| 摘要 |
PURPOSE:To control the causing of a flaw on an inner surface and to easily perform a piercing roll by piercing rolling a top end part of a columnar metallic material under high friction force, and after the time of completing biting, piercing rolling under low friction force. CONSTITUTION:An angle of inclination and a distance between rolls are set in low levels respectively, and a round billet 14 is fed between the rolls 1 and 1'. When the piercing rolling is initiated, the top end draft rate is large and the angle of inclination is small, consequently, the top end of the billet 14 is surely and stably bitten to form a seamless hollow bland pipe 15. Then, when the top end position of the hollow bland material 15 is reached a base end of a plug 2, the angle of inclination and the distance between rolls are changed in the high level setting respectively. In this state, the top end draft rate is reduced at the position where the billet 14 is pierced by the plug 2 and the angle of inclination is enlarged. The billet 14 once bitten is easily bitten succerssively to form the hollow blank pipe 15 free from the flaw in the inner surface and possessed of high quality. |
