Patent ID: 8020421

Claim:
A pusher device for piercing and rolling provided on the inlet side of a piercing mill piercing and rolling a billet, comprising: a cylinder device including a cylinder shaft; and a rod shaped pusher mandrel attached at a tip end of said cylinder shaft and having its tip end abutted against the rear end of said billet, the cross sectional area Sp of said pusher mandrel and the cross sectional area Sb of said billet satisfying Expression (1), the length Lp of said pusher mandrel and the cross sectional area Sp of said pusher mandrel satisfying Expression (2), the moving distance Lc of the tip end of said cylinder shaft during piercing and rolling and the outer diameter Dc of said cylinder shaft satisfying Expression (3). 0.3≦ Sp/Sb (1) Lp/Sp≦ 1.2 (2) Lc/Dc≦ 45 (3)