| 摘要 |
PURPOSE:To offer a manufacture of a pipe fitting of double layer structure synthetic resin excellent in dimensional precision and in the bonding strength between the inner and outer layers by leaving a clearance between the mold of the outer layer and the outer circumference surface of the outer layer in the injection mold of the inner layer and equalizing the clearance nearly to the amount of molding shrinkage of the inner layer. CONSTITUTION:After the outer layer 1 is set into the mold leaving a clearance among a movable mold 4, the outer layer supporting part 5 and the outer circumference surface of the outer layer 1, synthetic resin fluid is injected into the space. At this time, the outer layer 1 is expanded by the pressure of the fluid with which the space of the inner layer 2 is filled but this expansion is limited by filling the clearance between the mold and the outer circumference surface of the outer layer 1 with the outer layer 1. After injection of resin, molding shrinkage occurs in the inner layer 2 but this shrinkage is absorbed by the return of the outer layer 1, no strain occurs in the inner layer and precise size can be obtained. Durability is improved. The injection molding of the inner layer is carried out only by leaving a clearance corresponding to expansion of the outer layer between the outer circumference surface of the outer layer and the mold. No special difficult method is required. |
