An injection molder screw is a critical component of the injection molding machine, responsible for melting, mixing, and conveying the plastic material before it is injected into the mold. The screw is typically divided into three distinct zones, each with specific functions:
1. Feed Zone
Description:
- The feed zone is the first section of the screw where the plastic pellets are introduced from the hopper and begin their journey through the screw.
Function:
- Material Transport: The primary function of the feed zone is to transport the plastic pellets from the hopper towards the next section of the screw.
- Initial Compression: The plastic pellets are slightly compressed as they move forward, but they remain mostly in solid form.
Characteristics:
- Flight Depth: The flight depth (the distance between the screw root and the flight tip) is relatively deep in this zone to accommodate the volume of solid pellets.
- Temperature: This zone typically does not have heating elements, as the material is still solid and just beginning to warm up due to friction.
Importance:
- Ensures a consistent feed of material into the screw and starts the process of compacting the pellets.
2. Compression Zone
Description:
- The compression zone is the middle section of the screw where the plastic pellets are heated and begin to melt.
Function:
- Melting: The plastic pellets are subjected to increasing temperature and pressure, causing them to melt.
- Mixing: As the material melts, it is mixed thoroughly to ensure uniform temperature and composition.
- Compression: The screw flights become shallower, which increases the pressure and aids in the melting process.
Characteristics:
- Flight Depth: The flight depth decreases progressively in this zone to compress the material and facilitate melting.
- Temperature: Heating elements are present in this zone to raise the temperature and assist in the melting process.
Importance:
- Ensures the plastic material is completely melted and homogenized before it reaches the next stage.
- Proper compression and mixing in this zone are crucial for the quality and consistency of the final molded part.
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3. Metering Zone
Description:
- The metering zone is the final section of the screw where the molten plastic is prepared for injection into the mold.
Function:
- Homogenization: Ensures the molten plastic is thoroughly mixed and maintains a consistent temperature and viscosity.
- Pressure Build-Up: Builds up the necessary pressure to inject the molten plastic into the mold.
- Metering: Precisely meters the amount of molten plastic to be injected, ensuring the correct volume is delivered.
Characteristics:
- Flight Depth: The flight depth is shallow and consistent in this zone to maintain pressure and control the flow of the molten plastic.
- Temperature: Maintained at the optimal level to keep the plastic in a molten state and ensure smooth flow.
Importance:
- Ensures that the molten plastic is at the right temperature and consistency for injection.
- Precise control in this zone is crucial for producing parts with consistent quality and dimensions.
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Conclusion
The three zones of an injection molder screw—feed zone, compression zone, and metering zone—each play a vital role in preparing the plastic material for injection molding. The feed zone transports and begins to compress the solid pellets, the compression zone melts and mixes the material, and the metering zone homogenizes and prepares the molten plastic for injection. Understanding these zones and their functions is essential for optimizing the injection molding process and ensuring high-quality production.
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