| 摘要 |
PURPOSE:To make a tack welding operation simple and efficient by previously cutting the end face of blank material so that a part of tack welding line of the face provided with a butt welding edge of the end faces in the longitudinal direction of the unit semiformed blank material is formed into a projecting shape with respect to the transferring direction of a steel pipe. CONSTITUTION:A unit semiformed blank material 13 having the cross section formed nearly into a square steel pipe is transferred in its longitudinal direction and the side edges in the longitudinal direction of the material 13 are butt welded to each other by the contactors 32 of a high-frequency welder through forming rolls 4 and squeezing rolls 31 after providing a tack welding to the front and rear end-faces 22 of material 13 to join the materials 13 in one body. At that time, as for the joining part of material 13, a notched part 25-1 is previously formed at the rear end-face provided with a butt welding edge of the preceding material 13, and also a projected part 25-2 is formed at the front end-face of the succeeding material 13 corresponding to the former to relax a clamping force acting on the tack welding part. In this way, the tack welding operation of the joining part can be remarkably cut down, and a breakage trouble of this part is prevented. |
