| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively obtain the long size hollow bar steel with high dimen sional precision, small diameter and thick wall by making the bar steel a hollow base stock satisfying a specific formula after piercing the bar steel by a pierce, and adding diameter contracting working and thick wall satisfying a specific formula after inserting a mandrel into the hollow base stock. SOLUTION: By heating the bar steel to a prescribed temperature, and by making the bar steel the hollow base stock satisfying the formula I after piercing the bar steel by the piercer. After inserting the mandrel into this hollow base stock, the diameter contracting working and the thick wall working satisfying the formula II are added by a skew rolling mill with three rolls. Rt=(t0 -t1 )×t0×100 where t0 : Wall thickness of the hollow base stock t1 : Wall thickness of the hollow base stock after rolling Rt: Reduction of area of wall thickness Rd=(d0 -d1 )/d0×100 where Rd: Outside diameter contracting ratio d0 : Outside diameter of the hollow base stock d1 : Outside diameter of the hollow base stock after rolling.
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