| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a special shaped tube which has good cross-sectional shape and high symmetricalness in projecting and recessing parts. SOLUTION: After making a tube stock P0 by forming a metallic strip into a cylindrical shape and welding both end parts in the width direction, plural recessed parts which are extended in the axial direction of a tube are preliminarily formed on the tube wall of the tube stock P0 with forming rolls 11-14 having plural projected parts 11p-14p in a preforming stand 10 and, next, forming for finishing the tube stock into the projecting and recessing parts having a target shape while forcing forming rolls 21 of the number equivalent to that of the recessed parts into the recessed parts is performed at a finishing stand 20. In the case of forming helical projecting and recessing parts as to the axial direction of the tube, the tube stock is formed with the preforming rolls and finish rolling which are arranged obliquely to a plane orthogonal to the tube axis of the tube stock P0.
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