PURPOSE: To prevent defects of an outer surface and miss roll and to improve the quality and yield by limiting heating temp. of a solid billet and the surface temp. of the solid billet at an inlet side of a roll and by setting a tilt angle of the rolls and a crossing angle of the rolls based on an inequality to piece and to roll.
CONSTITUTION: A two rolls skew rolling type piercing mill is used and the heating temp. of the solid billet of a titanium or titanium alloy is set 800W1200°C and the surface temp. of the solid billet at the inlet side of the rolls before biting is regulated to ≥700°C. Then, the tilt angle β between rolls 11, 11' and the cross angle γ of the rolls 11, 11' are set to satisfy the inequality, the solid billet is piercing rolled. In this way, without generating flaws on inner and outer surfaces of a hollow piece, the piercing rolling is performed without causing a faulty biting to the rolls and faulty passing through of the rolled stock.
KURODA ATSUHIKO
KAWABATA HIROKI
HAYASHI CHIHIRO
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