| 摘要 |
PURPOSE:To improve manufacturing efficiency of a wrapped steel tube with a prescribed lap width by controlling a pressing force of a bending roll loaded on a steel plate and bending the steel plate with smaller radii of curvature than that at expansion work and the radii sequentially changed. CONSTITUTION:A steel plate 1 is bent by bending rollers 4, 5a, and 5b to manufacture a wrapped steel tube 6. The pressing force of the upper roller 4 onto the plate 1 is controlled to make radii of curvature Ra, Rb, and Rc of respective parts (a), (b), and (c) sequentially larger in due order. The radii Ra, Rb, and Rc at bending work are made to be smaller than the radius Ro at expansion work to positively obtain an accurate roundness of the outside surface of a cylindrical shape after the expansion work. As the result, the wrapped steel tube 6 with a prescribed lap width is manufactured.
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