An Improved Electronic Control for Capacitor-Discharge Resistance Welding

Field and laboratory tests on the control described prove that the full-cycle discharge system produces welds which are metallurgically sound. Also this new discharge system increases the operating speed, aids in resetting the flux in the welding transformer, and reduces sparking at the electrodes to a point where the spark (if any) does not mark the material being welded. Speeds up to 200 spots per minute were obtained on a large press-type welding machine when using a 480-microfarad capacitor bank which was being charged to 2,500 volts. The following speed ratings have been applied to the control: Continuous Speed, Spots Per Min Maximum Speed, Spots Per Min Capacitance, ¿f Capacitor Volts 200. 480. 2,500 200.. 480. 2,500 60..... 2,640..... 2,800 25. 2,640. 2,800 The flux-resetting circuit eliminates the large reversing contactors which were formerly used to reverse the connections to the primary of the welding transformer between each weld. This helps to make possible the high operating speeds obtainable and reduces the maintenance cost on the control. The amount of iron used in the welding transformer can be reduced since greater flux changes can be obtained because of the flux bias produced by the flux-resetting current. The charge-control circuit controls the voltage to which the capacitor bank charges to any desired valve between 1,500 and 2,800 volts and regulates the voltage to within plus or minus two per cent of the desired value without undershooting or overshooting.