PURPOSE: To easiy manufacture steel tubes where only the rack-working part is flattened in a highly efficient manner by using a roll where the caliber part of the roll at the final stand of the stretch reducer is flatly bottom-raised.
CONSTITUTION: In order to flatten the section of a steel tube the bottom part of the roll caliber part is flattened with reference to the radius (a) of the product, and the arc part of the caliber is bottom-raised at the position of (b) off the product center. As a result, the whole section consisting of the part where the product radius is (a) and the flattened part where the distance from the product center is (b) is made to manufacture a flattened steel tube. Then, the caliber arc part which is at the position of (b) off the product center with the center angle of α around the roll center is bottom-raised for the bottom part of the roll caliber part in order to flatten a part of the section of the steel pipe with reference to the product radius (a). Consequently, a steel tube having a truely circular sectional part and a flattened sectional part of the length C which is obtained by the angle α multiplied by the roll radius is manufactured. The flattened steel tube can be manufactured by this arrangement by manufacturing the bottom-raised flattening of the caliber, and applying it to the final roll of the sizer.
HATANAKA MASAYUKI
SANO SHIGERU
