Feeding Polymer into a Twin Screw Extruder: Techniques and Best Practices
Feeding polymer correctly into a twin screw extruder ensures consistent output and high-quality compounding. Several factors influence the best feeding method, including:
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The extruder design (parallel or conical, co-rotating or counter-rotating)
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The type of material used
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The location of feed introduction
Starve Feeding in Twin Screw Extrusion
Most parallel counter-rotating and co-rotating twin screw extruders use starve feeding for accurate and efficient material delivery.
In starve feeding:
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Feeders deliver polymer resins and additives directly onto the extruder screw.
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The screw rotates faster than the feed rate, preventing material build-up in the feed zone.
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The feed rate alone determines the throughput, not the screw speed.
This method enables operators to control the formulation precisely. You can introduce additives, fillers, and secondary resins at multiple points along the extruder—either through gravity feed or a side feeder. Use liquid pumps and injection systems to feed liquid additives accurately into the melt.
Benefits of Starve Feeding
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It maintains consistent ingredient ratios.
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It prevents common problems like bridging and slippage in the hopper.
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It allows direct, controlled material delivery to the screw.
Optimal Feeder Placement
Install feeders:
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Directly above the feed throat, or
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On a platform above the extruder to allow gravity-assisted feeding.
This placement ensures materials drop cleanly onto the screw, which promotes a smooth and uninterrupted feed flow.
Feeding in Conical Twin Screw Extruders
Operators also use starve feeding in conical counter-rotating extruders, especially for heat-sensitive compounds or complex blends. These systems often include side feeders or stuffers to introduce additives into the melt stream downstream.
Side feeders, designed as zero-compression single or twin screws, push additives into the melt with high accuracy. This positive conveying system offers better control and higher throughput than gravity feeding.
High-Rate Feeding Considerations
To manage high downstream feeding rates, you need the right screw design. A properly designed screw:
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Handles the increased material load
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Ensures thorough melting, mixing, and distribution
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Prevents surging and ensures consistent melt quality
extruder feeding ( sample )