| 摘要 |
PURPOSE:To improve the weld quality by decreasing a firing angle gradually from the time when an electric current is started to apply and controlling a preheating slope and next, shifting it to constant-current control via firing angle control after the lapse of a prescribed time. CONSTITUTION:Two thyristors 7 and 7 are provided in antiparallel to the primary circuit 2 of a power source and a switching circuit 8 is provided to form a firing circuit 6. A control circuit 10 starts a control action at the same when the electric current is started to apply on a pressurized welding machine and controls the preheating slope to decrease the firing angle gradually in the first prescribed time and raise an electric-current value i1. Continuously, the constant- current control is performed via the firing angle control after the lapse of the prescribed time. In this way, the electrode tip deposition, the surface roughness of a work, etc., due to attached dust to base metal can be prevented. Accordingly, the weld quality and the reliability of the welding can be improved.
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