In the automotive industry’s pursuit of "Lightweighting" and "High Strength," Long Glass Fiber Reinforced Thermoplastics (LFT-PP, LFT-PA) have become mainstream for manufacturing instrument panel supports, front-end modules, and trunk floors. However, the performance of Long Glass Fiber (LGF) depends heavily on its retained length within the polymer matrix. During processing in a twin screw extruder, improper screw geometry can cause excessive fiber fragmentation, significantly reducing the impact strength of the final product.
Fiber breakage typically occurs in the melting and mixing zones of the extruder.
Over-shearing: Traditional compact kneading blocks generate extremely high radial shear. For glass fibers with an initial length of 10mm-25mm, excessive shear can reduce the retained length to less than 0.5mm, negating the reinforcement effect.
Improper Compression Ratio: Sudden changes in screw channel depth cause rapid fluctuations in material flow velocity, creating mechanical stress that snaps the fibers.
To enhance fiber retention, the design of the screw and barrel must shift from "High Shear" to "Flexible Mixing."
Function: In the downstream sections after fiber injection, increasing the use of large-pitch elements provides more space within the flow channel. This reduces the filling degree and minimizes collisions between fibers and the metal walls.
Technical Parameter: The pitch is typically set to 1.5 to 2 times the screw diameter.
Wide Kneading Blocks: Utilizing kneading blocks with wide widths and smaller staggering angles (e.g., 30-degree or 45-degree forward staggering) provides more distributive mixing rather than dispersive (high-shear) mixing.
Eccentric Elements: Eccentric screw elements generate a pulsating flow field, achieving uniform wetting of the fibers by the polymer melt without destroying the fiber skeleton.
Parameter Support: The unilateral clearance between the screw and barrel should be maintained between 0.05 mm and 0.10 mm.
Logic: A clearance slightly larger than that used in standard compounding allows room for the fibers to flow, preventing the "grinding effect" that crushes LGF in tight spaces.
Long glass fiber exerts significant abrasive force on metal surfaces.
Hardness Requirement: Screw elements must undergo vacuum quenching to reach a hardness of 58-64 HRC.
Material Recommendation: High-vanadium alloy tool steels or bimetallic barrels with an inner liner hardness of over 60 HRC are recommended to withstand the scouring effect of LGF on the flow channels. (Reference: Material Wear Comparison Report - Ref: #QC-2024-EXP-08)
For automotive parts manufacturers, every 0.1 mm increase in fiber retention leads to a qualitative improvement in material toughness. By optimizing screw geometry, maintaining processing temperatures within +/- 2°C, and choosing high-precision parts compatible with Coperion or JSW standards, manufacturers can ensure structural components meet rigorous safety standards while maintaining high throughput.
