The Impact of TPE Pelletizing Methods on Product Quality And Solutions To Common Issues

1. Key Advantages of Using TPE Pellets in Processing

Compared to powder materials, TPE pellets offer several advantages in molding and extrusion processes:

1. Easier Feeding: Pellets flow more smoothly into the extruder, eliminating the need for a forced feeder.

2. Better Product Quality: Higher bulk density reduces defects, improving overall consistency and finish.

3. Lower Risk of Bubbles: Pellets contain fewer volatiles and less trapped air, minimizing bubble formation in final products.

4. Improved Additive Dispersion: When combined with masterbatches, additives disperse more uniformly than when added directly.

2. Key Factors Affecting TPE Pellet Quality During Extrusion

(A) Extrusion Process Parameters

• Melt Temperature: Proper settings reduce viscosity, enhance flowability, and lower power consumption. Overheating, however, may cause melt sagging and uneven wall thickness.

• Melt Pressure: Stable pressure ensures homogeneous mixing and consistent product performance. Installing a melt pressure sensor at the die head allows real-time monitoring.

• Melt Conveying Speed: Faster conveying reduces sagging and increases wall thickness, while slower speeds may cause thin or unstable walls.

(B) Pelletizing Methods

Cold Cutting

• Sheet Cold Cutting: Materials are mixed and calendered into sheets, cooled, then pelletized.

• Extrusion Sheet Cutting: Plasticized sheets from the extruder are cooled and cut.

• Extrusion Strand Pelletizing: The most common method for thermoplastic elastomers (TPE). Strands are cooled (air or water) before being cut into cylindrical pellets.

Hot Cutting

• Dry Hot Cutting: Rotating blades cut molten strands directly at the die head.

• Underwater Pelletizing: Advanced method for polyolefin-based TPE, with cutting under circulating hot water for efficient pelletizing.

• Air-Cooled Hot Cutting: Similar to dry cutting, but pellets are cooled by air or water spray to prevent sticking.

3. Common TPE Pellet Quality Issues and Solutions

1. Long Strands – Caused by poor strand direction, insufficient cooling, or worn cutter blades. Solution: Adjust strand alignment, optimize cooling length, replace blades.

2. Pellet Bridging – Linked pellets due to high die temperature or improper cooling. Solution: Use guide rollers, extend cooling section, lower die temperature.

3. Centipede Strands – Caused by uneven pulling speed or dull cutters. Solution: Maintain steady pulling, adjust extrusion process, replace blades.

4. Black Spots – From dirty screw, degraded resin, or contamination. Solution: Clean screw and barrel, control processing temperature, improve raw material inspection.

5. Discoloration – Caused by uneven mixing, overheating, or wrong additives. Solution: Follow mixing protocols, lower processing temperature, use optimized screw design.

6. Poor Vacuum Venting – Due to leaks, backflow, or damaged vacuum system. Solution: Maintain vacuum pumps, clean filters, fix sealing issues.

7. Metal Particles – From screw wear or raw material contamination. Solution: Inspect and replace damaged parts, use metal separators during production.

8. Poor Plasticization – From low temperature, high feeding speed, or excess lubricant. Solution: Adjust temperature, feeding rate, and optimize formulation.

9. Excess Moisture – Due to overcooling or improper strand separation. Solution: Adjust cooling length, improve cutting speed, ensure proper strand separation.

10.Powder Formation – Caused by excessive filler or worn cutters. Solution: Optimize filler content, replace cutters, reduce cooling intensity.

11. Carbonization – From overheating or uncleaned screws after shutdown. Solution: Regular screw cleaning, control heating system, timely screen and die plate maintenance.

Conclusion

TPE pelletizing quality directly impacts the mechanical strength, appearance, and stability of final products. By optimizing extrusion parameters, selecting the right pelletizing method (cold cut vs. hot cut), and implementing effective quality control measures, manufacturers can significantly improve production efficiency and product performance while reducing waste and defects.

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