GB639421A - Improvements relating to electrode feed control apparatus - Google Patents

Abstract

639,421. Automatic arc control systems. ENGLISH ELECTRIC CO., Ltd., and BARLOW, K. F. Sept. 5, 1947, No. 24481. [Class 38 (iv)] An A.C. arc welding electrode is fed by a single phase commutator motor, the armature of which is supplied by the resultant of a voltage proportional to arc voltage and a reference voltage of opposite phase, whereby any deviation of arc length from a predetermined value varies the speed of.the motor in a sense tending to correct the deviation. The arc is supplied by one phase a<4>, n, of the interstar connected secondary of a multi-operator welding transformer 2, Fig. 2; and is started by closing contacts 3, Fig. 1, which close contactor 4 to energize the electrode 1; to energize the primary 7a of a transformer, the secondary 7b of which supplies both the field 10a and the armature 10 of .the electrode feed motor; and to energize a highfrequency generator 12 which initiates the arc. When the arc strikes, a current transformer 13 energizes a relay 15 which closes hold-in contacts 15a, and closes contacts 15b to energize a relay 8. This closes contacts 8c connecting a voltage transformer 16 across the arc; changes over contacts 8a connecting the field of the feed motor to transformer winding 7c; and changes over contacts 8b connecting the feed motor armature to one end of the secondary of the arc voltage transformer 16. This winding is in series with a reference voltage 180 degrees out of phase with the induced voltage and of such magnitude that when the arc voltage is normal, the resultant voltage applied to the motor armature feeds the electrode at the normal burning speed. If the arc shortens, the voltage induced in the secondary of transformer 16 falls and hence the resultant voltage, applied to the motor falls, and vice-versa. If the arc becomes so short that its voltage falls below the reference voltage, the motor will reverse and retract the electrode. The reference voltage is the resultant of two components, Fig. 3 (not shown), one obtained from terminals n, c<4>, of transformer 2 and injected into the secondary circuit of transformer 21, the other obtained from terminals a4, b<4>, of transformer 2 and applied to the primary of transformer 21. The resultant voltage is amplified by autotransformer 20 and the reference voltage obtained is applied through a series resonant circuit 18, 19 (to reduce harmonics due to the distorted wave form of transformer 16), to the secondary of transformer 16. An overcurrent relay 28 protects the feed motor by contacts 28a in series with the " stop " button 25. If the arc goes out of its own accord the full supply voltage is applied to transformer 16, choke 18 is therefore made saturable to protect the feed motor; and since contacts 8a, 8c, would have to break abnormally high currents a contact 8a maintains relay 8 energized until contactor 4 drops out. In a modification, Fig. 6 (not shown), the welding current is supplied by a single phase transformer connected across two lines of a 3-phase supply, and auto-transformer 20 is supplied by two separate transformers having their secondary windings connected in series, and their primary windings connected to the 3-phase supply to form a mesh connection with the welding supply transformer.