In thermoplastic yarn production, temperature control is the critical factor determining fiber quality (e.g., strength, uniformity, melt performance). Below are temperature control methods and key technical considerations for each production stage:
1. Raw Material Drying Stage
Objective: Remove moisture from polymers (e.g., PA, PET, TPU) to prevent hydrolysis during melting.
Temperature Range: 80–120°C (adjusted based on material hygroscopicity; PA requires higher temperatures).
Control Methods:
Use infrared moisture sensors for real-time humidity monitoring and automatic adjustment of drying temperature/time.
Apply multi-zone circulating hot air drying to avoid localized overheating or insufficient drying.
2. Melt Extrusion Stage
Objective: Ensure complete polymer melting and stable viscosity while avoiding thermal degradation.
Zoned Temperature Control:
Feeding Zone: Low temperature (100–150°C) to prevent premature melting and clogging.
Compression Zone: Medium temperature (150–230°C) for gradual material softening.
Metering Zone: High temperature (200–280°C, material-dependent) for homogeneous melt.
Example: TPU requires strict control at 190–220°C, while PA6 needs 260–280°C.
Key Technologies:
PID Closed-Loop Control: Dynamically adjust heater power via thermocouple feedback.
Melt Pressure Sensors: Monitor extruder head pressure to detect temperature anomalies.
Nitrogen Protection (for oxidation-prone materials like PA): Minimize oxidation risks at high temperatures.
3. Spinning and Cooling Stage
Objective: Precisely regulate cooling rate to optimize crystallinity and mechanical properties.
Melt Temperature:
Spinning assembly (spinneret) temperature should be 5–10°C lower than extrusion temperature to prevent melt fracture.
Cooling Parameters:
Air Temperature: 10–30°C (e.g., PA requires rapid cooling, PET needs gradual cooling).
Air Velocity: 0.3–1.5 m/s, adjusted via variable-frequency fans.
Control Methods:
Side/Annular Blowing Systems: Use perforated flow plates for uniform airflow.
Online Infrared Thermometers: Monitor fiber surface temperature in real time to adjust cooling conditions.
4. Post-Processing Stage (Heat Setting, Winding)
Objective: Eliminate internal stress and stabilize fiber dimensions.
Heat Setting Temperature:
Set based on the material's glass transition temperature (Tg), e.g., PET: 120–140°C, TPU: 80–100°C.
Temperature Uniformity Control:
Divide heat-setting ovens into multi-zone stages (preheating, holding, slow cooling) with ±2°C tolerance.
Use hot air circulation systems with baffles to avoid localized temperature deviations.
5. Composite Processing (e.g., Core-Sheath Structures)
Objective: Ensure sheath-layer melting and bonding while protecting core-layer integrity.
Sheath Melting Temperature:
Must exceed the sheath material's melting point but stay below the core material's softening point (e.g., TPU sheath: 190°C, PET core: <250°C).
Composite Roller Temperature:
Maintain ±5°C precision using thermal oil circulation systems.
6. Advanced Temperature Control Technologies
Multi-Variable Collaborative Control:
Link temperature, pressure, and screw speed adjustments (e.g., reverse compensation between extruder temperature and screw speed).
AI Predictive Control:
Train models on historical data to predict melt viscosity changes and pre-adjust heating power.
Thermal Imaging Monitoring:
Scan critical areas (e.g., spinnerets, cooling ducts) to identify temperature anomalies.
Common Issues and Solutions
| Issue | Root Cause | Solution |
|---|---|---|
| Excessive Fiber Surface Fuzz | Uneven crystallization due to rapid cooling | Increase cooling air temperature or reduce velocity |
| Melt Flow Interruption | Degradation from excessive temperature | Lower metering zone temperature; add antioxidants |
| Winding Tension Fluctuations | Unstable heat-setting temperature | Calibrate heating elements; optimize airflow paths |
