Patent ID: 7757528
Filing Date: 2010-07-20
Classification: B21B

Abstract:
1. A method of manufacturing a seamless pipe or tube by piercing and rolling a billet using a piercing mill comprising a pusher provided on an inlet side along a pass line, a plug provided on an outlet side along the pass line, and a plurality of inclined rolls provided opposed to one another with the plug therebetween, said method comprising the steps of: placing said billet on the pass line between said pusher and said plug; advancing said billet to be caught between said plurality of inclined rolls; and pushing said billet forward by said pusher so that at least between when said caught billet contacts said plug and when the piercing and rolling reaches a steady state, a advancing speed of said billet is at least equal to the advancing speed of said billet when the piercing and rolling is carried out without pushing said billet forward by said pusher in the steady state, and further comprising the step of setting the position of said inclined rolls before the piercing and rolling so that Expressions (1) and (2) are satisfied, where Dg is a roll diameter (mm) of a gorge part of said inclined roll, d is a outer diameter (mm) of said billet, DFT is a gorge draft ratio, and EL is a piercing and roiling ratio in Expression (2), and said ratios are defined by Expressions (3) and (4): where Rg is a roll interval (mm) that is minimized at the gorge part, L 0 is a length (mm) of said billet, and L 1 is a length (mm) of a hollow shell after piercing.