How Venting Screw Design Enhances Degassing Efficiency in PET and PLA Extrusion
In the extrusion of polymers like PET and PLA, efficient degassing during the melting process is crucial to ensure high-quality output free from bubbles, gels, and impurities.
A well-designed venting screw section can dramatically improve melt quality, increase throughput, and reduce downtime.
Here’s how specific screw structure innovations boost degassing performance for PET and PLA extrusion lines.
Why Degassing Matters for PET and PLA
- PET (Polyethylene Terephthalate) is sensitive to moisture and volatile residues that cause bubbles and degrade mechanical properties.
- PLA (Polylactic Acid), a biodegradable polymer, is even more sensitive to thermal degradation and residual moisture.
Effective venting removes:
- Moisture vapor
- Residual solvents and monomers
- Gases generated by thermal decomposition
Without proper degassing, products suffer from voids, poor clarity, weak mechanical strength, and surface defects.
Key Features of Venting Screw Design
1. Extended Venting Zone Length
- Longer venting section gives more time for gases to escape.
- Typical vent zone length is 8–12 times screw diameter (D).
2. Reduced Channel Depth (Shallow Flights)
- Narrow channel depth in the vent zone improves melt surface exposure.
- Larger melt surface area contacting vent ports enhances gas release.
3. Multiple Vent Ports with Vacuum Connection
- Vent ports arranged evenly around the barrel circumference ensure uniform degassing.
- Vacuum system attached to vent ports lowers pressure, aiding gas evacuation.
4. Incorporation of Mixing Elements Near Vent Zone
- Spiral or Maddock mixing elements improve melt homogenization.
- This helps release entrapped gas bubbles by breaking up melt strands.
Specialized Vent Screw Designs for PET and PLA
| Design Element | Benefit |
|---|---|
| Barrier Screw with Vent Zone | Keeps unmelted solids separate; venting only melt improves gas removal |
| Vent Screw with Spiral Mixer | Increases melt surface renewal and exposure to vacuum |
| Conical Vent Screw | Enhances pressure drop, improving gas escape |
Juyuan’s Experience in PET & PLA Venting Screw Solutions
- Customized venting screw sections tailored to your machine model and polymer grade
- Precision machining with high hardness coatings to resist wear from fillers
- Proven improvements in output rate (+10–15%) and product clarity
- Reduced scrap rate by up to 30% through effective degassing
Final Tips for Optimal Degassing
- Maintain vacuum pump efficiency and seals
- Keep vent ports clean and unobstructed
- Monitor melt temperature to avoid premature polymer degradation
- Periodically inspect vent screw and barrel for wear affecting seal
Contact Juyuan for Expert Venting Screw Design
Ensure your PET and PLA lines achieve the best melt quality and productivity with our advanced venting screw solutions.
Zhoushan Juyuan Machinery Co., Ltd.
📧 Email: cxj.job@gmail.com
📱 WhatsApp: +86 13905808474
🌐 Website: https://juyuan-machinery.com