| 摘要 |
PROBLEM TO BE SOLVED: To prevent occurrence of a shrink mark by a method wherein a pressure gas injection port is set at one place of a ring-shaped reinforcing rib and a pressure gas relief part enlarging the sectional shape of the reinforcing rib is formed at an almost opposite position in the direction of the ring to the pressure gas injection port. SOLUTION: Pressure gas is injected from pressure gas pressing-in parts 13 immediately after thermoplastic resin is injected and before the inside of a ring-shaped reinforcing rib 12 is hardened. The pressed-in pressure gas flows, branching to the right and the left in the longitudinal direction of the ring- shaped reinforcing rib 12, and advances, expanding softened resin, and a first gas channel 15A and a second gas channel 15B are formed in advance inside the ring-shaped reinforcing rib 12. Both of the first gas channel 15A and the second gas channel 15B collide with themselves in the vicinity of pressure gas relief parts 14. Since the pressure gas relief parts 14 are formed at places where the gas channels 15A and 15B strike against themselves, the fore ends of both of the first and second gas channels 15A and 15B striking against themselves are so bent as to escape in the direction of projections of the pressure gas relief parts 14 and are connected by joining. |
