PURPOSE: To prevent the generation of bad biting, bad running-out and the rupture of hollow by satisfying a specified relation by the wall thickness on the inlet side of hollow tube stock of a material to be rolled, wall thickness on the outlet side of tube, total rolling reduction, wall thickness at the gorge part and the rolling reduction of wall thickness to the gorge part.
CONSTITUTION: The wall thickness on the inlet side of the hollow tube stock 32A at the formeost starting point of rolling where the material to be rolled starts to contact with a plug 34 is expressed by ti, the wall thickness on the outlet side of tube 32B at the completing point of rolling where the material to be rolled reaches the reeling part of the plug 34 by to, the total rolling reduction Δt (=ti-to) of the material to be rolled, the gorge-part wall thickness of the material to be rolled at the gorge part of roll by tg and the rolling reduction of wall thickness of the material to be rolled to the gorge part by Δtg (=ti-tg). Rolling is executed so that 0.15Δt≤Δtg≤-0.7Δt is satisfied. In this way, a highly expanded tube is manufactured without hindering yield and productivity.
SHIMIZU TETSUO
TOYOOKA TAKAAKI
