GB1495321A - Apparatus for pulsed arc welding and building-up of articles - Google Patents

Abstract

1495321 Arc-welding systems INST ELEKTROS IMENI EO PATONA AKAD NAUK UKRAINSK SSR 16 April 1975 15602/75 Heading H2H Arc welding apparatus comprises a rectifier circuit 7-12 having a choke 13 at its output, a current pulse generator including bridge rectifier 20 comprising thyristors 21, 22, the bridge being connected in series with an electrodeworkpiece arc gap 1, 2 and the choke 13 and arranged so that a welding current can continuously flow through the choke and are-gap irrespective of the state of conduction of the thyristors 21, 22. As shown, a 3 phase mains supply 5 is provided and passed via transformer 3-6 tothe rectifier and choke 7-13. One phase of this is also applied across primary 18 of transformer 14 the output of which is applied to A.C. terminals of the bridge 20. An A.C. supply which is synchronized with that across primary 18 is applied to a bridge rectifier 80 and the circuit including transistor 87 provides a sawtooth voltage across the capacitor 90. This is compared with a fixed voltage across capacitor 91 by transistor 46 which is thereby caused to produce a square wave output of about ¢ markspace ratio. Conduction of transistor 46 controls that of transistor 50 which allows the capacitor 55 to charge linearly whilst the transistor 50 is off. This periodic ramp voltage is compared with a voltage across capacitor 61 which is derived by voltage divider 56 via switch 62 from that determined by a setting potentiometer 39. As soon as the ramp voltage is in excess of that across capacitor 61 transistor 63 becomes conductive and transistor 65 is turned off. A pulse is thereby produced by differentiator 68, 69 and via transistor 70 flows in the primary of transformer 73 to provide via secondaries 74, 75 triggering pulses for both thyristors 21, 22. Thus a D.C. pedestal voltage is applied continuously across the arc gap 1, 2 with periodic D.C. pulses superimposed whose amplitude and duration is dependent on the setting at 39. For automatic operation the switch 62 may be moved to its alternative position where the voltage at capacitor 61 is proportional to the mean arc voltage as determined by feedback integrating circuit 31. This is compared with the ramp voltage as above which is still generated via setting resistor 39. Mean voltage variations across the arc may thus be compensated.