GB1449674A - - Google Patents

Abstract

1449674 Welding by fusion CLARKE CHAPMAN Ltd 19 April 1974 [24 March 1973] 14304/73 Heading B3R In internal non-consumable electrode, filler wire, arc welding of a tube or tubular stub to a tube plate or tubular stub extending from (e.g. brazed, friction welded or diffusion bonded to or formed from) a plate, two or more equiangularly spaced non-consumable electrodes are moved together relatively to a workpiece so that each electrode effects a weld or welds along an arcuate path of less than 360 degrees extent but sufficient to overlap the path of its preceding neighbour. In the tubular stub/plate TIG welding shown, a head 20 extending through a stub 14 rotatably carries two diametrically opposed non-consumable electrodes 22. Electrode rotation about an angle slightly more than 180 degrees is effected by drive means (not shown) at the upper end of the head. Welding current is fed to the electrodes through a conductor 24. Shielding gas and cooling water are fed to the vicinity of the electrodes respectively through a conduit 26 and further conduits (not shown) within the head. A head locating clamp 30 engages the stub bore and/or, as shown, a bore 12 of a plate 10. The stub is held in position on the plate by a clamp 48 which comprises a two part body, is secured to the plate by means not shown, and is tightenable on to the stub by a flexible steel band 46 acted on by a screw (42, Fig. 2, not shown). The clamp body also provides an enclosure for inert backing gas fed through a conduit 50. In Fig. 3 (not shown), the head is extended through the plate and clamp located in a tube and/or in the plate. In operation, initially two tack welds may be made, with the electrode stationary, and after checking stub/plate alignment the complete welding effected. The electrodes may be adapted for plasma arc welding and both constant and pulsed welding current may be used. TIG welding preferably includes arc length control. The electrodes are preferably variably disposed at angles within Π60 degrees with respect to the plane of the joint. The drive means may produce intermittent electrode movement. Welding current may be varied at starting and finishing, and, if desired, and if a series of overlapping welds is required, as by pulsing during the arcuate movement to effect intermittent welds either with uniform or intermittent movement. Preferably, welding current is controlled in respect of materials welded and weld penetration and profile, by feedback means based on frequency and/or slope of current pulses and current on/off ratios. The stub engaging surface of the plate may be a layer applied by explosion welding, roll cladding or weld deposition. The stub may be a transition piece of material suitable for welding to plates and tubes of different materials.