Method for producing ultrathin-wall seamless metal tube by cold rolling method

A method for producing an ultrathin-wall seamless metal tube by a cold rolling method in which employed is a cold pilger mill of mechatronics drive type that includes:

• an electric control system to control a reciprocating movement of a roll stand and a shell drive of a tube material;
• and a mechanism to give a feed and a turn angle to the tube material immediately before the start of a forward stroke and immediately before the start of a backward stroke, the method comprising:
• utilizing a roll having a groove whose diameter gradually increases, remains constant, or gradually decreases from an engaging entry side to a finishing exit side of a pair of rolls, and a tapered mandrel whose diameter similarly gradually increases from the engaging entry side to the finishing exit side;
• and
• giving a turn angle and a feed to the tube material immediately before the start of a forward stroke, and also giving a shell drive to the tube material immediately before the start of a backward stroke so as to elongate the tube material by reducing a wall thickness while expanding a mid-wall diameter which is an average diameter of an outer diameter and an inner diameter of the tube material.