PURPOSE: To enable the reuse of a mandrel bar by replacing a part of sleeves when repair is necessary because plural sleeves are fitted on the body part of a mandrel bar.
CONSTITUTION: The mandrel bar 1 is made into a long bar shape and armored with the sleeves 2. The tip of the mandrel bar 1 on a side where a material to be rolled is fit and removed is formed into a pointed cone 3. A small diameter part is continued so that a stepped part 4 is formed succeeding to the cone 3 and a gripping part 6 whose diameter is reduced by tapering is provided in the rear end part on the opposite side of the tip part to add axial force to the mandrel bar 1. The rear end part is a tapped sleeve 7 having an external thread, fit to the internal thread provided in the rear end part of the mandrel bar 1 and all the sleeves are tightened between itself and the stepped part which is formed in the vicinity of the tip of the mandrel bar 1. In this way, by replacing a part of the sleeves, the mandrel bar is reused and approximately permanently usable.
HIRASAWA TAKESHI
YASUKAWA MASAYUKI
IKUI KENJI
SOTANI YASUHIRO
