Method and apparatus for arc welding of metal plates from one side only

In electric arc welding apparatus for depositing weld metal in the horizontally extending gap between a pair of workpieces wherein the bottom of the gap is bridged by a back-up plate having an upwardly facing surface, said apparatus including first and second welding heads supported for simultaneous tandem movement parallel to said gap, said heads including:

• means for feeding in tandem a first leading and a second trailing consumable electrode downwardly on first and second predetermined lines of movement;
• and, first and second electrode contact means associated with the first and second electrodes respectively;
• first and second power leads from said first and second contact means respectively, each adapted to be connected to a separate terminal of an arc welding power source whereby there will be a series arc between said electrodes;
• the improvement which comprises:
• means fixing said heads relative to each other so that said tandem lines of movement intersect at a point aligned with said gap and above said upwardly facing surface of said back-up plate and at a distance of at least 1/8 inch above the lower surfaces of the workpieces;
• and, a third substantially zero impedance power lead effectively connecting said workpieces to one of said contact means whereby said contact means will be at substantially workpiece potential and a substantial portion of the welding current flowing through the other of said contact means will flow through said third power lead.