| 摘要 |
PURPOSE:To obtain a bent pipe having a predetermined wall thickness in a good yield. CONSTITUTION:In a plastic straight pipe used in the bending processing of a plastic bent pipe, the cross sections of the outer and inner peripheral surfaces of the straight pipe are almost circular and the centers of the circles of both surfaces are shifted. Therefore, the part 3 becoming the back wall part of a bent part is made thick by predetermined thickness and the part 4 becoming the abdominal wall part of the bent part is made thin by predetermined thickness. As a result even when the wall thickness t6 of the back wall part 3 is reduced, the back wall part 3 does not become nonstandard and the wall thickness t7 of the abdominal wall part 4 does not also become nonstandard. Further, it is prevented that an inner diameter becomes small and flow rate efficiency is reduced. Since marking 5 is applied to the increased wall thickness part, bending processing can be efficiently performed. |
