Patent GB-610903-A (GB)
Title: Methods of and apparatus for electric welding
IPC: B23K11/26
Filed: 1944-07-04
Abstract: 610,903. Control systems for resistance welding. STEVENS, A. H. (Progressive Welder Co.). July 4, 1944, No. 12744. [Class 38 (iv)] [Also in Groups XXXVI and XXXVII] Work is electrically heated, as in welding, by a pulse or pulses of current having a maximum value and the current in each pulse being modified to effect a gradual rise and/or a gradual fall during a minor portion or portions of the period of flow. A welding system comprises a combined pneumatically and hydraulically operated contactor C (Figs. 1, 5 and 11), characterised by co-operating carbon elements 30, 32, which gradually increase, decrease and interrupt the welding current derived from an energy storage means such as a battery, B1, B2, B3 (Fig. 1). Initiation of decrease of current after welding may be controlled by  apparatus responsive to the temperature of the work. Operation of switch P in the auxiliary control circuit, Fig. 1, closes contacts R1a and R1b of relay R1 to complete a holding circuit for P and an energizing circuit for valve C1 associated with means for causing electrodes 10, 12 to engage the work W. Relay R2 closes its contacts R2a and R2b, the former completing an energizing circuit for coil 54 actuating valve 52, which operates to connect the contactor to the source 66 through regulator 64. Air at desired pressure flows into cylinder space 186, Fig. 11, and to passage 194 associated with needle valve 196 (Fig. 12). Pressure on 186 builds up at a rate determined by valve 62, Fig. 1, sufficiently to overcome the spring 116 and to move the carbon elements into engagement through piston 112, piston-rod 164 and piston 162. Air also passes to cylinder space associated with piston 232 of valve 70 (Fig. 10) to open it either simultaneously, prior to or after the pressure between the carbons has attached the value determined by valve 64. This action connects space 150 above cylinder 144 (Fig. 11) to source 66 through needle valve 72, surge tank 73 and regulator valve 74 (Fig. 1) and pressure is built up which forces piston 152 downwards against spring 146 (Fig. 5) during which time oil is trapped in space 120, whereby increased pressure is applied to piston 112 and therefore to the carbon elements 30, 32 at a rate determined by the setting of a needle valve (not shown), the pressure ultimately depending upon the setting of valve 74 and determining the maximum welding current. Pyrometer Py operates in response to a predetermined temperature in the weld to energize relay R5 which opens contacts R5a and R5b to interrupt the circuits of coil 54 and transformer T3 respectively and disconnect the contactor from source 66 at valve 52. Valve 70recloses, valve element 220 isolates space 150 from 66 and connects 150 to exhaust through passage 230, connected to a rate controlling needle valve 231 (Fig. 10), which controls rate of exhaust from 150 and the rate of reduction of pressure between carbons 30, 32, which are ultimately separated by the action of the return spring 116. Interruption of welding current de-energizes relay R4 and R2b to close contact R4a and open its contact R4b, the former completing a circuit for transformer T2, which supplies charging current to condenser C2 and blocking potential to valve V1 to render it non-conducting to deenergize relay R1 after the " hold time " determined by condenser C1. R1a and R1b open to de-energize coil of valve 61, the former also opening the circuit for T1, the latter the circuits for relay R3 and transformer T4. Contacts R5a and R5b reclose after relay R5 " times out " which may be at any suitable time after de-energization of relay R1. Valve V1 becomes conducting, to energize relay R1 in response to reclosure of switch P1 when condenser C2 has discharged through the local circuit. Throw over switch S<SP>11</SP> may be provided to render valve 61 &c. directly responsive to switch P. In a modified system, a succession of welding pulses may be effected by means of a modified valve 701, Fig. 14, actuated by solenoid 300; said valve operating to successively increase the welding current to the maximum and decrease it to a desired minimum several times and finally to interrupt the current. For such a system, sequencing of valves 52, 70<SP>1</SP> and 306, Fig. 14, may be effected by a pulsation timer comprising motor-driven drums 322, 324 and 326, controlling circuits for valves 54 and 306; valve 701 and re-setting arrangements respectively.