| 摘要 |
PROBLEM TO BE SOLVED: To provide a contracting method for a pipe diameter and contracting device therefor suppressing the increase in the wall thickness of the pipe, and contracting the pipe diameter with a large contraction rate and a low cost. SOLUTION: In a manufacturing device for a seamless heat transfer pipe provided with a groove on the inner face, a pair of shoes 17 is provided between rolling balls 6 and a die 8 so as to clamp a raw pipe 1 from the upper side and lower side. And the upper and lower faces of the pair of the shoes 17 are connected to a U-shaped clamp 18. The contracting device is composed of the shoes 17, the clamp 18, the die 8, and a drawing device for the raw pipe 1. By pressing of the shoes 17, a friction force is produced between the shoes 17 and the raw pipe 1 so that a backward tension is impressed to the raw pipe in the direction reverse to the reduction drawing direction. The strength of the backward tension is made to be 10-70% of the strength of the reduction drawing force. In this way, the increase of the wall thickness of the raw pipe 1 accompanying the contraction of the diameter of the raw pipe by the die 8 can be suppressed.
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