GB1245589A - Improvements in welding apparatus - Google Patents

Abstract

1,245,589. Control of D.C. motors. LINCOLN ELECTRIC CO. Ltd. 15 April, 1969 [18 April, 1968], No. 18423/68. Heading H2J. [Also in Divisions B3 and G3] In consumable electrode arc-welding, wherein electrode wire is moved towards and away from a workpiece, at 2, by an electric motor 5 responsive to the difference in output voltages respectively of a main welding current source 1 and a control current generator 4 so as to provide a self-adjusting arc, the main source 1 provides rectified D.C. from A.C. input, the polarity of current supplied by the generator 4 to the motor 5 is determined by a relay 11 responsive to potential difference across 2, and a starting source 3, in parallel with the main source, is arranged to heat but not melt the wire and to be rendered inoperative when the main source is operative. In operation, the main and starting sources and an auxiliary supply 13 are switched on and the armature of the generator 4 set in motion. A triple pole selector switch 8 connects the starting source 3 across 2, the auxiliary supply 13 across a starting switch 20 and its holding contacts 22, and the armature winding of the generator 4 in series with that of the motor 5 across 2, the latter circuit being initially broken by initially open contacts 9, 10. The polarity relay 11, sensing the potential difference across 2, (i) changes over contacts 6, 7 between the generator 4 and the motor 5 so that the latter is so driven that the wire is moved towards the workpiece, and (ii) changes over a contact 24 so as to connect the field winding of the generator 4 across the auxiliary supply via a variable resistor 18 and a rheostat 19. When the wire touches the workpiece, the polarity relay 11 is de-energized to revert the contacts 6, 7, 24 and the short circuit current from the starting source heats the wire to just below melting point. The starting switch 20 (e.g. push-button) is then actuated to energize a main relay 16 actuating (i) holding contacts 22, (ii) contacts 25 to connect the main source 1 across 2, (iii) contacts 15 to connect the field winding of generator 4 in series with a rheostat 17, and (iv) contacts 23, operative as the main source current increases, to disconnect the starting source 3 from 2. The starting switch 20 also actuates an auxiliary relay 21 which closes contacts 9, 10 to connect the armature windings of the generator 4 and the motor 5 in series across 2, the current determined by the contacts 6, 7 being such as to lift the wire, in opposition to the current of the main source 1 which tends to move the wire towards the workpiece. The auxiliary relay 21 also opens a contact 12 so that the polarity relay is not operative once the main source supplies current to 2. The generator 4 is so designed that its output current rises more rapidly, once switched on, than the output current of the main source 1, so that the wire is initially lifted to establish the arc. The main and starting sources and the auxiliary supply 13 all provide rectified D.C. from A.C.