Injection molding machine nozzle

With backpressure the process is performed in conventional injection molding machines (IMMs) (Chapter 4). The cover stock is inserted and located in an open mold. A shear edge mold permits draw-in of the cover stock during the closing cycle to avoid wrinkles and damage by stretching of the fabric. Molds require special attention. They generally use a hot runner system with its shut-off nozzle(s). All mold elements such as ejector, core pulls, and slides have to be on the injection side mold half. 

The SCORIM unit is placed between the nozzle of the injection molding machine and the mold (Figs. 14.11-14.13).The gates (i.e., the sprues and runners) are located so that all potential weld lines are placed between them from the flow point of view. 

The SCORIM process employs a unique hardware component that is retrofitted to a conventional injection molding machine. Located between the injection nozzle and the mold, this unit contains a pair of pistons that exert pressure on the melt after it is injected... 

Melt homogeneity in injection molding was further enhanced with the introduction of motionless mixers in the early seventies (37). These devices are placed in the nozzle of the injection molding machine. The mixers enhance the radial uniformity of temperature and composition of the melt. The devices are good for getting better cavity filling and also for saving on color concentrate. 

For PFA, FEP, and ETFE injection molding machines, materials like Xaloy 309 and Bemex C240 can be used for construction of barrels and Hastelloy C-276 for the screw, adapter, and nozzles. 

For this reason, most injection molding machines for thermoplastics are equipped with screws, that can move in the axial direction. However, there are also other designs. The conveyance of the compound in the direction of the nozzle causes the material to collect in front of the screw tip (ante-chamber). As this happens, the screw is forced backward. As soon as the screw has traveled a certain predetermined distance and the desired amount of melt has aceumulated in front of the screw, the rotational movement of the screw ceases and no further material is processed. 

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