Process Logic of Injection Temperature Control for Reinforced PA6
Reinforced PA6 (Nylon 6 with glass fiber) is one of the most widely used engineering plastics, with excellent strength, stiffness, and heat resistance making it dominant in automotive components, power tools, and mechanical structural parts. Injection temperature is one of the most critical process parameters in reinforced PA6 molding — improper temperature settings affect fiber distribution, crystallinity, mechanical properties, and can even cause material degradation.
Recommended Injection Temperature Range for Reinforced PA6
PA6 is a semi-crystalline polymer with a melting point of 220-225°C. After glass fiber reinforcement, melt viscosity increases, requiring higher processing temperatures for flowability. The standard barrel temperature profile for reinforced PA6 is recommended as follows:
Rear zone (feeding): 230-250°C. Due to PA6's high moisture absorption, the feeding zone temperature should not be too low, otherwise moisture in powder form cannot be expelled. Middle zone (compression): 250-270°C. This is the main melting and plasticizing stage, where sufficient temperature ensures uniform mixing of glass fiber and PA6 matrix. Front zone (metering): 270-290°C. Ensures uniform melt temperature. Nozzle temperature: 270-285°C. Typically 5-10°C lower than the front zone. Mold temperature: 80-120°C, recommended 90-110°C.
Mold temperature has a decisive impact on crystallinity and final product performance of reinforced PA6. Higher mold temperature means more complete crystallization, resulting in better stiffness and heat deflection temperature, but also greater shrinkage and longer cycle time. Conversely, too low mold temperature leads to incomplete crystallization, poor dimensional stability, and potential post-shrinkage.
Temperature Adjustment Strategy for Different Glass Fiber Contents
PA6+GF30 (30% glass fiber) and PA6+GF50 (50% glass fiber) have slightly different injection temperatures. Higher glass fiber content means greater melt viscosity, requiring higher injection temperatures. For PA6+GF30, barrel temperature is recommended in the 240-280°C range with melt temperature controlled at 275-295°C. PA6+GF50 recommended temperatures are 5-10°C higher, with barrel temperatures reaching up to 290-300°C. However, special attention is needed: above 310°C, the PA6 matrix will undergo significant thermal degradation, producing gel and black spots.
Temperature Control Key Points for Reinforced PA6 Injection
Reinforced PA6 is extremely moisture-sensitive — even trace moisture in the molten state can cause hydrolytic degradation, leading to molecular weight reduction, brittleness, and surface silver streaks. Therefore, material must be thoroughly dried before injection: recommended drying at 100-120°C for 3-4 hours to bring moisture content below 0.2% (ideally below 0.1%). Using a desiccant dryer provides more reliable results.
For temperature monitoring, it is recommended to use melt temperature probes to regularly check actual melt temperature rather than relying solely on barrel setpoint temperatures. The actual melt temperature may differ from the setpoint by 10-20°C, depending on screw speed, back pressure, and barrel temperature control strategy.
Other Critical Process Parameters for Reinforced PA6 Injection
Beyond temperature, the following parameters are also crucial: Injection pressure: 800-1400 bar (depending on part complexity and glass fiber content); Holding pressure: 50%-80% of injection pressure; Back pressure: 5-15 bar (back pressure helps improve glass fiber dispersion uniformity); Screw speed: 30-60 rpm (excessive speed causes over-shear breakage of glass fibers, reducing reinforcement effectiveness); Injection speed: Medium to high speed to ensure the melt front advances quickly, avoiding uneven fiber orientation.
Temperature-Related Solutions for Common Defects
When reinforced PA6 parts show surface fiber exposure (glass fibers visible), it can typically be improved by increasing mold temperature (to 100-120°C) and injection speed. Black spots or scorching are usually caused by excessively high melt temperature or prolonged residence time — reduce barrel temperature and shorten residence time. Warpage and distortion are related to uneven mold temperature — check if mold cooling channel design is reasonable.
In summary, injection temperature control for reinforced PA6 is a multi-variable optimization project, requiring process engineers to fine-tune based on specific product structure, mold design, and material batches.
