Understanding the Three Main Sections of an Extruder Screw
June 10, 2026
Understanding the Three Main Sections of an Extruder Screw
In plastic extrusion, the screw is the core component that determines melting efficiency, mixing quality, output stability, and final product quality. A well-designed screw ensures efficient plasticization, uniform melt temperature, and stable production performance.
Generally, an extrusion screw consists of three main sections: the Feed Section, Compression Section, and Metering Section. Each section plays a unique role in the plastic melting and conveying process.
1. Feed Section
Function
The feed section is responsible for conveying and preheating plastic materials. Its primary purpose is to ensure that the polymer begins to soften and approaches its melting temperature before entering the compression section.
Design Considerations
Different materials require different feed section lengths because their thermal properties vary significantly.
Materials with:
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High specific heat capacity
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High melting temperatures
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Slow heating characteristics
require more energy to reach the melting point. Therefore, they typically need a longer feed section.
Typical examples include:
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PA (Nylon) – longest feed section among common materials due to its crystalline structure.
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PU (Polyurethane) – moderate feed section length.
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PVC (Polyvinyl Chloride) – the shortest feed section because of its heat-sensitive nature.
Feed Depth
A deeper screw flight in the feed section increases conveying capacity and improves material intake. However, excessive depth may reduce the mechanical strength of the screw and should be carefully balanced during design.
2. Compression Section
Function
The compression section is responsible for:
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Material melting
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Compression
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Mixing
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Pressure buildup
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Degassing
By the time the material enters this section, most of it has already begun melting. However, the melt may not yet be completely homogeneous.
As plastic melts, its volume decreases. Therefore, the screw channel volume must gradually reduce to match the decrease in material volume. If the channel volume remains too large, insufficient compression can occur, resulting in:
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Poor heat transfer
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Inadequate melting
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Unstable pressure
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Inefficient venting
Compression Section Length
The compression section typically accounts for more than 25% of the screw working length.
However, the ideal proportion depends on the material characteristics.
For Crystalline Materials
Crystalline polymers generally have a relatively narrow melting range.
Examples:
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Nylon (PA)
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Polyethylene (PE)
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Polypropylene (PP)
For these materials, the compression section can be relatively short. In nylon screw designs, it often accounts for approximately 15% of the working length.
For Amorphous Materials
Amorphous plastics do not have a distinct melting point. Instead, they gradually soften over a wide temperature range.
Examples:
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Polycarbonate (PC)
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ABS
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PMMA
For these materials, a longer and more gradual compression section is preferred. If compression occurs too rapidly, excessive shear heating may lead to material degradation or even processing instability.
For High-Viscosity Materials
Materials with:
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High viscosity
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Poor thermal conductivity
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Low heat resistance
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High filler content
usually require a longer compression section, often 40–50% of the screw working length, to ensure complete melting and proper mixing.
Special Considerations for PVC
PVC is extremely sensitive to heat and shear. To minimize excessive shear heating, PVC screws may use an extended compression profile that spans nearly the entire working length of the screw.
3. Metering Section
Function
The metering section ensures that the polymer is:
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Completely melted
-
Uniformly mixed
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Consistent in temperature
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Stable in pressure
This section is critical for producing high-quality extrusion products with consistent dimensions and surface finish.
Metering Section Length
Typically, the metering section accounts for 20–25% of the screw working length.
A longer metering section generally provides:
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Better melt homogeneity
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Improved mixing performance
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More stable extrusion output
However, an excessively long metering section can increase material residence time, which may lead to thermal degradation.
Conversely, a metering section that is too short may result in uneven melt temperature and insufficient mixing.
Considerations for Heat-Sensitive Materials
For heat-sensitive materials such as PVC, long residence times should be avoided. In some cases, a shorter metering section—or even a modified design without a conventional metering section—is preferred to reduce the risk of thermal decomposition.
Metering Flight Depth
A shallower metering flight increases shear action, which improves:
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Plasticization efficiency
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Melt temperature uniformity
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Mixing quality
However, excessive shear can cause overheating and material degradation, especially when processing heat-sensitive plastics.
Choosing the Right Screw Design for Different Materials
The performance of an extrusion line depends heavily on matching the screw design to the material being processed.
| Material Type | Feed Section | Compression Section | Metering Section |
|---|---|---|---|
| Nylon (PA) | Long | Short | Medium |
| PE / PP | Medium | Medium | Medium |
| ABS / PC | Medium | Long | Medium |
| PVC | Short | Very Long | Short |
| High-Filler Compounds | Long | Long | Medium |
There is no universal screw design suitable for all materials. Factors such as melt temperature, viscosity, thermal conductivity, crystallinity, and additive content must all be considered during screw engineering.
At Dongguan Wirecan Technology Co., Ltd., we design and manufacture extrusion screws optimized for cable extrusion, optical fiber cable production, and various plastic processing applications. Proper screw configuration helps improve output, enhance product quality, reduce energy consumption, and extend equipment service life.