| 摘要 |
A method and apparatus for piercing a seamless metal pipe, by which a hollow pipe having a high quality and having no surface scratches is produced without causing any trouble during the piercing at a pipe expansion ratio of more than 1.15. Piercing is characteristically carried out at a pipe expansion ratio of more than 1.15 using a piercer equipped with a cone type main roll and a disc roll under the following condition, 3 </= D1/d </= 7 (1), 9 </= D2/d </= 16 (2), 2 < D2/D1 </= 3 (3), 2.5 DEG </= theta 1 </= 4.5 DEG (4), 3 DEG </= theta 2 </= 6.5 DEG (5), where D1 is the diameter of gauge of the main roll, D2 is the diameter of groove bottom of the disc roll, d is the outer diameter of a billet, theta 1 is the inlet surface angle of the main roll, and theta 2 is the outlet surface angle of the main roll. The apparatus of the present invention is characterized in that D1 is in a range of 510 to 2,000 mm and D2 is in a range of 1,530 to 4,000 mm, satisfying the inequalities (3) to (5). Piercing can be carried out without causing misrolling such as roll-in and tail-off and without producing any flaws in both inner and outer surfaces of the hollow pipe. Further, the larger outer diameter of the bottom portion of the hollow pipe, which is a problem at the elongating process of the succeeding stage, can be prevented.
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