GB837794A - Improvements in or relating to control circuits for welding systems - Google Patents

Abstract

837,794. Control systems for resistance welders. ROBOTRON CORPORATION. Feb. 20, 1958 [April 29, 1957], No. 5549/58. Class 38 (4). A timing circuit for controlling the "squeeze" "weld" " hold " &c. operations of a welding system, wherein an additional timing circuit allows the welding current to flow during the " hold " period comprises a number of interconnected valves preferably thyratrons connected to capacitive resistance timing circuits. On closing a starting switch 8, a thyratron 6 conducts, energizing a relay 3 and closing contacts 9, 17, 18, contact 9 completing the electrode closing circuit, and contacts 18 shunting the starting switch 8. Contacts 17 complete the thyratron 12 circuit, but this does not conduct until the negative potential on the grid 24 supplied by the capacitor 28 falls. Conduction of thyratron 12 shunts a capacitor 48 which has been charging over a rectifier 44, and this discharging through a resistance 47 fires a thyratron 34 energizing transformer 37, firing thyratron 64 and operating a relay 66, 67 controlling the welding current. After a time interval, the discharging of capacitors 48, 56 in opposite senses blocks the thyratron 34, but thyratron 64 still conducts temporarily until the charge on a capacitor 55 becomes less than that of capacitor 56. At the same time as thyratron 34 is blocked a thyratron 74 is also blocked through a conductor 79, causing a capacitor 77 in the anode circuit which determines the hold period to discharge, after which time a thyratron 84 conducts and supplies a blocking potential to the thyratron 6 permitting the welding electrodes to open. If the starting switch 8 is held closed a further cycle of operations will follow as soon as a capacitor 89 in the anode circuit of thyratron 84 discharges through a resistor 87. Specification 833,389 and U.S.A. Specification 2,776,383 are referred to.