When the PA66 filling ratio is increased from 50% to 70% in the "limit zone", how should you choose the extruder parts?

When the PA66 filling ratio is increased from 50% to 70% in the "limit zone", how should you choose the extruder parts?

When the PA66 filling ratio increases from 50% to 70%, the processing system undergoes a fundamental transformation. This is no longer traditional melt mixing, but rather a process where “a small amount of resin wets a large glass fiber skeleton.” At this stage, the resin accounts for less than 30% and can no longer form a continuous phase—glass fiber becomes the dominant structure.

As a result, the key to production stability shifts from formulation to the performance and matching of extruder components, especially the comprehensive capability of extruder screw elements, extruder shaft, and extruder barrel.

From “Shear Mixing” to “Wetting-Dominated” Screw Element Design

In a 70% filled system, the traditional approach relying on shear dispersion is no longer applicable. High-intensity kneading blocks will lead to a sharp torque increase, glass fiber breakage, and PA66 degradation.

Therefore, extruder screw elements must shift toward a low-shear, high-distribution design. A large number of toothed mixing elements (such as ZME/SME) should be used to split and recombine the melt flow channels, enabling the melt to achieve “penetrative wetting” within the glass fiber skeleton.

This design essentially follows a “zero-shear” concept, placing higher demands on the structural precision and configuration logic of screw elements. The goal is no longer strong shear, but stable conveying and uniform distribution.

Melting and Feeding: Building the Foundation for 70% Glass Fiber Processing

Under high filling conditions, the resin must be fully melted before glass fiber is introduced; otherwise, effective coating is almost impossible.

Thus, the front-section screw elements must provide stable and gentle melting, ensuring melt uniformity while avoiding local overheating.

At the same time, 70% glass fiber cannot be fed at a single point. This would instantly exceed the equipment’s throughput limit, causing material accumulation or even machine blockage. A more effective method is segmented feeding (e.g., 35% + 35%), allowing gradual wetting.

During this process, the conveying rhythm and load capacity of the extruder screw elements are critical to ensure that each portion of glass fiber is properly “absorbed.”

Extruder Shaft: The Core of Stability Under High Torque Conditions

As the filling ratio increases, the operating mode shifts from “high-speed shear” to “low-speed, high-torque.”

Under such conditions, the extruder shaft becomes the key factor determining system stability.

The torque load in high-filled systems is extremely high. If the shaft lacks sufficient strength or rigidity, micro-deformation may occur, leading to changes in the clearance between screw elements. This ultimately affects material conveying continuity and stability.

Therefore, a shaft with high torque density and excellent fatigue resistance is essential. To address this, we have developed the TR series material, which effectively meets the requirements of high strength and toughness under high torque conditions.

Extruder Barrel: The Key to Withstanding “Grinding Wheel-Level” Wear

At 70% glass fiber, the wear on equipment is extremely severe—almost equivalent to continuous “grinding wheel abrasion.”

If the extruder barrel lacks sufficient wear resistance, rapid wear will occur, increasing clearances and causing melt backflow and process instability.

Therefore, the barrel must use high-hardnessliners, such as bimetallic structures or Nickel alloy (OS60 (BLM60)) liners, typically with hardness above HRC 58–65.

Wear and corrosion resistance not only determine equipment lifespan but also directly affect production stability, product consistency, and overall output efficiency.

Venting and Structural Design: Preventing “Powder Suction” and Process Instability

High-filled systems involve significant air entrainment and glass fiber dust. If the venting design is improper, “powder suction” can easily occur.

At this stage, the structural design of extruder components becomes critical.

Typically, reverse screw elements are installed before the vacuum port to form a dynamic seal. In the venting section, screw elements with large lead and deep channels are used to provide sufficient space for gas release.

This design ensures effective degassing without compromising material conveying stability.

Conclusion: The Essence of 70% Filling Lies in “System Capability”

Achieving stable production of 70% filled PA66 is not a single process breakthrough, but a systematic engineering solution centered on extruder components.

Only when:

extruder screw elements provide low shear and high distribution,

extruder shaft withstands high torque,

extruder barrel ensures long-term wear and corrosion resistance,

can the equipment operate stably under extreme conditions.

In other words, 70% filling is not just a “high-fill upgrade,” but a comprehensive test of equipment capability. Whoever can balance high torque, low shear, and wear resistance will truly gain access to the high-end modified materials market.

If you also happen to have such confusion, contact us immediately to get a customized solution.