| 摘要 |
PROBLEM TO BE SOLVED: To smoothly accurately execute the U-bending of a steel sheet by a bending roll. SOLUTION: One upper roll 2 which is parallel to lower rolls is arranged above two before and behind parallel lower rolls 1, 1' and, by feeding the steel sheet between the lower rolls 1, 1' and the upper roll 2, the steel sheet is bent into a U-shape. At this time, the steel sheet is rolled (passed) through between the upper and lower rolls plural times and gradually formed into smaller curvature at every pass. Like this, when the steel sheet is gradually formed into smaller curvature, the steel sheet is gradually plastically deformed, buckling is difficult to generate and accuracy is raised. Because the curvature is reduced toward a part in the U-bending, forming is executed so that the forming by each pass is narrowed toward the minimum carvature part. In the above- mentioned manner, smooth U-bending is efficiently executed.
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