Patent GB-145330-A (GB)
Title: Improvements in and relating to methods of and apparatus for automatic arc welding
IPC: B23K9/073
Filed: 1919-10-24
Abstract: 145,330. British Thomson - Houston Co., (General Electric Co.). Oct. 24, 1919. Heating by electricity. - In an arc welding apparatus, an electrode is moved automatically towards and away from the work in accordance with the difference between the electric pressure across the arc and a substantially constant pressure less than the normal arc pressure. A reversible electric motor having low momentum and low armature and brush resistances may be used. In one arrangement, the constant pressure is that across an adjustable part 14b, Fig. 1, of a resistance 14 connected to constant-pressure mains 12, 13, which are distinct from the mains 15, 16 supplying the welding current. The motor armature 8 is connected to the electrode 5 and work 1 through the resistance section 14<b>. By adjustment of this section, the rate of feed may be arranged so as just to compensate for normal consumption of the welding electrode. The normal arc pressure may be 15 volts, the constant pressure 10 volts, and the resistance drop of the motor 1 volt. A constantly-excited field winding 11 is employed. The work may be traversed by a screw 4. In another arrangement, a Wheatstone bridge is formed by the are and three resistances, the independent supply circuit 12, 13 being omitted. The main supply circuit and the feeding motor are connected to opposite pairs of corners of the bridge, and the two resistances in opposite sides of the bridge are adjustable for controlling the arc current and the fixed pressure respectively. In this and the previously-described arrangement, the high pressure across the electrodes when no current is flowing through them may be counteracted by an increased potential obtained by tapping the resistance such as 14, Fig. 1, at a different point. When the arc is in existence, a series coil closes a short-circuit across the section of the resistance between the two tappings. In another arrangement, a motorgenerator provides the fixed electric pressure. The motor has its armature and field in parallel across the supply mains, while the generator field coil is connected to the mains through an adjustable resistance which is short-circuited while no current flows through the electrodes, in order to produce in the generator a higher pressure to oppose the open-circuit pressure of the welding circuit. This short-circuit is opened by a series magnet during working, but the generator may be arranged so that its pressure is not instantaneously reduced when the electrodes meet, in order that the motor may act quickly to separate them. A second motor-generator of the kind described in Specification 133,439 supplies the welding current. Another arrangement of the Wheatstone-bridge type is shown in Fig. 5. The four arms of the bridge contain respectively (1) the electrodes 1, 5, (2) the regulating resistance 31, (3) resistances 108, 109, and (4) resistances 104 - - 106, of which the last is adjustable. The resistances 104 - - 106 may be replaced by a generator as above described. When no current is flowing through the electrodes, and a switch 98 is moved to the left, current is supplied to the feed-motor armature 8 through the resistances 106 - - 104, a, conductor 102, the switch 98, and the resistance 31. A switch 90 having previously been moved to the right or welding position, contact of the electrodes allows current to flow through this switch and one winding 111<a> of an electromagnetic switch, the other winding 111<b> which previously neutralized the first winding being thus short-circuited. The electromagnetic switch 115 then closes (1) the welding circuit, (2) a circuit 117, 118 in shunt to the resistance 104, to reduce the electric pressure which opposes the arc pressure in the feed-motor circuit as in the other arrangements, (3) a circuit connecting a resistance 122 and second electro-magnetic switch 119 through conductor 121 to one supply main and through wires 130, 131 to the fusible electrode 5. The second electro-magnetic switch 119 is thus responsive to the arc potential, and when this rises to a working value the switch opens a short-circuit to resistance 108, by which short-circuit, the pressure on the feeding motor has been increased to expedite separation of the electrodes. The same switch 119 also closes a circuit through contacts 124 and a hand reversing switch 91 to a motor 60 which causes relative motion of the work and the fusible electrode. If the electrode encounters a projection on the work, this motor circuit is re-opened, the motor being braked by a shunt resistance 128. When it is desired to feed or withdraw the work without welding, switch 90 is moved to the left, thus closing the circuit through the traversing-motor 60 and reversing-switch independently of the contacts 124. In order to raise the fusible electrode when there is no current through the work, the switch 98 is moved to the right to connect the feedmotor to a section of the resistance 104. Fig. 6 shows the work 1 clamped on a table which is adjustable laterally with reference to the seam by a screw and hand-wheel 62. Above the'table is a carriage propelled along guides 55 by a screw 54 driven by the motor 60. To a vertical plate 50 on the carriage a bracket 46 supporting the electrode and feed motor 8 is adjustably secured by means of bolts 52 and a series of holes 53. The electrode 5 can thus be adjusted in the plane of the electrode and seam. A guide 49 and brushes 17 engage the electrode. Feed-rollers 63 may have several grooves for electrodes of different sizes.