| 摘要 |
PURPOSE:To prevent the biting of a scale between a plug and blank pipe and to improve the quality by rolling with extension the roll and plug having the outer peripheral face part in parallel to a pass line with moving in the same direction as the progressing direction of a hollow blank pipe. CONSTITUTION:A plug 2 is moved to the progressing direction of a hollow blank pipe P from the position advancing it so that at least one part of the parallel face part 2a of the plug 2 may be superposed on the parallel part 1a of a roll 1. By this method, the gap between the roll 1 and plug 2 is not varied, so the biting of scales is prevented and the inner face quality can be improved.
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