a. The injection Molding Screw:

The general purpose injection molding screw has three main sections. Each section has its own geometry and purpose. They are described below:

• Feed Zone: The portion of the screw that picks up the material from the feed opening (base of the hopper) and begins to soften the material as it is being conveyed. The flight depths are constant.
• Transition Zone (Compression Zone): The portion of the screw where the root diameter increases gradually resulting in the decrease of the flight depth. This causes the softened plastic pellets to further melt and compress eliminating any of the air pockets.
• Metering Zone: The depth of the flights in this section are minimum but constant. This helps the accurate control of the melt discharge for the molding shot. In other words, it meters the amount of melt. The flight depths are constant.

b. The Check Ring:

The check ring is used to prevent the plastic from being blown back during the injection phase of the molding cycle. It is similar to a non return valve.