19, 20, 21, the secondary windings of which, when desired, initiate firing of the ignitrons in another phase. The welding current developed in winding 15a of transformer 15 passes through the work 6 held between electrodes 8, 9 by fluid pressure in cylinder 117 and through winding 13 whereby an armature 11 carrying electrode 9 is attracted downwards to increase the pressure by an amount proportional to the strength of the welding current as in the parent Specification. The ignitors 16c, 17c, 18c are energized respectively with peaked voltages superimposed on constant but adjustable voltage bias from similar phase-shift networks 37, 54, 63 through switching triodes 23, 51, 60. To supply a single unidirectional welding current impulse, switches 71, 94 are closed and switch 96 held in its midposition. When main switch 91, which may be operated by the fluid-pressure in the welding cylinder 117, is closed, relay 31 is operated to close contacts 31a connecting network 37 to the grid of valve 23 which is rendered conducting. A half-cycle of current passes through winding 15b, induces welding current in secondary winding 15a, and also passes through windings 19a and 22a of transformers 19, 22, respectively. Short-circuiting of winding 19b by switch 94 prevents the pulse developed in transformer 19 from bringing about energization of the other ignitrons 17, 18, and the pulse developed in transformer 22, by firing valve 73 and thereby increasing the bias on cathode 23c of valve 23 to a value at which this valve cannot conduct, prevents further firing of ignitron 16. If it is desired that windings 15b, 15c, 15d shall be energized in turn, switch 94 is opened and switch 96 put in its right-hand position so that the pulse developed in winding 19b is added to the bias and pulse applied by phase-shift network 54 to the grid of valve 51 whereby this is fired and the igniter 17c is energized. The resulting pulse through ignitron 17 and winding 15c of the welding transformer acts through transformer 21, similarly to energize ignitron 18 and winding 15d by way of switch 70 which is in its right hand position, phase-shift network 63 and valve 60. The voltage pulse induced in transformer 21 is short-circuited by switch 71 which is now closed, through switch 102, which has been set in its left-hand position. Valve 73, having been rendered conducting through transformer 22, prevents valve 23 from conducting and restarting the cycle. By having switch 71 closed, switch 94 open and switches 70, 96 in their left-hand positions, and switch 102 in its right-hand position, the welding transformer windings are energized in the order 15b, 15d, 15c. Also by suitable settings of switches 70, 71, 94, 96, 102, each operation of switch 91 may result in pulses to windings 15b, 15c, or to windings 15b, 15d. With switch 71 open any se. quence of operation for which the other switches are set will be repeated continuously while switch 91 is operated.