What is the compression zone in injection molding?

May 20,2024

The compression zone in injection molding refers to a specific section of the screw within the injection molding machine. The screw typically has three main zones: the feed zone, the compression zone, and the metering zone. Each of these zones has a distinct function in the process of melting and homogenizing the plastic material before it is injected into the mold.

Functions of the Compression Zone:

Melting: In the compression zone, the plastic pellets that were fed into the machine begin to melt. This zone applies pressure and heat to the material, causing it to transition from a solid to a molten state.
De-airing: As the plastic melts, air trapped between the pellets is expelled, ensuring that the material is homogeneous and free of air pockets.
Compression and Mixing: The gradual narrowing of the screw channel in the compression zone increases the pressure on the plastic material. This increased pressure helps in further homogenizing the melt and improving the consistency of the plastic.
Heating: The mechanical energy generated by the screw's rotation combined with external heaters ensures that the plastic reaches the desired temperature for injection. The material should be uniformly melted without overheating, which could degrade the plastic.

Importance in Injection Molding:

Material Quality: Proper functioning of the compression zone is crucial for ensuring the plastic material is thoroughly melted and mixed, which affects the quality of the final product.
Process Efficiency: Efficient compression and melting reduce cycle times and improve the overall efficiency of the injection molding process.
Product Consistency: A well-mixed and homogenous melt leads to more consistent product characteristics, such as strength, appearance, and dimensional accuracy.

In summary, the compression zone plays a critical role in transforming the plastic pellets into a molten state, ensuring the material is properly mixed and free of air pockets before it reaches the metering zone and is subsequently injected into the mold cavity.
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