GB1502288A - Method and an apparatus for automatic electric welding - Google Patents

Abstract

1502288 Welding by fusion AKADEMIET FOR DE TEKNISKE VIDENSKABER SVEJSECENTRALEN 21 Feb 1975 [25 Feb 1974] 7345/75 Heading B3R [Also in Division G3] In electric fusion welding wherein at least two electrodes, each series connected with a common workpiece, are mounted in a common holder manually or mechanically movable in relation to a workpiece and at least one of said electrode is consumable and mechanically fed to the arc zone, said electrodes are mounted and fed at a relative angle of between 0 and 180 degrees such that they meet at a point of intersection where electrode melting occurs. On protrusion of one electrode beyond another, said one electrode carries total current and consequently melts away to maintain the melting ends of the electrodes at fixed positions, this arrangement enabling maintenance or control of the electrode/workpiece distance as desired independently of variations in the position of the molten pool surface. The invention is applicable to open, gas-shielded (with A or CO 2 ), plasma or electrogas arc welding or electroslag welding, to the use of solid or cored, coated, flux-filled or bare, or wire or strip electrodes of the same or mixed types and dimensions, and to butt, corner and fillet welding or surfacing by weld metal. Third and fourth electrodes need not be coplanar with two first electrodes. The electrode/workpiece inclination may be 0-90 degrees and the inclination of the electrodes to the electrodes/workpiece traverse direction may be 0-180 degrees, e.g. 90 degrees. An electrode holder carriage may engage a workpiece surface or a separate rail. Electrode feed devices may be rigid with or separate from the holder and may be hydraulic, pneumatic or, as shown, electric, the latter using separate current supplies or tappings from welding power sources. Welding power sources may be D.C. or A.C. with drooping current-voltage, constant potential or constant current, and may be separate or tapped for each electrode. Feedback control, e.g. electrode/workpiece potential responsive, may control feed rate, power, electrode holder/workpiece traverse speed or distance, or amount of weaving movement. As shown, two consumable electrodes 1, 2 mounted in a common holder 3 are energized by power sources 15, 16, and potential between the electrodes is measured by a device 14 connected to a feedback control device 13 in turn connected to the power sources and, via the latter, electrode feed motors 17, 18. The feedback control acts on electrode feed (either to vary same or to start stepping motors), welding current intensity, or, for constant level filling, holder/workpiece traverse, to maintain interelectrode potential at a preset value, which is less than 10% of arc voltage, variation from said value arising from variation of electrode/ workpiece potential and such control ensuring additional maintenance of the melting of the electrodes at the point of intersection. In two similar arrangements, one of the two electrodes functions as a measuring electrode: in Fig. 3 (not shown), one of the two consumable electrodes is very thin and melted with a low current and feed rate so that it only contributes less than 10% of the total melt, and in Fig. 4 (not shown), one of the two electrodes is non-consumable, e.g. metal-ceramic. In a further embodiment, one of the electrodes is supplied with a current higher, e.g. 25%, than that to the remaining electrodes to ensure additional maintenance of the melting of the electrodes at the intersection point.