| 摘要 |
PURPOSE:To prevent the spring-back of a tubular body by forming a strip plate in circular or similar shape to circle after repeating the work of forming one part of the right or left side of the strip plate in the approximate radius to a product pipe and the other part in smaller radius than the product pipe in the right and left alternately at the forming finish step. CONSTITUTION:The rightside of a tubular body 2 is formed in the approximate radius to a product pipe and the left side in the smaller radius than the product pipe by passing the tubular body 2 of a strip plate through the upper and lower roll 3, 4 of a roll step I at the forming finish step of the strip plate. The left side of the tubular body 2 is then formed in the approximate radius to the product pipe and the right side in the smaller radius than the product pipe by passing through the roll step II. The tubular body 2 is further passed through in the order of the roll step II I alternately. After asymmetrical forming at the rolling step I, II it is passed through the rolling step III having the right and left symmetrical hole die in circular or similar shape to a circle. In this case the spring-back of the tubular body 2 is prevented because of the minute part having received the bend-back deformation of the tubular body 2 being formed with this bend again.
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