| 摘要 |
<p>According to the present invention, a roll forming method includes a first roll forming process (11) for forming a trapezoidal projecting portion (416) at a center portion, a second roll forming process (12-18) for gradually narrowing an upper side of the trapezoidal projecting portion to form a turnup projecting portion (43, 44), a third roll forming process (21, 22) for forming perpendicularly folded portions (456) at both sides, and a fourth roll forming process (23-28) for folding a middle portion between the perpendicularly folded portion and the turnup projecting portion in a semi-circular shape. In this way, it is possible to form a turnup projecting portion, insides of which are closely contacted to each other with a curvature which is larger than the conventional curvature, with high speed. <IMAGE></p> |
