ROLLING METHOD FOR PIPE BY STRETCH REDUCER

PURPOSE:To suppress effectively the thickness increase in the head part at the end of a pipe and to improve the yield of material by decreasing the number of revolutions in each stand on the upper stream side in the initial stage in rolling of the head part of the pipe end and increasing the number of revolutions of each stand at the point of the time when the wall thickness of the product decreases smallest. CONSTITUTION:In a stretch reducer, a curve 1 indicating the combinations of the number of revolutions of rolls in each stand when the central part of a pipe is going to be rolled is used as a bssic pattern. At the time when the head part at the pipe end passes the l-th stand, the number of revolutions of the rolls of the stands on the upper stream sides thereof is made lower than the state before the head part of the pipe end passes through the l-th stand, whereby the gradient of the number of revolutions is increased and the number of revolutions is distributed 3. The gradaton of the number of revolutions is increased and when the head part of the pipe end arives at, for example, the m-th stand, the number of revolutions is distributed 5 and arrives at the point of the time when the wall thickness of the product decreases smallest when the gradation is increased more than the same. In this case, in the stage of passage through the m+1st stand, the number of revolutions of the stands on the upper stream side thereof is increased to a distribution 6 of the number of revolutions. The nearer the final stand, the gradation is made the gentler to bring the curve closer to the basic pattern.