| 摘要 |
PURPOSE:To obtain a seamless steel pipe excellent in inner surface properties as well as to lengthen the service life of a plug and to improve operating efficiency by directly cooling and/or lubricating the contacting surface of the inner surface of a pipe stock to be rolled and the outer surface of a plug. CONSTITUTION:The 2nd piercing is performed by feeding a pipe stock 1 to be rolled to rotating rolls 2, and inserting a conical plug 4 on which a mandrel 3 having a pierced water introducing hole 11 is mounted into the pipe stock 1. At that time, the plug 4 consists of a plug main body 5 and a nozzle 6 provided to the front end of body 5 for spraying cooling water and/or a lubricant 12, and the spraying port 9 of nozzle 6 is provided to the position equivalent to the vertex of an imaginary circular cone of the outer peripheral surface of body 5. In company with the start-up of the 2nd piercing, the cooling water 12, etc. flows from the port 9 along the conically-spreading outer-peripheral surface of plug 4, to be supplied to the contacting surface of the inner surface of pipe stock 1 and the outer surface of plug 4. In this way, a seamless steel pipe free from inner surface flaws is obtained. |
