Single screw pelletizer systems are transforming PET recycling operations worldwide. As more PET bottle washing plants convert contaminated bottles into clean flakes, recyclers face a common challenge: how to add value beyond basic flake production. The answer lies in pelletizing—a process that converts PET flakes into versatile plastic pellets suitable for injection molding, sheet extrusion, and profile manufacturing.
For years, twin screw extruders dominated the plastic pelletizing market. Yet their high capital costs—particularly at larger capacities—create barriers for small to mid-sized recyclers. This gap in the market has driven innovation in single screw technology, making high-quality PET pelletizing more accessible.
What Makes Single Screw Pelletizers Attractive for PET Recycling?
Single screw pelletizers offer distinct advantages that address the core concerns of recycling operations: cost, efficiency, and quality.
Lower Capital Investment
Traditional twin screw systems can require investments exceeding $200,000 for mid-range capacities. Single screw pelletizers typically cost 30-40% less, making them accessible to operations with tighter budgets.[1]
Reduced Energy Consumption
Single screw systems consume approximately 20-25% less power than comparable twin screw configurations.[2] For a 600 kg/h operation running 6,000 hours annually, this translates to significant savings on electricity costs.
Simplified Operation and Maintenance
With fewer moving parts and simpler mechanical design, single screw pelletizers require less specialized training. Maintenance intervals are longer, and replacement parts cost less than twin screw equivalents.
Improved Output Capacity
Modern single screw designs incorporate specialized screw geometries that increase throughput by 15-20% compared to conventional models. This improvement brings single screw performance closer to twin screw levels while maintaining cost advantages.
How Single Screw Pelletizers Process PET Flakes
Understanding the pelletizing process helps operators optimize production and troubleshoot issues. Here’s how clean PET flakes transform into finished pellets.
Automated Feeding System
The process starts with controlled material feeding via conveyor belts and hopper systems. Feed rate consistency directly impacts pellet quality—fluctuations can cause diameter variations or incomplete melting.
Many systems integrate metal detectors at the feeding stage. These sensors halt production automatically when ferrous or non-ferrous contaminants are detected, preventing costly damage to downstream equipment.
Compaction and Moisture Removal
A high-speed compactor eliminates surface moisture through friction and mechanical compression. This step is critical because residual moisture reduces intrinsic viscosity (IV) during melting. Even 0.1% moisture content can drop IV by 0.05-0.08 dl/g, affecting final pellet strength and clarity.[3]
Single Screw Extrusion
The heart of the system is the single screw extruder, where PET flakes undergo melting and homogenization. Modern screws feature:
Material Construction: High-grade nitrided steel (38CrMoAlA) treated through specialized nitriding processes. This treatment creates an extremely hard surface layer (800-1000 HV) while maintaining a tough core, providing excellent wear resistance against abrasive PET materials.
Optimized Screw Design: Unlike general-purpose screws, PET-specific designs feature modified compression ratios, specialized mixing sections, and controlled shear zones. These modifications maintain gentle processing conditions that preserve IV while ensuring complete melting.
Progressive Heating: The screw advances material through multiple temperature zones (typically 4-6 zones) ranging from 240°C to 285°C. Each zone is independently controlled to match PET’s specific melting characteristics.
Barrel Configuration
The extruder barrel works in concert with the screw to control temperature and pressure. Key features include:
- Nitrided steel construction with hardened inner surfaces (minimum 600 HV)
- Individual heating elements for each temperature zone
- Integrated cooling fans to prevent overheating
- Temperature sensors providing real-time monitoring and feedback
Vacuum Degassing
Removing volatiles is essential for producing high-quality, food-grade pellets. The vacuum system typically includes:
Two-stage degassing: The first stage operates at -0.5 to -0.7 bar, removing bulk moisture. The second stage runs at -0.85 to -0.95 bar, extracting low molecular weight compounds and residual moisture.
Water-ring vacuum pumps: These pumps create stable, high vacuum levels while tolerating small amounts of condensed moisture without performance degradation.
Condensate collection: Filtered tanks capture volatiles, preventing environmental release and protecting the vacuum pump.
Proper degassing maintains IV loss below 0.03 dl/g—a critical threshold for applications requiring high mechanical properties.[4]
Melt Filtration
Before pelletizing, molten PET passes through screen packs that remove remaining contaminants. Two common configurations exist:
Single-plate screen changers: Require brief production stops for screen replacement. Suitable for cleaner feedstock with lower contamination levels.
Continuous screen changers: Allow screen replacement without stopping production. Four-station designs can process heavily contaminated materials while maintaining uninterrupted output.
Filter mesh sizes typically range from 60 to 120 mesh (250 to 125 microns), depending on end-use requirements.
Underwater Pelletizing
Most PET systems employ underwater pelletizing—a method that produces uniform, spherical pellets with excellent flow properties.
Process: Molten strands extrude through a multi-hole die face submerged in a water bath. Rotating knives cut the strands immediately upon exiting the die. Instant cooling in water prevents pellet deformation and sticking.
Self-adjusting die plates: These automatically compensate for thermal expansion, maintaining consistent strand diameter throughout operation. This ensures uniform pellet size—critical for downstream processing in injection molding or extrusion.
Drying and Packaging
After pelletizing, pellets contain 15-25% surface moisture. A two-stage drying process removes this moisture:
- Vibration screen dryer: Removes bulk water through mechanical vibration and air flow
- Centrifugal dryer: Reduces moisture to below 0.5% using high-speed rotation and heated air
Finally, dried pellets move to automated bagging stations calibrated for standard bag sizes (25 kg, 1000 kg big bags, or bulk storage).—
Quality Considerations: What to Expect from Single Screw Pellets
Output quality determines market value and application suitability. Here’s what properly configured single screw systems deliver:
Intrinsic Viscosity Retention
Well-designed systems maintain IV above 0.65 dl/g when starting with 0.70 dl/g flakes—representing less than 0.05 dl/g loss. This level is acceptable for most applications including:
- Polyester staple fiber (PSF) production
- Strapping band manufacturing
- Non-food packaging sheets
- Textile fiber spinning
For food-contact applications requiring IV above 0.72 dl/g, pre-crystallization dryers or solid-state polymerization may be necessary.
Pellet Appearance and Consistency
Quality pellets exhibit:
- Uniform diameter (typically 3-4 mm)
- Spherical or cylindrical shape
- Transparent to translucent appearance (blue, green, or clear depending on input)
- Smooth surface without voids or tails
- Consistent bulk density (0.6-0.7 g/cm³)
Contamination Levels
With proper filtration, final pellets contain less than 50 ppm non-PET contamination—meeting most industry standards for recycled content.
Single Screw vs Twin Screw: When to Choose Each
Both technologies have their place. Understanding the tradeoffs helps you make the right choice.
Choose single screw pelletizers when:
- Working with pre-washed, relatively clean PET flakes
- Budget constraints limit capital investment
- Energy costs are high in your region
- Production volumes range from 300-1200 kg/h
- Producing pellets for non-food applications or staple fiber
Choose twin screw extruders when:
- Processing heavily contaminated or mixed plastic streams
- Adding fillers, modifiers, or color concentrates
- Producing specialty compounds requiring intensive mixing
- Budget allows for higher capital expenditure
- Maximum IV retention is critical (food-contact applications)
For many recyclers focused on basic PET flake conversion, single screw technology provides the optimal balance of cost and performance.—
Rumtoo Single Screw Pelletizer for PET Flakes
Transform clean PET flakes into high-value pellets with proven single screw technology. Our systems deliver 20% higher capacity and 25% lower energy consumption than conventional designs.
Key Features:
- Capacities from 300 to 1200 kg/h
- Specialized screw design for PET materials
- IV loss less than 0.03 dl/g
- No pre-crystallization dryer required
- Automated feeding and packaging
Applications: Polyester fiber production, plastic strapping, sheet extrusion, injection molding, profile manufacturing
Contact us for detailed specifications, pricing, and installation support tailored to your recycling operation.
Maximizing Return on Investment
Getting the most value from your pelletizing system requires attention to several factors:
Feedstock Quality
Input cleanliness directly impacts output quality and system longevity. PET flakes should meet these specifications:
- PVC contamination: <50 ppm
- Moisture content: <1%
- Particle size: 8-12 mm
- Label and adhesive residue: <100 ppm
Investing in proper washing and separation upstream reduces maintenance costs and extends equipment life.
Operational Consistency
Maintaining steady feed rates, consistent temperature profiles, and stable vacuum levels prevents quality fluctuations. Modern PLCs can automate these parameters, but operator training remains essential.
Preventive Maintenance
Regular maintenance extends system life and prevents costly downtime:
- Weekly: Inspect screens, check vacuum seals, clean die plate
- Monthly: Verify heater calibration, examine screw and barrel wear
- Quarterly: Replace wear parts, service vacuum pump, calibrate controls
- Annually: Complete system inspection, bearing replacement as needed
Market Positioning
Understanding pellet markets helps optimize production decisions. Current recycled PET pellet prices (Q4 2025) range from:
- Clear pellets: $800-950/ton
- Light blue/green: $750-850/ton
- Mixed colors: $600-700/ton
Quality certifications (ISO 9001, GRS) and food-contact approval (FDA, EFSA) can command 10-20% price premiums.
Frequently Asked Questions
Q: Can single screw pelletizers handle multi-layer PET bottles?
Multi-layer bottles containing barrier materials (EVOH, polyamide) pose challenges. These materials have different melting points and can cause processing issues. For bottles with >2% barrier content, twin screw systems with better dispersive mixing are recommended.
Q: What happens if moisture content exceeds specifications?
Excess moisture causes several problems: IV loss increases dramatically (up to 0.10 dl/g per 0.5% moisture), pellets develop voids and bubbles, and production rates drop. Installing inline moisture analyzers helps catch problems before they affect quality.
Q: How long does a screw last before replacement?
With proper material selection and maintenance, screws typically last 8,000-12,000 operating hours when processing clean PET. Contamination with hard materials (glass, metal) dramatically shortens service life. Budget $8,000-15,000 for screw replacement depending on size.
Q: Can I switch between PET and other plastics?
Switching to materials with similar melting ranges (PBT, PC) is possible but requires careful purging. Switching to polyolefins (PE, PP) requires extensive cleaning or dedicated screw/barrel sets due to incompatible temperature profiles.
Q: What certifications are needed for food-contact pellets?
Food-contact applications require compliance with FDA regulations (21 CFR 177.1630) in North America or EU Regulation 10/2011 in Europe. This typically requires: IV >0.72 dl/g, contamination <10 ppm, heavy metals testing, and third-party certification. Additional solid-state polymerization may be required to meet these standards.
Taking the Next Step in PET Recycling
Single screw pelletizers represent a practical, cost-effective path for recyclers ready to move beyond flake production. By understanding the technology, specifications, and operational requirements, you can make informed decisions that align with your budget and production goals.
The shift from selling low-value flakes to producing finished pellets typically increases revenue by 30-50% per ton—a compelling return that can pay back equipment investments within 18-24 months for mid-sized operations.
Whether you’re planning a new recycling facility or upgrading existing equipment, modern PET pelletizing machine technology offers proven performance at an accessible price point. The key is matching system capacity to your throughput needs, ensuring feedstock quality, and maintaining operational consistency.
Ready to explore how single screw pelletizing can transform your PET recycling operation? Contact Rumtoo to discuss your specific requirements and receive customized system recommendations based on 15+ years of recycling equipment expertise.