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