| 摘要 |
PURPOSE:To manufacture a seamless steel pipe with almost uniform distribution of wall thickness in the longitudinal direction, at rolling a hollow blank pipe between rolls and a plug of a plug mill, by continuously changing the gap of said rolls according to a preset pattern. CONSTITUTION:A hollow blank pipe 1, processed by a stretch-draw forming method, is rolled through a gap provided between circular arc caliber rolls 2, 3 and a plug 4 into a tube 1' having a prescribed length and wall thickness. In this case, if the wall thickness of the tube 1' on the run-out side the of plug mill is designated by (t), similarly, the gap of the roll and the plug under no-load condition by S, the rolling load by P, and the mill stiffness by K, an equation t=S+ P/K is established. The figure A shows the longitudinal distribution of wall thickness of the tube obtained by rolling a hollow blank pipe of the same size through the said gap in selected several values. Accordingly, in order to roll a tube free from the thickness deviation over all the longitudianal direction from a hollow blank pipe of the same size, the said gap S is changed from the start of the rolling work following to the pattern shown in the figure B. Hereupon, the said gap S is represented by S=S(T). |
