Patent GB-434018-A (GB)
Title: Improvements in or relating to electric welding apparatus
IPC: B23K11/24
Filed: 1934-01-18
Abstract: 434,018. Switching systems for resistance welding ; converting. WESTING- HOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, Pennsylvania, U.S.A.- (Assignees of Dawson, J. W.; 7725, Edgerton Avenue, Wilkinsburg, Pennsylvania, U.S.A.) Jan. 18, 1934, No. 1847. Convention date, Jan. 25, 1933. [Classes 38 (ii) and 38 (iv)] In electric welding apparatus the welding circuit is connected to A.C. supply through a pair of inversely connected vapour discharge valves of the type utilizing starting and ignition electrodes which contact with their respective cathodes and control means, including a separate discharge valve 25 and 26 for each main discharge valve, are provided so that a predetermined portion of a half cycle of the A.C. and/or a predetermined number of half cycles of A.C. can flow in the welding circuit. The reversely connected discharge tubes 18, 19 are arranged directly in series in the primary circuit of the welding transformer 10 and are controlled by heating current in auxiliary electrodes 23 of boron or the like dipping into the respective mercury cathodes. The heating current for these electrodes is supplied by grid controlled vapour discharge valves 24, 25 which are connected across the respective main valves 18, 19. Closure of a push button switch 57 energizes the A.C. cathode heating circuits of all the auxiliary valves and energizes a relay 58 which controls the supply of D.C. to the anode circuit of a vapour discharge valve 31. The grid of this valve is negatively biassed and receives an instantaneous positive potential through brushes 56, 48 on a commutator switch 44 which is driven by a synchronous motor 50 from the mains 14, 15. The instant in the cycle at which this potential is applied is adjusted by the positioning of the brush 48. The resulting conduction of the valve 31 produces a p.d across a resistance 38 which overcomes the negative bias of a battery 34 in the grid circuits of the control valves 24, 25, rendering the valve 24 conductive 20 as to " open " the valve 18. During the next half cycle the valve 25 is conductive and " opens " the valve 19. The sequence continues until a brush 45 on the commutator switch 44 applies a positive potential to the grid of a discharge valve 41 which short circuits the resistance 38 thereby rendering the valves 24, 25 non- conductive and " stopping " the valves 18, 19 at the end of the last half cycle of conductivity. The instant of flow of welding current is thus effected at any point in the cycle of A.C. depending upon the position of the brush 48 and the duration of flow is controlled over a number of half cycles predetermined by the spacing of the brushes 48, 49. Further operation is suspended until the switch 57 is opened and re-closed. The sequence in which the valves 18, 19 are operated for each succeeding weld is reversed by the provision of two commutator switches such as 44, 180‹ out of phase, and a ratchet changeover switch which connects the grid circuits of valves 31, 41 to these commutator switches alternately for each weld in response to an electromagnetic control of the ratchet from the push button 57. In a modification the valve 31 is controlled from another grid controlled vapour discharge valve 93 supplied with A.C., the grid of which is energized through an adjustable phase shifting circuit 94 so as to control the instant of ignition of this valve and therefore that of valve 31. The cut-off valve 41 is grid controlled through a condenser 192 and resistance 141 connected across the resistance 38 so that the valve 41 conducts a predetermined time after the valve 31 conducts and de-energizes the control valves 24, 25. The time period is determined by the value of condenser and resistance in the control circuit of valve 41. A drum switch 125 in series with the push switch 57 is driven from a synchronous motor, which may also drive the work, and prevents actuation of the welding circuit a predetermined time after the last weld. A system of electromagnetic relays is provided to ensure that at each closure of the switch 57 the connections to the valve 93 are reversed so that residual magnetism and saturation of the welding transformer are prevented when an unbalanced number of half cycles is passed at each weld. The drum switch in series with the switch 57 may be driven by a variable speed commutator motor through gearing and may have coupled to it a drum reversing switch for the valve 93. The control electrodes 23 of the main valves 18, 19 may be preheated by A.C. from a transformer 60. The D.C. supply for the control valve 31 may be obtained from a battery or from a rectifier connected to the A.C. supply. A time delay relay 81 may be provided in the anode circuit of valve 31 to ensure that the cathodes of the valves have heated up after closure of the main switches 17 before the valve 31 can be rendered conductive by closure of the push switch 57. The Specification as open to inspection under Sect. 91 states that the main discharge valves 18, 19 may be arranged in the secondary circuit of a transformer the primary of which is in series in the circuit of the welding transformer primary. This subject-matter does not appear in the Specification as accepted.