JPS57187114A - Manufacture of square steel pipe - Google Patents

Abstract

PURPOSE:To prevent a square steel pipe from deformation by pressing rolls at the corner positions in the inside of the pipe and to improve the shape accuracy of the pipe, by inserting a mandrel, arranged with plural rolls, into the pipe axis on the way of forming in a continuous roll forming process. CONSTITUTION:An internal roll 20 is provided to the same position, being the axial lines of driving rolls 13 and side rolls 14, in the pipe of the 1st stand of a group of rolling rolls 7. Then, a steel pipe, passed through a sizing roll stand 6, is rolled, first, by a prescribed rolling by the driving rolls 13 and is pressed on the side rolls 14, immediately after the rolling, and rolled from all directions. At this time, each roll 29 of the roll 20 in the pipe is pressed from the inside at the adjacent position of the corner part of the square pipe. Thus, the determination of driving position of the pipe circumference is promoted to prevent the generation of the deformation, etc. by the rolling forces of rolls 13 and 14.