Patent ID: 7197906

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 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 1.0%, and wherein in relation to a pass schedule, an Area Rd expressed by the equation [2] as below is set in the range of 70 to 90%, an ID (inside diameter) Rd expressed by the equation [3] as below is set in the range of 25 to 40%, and a feed rate F (per one pass) of a workpiece material is set in the range of 1.0 to 3.0 mm: SR (%)={(2 ×Fx )/(2 ×Fx+Dx )}×100 [1] Area Rd (%)={1−(Section Area After Rolling/Section Area Before Rolling)}×100 [2] ID Rd (%)={1−( ID After Rolling/ ID Before Rolling)}×100 [3].