Views: 1 Author: Site Editor Publish Time: 2025-12-25 Origin: Site
Twin-screw extrusion is a core process in polymer processing and compounding. The stability of operation and final product quality depend heavily on precise process control—among which temperature control is the most critical factor.
Due to variations in extruder models, screw configurations, and material formulations, optimal processing conditions are usually established through long-term testing and operational experience. This article outlines the key temperature-related parameters in twin-screw extrusion processing, helping manufacturers improve efficiency, stability, and product quality.
1. Extrusion Process Temperature Design
The extrusion temperature profile must consider multiple factors. The primary reference point is the highest melting temperature among all material components.
For example, in polypropylene (PP) masterbatch production, the PP carrier has the highest melting point at approximately 170°C, so barrel zone temperatures are typically designed around this value. Heating methods also affect temperature settings—electrical resistance heating usually requires higher temperatures than electromagnetic induction heating, which is more energy-efficient.
Extrusion temperature is also closely related to extruder size and production rate. Higher output requires more thermal energy to soften and melt materials. Temperature zoning should be designed based on conveying and shear requirements:
Higher temperature → lower melt viscosity → lower shear force
Lower temperature → higher viscosity → higher shear force
Material rheology and viscosity characteristics must always be considered when adjusting process temperatures.
2. Feed Throat Temperature Control
The main objective of feed throat temperature control is to prevent material sticking to the screw, which can disrupt feeding.
To promote early melting and effective shear dispersion, the feed zone temperature should be set as close as possible to the carrier resin’s melting point, without causing screw adhesion. In formulations containing only small amounts of low-melting additives, slight melting does not significantly affect feeding.
However, formulations rich in low-molecular-weight components can melt easily due to heat transfer from downstream zones, leading to material bridging and feed blockage. Therefore:
Keep the feed zone at a lower temperature during startup
Activate cooling if necessary
Reduce temperature after startup if required to prevent screw slippage and feeding failure
3. Vent Port Temperature Management
Vent port temperatures are usually set slightly lower to prevent melt leakage or material surging from the vent opening. This is typically achieved by coordinating the temperatures of upstream and downstream barrel zones.
In well-optimized processes with stable flow, good dispersion, and low melt pressure, vent zone temperature adjustments may not be critical. However, vent temperature remains an important parameter when processing materials with high volatile content.
4. Temperature Control in the Mixing Section
The mixing section is the core zone for masterbatch and compound production, where pigment dispersion quality is determined.
Shear force is strongly influenced by temperature:
Excessively high temperature → low viscosity → weak shear → poor dispersion
Moderately lower temperature → higher viscosity → stronger shear → improved dispersion
In practice, experienced operators often monitor main motor current to fine-tune the mixing zone temperature, as shear intensity directly affects energy consumption.
5. Die Head Temperature Adjustment
As the melt exits the barrel and enters the die head for pelletizing—whether via water-ring pelletizing or strand pelletizing—a slightly lower temperature is usually required.
Operators should monitor the strand exit temperature and compare it with the melt temperature inside the barrel. Additionally, for systems equipped with continuous screen changers, die head temperature plays a crucial role in melt viscosity and flow stability during screen changes.
6. Feeding Speed Control
Feeding speed directly determines output. Under stable conditions, extrusion throughput equals feeding rate.
Increasing feeding speed → higher material load → indirect temperature reduction
Decreasing feeding speed → indirect temperature increase
Feeding speed adjustments influence dispersion quality and overall process stability, so they must be optimized with a holistic view of product quality and production consistency.
7. Screw Speed (Main Motor Speed)
Screw speed primarily affects shear intensity and dispersion efficiency. With constant feeding speed, changes in screw speed only temporarily affect output.
High-shear products require higher screw speed
Low-shear formulations require lower screw speed combined with optimized temperature control
Always operate within the extruder’s maximum allowable speed and maintain a safety margin to protect equipment.
8. Melt Pressure Monitoring
Melt pressure is typically maintained below 1 MPa and reflects multiple process variables, including:
Screen mesh size
Dispersion quality
Melt temperature and viscosity
Smaller screen mesh, poor dispersion, or low viscosity generally result in higher pressure. Melt pressure should be used as a reference indicator, not as a single decisive parameter.
9. Screen Pack Configuration and Replacement
Screen packs provide filtration and increase melt backflow to enhance shear. Proper selection and replacement frequency should be based on product requirements and quality standards.
10. Environmental Considerations in Twin-Screw Extrusion
Key environmental focus areas include:
Dust control at the feed throat
Gas emissions from vent ports and die head
Cooling water treatment and recycling
Effective collection, filtration, and disposal systems are essential for compliant and sustainable operation.
Conclusion
Temperature is the central variable throughout the entire twin-screw extrusion process, tightly coupled with feeding rate, screw speed, and melt pressure. Together, these parameters determine material melting, conveying, dispersion, devolatilization, and final shaping.
A stable, high-quality twin-screw extrusion process depends on systematic, precise, and global temperature control, supported by coordinated adjustment of all related process parameters.
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