| 摘要 |
PURPOSE:To manufacture thick steel tubes at high yield and at high efficiency by making reducing work that does not involve thinning in rolls of stands of upstream side, and making skin pass work that involves thinning and reducing work in downstream side. CONSTITUTION:When a mandrel bar 2 is inserted in the inner face of a crude tube 1 and rolled by caliber rolls 31a-36a of upstream side roll stands 31-36, the mandrel bar 2 does not restricts inner diameter of the crude tube 1. Accordingly, inner diameter of the crude tube is reduced corresponding to reduction of outer diameter, and thinning work is not carried out. When rolling is advanced further, and the crude tube 1 is rolled by caliber rolls 37a, 38a of downstream side roll stands 37, 38, the mandrel bar 2 restricts inner diameter of the crude tube 1. Accordingly, thinning work is made corresponding to reduction of outer diameter. |
