Patent GB-193386-A (GB)
Title: Improvements in and relating to electric arc welding systems
IPC: B23K9/073
Filed: 1923-01-30
Abstract: 193,386. British Thomson - Houston Co., Ltd., (Assignees of Noble, P. O.). Feb. 16, 1922, [Convention date]. Heating by electricity. - In an arc welding system wherein the arc voltage is the resultant of a number of voltages one of which varies sensitively with the length of the are, the electrode feed motor is provided with a regulating field winding energized in accordance with said sensitively varying voltage. In the system shown in Fig. 2 a generator 14 of the type described in Specification 159,374, [Class 35 Dynamo-electric generators &c.], has its main brushes 1, 2 connected to the welding mains 3, 4 which supply the welding electrode 5 and work 6, a, reactance 7 being arranged in the circuit. The generator 14 is constructed so that the voltage between the brushes 1, 8 is substantially constant but the voltage between brushes 2, 8 reverses and varies with the length of the arc, so that the arc voltage is the algebraical sum of the voltages referred to, that is, the voltage between the main brushes 1, 2. The armature 18 and field winding 19 of the electrode feed motor are connected across the brushes 1, 8 and 2, 8 respectively. On closing the switch 22 the contacts 31, 28 are closed in succession, so that the armature 18 and field 19 are energized to start the motor to feed the electrode. The solenoid 30 is energized and opens the contact 29 before the contact 28 is closed so that the solenoid 25 which operates the reversing switch 24 is not energized at this stage. When the electrode touches the work the voltage between brushes 2, 8 reverses to full value in the opposite direction and becomes equal and opposite to the voltage between brushes 1. 8. The current in the field winding 19 is thus reversed and the motor now operates to withdraw the electrode, also the solenoid 30 is de-energized so that the contact 29 closes and completes the circuit through the solenoid 25. When the arc voltage reaches a certain value the solenoid 35 operates the switch 24 so that the current in the field 19 is again reversed and the motor now operates to feed the electrode. A reactance 23 may be fitted in the circuit of the armature 18 to diminish the increase in the armature current when the field 19 is de-energized. Where the brushes of the 'motor are set back with reference to the normal direction of rotation, the armature produces a magnetizing effect which tends to strengthen the field 19 during withdrawal of the electrode. This magnetizing effect would be sufficient to prevent reversal of the motor when the switch 24 was operated if the are voltage was nearly equal to the voltage between brushes 1, 8. To ensure reversal the switch 24 is provided with an extra arm which opens the armature circuit during the reversal of the switch. In a modification, the armature circuit is normally closed by a relay operated by a solenoid in the circuit of the field winding so that the relay opens the armature circuit during reversal of the switch 24. In a further modification, when this relay switch opens the armature circuit it closes a circuit from the brushes 1, 8 through an electrically operated brake fitted to the motor shaft. The reversing switch 24 may be arranged in the armature circuit instead of the field circuit, in which case the motor is provided with a series field winding which acts in the same direction as the field 19 during feeding of the electrode but in opposition to the field 19 during withdrawal. The effect of the series field may be obtained by shifting the motor brushes forward with respect to the normal direction of rotation. In another modification, the feed motor has an additional field winding connected in shunt to the armature through a switch arm operated by the reversing switch 24. After the arc has been struck the switch 24 operates to reverse the motor to feed the electrode and at the same time closes the circuit through the additional field winding which produces a constant field in the same direction as the field produced by the winding 19. This additional constant field may be provided in connection with the described arrangement in which the switch 24 is in the armature circuit, in which case the series field winding need not be fitted. Fig. 18 shows an arrangement in which the motor is provided with an additional field 38 and in which the current in the field 19 is reversed without the aid of a reversing switch or without opening the field circuit. The arrangement is provided with starting and stopping push-buttons 40, 41 which are normally open and closed respectively. When the starting button 40 is closed the solenoid 30<1> is energized and opens the contact 29' and closes the contact 29" to complete the circuit through the solenoid 39 which immediately closes the switch 22 of the welding circuit and the contacts 39a, 31<1>, 39<b>, 39<c>. The contacts 39<a>, 39<b> shortcircuit the starting button 40 and contact 29" respectively. Contact 39<c> completes the circuit of the armature 18 the field 19 of which is energized through the following circuit : from brush 2, through switch 22, resistance 42, field 19, resistance 43 to brush 8. The motor operates to feed the electrode 5 and when it touches the work 6 the voltages between brushes 1, 2 falls to zero so that the solenoid 30 is de-energized and closes the contact 29<1> thus completing the circuit through the solenoid 25<1> of the switch 24<111>. Also the voltage between brushes 2, 8 is reversed so that the current in the field 19 is reversed and the motor operates to withdraw the electrode. When the arc voltage reaches a certain value the solenoid 25<1> closes the swith 24<111>. This reverses the current in the field 19 and connects the resistances 42, 43 in parallel therewith and at the same time the additional constant field 38 is inserted in shunt to the armature. The motor reverses and feeds the electrode toward the work. Fig. 20 shows an arrangement in which the feed motor continues to operate in one direction, after striking the arc, the transmission gear between the feed motor and feed rolls 17 being arranged for reversal. The transmission gear is mounted on shafts provided with magnetic clutches 44, 46. Closing the switch 22 closes contacts 31, 28 in succession so that the solenoid 30 opens the contact 29 and current flows through the clutch 44, the motor operating through this clutch to feed the electrode. When the electrode touches the work the current in the field winding 19 is reversed and the solenoid 30 became de-energized so that the contact 29 is closed to complete the circuit through the coil 25<11>. The motor reverses and withdraws the electrode. When the arc voltage reaches a certain value the coil 25" reverses the contact 25a so that the clutch 44 is deenergized and the clutch 46 is energized. The motor now operates through the clutch 46 to feed the electrode. Fig. 21 shows the invention applied to welding apparatus of the type described in Specification 184,141, in which the electrode 5 is fed through a flexible tube 48 having at one end a. hand welding tool 50 provided with a pistol grip 51 and a circuit closing device 52. The operator closes the contact 52 and after touching the work 6 with the electrode 5 he withdraws the electrode to strike the are. The solenoid 53 closes the switch 22 as soon as the contact 51 is closed, but the solenoid 54 is constructed so that it only operates to close the contacts 54<a>, 54<b> which complete the armature and field circuit. when the arc current is between certain limits. When the arc current reaches this limited range the contacts 54a, 54<b> are closed and the motor operates to feedÀthe electrode. A push button having contacts 55, 56 is arranged in the circuit to enable the motor to operate to feed the electrode through the tube in the first instance. The double field winding arrangement may be used in connection with this modification if desired. Although all the arrangements described except the arrangement in Fig. 21, are provided with automatically operating relays for reversing the direction of the electrode feed when the arc has been struck, this reversal may be achieved by the operator by providing a push button for remote control of the device which effects this reversal. If the generator 14 is designed for 60 volts (,n open circuit then if one field winding 19 is fitted to the motor and the normal arc voltage is 20 volts, the percentage fluctuation of the excitation of the field winding will be double the percentage of fluctuation of the arc voltage. For a double field winding, if the field 19 is designed for 200. per cent normal excitation on open circuit, the constantly excited winding will be designed to supply 33 per cent normal excitation and a 10 per cent fluctuation of arc voltage produces 13.4 per cent fluctuation in excitation. If with this double winding the open circuit voltage of the generator is double the normal arc voltage and the winding 19 is designed for 200 per cent normal excitation, the constantly excited winding will be designed to supply 100 per cent normal excitation and the percentage fluctuation of the total excitation will be double the percentage fluctuation of the arc. Specifications 139,919 and 171,442, are referred to.