GB661671A - Improvements in and relating to automatic arc welding - Google Patents

Abstract

661,671. Control of two D.C. motors. FORD MOTOR CO., Ltd. Oct. 5, 1948. [Dec. 3, 1947] No. 25917/48. Class 38 (iii). [Also in Group XXXV] Automatic arc welding apparatus in which the welding electrode is fed by a motor energized from the main welding circuit, the feed motor being energized after a time delay, and a resistance being inserted in series with the motor armature to limit the speed at which the electrode is advanced to strike the arc. On closing the push button 16, relay 30 closes to start the carriage feed motor 29, and accelerating relays 31, 34, close after suitable delays. Simultaneously, relay 17 closes to short circuit resistor 18 in the field of exciter 19 to provide full output from the welding generator 10. After a delay to allow the voltage of generator 10 to build up, relay 23 closes to energise the electrode feed motor 22, which is a series motor connected in series with a speed limiting resistor 24 across the output of the welding generator. When the arc is struck, the voltage across a shunt 28 in the arc supply line closes relay 27, shorting out the speed limiting resistor 24 to allow normal regulating operation of the feed motor 22. Relays 17C and 30C (in parallel with relays 17 and 30) are also energised from the shunt 28 so that on shutting down (by releasing push button 16), the generator output and carriage feed are maintained until the arc is extinguished. In a modification, Fig. 2, (not shown) a voltage sensitive relay starts the electrode carriage motor when the generator output has built up, and the electrode motor speed limiting resistor is normally short circuited by a relay which opens to place the resistor in circuit when the generator voltage is above the normal welding voltage (i.e. before the arc is struck). As an alternative, in either embodiment, the electrode feed motor may be separately excited, with the armature across the welding circuit. A further time delay relay, Fig. 3 (not shown), also energized when push button 16 is closed, energises a solenoid to retract the electrode assembly to assist in striking the arc. Alternatively, a relay energized by the welding current shunt 28 may control the solenoid. In a further modification, Fig. 4 (not shown), a current/voltage relay closes to short circuit resistance 21 in the exciter circuit as the voltage builds up, and opens when the welding current flows. This provides a very heavy starting current to initiate the arc.