GB705164A - Improvements relating to arc welding equipment - Google Patents

Abstract

705,164. Supply systems for welding arcs. BRITISH ELECTRICAL & ALLIED INDUSTRIES RESEARCH ASSOCIATION. Aug. 10, 1951 [Aug. 11, 1950; May. 3, 1951], Nos. 20032/50 and 10437/51. Class 38 (4) To improve the stability of an A.C. welding arc whilst allowing a reduction of open circuit voltage of the main current source, a switching device is effective, immediately the arc commences to extinguish, to connect to the arc an auxiliary low power source which then supplies the arc gap with voltage impulses to maintain ionization. The switching device may be responsive to voltage rise of the arc, to a marked increase of its resistance, or to the occurrence of zero current. In the arrangement shown in Fig. 1 a value amplifier 10, responsive to the voltage across an arc 1, 2 supplied from a main source WT, triggers a cold cathode thyratron 6 if the arc voltage rises and causes a condenser 3 to discharge into the arc and thus maintain it. The condenser is continuously charged over a resistor 5 from a battery 4 of, say, 450 volts. In modified arrangements the condenser may discharge in series with the main source, or the amplifier 10 may be dispensed with. Several other arrangements are described in which the condenser is coupled to the arc circuit by a transformer either for the purpose of matching the impedances of the two circuits, or for obtaining a high impulse voltage sufficient for the initial striking of the main arc. Fig. 9 shows one such arrangement in which the condenser 3 discharges through two transformers. Transformer ATI (and associated condenser 27) provides a short high voltage pulse over a spark gap 28 to ionize the welding gap 1, 2, this pulse being followed by a longer pulse of lower voltage (to maintain the ionization) by transformer AT and associated condenser 35.