| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a small diameter welded tube with high production efficiency by forming the small diameter welded tube cylindrical with high accuracy in a non-lubricated manner using a large diameter roll stand in which rolls having diameters obviously larger than an external diameter of a tube to be formed are arranged.SOLUTION: A roll stand includes four rolls as one set, the four rolls being arranged on the right, left, top and bottom of the roll stand. The four rolls comprise: a pair of large diameter side rolls each of which is designed in such a manner that an external diameter ratio &phgr;/&phgr;of an external diameter &phgr;of a forming roll to an external diameter &phgr;of a tube to be formed is 10 or more; a bottom roll which is disposed in a lower side between the pair of large diameter side rolls; and an upper roll which is disposed in an upper side between the large diameter side rolls, the four rolls being arranged in a four-way roll format. With the use of the roll stand, a metal band is passed through the roll stand that is a single stand to be thereby formed cylindrical, then an abutted portion of the metal band edge is welded and joined. |
