WELDING CURRENT SOURCE FOR ARC WELDING WITH AC CURRENT.

摘要

1338187 Arc welding systems MESSER GRIESHEIM GmbH 20 April 1972 [20 April 1971] 18394/72 Heading H2H An arc welding system comprises means whereby the voltage across the electrode and workpiece is reduced when an arc is not struck. An electrode 14 and workpiece 15 is supplied from an A.C. source 1, 2 by way of a transformer 4 and a pair of back-to-back connected rectifiers 6, 7. When an arc is not struck between the electrode and workpiece relay 10, and hence relay 8, are not energized, the rectifier 7 thus being disconnected. In this case the output of the transformer 4 is half-wave rectified and the voltage across the electrode and workpiece does not exceed a safe value. When the electrode strikes an arc with the workpiece, relay 10 is energized. Closure of contacts 11 causes energization of relay 8 from a winding 5 on the transformer 4. Contact 9 thus closes to connect rectifier 7 into the system, whereby the voltage across the electrode and workpiece is now the full-wave rectified transformer output voltage. Resistor 12 and capacitor 13 provide smoothing. In other embodiments, the rectifier 7 is replaced by a thyristor and the relay 8 dispensed with. A high frequency impulse system may be provided for starting the arc and a contactor 3 in the A.C. supply may be opened automatically if the arc voltage assumes an excessive figure. The output of the transformer 4 may be rectified and a changeover switch provided whereby welding may be carried out using either A.C. or D.C. When the welding apparatus is a plasma arc device means are provided whereby an auxiliary arc is struck between the gas nozzle and the workpiece.