Patent GB-653371-A (GB)
Title: Improvements in electric switches and to electric welding arrangements incorporatingsuch switches
IPC: H01H35/24
Filed: 1945-02-26
Abstract: 653,371. Control systems for consumption apparatus. PHILIPS LAMPS, Ltd., SLADE, C. E., and YORSTON, J. Feb. 26, 1945, No. 4813. [Class 38 (iv)] [Also in Group XXXVII] A welding-machine is provided with fluidoperated switching-apparatus (see Group XXXVII), for controlling two or more operations in the machine with definite time intervals between the operations. The switching apparatus may be constructed to ensure that operations are carried out in correct sequence. Fig. 11 shows a circuit for supplying current to welding electrodes 71, 72 and for automatically cutting it off after a predetermined interval of time. A switch 67 is connected in series with a normally-closed switch 18 and a coil 68 controlling an air valve 69. When the switch 67 is closed the coil 68 is energized and the valve 69 opened to admit compressed air which actuates the piston 70 to move the electrodes 71, 72 into contact with the work. At the same time air passes into the chamber 2 and lifts a diaphragm 9 which closes a normally-open switch 17, thus completing a circuit through the contactor coil 76 and closing the contactor contacts 75. Current is thus supplied to the primary winding 74 of the welding transformer. Connected to the chamber 2 by an opening controlled by a needle valve 7 is a second chamber 4 closed by diaphragm 9 which actuates the switch 18. Air leaks from chamber 2 to chamber 4 and after a definite interval of time builds up sufficient pressure to raise the diaphragm 9 and open the switch 18. The coil 76 is thus deenergized and the contactor 75 opened. The coil 68 is also de-energized and the valve 69 closed, thus cutting off the air supply and putting the chamber 2 and the cylinder of piston 70 into communication with the atmosphere. The electrodes 71, 72 move apart and the apparatus is ready for a fresh cycle of operations. In a modification, Fig. 12 (not shown), the switch 17 is used to initiate the operation of a timing device which is energized from the mains and includes a relay connected in series with the contactor coil 76. The contactor comprises a second set of contacts connected across the switch 67 and switch 18 and serving to maintain the coil 68 energized while the contactor is energized. As in Fig. 11 the closing of the switch 67 opens the air valve 69 to bring the electrodes 71, 72 together and to close the switch 17. The timing device commences to operate and closes the circuit for the contactor coil 76 for a predetermined period of time during which current is supplied to the electrodes. The second pair of contacts of the contactor are in parallel with the switches 67 and 18, thus energizing the coil 68 during the period that the welding transformer is supplied with current even though the switch 67 is opened. When the timing device 77 breaks the circuit of the coil 76 the switch 18 opens under the pressure in the chamber 4 and the coil 68 is de-energized and the moving parts of the apparatus returned to their initial position. in a further modification, Fig. 13 (not shown), the chambers 2, 4 are separated, the chamber 2 being directly associated with the welding head and connected to the chamber. 4 by a long length of pressure tubing which takes the place of the needle valve 7. Fig. 14 shows another modification in which three air chambers are provided to operate three switches 40, 41, 42 in timed sequence to close and open the contactor for the welding current and to ensure that the electrodes 71, 72 cannot move apart while carrying current.