| 摘要 |
PURPOSE:To form sound weld beads free from lack of penetration and cracks in welding a narrow groove by AC welding by providing a preheating plasma torch ahead in the welding advance direction of a welding torch and preheating the groove. CONSTITUTION:In the stage of welding the narrow groove 3 of base materials 1, 1 with an AC welding torch 4, a preheating plasma arc torch 7 is provided <=30cm ahead of the torch, and while the groove 3 is preheated with a plasma arc 8, the groove is welded with the torch 4. Alternating magnetic fields 6 which are in parallel with the surfaces of the base materials and are roughly vertical to the groove line direction are formed around the torch 4. The plasma arc 8 of the torch 7 is deflected alternately back and forth along the groove 3 by the effect of such alternating magnetic fields to provide a spreading of length l, and since the groove can be heated without melt-down of the groove, the beads 2 by the subsequent AC welding are kept free from lack of penetration and cracking. |
