Patent GB-673743-A (GB)
Title: Improvements in and relating to electric arc stud welding
IPC: B23K9/20
Filed: 1948-12-14
Abstract: 673,743. Welding by pressure. CYC-ARC, Ltd., and SAYER, C. A. Dec. 14, 1949 [Dec. 14, 1948], No. 32354/48. Class 83 (iv). [Also in Group XXXY] In a method and apparatus for welding studs to plates, current of a limited value at full voltage flows between the stud and the plate, the stud is separated from the plate to strike an arc of low intensity, the current is subsequently increased to full strength and, after a predetermined interval, the stud is returned to the plate to effect the weld. The main welding circuit extends from a supply terminal 5 to the stud-holder 6 through a main contactor 7 operated by a coil 8 and through a resistance 9 into which the welding cable 10 of the tool is plugged. The main contactor is bridged by a circuit comprising a variable inductance 37 and a switch 36 operatedby a coil 42 and, in parallel with this circuit, is the operating coil 38 of a switch 39 which is fitted in the circuit from the control supply terminal 12 to the main contactor coil 8. Auxiliary contacts 18 connected to a condenser-charging timing device 21 and auxiliary contacts 45 in the circuit containing the switch 39 are also operated by the main contactor coil but are arranged to close before the main contactor. When the local control switch 14 on the tool is closed, the coil 42 is energized and closes switch 36 so that current flows through the inductance circuit and by way of the resistance 9 to the stud 2, plate 3 and return cable 11. At the same time, the coil 38 is energized and closure of switch 39 operates the main contactor coil 8. As the auxiliary contacts 18, 45 close before the contacts 7, current is supplied to the timing device through lead 19 and to a solenoid 4 on the tool so that the stud is separated from the plate and a low-intensity arc is struck. At the same time, the timing condenser 22 begins to charge, at a rate determined by a resistance 26. The main contact 7 has meanwhile closed, so developing the full arc and short-circuiting the inductance circuit, deenergizing coil 38 and opening switch 39. The function of switch 39 has, however; been taken over by the contacts 45 and contact 7 remains closed. When the condenser has charged, a coil 23 of a relay 20 is energized and the relay contacts thrown over, discharging the condenser and de-energizing the solenoid 4 so that the stud returns to the plate. The welding circuit is then broken at contact 7 when the circuit of coil 8 is broken by, for example, a switch 33 operated by the return of the stud to the plate, or by other means. Contacts 60 in the timing device may be opened after the predetermined time to de-energize the coil 42 and isolate the circuit of the inductance. In an alternative system, the coil 38 may close two switches, one for striking the low-intensity arc and the other short-circuiting the switch 14 on the tool so that current is supplied through the coil 42 and the tool switch 14 may be released. In another system, the main contactor coil 8 may be controlled by the timing device and closure of contacts 45 may open a coil-operated switch in the circuit of coil 42. A basic method of stud-welding, in which the inductance circuit is omitted and in which the contacts 18 close after the main contact 7 'to energize the solenoid 4, is also described.