US Patent 7757528 Method of manufacturing seamless pipe or tube

A billet is provided on a pass line between a pusher and a plug, and the billet is advanced and caught between a plurality of inclined rolls. At least between when said caught billet contacts said plug and when the piercing and rolling reaches a steady state, the advancing speed of the billet is not less than the advancing speed of the billet when the piercing and rolling is carried out without pushing the billet forward by the pusher in the steady state. By this manufacturing method, inner surface defects at a tip end of a hollow shell can be restrained.