Patent GB-779431-A (GB)
Title: Method and apparatus for electric arc welding
IPC: B23K9/073
Filed: 1955-09-22
Abstract: 779,431. Automatic control systems for arc welding. AIR REDUCTION CO., Inc. Sept. 22, 1955 [Oct. 8, 1954], No. 27126/55. Class 38 (4). In a system for maintaining constant the arc voltage in automatic arc welding apparatus. electrode position is adjusted by a two-phase servomotor, one phase winding of which is energized by a full-wave rectifier automatically grid-controlled in dependence on the amplified difference between the arc voltage and a reference voltage. As shown, work-pieces 10 and 11 to be arc welded together are moved to form a continuous weld by a motor-driven carriage 15, and voltage from a generator 37 is applied between a non-consumable tungsten welding electrode 12 and the work. The electrode is surrounded by a stream of inert gas. The arc voltage, as indicated by a voltmeter 53, and a stabilized reference voltage from a potentiometer 67 are applied differentially to a pair of triode valves 71 which control, through a further pair of triodes 90, a pair of grid-controlled rectifiers 92 and 93 energizing one phase winding 36 of a two-phase induction motor M. If the arc voltage deviates from the reference voltage, winding 36 is energized with pulsating D.C. of such phase relative to the fixed energization of the other motor winding 34, that the motor runs in the appropriate direction to restore the arc voltage automatically to the desired value by adjustment of the vertical position of electrode 12 through gearing 26, 19, 16. Resistance-capacity networks 79, 81, 82, 83, 84, 86 introduce differential and integral components of control. Closure of a switch 102 prior to the start of welding energizes solenoid valves 107 and 108 to allow an initial flow of inert gas and cooling water for a time determined by a time delay relay 121. Closure of a switch 132 to start the weld de-energizes relay 121 to cause inert gas and cooling water to flow continuously. If the flow of cooling water is inadequate a flow switch 131 operates to prevent welding. Otherwise motor M moves electrode 12 downwards until it touches the work whereupon a relay 119 is energized. This causes a solenoid 31 to be energized, moving gear 19 along to a limit stop 27 so that electrode 12 is raised a predetermined distance from the work independently of motor M. Simultaneously a relay 38 is energized to connect generator 37 directly to the work and an oscillator 43 is switched on to supply high-frequency current through a transformer 41 to strike the arc. Fall in voltage when the arc is struck de-energizes a relay 118 to switch off oscillator 43 which is for starting purposes only. Under these conditions carriage 15 moves to advance the work continuously. The effect of gravity on the electrode and its holder is balanced by the effect of a circuit, including contacts 114a, by-passing valve 92. When switch 132 is opened to stop the weld, motor field winding 36 is connected across a D.C. supply in series with a condenser 109 and a resistor 110 so that the motor is braked momentarily to prevent overtravel. An arrangement in which the electrode is a consumable wire, the position of which is controlled by adjustment of nip rollers, is referred to.