The “Big Three” of Plastic Injection Molding

1.  No Screwing Around With Screw Plunger Injection Molding

There are two chambers in a screw plunger injection molding machine:

• one chamber is used to plasticize (heat) the raw material
• the second chamber (barrel) is used for injecting that heated material inside the mold

  Plastic Injection Molding Machine

The first chamber, or upper section, utilizes a hopper containing the raw plastic resin.  After it’s liquified, the hot plastic is conveyed to the injection plunger area (the barrel), via a rotating screw.  While the screw is turning, the material maintains its liquidity via “band heaters” that prevent it from solidifying too soon.  Next, the melted plastic is injected via the screw into the mold itself where it fills every nook and cranny. Finally, the finished part is ejected from the mold into another container where it completes its cooling to room temperature.

2.  Take the Plunge: Plunger Injection Molding Machine  

As its name implies, the plunger injection molding machine uses its plunger to push the plastic in the barrel forward. The diverter shuttle then injects the plastic into the mold through the nozzle. The process of plastic melting into a flow state is accomplished by electric heating.

Because it’s simple, convenient, and has low technical requirements, the plunger injection molding machine is generally used for small parts or parts with few requirements.  Although it’s the least common injection molding process today, plunger injection molding is still used in small-scale industries because of its simplicity.

3. Reciprocal Agreement:  Reciprocating Screw Injection Molding

A reciprocating screw molding machine features heating elements attached to the barrel, which is divided into three zones,

1. feed zone
2. transition zone
3. metering zone

In the feed zone, the material is transferred from the hopper to the barrel, where it’s melted. In the transition zone, also known as the compression zone, the material is heated further and compressed by a reciprocating screw as it’s being “charged.” In front of that screw there is a “non-return valve”, which prevents backflow of material back into the hopper. Then the melted resin is injected into the metering zone.

But one more step awaits. The mold includes a clamping system:  either a toggle ram or fully electric clamp.  After the mold is closed, the cooling pipes cool the mold with with a water system or temperature controller.  Reciprocating Screw Injection Molding is the most efficient and common injection molding machine in the plastic industry.