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عربىThe screw extruder mixing system is a core component used for material melting, mixing, and homogenization in the plastics, rubber, and food industries. Its performance directly impacts the quality of the final product (such as uniformity, strength, and color).
1. Functions of the Mixing System
Material Melting:
Solid raw materials (such as plastic granules and powders) are melted into a viscous flow state through shear heat and external heating.
Dispersive Mixing:
Break up agglomerated particles (such as pigments and fillers) to achieve uniform nano/micron-scale distribution (such as carbon black dispersion).
Distributive Mixing:
Ensures macroscopic uniform mixing of different components (such as resins and additives) to avoid local concentration differences.
De-Volatilization: Some designs are equipped with a de-gassing section to extract volatiles (such as water and residual monomers) from the melt.
2. Key Components of the Mixing System
| Components | Function |
| Screw | This core component conveys, compresses, and shears materials through its screw structure. It is categorized by function as follows: Conveying section (for solid material conveying), Compression section (for compaction and initial melting), and Mixing section (for high-shear mixing). |
| Mixing elements | Specialized screw designs enhance mixing. Common types include: shear blocks, pin mixing sections, Maddock screws, and wave screws. |
| Barrel | The inner wall of the barrel cooperates with the screw to provide heating/cooling temperature control. Some barrels feature internal grooves to enhance conveying efficiency. |
| Venting System | Exhausts volatiles during the decompression section to prevent bubbles and degradation (e.g., the vacuum vent in a twin-screw extruder). |
3. Mixing Principles and Technology Classification
Shear-Dominated Mixing
Applications: High-viscosity materials (e.g., PVC, rubber)
Principle: High-speed screws generate strong shear forces to break up particle agglomerates (e.g., carbon black dispersion).
Disadvantages: Can easily cause localized overheating; caution is advised with heat-sensitive materials.
Extensional Flow Field Mixing
Applications: Shear-sensitive materials (e.g., biodegradable plastics)
Principle: Utilizes special screw geometry (e.g., corrugated threads) to generate extensional flow, reducing mechanical degradation.
Distributive Mixing Optimization
Method: Use pinned mixing sections or static mixers (e.g., spiral plates) to increase the number of material divisions and reorganizations.
4. Common Problems and Solutions
Problem 1: Uneven Mixing
Solution: Increase the mixing section length or use a pin element.
Problem 2: Material Degradation
Solution: Reduce screw speed and optimize the temperature profile.
Problem 3: Poor Exhaust
Solution: Check vacuum pump efficiency or adjust the exhaust section position.
