| 摘要 |
PROBLEM TO BE SOLVED: To secure excellent flexibility and a uniform and smooth bending characteristic by covering only the reinforcing core part spirally wound on an inner layer pipe with synthetic resin band type material for forming a hollow spiral projection, forming a ridge part of the hollow spiral projection and an outer layer pipe part, and forming a valley part of the outer layer pipe part. SOLUTION: A hollow spiral projection 2 is spirally wound on the outer circumferential face of an inner layer pipe 1, in which an inner circumference face is formed into a flat surface 1a, and inside the hollow spiral projection 2, a reinforcing core material 3 made of synthetic resin or metal is arranged as a continuous spiral, while on the outer circumference face of the inner layer pipe 1 including the outer circumference face of the hollow spiral projection 2, an outer layer pipe 4 is layered. In the outer layer pipe 4, a part covering the hollow spiral projection 2 is formed into a ridge part 7 having height equal to a total of thickness of the inner layer pipe 1, the hollow spiral projection 2, and the outer layer pipe 4. A pipe wall part between the adjacent ridge parts 7 is formed into a valley part 8 by the outer layer pipe 4 part directly layered on the outer circumference face of the inner layer pipe 1, while the pipe wall outer circumference face directed from the ridge part 7 to the center of the valley part 8 is formed into a gentle circular arc type recessed face 9.
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