Patent ID: 7188501

Claim:
A cold rolling process for metal tubes in which the cold rolling process by pilger rolling that employs a pair of roll-dies with a roll caliber comprising a roll caliber diameter Dx and a side relief amount Fx and holds a mandrel between each of said roll-dies is applied as a final finishing process: wherein a side relief rate SR of said roll-dies expressed by the equation [1] as below is set in the range of 0.5 to 1.5%; wherein said mandrel is configured in such a way that a taper θ 1 in the primary deformation zone of said mandrel is set to 0.25 degree or less, and a taper θ 2 in the final size reduction zone of said mandrel is set to 0.1 degree or less; and wherein a feed rate F (per one pass) of a workpiece material is set in the range of 1.0 to 2.5 mm, the relationship between the side relief SR and the feed rate F expressed by the equation [2] as below being satisfied: SR (%)={(2 ×Fx )/(2 ×Fx+Dx )}×100 [1] F≦ 3.0 −SR [2].