PURPOSE: To restrict an increasing phenomenon of wall thickness of the end part of a pipe, by setting a combination of the number of revolutions of a roll of each stand at the time when said end part passes through the final stand, as a basic pattern and making the number of revolutions of a roll larger at a stand where the end part is passing through and that at stands where it has passed through smaller.
CONSTITUTION: In rolling a pipe material to be stretched by plural numbers (n) of stands, a combination of the number of revolutions of a roll at each stand at the time when the middle part of the pipe is rolled is set as a basic pattern A. A combination of the numbers of revolutions of the 1stW(n)th stands in a period, from the time before the start-up of rolling to the time that the end part of the pipe passes through the (k)th stand (2≤k<n) is set to be the curves B and B'; that is, to restrict an increase of the wall thickness of the end part of the pipe, the number of revolutions of the (k)th stand is made larger than that of the pattern A and the number of revolutions of the 1st stand roll is made smaller, as shown by the curve B. When the number of stands through which the end part has passed exceeds (k), each stand roll is made to have the number of revolutions as shown by the curve B', and a stand roll through which the end part has already passed is made to have the number of revolutions as shown by the curve D which is smaller than the curves B and B'.
KAWAHARA SHIGEO
MASUDA ICHIROU
NODA KATSUTOSHI
OONISHI TADAHARU
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