| 摘要 |
PURPOSE:To positively reduce flange thickness and to prevent generation of defects in a 2nd stand by using rolls having a caliber whose circular curved face corresponding to a target sectional shape occupies a large proportion in a 1st stand. CONSTITUTION:In a mandrel mill installed along the rolling line for seamless steel tubes, rolls 1a, 1b having a caliber whose peripheral face has a central angle of 65-80 deg. are assembled in a 1st stand. Recessed parts 2a, 2b having a curvature corresponding to a target section are formed on the rolls 1a, 1b; the recessed parts 2a, 2b are formed to have peripheral shapes consisting of circular curved faces 4a, 4b spreading by a central angle theta in the axial direction and having their central points 3a, 3b agreeing to the axial direction center of the rolls 1a, 1b and escape faces 5a, 5b, respectively. The width of grooved bottom parts whose thickness is reduced are increased along the peripheral direction of a tube stock. Thus, draft for the stock in a 2nd stand is reduced and thin wall parts are avoidable from being loaded by excessive tensions. |
