| 摘要 |
PROBLEM TO BE SOLVED: To enable the rolling formation of a flat tube in high precision and at high speed by forming a truncated projecting part formed at the center part of a band sheet to a folded projecting part and the bending part to both ends in the width direction of the band sheet, bending this bending part so as to closely contact with both sides of the folded projecting part and making the large curvature and the small recessed part to the folded projecting part in a reinforcing part. SOLUTION: In a first process and a second process, the truncated projecting part 416 is formed at the center part in the width direction of the band sheet, and the width L1 at the upper side is gradually narrowed, and after forming almost triangular shaped projecting part 426, the insides of projected two sides are brought into close contact with mutually the other parts and folded to form the projecting parts 43, 44. In this result, since the curvature radius at the bending part in the truncated shape becomes large, bending stress becomes small and also, the range working the stress is dispersed, and since the width L1 of the upper side in narrowed and the bending position is shifted the tension stress is not concentrated. By this method, the bending part in the projecting part is not contracted and not thinned, and the rolling formation can be executed in the high precision and in the high speed. |
