| 摘要 |
PURPOSE:To reduce the length of a thick wall-thickness part at the end of a pipe by welding the pipe end before or after the reheating which is performed afte the 1st drawing and providing a tension to the pipe at the time drawing, in rolling a hollow blank pipe into a small diametral seamless steel pipe by a stretch reducer. CONSTITUTION:A hollow seamless steel blank pipe is manufactured by a plug mill and a mandrel mill, and successively the blank pipe is drawn plural times into a small diametral seamless steel pipe by a stretch reducer. In performing the 2nd drawing by heating the blank pipe by a reheating furnace after performing the 1st drawing by the stretch reducer; the radially reducing rolling is performed by controlling the number of revolutions of a stand so as to produce a tension larger than the tension produced at the time of rolling normal part excepting a welded part, when the end part of pipe is welded and is passed through rolling rolls before the pipe is charged into the reheating furnace or after it is discharged from the furnace. Thus the length of the thick wall-thickness part at the joining part is remarkably reduced, and a small diametral seamless steel pipe is manufactured in an excellent yield. |
