PRODUCTION OF SPIRAL STEEL PIPE

摘要

PURPOSE:To obtain an intact weld zone having a uniform bead shape by providing a coil near the weld zone to generate a shifting magnetic field, and applying the thrust in the direction opposite from the outflow direction of a molten metal on said metal that flows downward as a pipe inclines in its position according to its rotation. CONSTITUTION:A welding position 15 where a steel hoop 7 and a spiral pipe 14' contact with each other is internally welded by a welding torch and a shifting magnetic field heading toward the rotating direction (b) of the pipe is generated from a magnetic field coil L attached near a molten metal 22. As a result, the thrust in a direction F is acted on the molten metal 22 moving diagonally upward according to the rotation of the pipe and the outflow of the metal 22 going to flow downward by its own weight is prevented by such thrust. An electromagnetic stirring effect by the shifting magnetic field is generated in the metal 22 in this stage. The formation of a recess in the weld bead of the spiral steel pipe is thus averted and the intact weld zone is obtd.