Twin-Screw Extruder Screw
A compounder that manufactures flame-retardant engineering plastics (PA6, PA66, PBT, PP, ABS, and PC/ABS) for new-energy vehicles, electrical/electronic, connector, and appliance applications required products that consistently met UL94 V-0, GWFI, and GWIT while maintaining mechanical performance, appearance, and long-term reliability. The primary issue in a flame retardant system is to disperse the flame retardant evenly while avoiding polymer degradation and retardant deactivation during processing. Screw selection affects not only dispersion but also the material's heat history, processing stability, and ultimate uniformity.
The crucial mixing zone element life increased from 4-5 months to 12-16 months, while tensile strength and impact performance improved by ~5-10% and ~8-15%, respectively. Additionally, UL94 pass rates increased and overall operating costs decreased by ~18-22%.
The flame-retardant rating of the same formulation varied from batch to batch, with certain products failing to pass UL94 consistently due to insufficient retardant dispersion uniformity in the melt and localized concentration variances.
The original screw layout employed a large fraction of kneading parts to force dispersion via mixing intensity. However, high shear energy damaged the polymer chains, resulting in lower melt viscosity, decreased mechanical characteristics, increased embrittlement risk, and inferior batch stability.
Some retardants, particularly high-loading, high-polarity halogen-free systems, agglomerated when mixing efficiency was low, resulting in black and white flecks, colour fluctuation, and reduced surface quality that carried over to downstream processing.
Long-term use of phosphorus-based and some halogen-containing retardants caused acidic media generated during high-temperature processing to erode the element and barrel surfaces. The mixing and venting parts experienced wear and corrosion, significantly decreasing critical-part life.
The previous supplier was capable of providing routine spare-parts supply, but lacked the specialized design capability necessary for flame-retardant systems. The approach they employed was overly reliant on high-shear mixing to disperse the retardant, which increased the risk of degradation. Additionally, they applied a wear-resistant material scheme to the entire screw without considering the corrosive environment. The customer sought a partner who could provide a comprehensive solution that addressed material life and stability, in addition to high-quality parts.
Lesun's technical team rebuilt the dispersion path by balancing dispersion with regulated thermal history:
A low-degradation processing method for the customer's material system maximizing property retention while retaining flame retardant performance:
Zoned material arrangement that matches the corrosion profile of the flame-retardant system:
A specialized parts database for the customer's key machines, which tracks life data, wear patterns, and failure mechanisms to reduce unexpected downtime through proactive maintenance.
| Benchmark | Outcome |
| UL94 pass rate | Improved; batch-to-batch variation markedly reduced |
| Product consistency | More uniform dispersion; fewer specks and color-variation defects |
| Tensile strength | +5–10% |
| Impact performance | +8–15% |
| Critical mixing-zone element life | 4–5 months to 12–16 months |
| Overall operating cost | Reduced ~18–22% |
Screw elements are valuable in flame-retardant compounding not only for their wear life, but also for their ability to regulate retardant dispersion, polymer thermal history, and processing stability. This project transformed twin-screw parts from a simple spare supply into a process unit that ensures stable, long-term flame-retardant production by optimizing the dispersion path, designing a low-degradation screw configuration, and upgrading to a corrosion-resistant material system. Consequently, flame-retardant consistency, product quality, and equipment life were all enhanced.