Patent GB-649951-A (GB)
Title: Improved methods and apparatus for the electric arc welding of metal or alloy studs,tubes and the like to metal or alloy plates, bodies and the like
IPC: B23K9/20
Filed: 1948-04-27
Abstract: 649,951. Supply systems for arc welding. MARTIN, H. April 27, 1948, No. 11491. [Class 38 (iv)] [Also in Group XXII] Control means for electric arc stud welding apparatus comprises a starting switch 53, a welding circuit contactor 23, a timing device 1, a switch 9 under the control of the timing device and a multiple contact relay 26-29 so connected that, on closing the starting switch, the welding circuit is closed and the timing device times the duration of the arc and then allows the stud 35 to move against the plate to which it is to be welded and renders effective an auxiliary control circuit whereby the welding circuit cannot again be closed after opening so long as the starting switch is maintained closed or retaining relay acting in place of the switch is operative. An insertion resistance 86, Fig. 2, and contactor arm 87 may be fitted for reducing the current intensity when the stud contacts the plate to effect the weld and it is stated that a second contactor may be fitted for reducing the current intensity towards the end of the welding operation, for minimising the current breaking duty of the main contactor or to provide for preheating the stud end previous to the striking of the arc. The method of timing may be pneumatic or alternatively may be one in which the rate of charging or discharging of an electrical condenser in a direct-current circuit determines the time periods. Pneumatic timing devices. The rate of upward movement of a diaphragm 2 under the action of a spring 8, Fig. 1, is controlled by an adjustable needle valve 16 and the diaphragm is connected by a rod 4 to a bar 7 which has an abutment 14 for operating the switch 9 and on which an arm 24 connected to the welding circuit contactor 23 rests, when the contactor 23 is open, and depresses the spring 8. Alternatively the contactor may be connected directly or through linkage, to the timing device by a tension spring which is relaxed when the contactor is open and is stressed to operate the timing device when the contactor is closed. In a modified timing device, the diaphragm is connected by a rod 60, Fig. 2, to a bell-crank 61 operating a switch 65, 66 through an adjustable contact 64 and is raised by a spring 77 and depressed by an arm 78 on the welding circuit contactor 79. Operation. When the starting switch 53, Fig. 1, is closed, a coil 44 is energized to close the contactor 23 and establish the welding circuit through the stud 35 and plate 36. The closing movement of the contactor 23 closes the switch 25, so that a coil 50 is energized to lift the stud and thus strike the arc and so that the arm 24 is removed from the bar 7. After the required interval, the timing device changes over the switch 9 and so de-energizes the coil 50, thus returning the stud to the plate. At the same time, a relay coil 30 is energized, closing the relay contacts 26, 28 and opening the contacts 27, 29 so that the coil 44 is deenergized, the contactor 23 opened, the welding circuit broken and the switch 25 opened. The relay coil 30 remains energized by current through the leads 43, 47 so long as the starting switch is kept closed. Since the circuit for the contactor coil 44 requires to be closed through the contacts 27 and 29, it cannot again be closed while the switch 53 is closed. In the modification shown in Fig. 2, when the starting switch 111 is closed, a relay coil 92 is energized through closed contacts 100, 103 of a relay 97 and a bridging condenser 105 for the coil 92 is energized ; the condenser may be cut out by a switch 106. The contacts 93, 95 of a relay 91 are closed by coil 92 and so the circuit for that coil is diverted from switch 111 to the contacts 93 95. Closure of the contacts 94, 96 also results in energization of the contactor coils 89 and 88 controlling respectively the welding circuit contactor arm 79 and an arm 87 which short-circuits the insertion resistance 86, but the arm 79 lags behind owing to the bridging condenser 107 in the circuit of coil 89. The arm 79 closes contact 90, thus energizing the tool coil 108 and its bridging condenser 110 to withdraw the stud and withdrawing arm 78 from the timing device, which then times the duration of the arc. After the required interval, the contacts 65, 66 are made, so energizing coil 98 and changing over the contacts of relay 97. The breaking of contacts 101, 104 breaks the circuit for coils 108 and 88, thus. allowing the stud to move down on to the plate and bringing in the resistances 86. The separation of contacts 100 and 103 de-energizes the coil 92, while the making of contacts 99 and 102 allows the coil 98 to remain energized if the starting switch 111 is still closed. However, if the starting switch is open, the delay in deenergizing coil 92, because of condenser 105, retains contacts 93, 95 closed to keep coil 98 energized until the contacts it controls have finished their operation. When coil 92 is de-energized, its retaining circuit is broken through the opening of contacts 93, 95 and the opening of contacts 94, 96 opens the contactor 79 to cut off the welding current. The retention of the starting switch in the closed position may be obviated if, in the open position, it closes a circuit from the contact 99 to the negative supply terminal 118, or if a second switch is provided for this purpose. A simplified system, adapted for welding small studs and similar to that of Fig. 1, is also described, in which the timing device and switch 65, 66 of Fig. 2 are employed and in which a resistance is fitted to minimize arcing at the contacts of the timing device and bridging condensers are fitted in the tool, coil and relay coil circuits. Specification 580,732 is referred to.