GB521956A - Improvements in or relating to arc welding systems - Google Patents

Abstract

521,956. Supply systems for welding arcs. MORELISSE, J. Nov. 29, 1938, Nos. 34714 and 34715. Convention dates, Dec. 21, 1937, and Dec. 23, 1937. [Class 38 (iv)] In a supply system for a welding transformer, wherein an electromagnetic switch in the primary circuit of the transformer is energized, at the commencement of welding, by means of an auxiliary transformer, and the primary circuit of the welding, transformer is broken when the welding circuit is broken, the electro- .magnetic switch is held during welding by a current which is dependent on the existence of welding current. The primary 1 of the welding transformer is adapted to be connected to the supply mains through the electromagnetic switch contacts 7 when the latter is energized, the ends of the secondary being connected respectively to the work 12 and through a transformer primary 10, to the welding electrode 13. The auxiliary transformer comprises an earthed primary winding 3, and a secondary 4 which is connected through the back contacts 8 of the switch, and the secondary 11 of transformer 10, 11, across the leads to the work and welding electrode. The solenoid coil 5 of the switch is shunted across the winding 11. When the electrode is applied to the work the circuit of the auxiliary transformer secondary 4 is closed and the solenoid is energized to close the primary circuit of the welding transformer, contacts 8 simultaneously being broken. Welding current then flows through the primary 10 'of the transformer, so that its secondary 11, in series with coil 5, is energized to maintain the primary of the welding transformer closed. Instead of the detaining current for coil 5 being obtained from the transformer primary 10 the coil may be connected across a resistance in the welding circuit, or the winding 10 may be inserted in a shunt circuit of the welding current circuit. Coil 5 is de-energized when the welding arc is extinguished, thereby breaking the contacts 7 of the primary 1 of the welding transformer. A retarding device, e.g., a liquid damper may be inserted to introduce a time lag. Since, in the arrangement shown the retaining current for the coil 5 is dependent on the current in the welding circuit, which current may vary considerably, in an alternative arrangement the transformer 10, 11 is replaced by a coil which is wound around both limbs of the welding transformer, whereby the voltage induced therein is less variable. In a further modification the electromagnetic switch is provided with a switching - on coil which operates when the electrode is applied to the workpiece, and a retaining-coil in parallel with the secondary of the welding transformer.. A relay in the retaining coil circuit operates to open the latter upon a predetermined rise in potential, as when the arc is extinguished.