GB584937A - Improvements in or relating to the control of electric spot welders - Google Patents

Abstract

584,937. Control systems for resistance welding. BATEMAN, J. R. May 19, 1944, No. 9704. [Class 38 (iv)] A welding machine has electromagnetic means 40 to maintain electrode pressure independently of a foot pedal or the like and welding current cannot commence until this means is effective, a relay 42, sensitive to current in coil 40, controlling the welding contactor. To forge the weld, release of the pressure is delayed for a timed period after cessation of welding current, the period of application of which is separately timed. As applied to a control system according to Specification 550,615, a switch 1 is closed when electrode pressure is applied to prepare the circuit of contactor 3, 4. A manual switch 39 energizes the coil 40. These two circuits may be supplied by rectified current from a winding S2 and pass respectively through contacts 6 and 46 of relay 7. After the current in coil 40 has become sufficient to lock the pressure means, relay 42 operates and contactor 4 closes to start welding, whereupon relay 14 actuates its contact 53 and coil 40 becomes independent of relay 7 which after the discharge of the weld timing condenser actuates its contacts 6 and 49 to cause respectively contactor 4 to open and to discharge a condenser 35 through contacts 23 and 51, to maintain energization of relay 14 for a period determined by a variable resistance 43. When relay 14 finally releases, its contact 53 de-energizes coil 40 and electrode pressure is released. A manual switch 41 may be used to release the electrodes and cut off welding current at any time.