To solve a problem that a conventional technique has difficulty to obtain an electric resistance welded tube excellent both in out-of-roundness and buckling resistance.
In the manufacturing method of an electric resistance welded tube, roll-forming is applied while a band steel is passed through, with the abutted both ends in the width direction resistance-welded to form a tube 10 and, after heat treatment on a resistance welded zone, the tube is straightened. In straightening the tube, rotary straightening machines 8 are used, wherein a distance between the stands of the machines is set not less than the outer diameter of the tube 10 and not more than eight times the outer diameter of the tube. Further, the rotary straightening machines are three strands or more in total, wherein the front stage is an entrance stand, the rear stage is an exit stand, and the stand in-between is the center stand. The roll height in the entrance and exit stands are made nearly equal, and the roll height of the center stand is elevated or lowered in the range of 1-40 mm with respect to the roll height of the entrance and exit stands.
KENMOCHI KAZUHITO
SAKATA TAKASHI
INOUE TOSHIHIRO
KUMAZAWA SHINTARO
