How To Adjust Pelletizer Temperature And Solve Pellet Sticking And Hollow Pellet Problems

In plastic pelletizing production, temperature control and pellet quality directly affect final product performance, production efficiency, and material cost. Improper temperature settings can easily lead to defects such as pellet sticking or hollow pellets. Understanding how to properly adjust pelletizer temperature and troubleshoot common pelletizing problems is essential for achieving stable and high-quality granulation results.

1. How to Adjust Pelletizer Temperature

Temperature Control Principles

Pelletizing temperature must be set according to the material’s melting point, melt flow characteristics, and thermal stability. In most plastic compounding and pelletizing processes, the temperature profile typically follows a “low-to-high” or stepwise heating principle, which prevents premature melting at the feeding zone and avoids thermal degradation at the discharge end.

Basic Temperature Adjustment Steps

1. Refer to Material Processing Data

Different polymers have different processing temperature ranges. Operators should always consult the material supplier’s technical datasheet or processing guideline before setting machine parameters.

Typical reference processing temperatures include:

• PP (Polypropylene): 180 – 230°C

• PE (Polyethylene): 160 – 220°C

• ABS (Acrylonitrile Butadiene Styrene): 190 – 240°C

• PVC (Polyvinyl Chloride): 160 – 190°C (requires strict thermal stability control)

2. Set Heating Zones

Most pelletizing extruders are divided into 3 to 5 heating zones. The temperature should gradually increase from the feeding section to the die head, with a temperature difference generally controlled within 5 – 20°C between adjacent zones.

3. Preheat and Stabilize

After setting the target temperatures, the extruder should be preheated and kept at the set temperature for 15 – 30 minutes to ensure thermal stability and uniform heat distribution.

4. Observe and Fine-Tune

During operation, monitor key indicators such as:

• Melt pressure

• Main motor current

• Melt plasticization condition

• Extrusion stability

Operators can fine-tune temperature settings within ±5°C to achieve optimal melt homogeneity.

5. Record Standard Processing Parameters

Once stable production is achieved, record all parameters including:

• Temperature profile

• Screw speed

• Motor load

• Throughput

These data serve as standard production references for future operations.

Important Temperature Control Notes

• Excessively High Temperature May Cause:

• Material degradation

• Yellowing or discoloration

• Gas bubbles

• Burnt particles

• Excessively Low Temperature May Cause:

• Poor plasticization

• High motor load

• Rough or irregular pellets

• Recycled Materials Adjustment:

Recycled or regrind materials typically require temperatures 5 – 10°C lower than virgin materials.

2. Solutions for Pellet Sticking and Hollow Pellet Problems

A. Pellet Sticking (Pellet Agglomeration)

Main Causes

1.Cutter speed is too slow or blades are worn

2.Melt temperature is too high, resulting in low melt viscosity

3.Cooling water temperature is too high or cooling flow is insufficient

4.Air conveying system provides insufficient airflow, preventing proper pellet cooling

Solutions

Adjust Cutter System

• Increase cutter speed appropriately

• Inspect blade sharpness

• Replace or regrind worn blades

Reduce Melt Temperature

• Lower die head or melt temperature by 5 – 10°C

• Increase melt viscosity to improve pellet separation

Improve Cooling Efficiency

• Reduce cooling water temperature (recommended 15 – 25°C)

• Increase cooling water flow rate

• Ensure pellets are fully cooled before collection

Optimize Air Conveying System

• Check and clean blocked air pipelines

• Adjust airflow volume to ensure smooth pellet transportation and cooling

Adjust Cutting Distance

• Slightly increase the distance between cutter and die surface

• Allow additional cooling time before pellet cutting

Hollow Pellets (Pellets with Internal Bubbles)

Main Causes

1.Raw material moisture content is too high, especially recycled or hygroscopic materials

2.Insufficient vacuum degassing or blocked vent port

3.Excessively high melt temperature causing material decomposition and gas formation

4.Improper screw compression ratio or insufficient degassing efficiency

Solutions

Proper Material Drying

Hygroscopic polymers must be thoroughly dried before extrusion:

• PET, PA, ABS and similar materials

• Recommended drying condition: 80 – 120°C for 2 – 4 hours

Check Vacuum Degassing System

• Clean vent port blockage

• Inspect vacuum pump performance

• Ensure vacuum level reaches above -0.08 MPa

Lower Melt Temperature

• Reduce melt temperature appropriately

• Prevent polymer thermal decomposition and gas generation

Optimize Processing Parameters

• Increase screw speed moderately

• Reduce feeding rate to enhance degassing performance

Inspect Screw Design

If hollow pellets occur frequently, screw configuration or compression ratio may need optimization to improve melt compression and gas removal efficiency.

3. Importance of Proper Pelletizing Process Control

Stable temperature control, efficient cooling, and proper degassing are critical for producing high-quality plastic pellets. Advanced pelletizing systems, especially twin-screw extruders, provide better mixing, degassing, and temperature control performance, making them ideal for compounding, recycling, and masterbatch production.

By optimizing processing parameters and maintaining pelletizing equipment properly, manufacturers can:

• Improve pellet quality consistency

• Reduce production waste

• Lower raw material cost

• Enhance overall production efficiency

NANJING HAISI is professional manufacturer of Plastic Extruder Machine, we supply Twin Screw Extruder, Single Screw Extruder, Plastic Recycling Extruder, Two Stage Extruder, Lab Scale Extruder, Mixing and Feeding Machine, Cooling and Pelletizing Machine, Crushing Machine and so on.