| 摘要 |
PURPOSE:To prevent thickness deviation on the shell inside surface by bringing the total periphery of the inside surface of a hollow tube stock into contact with a mandrel bar at an intermediate stand, rolling the stock with a local part in the periphery of the stock formed into a thickness-walled part, and rolling the thick-walled part in a succeeding stand. CONSTITUTION:A thick-walled part 11a is formed on a hollow tube stock 11 whose thickness and outside diameter are largely reduced in an upstream stand of a mandrel mill by influence of a roll gap part 5b in the outlet side of a No.4 stand. The thick-walled part 11a abuts on a grooved part 5a formed at the central part of the groove bottom of a grooved roll 5A of a No.5 stand, so that other parts of the stock 11 are uniformly rolled down by the grooved roll and the periphery of the inside surface is rolled to get closely and totally contact with a mandrel bar 4. Then, the thick-walled part 11a abuts on the roll gap 5b, is not screwed down, and is further locally thickened in a No.6 stand because a grooved roll 5 of the No.6 stand is oriented to till by 90 deg. to the No.5 stand. Only the thick-walled part 11a is locally rolled in a No.7 stand. |
