GB585437A - Improvements in or relating to electronic control systems suitable for capacitor discharge welding systems - Google Patents

Abstract

585,437. Capacitor discharge welding. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Nov. 17, 1944, No. 22802. Convention date, Nov. 24, 1943. [Class 38 (iv)] In a circuit for controlling the discharge of an adjustable capacitor 3 through an inductive load, e.g. the primary winding 9 of a welding transformer 11, reversibly-connected ignitron valves 55, 57 are interposed between capacitor 3 and the load, control circuits being provided for rendering the said ignitrons conductive to permit a single cycle of oscillating current to flow in the discharge circuit. Capacitor 3 is charged from an A.C. source 5 through a rectifying circuit 7 incorporating grid-controlled valves 25, 27 of the type known under the Registered Trade Mark of " Thyratron." Welding is initiated by the closure of a switch 117 which energizes a hydraulic controller 127 to move the welding electrode 17 on to the.material 19 at the same time operating a pressure switch 109. The latter switch opens contacts 107 which disconnect a flux-resetting circuit 96 from the transformer 11, and closes contacts 141 which energize a relay 145. This relay closes contacts 157 to connect a source of biassing potential 159 across the grid circuits of valves 25, 27, thereby rendering them non- conductive and terminating the charging of capacitor 3. At the same time contacts 147 are opened to disconnect an auxiliary capacitor 149 from its charging circuit 153 and connect it across the primary 155 of a peaking transformer 75, the subsequent impulse from which renders a valve 63 connected across the anode 61 and ignition electrode 67 of ignitron 55 conductive, in turn rendering ignitron 55 conductive and discharging capacitor 3 through the welding transformer 11. Due to the inherent inductance of the discharge circuit, capacitor 3 is charged with opposite polarity, whereupon a valve 85 connected across ignitron 57 is rendered conductive since the grid 91 and cathode 75 thereof are connected together through a resistor 93, thereby rendering ignitron 57 conductive and again discharging capacitor 3 through transformer 11. This inverse discharge, although of insufficient magnitude to produce a further weld, returns the flux of transformer 11 a considerable way towards its original value, the remaining charge being stored in the capacitor 3 at the correct polarity in readiness for a further charge. Switch 117 is then opened, permitting movement of the material 19 to a new position and also allowing the capacitor 3 to receive a further charge by the consequent opening of contacts 141 removing the bias on valves 25, 27. The simultaneous closure of contacts 107 reconnects the flux-resetting circuit 96 across part of the primary 9 of transformer 11 to return the flux thereof to its original value, thereby preventing saturation of the transformer. Switch 117 may be operated manually or automatically by a suitable timing circuit.