Nippon Steel Corporation

Toshio Hirokawa

Tsuyoshi Kawano

Matsuo Usuda

Yoshito Tsuyama

Yasumi Shimazaki

Kazutoshi Kakita

In the manufacturing of a spiral pipe, there is first determined a maximum curvature which should be imparted to a strip of pipe forming material in order that a desired residual moment will be imparted to the finished pipe after the strip bent to the maximum curvature is allowed to spring back from the bent condition, which maximum curvature is determined based on the thickness, Young's modulus and yield stress of the strip, the desired curvature of the finished pipe, and the residual moment to be imparted to the finished pipe. By adjusting the position of three rows of forming rolls positioned at the apexes of a triangle, the flat strip is continuously bent into a spiral that has the thus determined maximum curvature. Then, the spirally formed strip is allowed to spring back toward its unbent shape to the diameter of the finished pipe, being stopped in the expansion due to the springback if it reaches the finished pipe diameter before completing springback or being expanded if it completes springback before it reaches the finished pipe diameter. Finally, the seam of the formed strip is welded when the strip is at the desired diameter of the finished pipe.

Method and apparatus for manufacturing spiral pipe

Rolled steel plate is press-fabricated into cylindrical UO pipe with a large wall thickness, by the steps of crimping, U-ing and O-ing. In the U-ing process, a collapsible U-ing punch, including a center block carrying paired side punches on both sides and a bottom punch at the bottom, is used. The U-ing punch insures that the O-shaped workpiece has the desired butt gap by decreasing the ratio of its height to its width when the gap proves to be smaller than the desired butt edge gap, and vice versa when the gap proves to be larger than the desired butt edge gap.

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Kisarazu, Japan

Toshio Hirokawa