Key Considerations for PA Plastic Injection Molding Processing
2026-02-25 10:43:06
Plastic Molds
Nylon (PA) is one of the most widely used crystalline engineering plastics, renowned for its excellent mechanical strength, chemical resistance, and wear resistance. However, its high crystallinity makes it highly sensitive to fluctuations in process parameters, requiring precise control over drying, temperature, pressure, and cooling to produce high-quality PA products. This article outlines the critical considerations for PA injection molding from a full-process perspective.
1. Pre-Molding Drying: The Foundation of Quality
PA has a strong affinity for moisture, with an equilibrium moisture content of up to 9% in humid environments. Even a moisture content as low as 0.1% can cause surface defects like silver streaks, bubbles, and internal voids, as well as a significant reduction in mechanical properties due to polymer chain hydrolysis. Therefore, mandatory pre-drying is non-negotiable.
For most PA grades, hot air dehumidifying dryers are recommended, operating at 80–100°C for 4–8 hours, depending on the initial moisture content. For reinforced grades (PA66-GF30), higher drying temperatures (100–120°C) and longer times (6–10 hours) are required to ensure moisture is reduced to below 0.05%. Monitoring dew point is crucial; it should be maintained at -40°C or lower to guarantee drying efficiency.
2. Temperature Control: Balancing Flow and Crystallinity
PA processing temperatures vary significantly between grades: PA6 typically ranges from 230–260°C, while PA66 requires 260–290°C. The barrel temperature profile should be set to increase gradually from the hopper to the nozzle, preventing premature melting and material degradation. The nozzle temperature is critical and should be 5–10°C lower than the barrel's final zone to avoid drooling.
Mold temperature directly impacts crystallinity and part performance. A low mold temperature (40–60°C) results in rapid cooling, lower crystallinity, and better dimensional stability, suitable for thin-walled parts. Conversely, a high mold temperature (80–120°C) promotes complete crystallization, enhancing tensile strength and heat deflection temperature, ideal for structural components.
3. Injection and Holding Pressure: Controlling Shrinkage and Warpage
PA exhibits high melt viscosity and significant shrinkage (1.5–2.5%), making pressure control essential. Injection pressure should be set between 80–140 MPa to ensure complete mold filling, especially for complex geometries. Holding pressure is equally vital, typically set at 50–70% of the injection pressure, to compensate for volumetric shrinkage during cooling and prevent sink marks and warpage.
Holding time is determined by the part thickness; a general rule is 10–15 seconds per mm of thickness. Insufficient holding time leads to shrinkage defects, while excessive time increases residual stress and cycle time.
4. Cooling and Ejection: Ensuring Dimensional Accuracy
Uniform cooling is critical to minimize internal stress and warpage. Cooling channels should be designed to be as close to the cavity surface as possible, with a diameter of 8–12mm and a spacing of 2–3 times the channel diameter. The cooling water temperature should be maintained at 20–40°C, with a temperature difference of no more than 2°C across the mold to ensure consistent cooling.
PA has a high coefficient of friction, so mold surfaces should be polished to a roughness of Ra ≤ 0.8μm. Ejector pins should be generously sized and strategically placed to avoid stress concentrations and part damage during ejection.
Conclusion
PA injection molding is a precision process that demands meticulous control at every stage. By prioritizing proper drying, precise temperature management, optimized pressure settings, and uniform cooling, manufacturers can consistently produce high-quality PA components that meet the most stringent performance requirements.
