ROLLING METHOD OF SEAMLESS STEEL PIPE

摘要

PURPOSE:To prevent generation of the flaw caused by the scale on the inside surface of a steel pipe in a rolling method of a hollow blank pipe by a roll piercing method by feeding fluid through the inside of a mandrel supporting a plug from the ejecting holes provided to the plug. CONSTITUTION:A hollow shell M1 is axially fed between a set of skew rolls 1 and both guide shoes 7 of the 2nd piercer of, for example, a Mannesmann plug mill system. A plug 2 is disposed in the direction opposite from the advancing direction of a blank pipe and rolling is performed by regulating the position of the inside surface of the shell M1 during passage through the rolls 1. Cooling water or lubricating fluid is fed through the passage 6 in a mandrel 3, the through-passage 9 of a fitting 4 attached to the top end thereof and the cavity 2' in the plug to plural pieces of ejecting holes 8 disposed equidistantly in the circumferential direction to the position corresponding to the rolling part L on the outside circumferential surface 3a of the plug. The cooling water is then injected to the circumference from the holes 8 to strip the inside surface scale generated successively during rolling and at the same time to prevent the cohesion of the stripped scale onto the plug surface and the generation of the flaw on the inside surface is suppressed.