Patent GB-183834-A (GB)
Title: Improvements in and relating to electric arc welding apparatus
IPC: B23K9/073
Filed: 1922-07-26
Abstract: 183,834. British Thomson-Houston Co., Ltd., (Assignees of Alexander, P. P.). July 26, 1921, [Convention date]. Heating by electricity.-An are welding system Fig 1, wherein the rate of feeding of the electrode 3 is controlled in accordance with the arc voltage as described in Specification 145,330, comprising a generator having a pair of main brushes 1, 2, connected to the electrode 3 and the work 4, a motor 7 operating the electrode feeding mechanism 6 and means for connecting one terminal of the motor armature to one side of the welding circuit, is provided with means such as an auxiliary brush 15, whereby the other terminal of the motor armature is connected to the generator armature so that the direction and speed of the motor is controlled in accordance with the difference between the arc voltage and a voltage which is a fraction of the open circuit voltage of the generator. The generator is of the type described in Specification 159,374 in which the curent supplied by the main brushes varies inversely with the voltage. The generator is a constant-speed machine, and has a third brush 11, the voltage between the brushes 1 and 11 being constant. The voltage between the main brushes is the algebraic sum of the voltage between brushes 1 and 11 and between brushes 2 and 11. The windings are such that with one half load current in the welding circuit the flux in the poles 10 is zero and when the are is short-circuited the voltages between brushes 1 and 11 and brushes 2 and 11 are equal and in opposition. The auxiliary brush 15 is adjustable and so arranged that the voltage between the brushes 2 and 15 is several volts lcwer than the arc voltage during welding and is substantially constant being produced by the pcles 9 only. The field winding 16 of the electrode feed motor 7 is supplied by the constant voltage between brushes 1 and 11. A switch 17 and a reactance 18 for stabilizing the current, are provided in the welding circuit. An adjustable resistance 21 is provided in the motor circuit to limit the armature current when the welding circuit is open, the voltage on the armature then being at a maximum. The resistance 21 is shunted by a control switch 19 when the welding current reaches a certain value. When the generator is started, the motor 7 feeds the electrode 3 towards the work 4, and when they are in contact the welding circuit is short circuited and the voltages between brushes 1 and 11 and brushes 2 and 11 become equal and in opposition, and the direction of current in the motor armature is reversed so that the electrode is withdrawn to strike the arc. As the electrode is withdrawn, the voltage between brushes 2 and 11 decreases until the current in the motor armature is again reversed and the motor feeds the electrode at the necessarv rate to maintain the arc. In a modification, the adjustable resistance 21 is replaced by a pair of contacts bridged by the control switch 19 when the welding circuit is open, one contact being connected through the motor armature to the brush 15 and the other being connected to a second auxiliary brush placed on the generator commutator at a point of higher potential. Fig. 6 shows an arrangement in which an ordinary constant voltage generator 23, having a shunt winding 27 is provided with main brushes 24, 25 connected to the welding circuit and an auxiliary brush 26 so arranged that the voltage between brushes 25 and 26 is substantially constant and less than the normal arc voltage. The field winding 33 of the electrode feed motor 29 is connected across the brushes 24, 25. An adjustable resistance 2b is provided in the welding circuit to limit the current therein when the circuit is short circuited and to decrease the arc voltage when the welding current increases. The current in the armature of the motor 29 is limited by an adjustable resistance 32 which is shunted by a control switch 31 similar to the device 19, Fig. 1. When the generator is started, the electrode 3 is fed towards the work 4, and when they are in contact the motor is impressed with the voltage between brushes 25 and 26 and withdraws the electrode 3. When the arc voltage exceeds the voltage between brushes 25 and 26, the armature current is again reversed and the electrode is fed at a rate to maintain the arc constant.