| 摘要 |
PURPOSE:To reduce the thickness of the end part of a pipe uniformly in a circumferential direction without complicating screw down mechanism and control in making the pipe by way of piercing, elongating, and reducing stages, by reducing the thickness of the end part the pipe by using special grooves rolls. CONSTITUTION:The 1st, 2nd stands of rolls 30 which have a caliber shape changing in a circumferential direction and of which the rolling reduction by the caliber changes with revolution and similar rolls 30 which are changed in configuration by 90 deg. are disposed in the rear stage of the mandrel mill of, for example, 8 stands. A pipe material 16 subjected to ordinary thickness reducing and stretch deformation is first finished to the thickness decreasing toward its leading end by the half revolution of the rolls of the 1st stand, and is reduced of the wall thickness in the direction 90 deg. from the previous one with the roll of the 2nd stand. Thereby, the pipe material is finished to the pipe of the thickness decreasing toward the leading end without deviation in thickness in the circumferential direction of an arbitrary section in the longitudinal direction. Upon completion of forming of the leading end part, the rolls of the respective stands are stopped of revolution in the parts where the caliber diameters are largest, and the central part of the material is passed idly without contact with the respective roll. On progression of the rolling, the trailing end part of the pipe is controlled of wall thickness in the same manner as mentioned above. |
