Patent GB-204473-A (GB)
Title: Improvements in and relating to control systems for electric arc welding apparatus
IPC: B23K9/12
Filed: 1922-08-16
Abstract: 204,473. British Thomson-Houston Co., Ltd., (General Electric Co.). Aug. 16, 1922. Systems for continuous-current motors only; systems for obtaining reciprocating motion.-A motor operating welding electrodes is started by a push button, and left in connection with a Wheatstone bridge arrangement, of resistances,. which cause it to stop and reverse when the electrodes are in contact. The arrangement further causes the motor to resume forward running when the arc has been formed. Starting and stopping push buttons 13, 14 which are normally open and closed respectively are arranged, as shown. When the button 13 is closed the coil of the protective relay 12 is energized and closes the contacts 12<a> and opens the contacts 12<b>. Current now flows through the coil 11 which closes the switch 10 and contacts 11<a> - - 11<d>, the contacts 11<c>, 11<d> shortcircuiting the coil of relay 12 and the button 13 respectively. The circuit is now closed through the motor field 4<1>, the contact 19 of vibratory relay 20, and the adjustable resistance 18, the relay 20 being de-energized due to the contacts 12b being open. A Wheatstone-bridge is formed as described in Specification 145,330, the two arms on one side being the resistance 9 and the open welding circuit and the two arms on the other side being the adjustable resistances 25, 24. The junctions of the arms on each sides are connected through the armature, of the motor 4 which thus operates to feed the electrode 1 toward the work 2. When the electrode and work are in contact, the protective relay 12 is shorted so that the contacts 12<a> are opened and the contacts 12<b> are closed so that the coils 20, 30 become energized. The current in the motor armature is now reversed and the motor operates to retract the electrode. The coil 30 is set so that when the arc voltage reaches its normal value the switch 28 is thrown over, breaking the circuit through resistance 25 and short-circuiting resistance 24. The armature of the motor thus receives the full welding voltage and the current is reversed so that the electrode is fed towards the work. Opening the button 14 de-energizes the coil 11 and opens the switch 10 and contacts 11<a> - - 11<d>. This interruption of the bridge circuits prevents and back circuits being formed. In Fig. 2, closing the button 13 energizes the protective relay 30 to close the contacts 30<a>, 30<b>, and open the contacts 30<c>, 30<d>. Closing the contact 30<a> energizes the coil 11 to close the switch 10, contacts 11<c>, 11<d> and the circuit through the motor field 4<1> and closing the contact 30<b> completes a circuit through the motor 4 and adjustable resistance 33, the motor operating to feed the electrode 1 towards the work. When the electrode touches the work the coil of relay 30 is de-energized and closes the contacts 30<c>, 30<d> and opens the contacts 30<a>, 30<b>. The current in the motor armature is reversed and the electrode is retracted. The closing of the contact 30<d> energizes coils 31 and 20, and when the arc voltage reaches its normal value the contacts 31<a> are closed, shortcircuiting the resistance 33 and impressing the full arc voltage on the motor in a reversed direction so that it operates to feed the electrode. The relay 31 has an additional member which operates either to close a circuit, 35 through the motor for operating the traverse of the work or to close a circuit 34 for braking said motor. In Fig. 3, a balancer set comprising a motor 36 and a generator 38 is provided, as described in Specification 133,439, so that the voltage in the welding circuit will vary inversely with the current. If desired, the set may be replaced by a single machine as described in Specification 159,374. When the button 13 is closed, the protective relay 43 is energized and closes the contacts 43a. 43<b> with a consequent closure of the switch 10 and contacts 11<c>, 11<d>, and the motor armature and field circuits. The motor feeds the electrode and when it touches the work the relay 43 is de-energized and closes contacts 43<c>, 43<d> to energize coils 44, 45 and reverses the motor to retract the electrode. In a modification, instead of the lead 53 being connected to the coil 11 it is connected to a contact engaged by the bridging-member 11<c>. Also, instead of the terminals of relays 44, 45 being connected to the lead 51 they are connected to a contact engaged by the bridging-member 11f. These modification prevent fluttering of the protective relay if the operator inadvertently shorts the electrode and the work by some conducting implement on the machine. Specification 139,919 is also referred to.