GB559658A - Improvement relating to electric flash welding - Google Patents

Abstract

559,658. Control systems for electric welders. WHITEHORN, H. K., YOUNG, W. F., and GORDON, S. H. Aug. 25, 1942, Nos. 11979 and 14723. [Class 38 (iv)] [Also in Groups XXII and XXXVII] In electric-flash welding the voltage of the welding current is automatically reduced in one or more steps during the flashing period by operating at least two contactors in rapid succession by the actuation of switches by the moving head of the machine i.e. switch into the primary-circuit one or more additional sections of the primary-circuiting of the transformer. Premature cutting of the work-pieces is thus avoided. For this purpose the primary of the welding transformer may be provided with tappings 1-6, each tapping in use being connected to a separate contactor 18, 20, 22 provided with windings 19, 21, 23 controlled by normally open switches 27, 31, and normally closed switches 29, 33, 35 which are actuated automatically by cams 26, 30, 28, 32, 34 on the bar 24 attached to the moving head 12 of the welding machine. A manually operated switch 36 is first closed to set in operation the traversing mechanism for the head and also to complete a circuit through the winding 19 via switch 29 to close the contactor 18 and thus start welding with a secondary at 10 volts. The flashing away of the ends of the work thus occurs and the bar 24 continues its motion until at a predetermined point the cam 26 closes the switch 27 and shortly thereafter the cam 28 opens the switch 29 so as to de-energize the winding 19 and open contactor 18. When the arc across the contactor 18 has broken, the voltage across its contacts is applied to the winding 21, the circuit being from contactor 18, wire 42, switch 44 connected to contactor 20, winding 21, switches 33, 27, 36. Contactor 20, is thus closed to supply welding current to tapping No. 4 to obtain a secondary voltage of 7 volts. Closing of contactor 28 closes alternative circuit through winding 21 leading direct to the left hand side of the mains 38 through switch 44 in its other position and wire 48. Continued movement of the bar 24 to the left next causes cam 30 to close switch 31 and then cam 32 to open switch 33 to cause contactor 20 to open and contactor 22 to close in a similar manner to that described in connection with contactors 18 and 20. Voltage across the secondary thus drops to 5 volts. The switch 35 is finally opened by the cam 34 on completion of welding. Any other tappings may be used and the cam on the bar may be longitudinally adjusted. Any number of contactors may be used with additional pairs of cams and switches. In another form the reduction in voltage may be effected by changing the connection of two similar sections I, II of the transformer primary from parallel to series, or three or more similar sections in successive stages. The tapping section 17 is connected to - the right-hand side of section II. The respective ends of sections I, II are initially connected together in parallel by contactors 52, 56, the sections being placed in series, by opening contactors 52, 56 and then closing contactor 54. The gap between the contacts of contactor 52 is wider than that of contactor 56, and the contactors 52, 56 are connected by a link 53 and made yieldable under constraint of compression springs so that both contactors may close and so that contactors 52, 56 may be opened in succession to prevent short circuits. The arms of contactors 54, 56 are provided with overlapping extensions 59, 61, so that if 54 is closed 52, 56 are open while with 52, 56 closed 54 must be open, but 54 can be opened with 52 and 56 open. The contactors 52, 56 are operated by winding 55 and the contactor 54 by winding 57. On manually closing switch 36 circuit through winding 55 via closed switch 29 is closed to close contactors 56, 52 in succession to start welding with the sections in parallel. As the bar 24 moves to the left it closes switch 27 to energize winding 57, which however is ineffective until switch 29 is opened by cam 28 when winding 55 is de-energized, and the contactors 52, 56 opened in succession and the contactor 54 closed to put the sections I, II in series and continue welding at a lower secondary voltage. Welding is completed when the cam 34 on the bar 24 opens the switch 35.