METHOD OF MANUFACTURING SEAMLESS TUBE BY THREE-ROLL MANDREL MILL

摘要

A method for manufacturing seamless tubes by a three-roll mandrel mill according to the present invention, wherein the ratio of the inner circumferential length of the tube material to the outer circumferential length of the mandrel bar is set in the range of 1.07 to 1.17 in the last two stands, that constitute said mandrel mill, in which the tube material is subjected to a wall thickness reduction process, makes it possible to effectively suppress the unsuccessful withdrawal of the mandrel bar as well as the inner surface scratch defects of the tube material by the mandrel bar without excessively increasing the wall thickness difference in the circumferential direction (the wall thickness eccentricity) after rolling, whereby a production run by said three-roll mandrel mill can be performed. Thus, the method for manufacturing seamless tubes by a Mannesmann-Mandrel Mill process can be widely applied.