GB1031821A - Automatic electric arc welding apparatus - Google Patents

Abstract

1,031,821. Welding by fusion. SUPERHEATER CO. Ltd. April 2, 1963 [April 2, 1962], No. 12629/62. Heading B3R. [Also in Division H2] In an automatic arc welding machine for joining tubes end-to-end by relative movement of a non-consumable electrode and the tubes, the heat input from the electrode to the tubes is reduced at a predetermined instant during the welding cycle to prevent over-penetration. This is effected by reducing the welding current and/ or increasing the traverse speed. The tubes A, B, Fig. 1, and Fig. 2 (not shown), are located by an abutment 12 and held in chucks 6 of rotary carriers 5 driven in unison by a motor 17 connected to a D.C. supply T6, T7. The output of a three-phase rectifier MR1 is connected to the electrode 7 and to brushes 44 mounted on leaf springs and engaging slip rings 46 on the carriers 5. The rectifier MR1 is supplied by the secondary windings TR1S of a main transformer controlled by a magnetic amplifier MTR having D.C. control and feed back windings. A control ring 27 journalled on one carrier 5 and rotated at a lower speed than the carrier 5 has projections actuating switches MS1, MS2. In operation after a preheat period the motor 17 is started and almost immediately switch MS2 energizes relay RL to drive the motor at a speed determined by resistance R1 and to set the full welding current determined by a resistance R3 in the control circuit of the magnetic amplifier MTR which control circuit is fed through a transformer TR2 from one of the primary windings TRIP of the main transformer. After, say, 270 degree rotation of the tubes, switch MS1 operates relay RL to short circuit resistance R1 to increase the speed of motor 17 and to connect resistance R2 in series with resistance R3 to reduce the welding current. When the weld is completed the tubes are rotated a further 30-90 degrees with steadily reducing welding current. In a two-pass weld, the tubes are halted after one revolution and the current is maintained to raise the temperature. The second pass is performed as described for a single pass weld, but with an increased current. The welding head 8, Fig. 5 (not shown), is water cooled, has a tungsten electrode 7, a ceramic nozzle 21 through which argon and hydrogen are passed and an enclosure 23. A block 24 pivotally mounted on the machine supports the welding head 8 by the cooling water pipes 9. Argon is supplied to the interior of the tubes.