| 摘要 |
PURPOSE:To manufacture the seamless metallic pipe with a large stretch ratio, by passing the work through the caliber formed by the first couple of rolls and the second couple of rolls whose axis is laid behind the first rolls so as to rotate perpendicularly to the first rolls, and by piercing this work with the conical plug. CONSTITUTION:At first, the work W is formed into an ellipse by the piercing rolls 3, 3', of the first couple of rolls 3a; after that, the piercing for the axial zone of the work W is commenced with the conical plug 7 whose diameter gradually increases toward the exit side of the piercing machine. After the plug 7 passes over the center line A-A of the couple of rolls 3a, the caliber 5 is gradually parted from the pass line in order to gradually expand the inner surface of the work W to bulge out. Next, the work W is rolled by the piercing rolls 4, 4', of the second couple of rolls 4a in the direction perpendicular to that of the rolls 3, 3'. Hereupon, the center line B-B of the rolls 4, 4', is shifted in a distance (m) backward from the center line A- A; hereby, the contact area of the roll on the exit side of the rolls 3, 3', is further increased so that a large onward force is impressed on the work W. As a result, the greatly stretched seamless metallic pipe free from the bite-out flaws can be manufactured. |
