To increase a seam welding speed of UOE steel tube and to improve quality by energizing a coil surrounding a welding tip of multi-electrodes, forming magnetic field and magnetically agitating molten metal.
A magnetic field is produced between a steel made outer shell 1 and a steel made inner shell 2 by causing alternating current flow to a coil 3 wound with an enamel copper wire from an alternating magnetic field power source 11. Because an enamel copper wire is wound in the circumferential direction of welding electrodes 12-15, the alternating magnetic field in the axial direction for welding current is generated. Welding arcs 22-25 are generated through the welding electrodes 12-15 from the welding power source while covering between a welding wire and base metal with a flux for submerged arc welding. The welding current is caused to flow in parallel and radial direction with a base metal face through a molten pool 26 and is roughly intersected in perpendicular with the alternating current, by causing a rotating force to the molten pool 26 due to the Fleming' left hand rule, molten metal is agitated.
TERADA YOSHIO
SUMIMOTO DAIGO
