Patent GB-696794-A (GB)
Title: Improvements in or relating to control circuits for welding apparatus
IPC: B23K11/26
Filed: 1951-09-07
Abstract: 696,794. Converting. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Sept. 7, 1951 [Sept. 15, 1950], No. 21155/51. Class 38 (ii). In a circuit for controlling welding apparatus energized by trains of low-frequency current pulses caused to flow in one direction or the other by main thyratrons 105, 107 in the circuits of transformers 125, 127 respectively, one is rendered incapable and the other capable of conduction upon the closure of the main switch (not shown) by transients rendering one of the auxiliary associated thyratrons 161, 163 conductive and the other non-conductive. The circuit is energized by lines 21, 23, 25 connected to transformer 29. On closing foot switch 271 to initiate a welding cycle, relay 33 operates and energizes anodes of thyratrons 5, 7 through contacts 31 and opens contacts 53 so that capacitor 43 discharges in a time during which the electrodes are seated on the material and pressure applied. Thyratron 5 then fires and operates relay 35 which energizes transformer 63 through contacts 73, double diode 67, and thyratron 79 which is in a conductive condition. The outputs from the secondary windings 93, 95 of this transformer are impressed on the grids of thyratrons 105, 107, both or one or other of which fire according as which one of their three positions, ganged switches 145, 147 are in. Contacts 59 also open to break the supply to condenser 45 which then discharges in the time during which one welding train of pulses must flow. The duration of each pulse in the train is determined by the discharging of condenser 197 as a result of capacitor 85 charging while thyratron 79 is conducting, and cutting off thyratron 91. When this pulse time has elapsed and condenser 197 is discharged, thyratron 213 conducts and through double diode 229 both charges capacitor 273 to cut off thyratron 79 and sends a pulse through transformer 239 which operates through the double diode 245 to alter the conditions of thyratrons 161, 163 from conductive to non-conductive and vice versa by means of a flip-flop effect involving condenser 179. As a result of the charging of condenser 267 through anode 251 of double diode 245 only the first pulse through transformer 239 is effective in this way. The states of thyratrons 105, 107 are likewise reversed but remain non-conductive, following the ceasing fire of thyratron 79 interrupting the supply of firing control potential. After the cutting off of thyratron 79, capacitor 85 begins to discharge until at a time determined in conjunction with the ripple introduced by heating coil 89, thyratron 91 conducts, capacitor 197 is charged, thyratron 213 becomes non-conductive and thyratron 79 again fires to start another train of pulses, by conductivity through transformer 63. The process is repeated to give a train of pulses, until capacitor 45 has discharged when thyratron 7 fires and relay 37 operates. The consequent opening of contacts 31 of relay 33, de-energizes relays 35, 37, breaking the supply of welding current at contacts 73 and closing contacts 53 and 57, 59 permitting capacitors 43 and 45 to charge respectively. The time of charging of 43 determines the time between trains of pulses. If the switch 271 remains closed, the welding cycle is then repeated.