| 摘要 |
PURPOSE:To produce a seamless pipe which has less surface defects such as chatter mark or the like easily by piercing, expanding or drawing a material to be rolled by using a plug which is split into plurality in the axial centerline direction and of which the split parts are formed rotatable independently from each other. CONSTITUTION:A plug 3 which is formed of a rolling part 31 of an approximately circular truncated cone shape having a round forward end part, a reeling part 32 of an approximately circular truncated cone shape continuous with said part and a relief part 33 having a reduced base part continuous with said part is divided to a part 34 on the forward end side and a part 35 on a base end side, and both parts are constituted rotatably independently around the respective axial centerlines and are connected pivotally to a mandrel M in a skew rolling mill which produces a seamless pipe by penetrating the above-mentioned plug 3 into the central part of a round steel billet B, which is a material to be rolled, while moving the same progressively in an arrow direction by means of a pair of rolling rolls 1l, 1r each provided with a gorge part 11 having a max. diameter, and an inlet surface 12 assuming a circular truncated cone shape and an outlet surface 13 on both sides thereof, thereby piercing a hole in the billet 2 and forming a hollow shell H. |
