PIERCING METHOD WITH CROSS HELICAL ROLL PIERCER

摘要

PURPOSE:To improve the quality of a pipe by setting and controlling a cross helical roll gap and plug lead so as to maintain the draft at the top end of the plug at a predetermined target value. CONSTITUTION:An arithmetic control part 25 reads the outside diameter and length of a blank pipe 5 from an outside diameter gage 21 and a length gage 22, compares the same with the predetermined target values of the outside diameter and elongation length and determines the correction rate for the cross helical roll gap and plug lead so as to make the read outside diameter and length coincident with the target values. Said control part calculates the rolling conditions for the succeeding piercing from the correction rates and calculates the draft. The control part compares the calculated draft with the target draft from a target value setter 27 to eliminate the difference thereof and corrects the cross helical roll gap and plug lead within the range where there is no influence on the wall thickness. The draft at the top end of the plug is thus maintained at a specified rate by the above-mentioned method, by which the flaws on the inside surface are decreased and the quality of the pipe is improved.