| 摘要 |
PURPOSE:To obtain freely a pipe provided with either a position residual moment or a negative one, by making several of subholding rolls act on the pipe regardless of a system having rolls for holding the pipe from its inside and outside surfaces. CONSTITUTION:At the initial stage of forming, rolling reductions of bending rolls 1, 2, and 3 arranged in three rows are determined so as to make a pipe obtain a positive residual moment, and then, a prescribed outer peripheral value is obtained by forming and welding the pipe of at least >=1 wind by providing, as a guide, rolls 4' for holding the pipe from its outside surface. Then, subrolls 7', at least >=1 roll, for holding the pipe from its inside surface, (usually 1-4 rolls in the axial direction of pipe) are arranged at the positions, where the rolls 7' contact with the inside pipe-surface at the upper part of it, to prevent the pipe after changing the rolling reduction from dropping downward. Thus a steel pipe having a desired negative residual moment is manufactured by changing the rolling redution (usually the rolling reduction is made larger) to provide the negative rolling reduction to the pipe. |
