Driven by the lightweighting of new energy vehicles and the high performance of electronics and electrical systems, ultra-high filled PA66 systems with 50% GF or even 60% GF have become a "mandatory course" for modification factories. However, PA66 has a narrow melting range, low viscosity, and is extremely sensitive to heat. Coupled with a very high proportion of glass fiber, it is prone to issues such as fiber floatation, degradation, torque fluctuations, and severe equipment wear. How can one achieve microscopic impregnation of the filler and stable performance while maintaining high output? This article will combine rheological theory with frontline production experience to comprehensively break down the production logic of highly filled PA66.

1. Rheology core: viscosity mutation and shear heat management In the ultra-high filling system, the material no longer appears as a simple Newtonian fluid.

Viscosity mismatch: The viscosity of the PA66 matrix melt is very low, while the high proportion of glass fibers significantly improves the apparent viscosity of the system. This large viscosity gradient requires that the extrusion process must shift from "resin flow" to "slurry delivery".
Viscous dissipation: After the filling volume exceeds 40%, the heat provided by the barrel heating plate accounts for only a small part, and the frictional heat of the screw on the material becomes dominant. If the shear is too strong, the local temperature rise will cause the rapid oxidation and chain breakage of PA66, and the mechanical properties will fall off a cliff.
Process guidelines: Maintain "stepped" temperature control, it is recommended to lower the front, medium high, and flat in the back. Focus on monitoring the actual temperature of the melt to ensure it is below 290°C.
2. Screw configuration design: The core of the screw design from "strong shear" to "high distribution" and high filling system is to replace destructive shear through distributive mixing under the premise of ensuring that the resin is completely melted.
1. The "narrow distribution" strategy of the molten area
The phase change of PA66 is violent, and if the molten section is not properly designed, the unmelted particles entering the glass fiber port will cause instantaneous pressure surges.
Optimization recommendation: Use a sheet knead block with a medium misalignment angle (e.g. 45°). Extend the residence time distribution (RTD) of the material in the melting section to ensure the consistency of the resin phase transition and avoid local overheating.
2. The "interface infiltration" logic of the glass fiber segment
Glass fiber fracture mostly occurs in the initial mixing zone after injection.
Component selection: Abandon the high-energy shear unit and introduce a toothed hybrid element (SME or ZME).
Physical mechanism: The component segmentation and recombination function is used to allow the low-viscosity PA66 melt to fully penetrate into the glass fiber bundle to achieve microscopic infiltration while maximizing the retention of the glass fiber's length-to-diameter ratio (the critical length is maintained at 0.3-0.5mm).
3. Direct hitting of production pain points and "pit avoidance" tips 1. In-depth treatment of floating fiber (glass fiber outcrop).
Exhaust Balance: High filling causes a surge in the amount of entrained air within the system. A forced exhaust device should be set above the side feeding port, and a set of large-lead left-hand threads should be set in front of the vacuum section to strengthen degassing by using the pressure relief effect, and the vacuum degree should be maintained above -0.08 MPa.
Interfacial compatibility: Silane coupling agents alone may not be sufficient. It is recommended to introduce 3%~5% maleic anhydride graft toughening agents (such as POE-g-MAH) to use its polar groups to establish a "chemical bridge" with PA66 and enhance interfacial adhesion.
2. Bottleneck between vacuum leaking and yield
Cause: Insufficient free surface area of high fill melt, difficult bubble rupture.
Countermeasures: Increase the thread lead of the vacuum section, reduce the filling rate, and leave enough space for gas escape.
3. Hardware loss: redundant design for "grinding wheel level" wear
The high filling PA66 wears more than 5 times more on the screw and barrel than the conventional variety.
Material upgrade: Integral carbide or powder metallurgy steel screw elements must be selected, and the barrel should be equipped with bimetallic bushings.
Torque control: For high filling conditions, a model with a high torque coefficient (T/D^3 ≥ 11) should be selected to achieve stable production of "low speed, high torque, and low temperature rise".
4 Expert summary: Three indicators of high-quality output Pressure regulation: The die pressure fluctuation is controlled within ± 0.5 MPa, which is the premise of product uniformity.
Length retention: After ash testing, the length of the glass fiber under the microscope should remain intact and evenly distributed.
Color: There are no obvious black spots or yellowing in the particle section, proving that the thermal stability control is superior.