Patent GB-842384-A (GB)
Title: Electrical power unit for arc welding systems
Inventor: DRACOPOLI JOHN LAWRENCE
IPC: B23K9/073
Filed: 1956-02-01
Abstract: 842,384. Control systems for welding arcs. HIVOLT Ltd., and SATURN INDUSTRIAL GASES Ltd. March 22, 1957 [Sept. 5, 1956], No. 3195/56. Class 38 (4). A control system for an arc-welding apparatus of the kind to which arc maintaining high voltage surges are supplied and wherein the arc is shielded by an inert gas, is characterized by the provision of a controlswitch operation of which in one direction opens a valve to allow the gas to flow to the welding arc, institutes a time delay and subsequently switches on the surge injector circuit whilst operation of the control switch in the reverse direction switches off the surge injector circuit, institutes a time delay and finally closes the valve to stop the flow of gas to the arc. With a switch S2-S3 in the requisite position and a control switch S4 on the welding torch handle open, capacitors C2, C3 will be charged from an alternating current sourceindicated by a plug P1-over rectifiers M1, M2 and relay contact B1. Relay A/3 is also energized to open all its contacts so that the anode supply to a surge injector valve V3 is broken at contacts A3. Closure of the control switch S4 energizes relay B/4 whereby a solenoid T2 is energized over contacts B3b to open a valve to allow an inert gas to flow to the arc. Opening of contacts B1 however removes the supply of the relay A/3 but this relay is held in by the discharge therethrough of the capacitors C2, C3, thereby instituting a delay before the relay A/3 drops out to close contacts A3 to restore the anode supply of the surge injector valve V 3 . At the end of a welding operation switch S4 is opened, relay B/4 is de-energized to open contacts B4 whereby the anode supply to valve V3 is removed to stop the surge injection. At the same time contacts B1 close to replace the supply to the relay A/3 which does not pick-up, however, until condensers C2, C3 are charged sufficiently. Thus a delay is effected before relay A/3 picks up to open contacts A3 to deenergize the solenoid T3 to stop the flow of gas to the arc. The surge injector valve V3 is under the control of a relay valve V2, whereby valve V3 is rendered conductive once every cycle of a welding transformer T4. Whilst the torch electrode is cold the arc voltage is sufficient to energize relay D/4 to close contacts D1 to place a capacitor C9 in the grid circuit of the valve V2 and because contacts D4 are open a very high voltage is developed by an ignition coil T3 by means of the valve V3 and a capacitor C12 which high voltage breaks down a spark gap K to reach the welding torch by way of a connection C. When the torch electrode is warm the arc will fire on both half-cycles of the supply, the arc voltage then being insufficient to energize the relay D/4. Contacts D4 then close to short-circuit the ignition coil T3, whereby the high-voltage surges now reach the torch by way of resistors R23, R24 and choke coil CH2. Contacts D1 open to remove the capacitor C9 from the grid circuit of valve V2, whereby the instants at which the surges occur are advanced. Capacitor C15 is a D.C. suppressor and may be cut out by means of contacts S6 when not required. Switch S2-S3 is provided for use with water-cooled torches to ensure that control switch S4 is out of circuit when water is not flowing. Specifications 705,164, 833,201 and 842,385 are referred to.