GB530177A - Improvements in or relating to arc welding systems - Google Patents

Abstract

530,177. Automatic control systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 20, 1939, No. 17929. Convention date, June 24, 1938. [Class 38 (iv)] Arcs. - An arrangement for controlling the feed of a fusible electrode 18 in an A.C. arc welding system comprises a reversible D.C. motor 24 the armature current of which is controlled in direction and magnitude by means, including a undirectional conducting device 56, operating in accordance with the voltage across the arc electrodes. The means comprise a generator 28 driven by a motor 30 supplied from a constant voltage generator 34 which also supplies current to the field of the motor 24 and to resistances 35, 36, 37 in series therewith. The generator 28 feeds the armature of the motor 24 in opposition to the voltage drop across resistance 37, and its field excitation is effected in accordance with the difference between the voltage drop across resistance 35 and the voltage at the D.C. terminals of the rectifier 56 so long as the latter predominates. Thus, on closure of switches 17, 42, 64 following depression of push-button 59, the generator 28 is fully excited and the motor 24 starts in a direction causing the fusible electrode to be fed forward into contact with the work 20. The resulting fall in voltage at the terminals of the rectifier 56 decreases the excitation of the generator 28, the voltage of which falls below that across resistance 37 whereupon the motor 24 reverses and causes the arc to be struck. The electrode feed is thereafter automatically regulated by control of the excitation of the generator 28 in accordance with the voltage at the terminals of the rectifier 56. In a modification, the reversible voltage applied to the armature of the motor 24 is obtained directly from the terminals of the generator 28 which is provided with two opposed field windings.