This is a very comprehensive and detailed guide to PA66 (nylon 66) processing, covering every key step and parameter from raw material pretreatment, injection molding, to post-processing.

Before beginning, it is important to understand two core characteristics of PA66, which directly determine success of processing:
High Hygroscopicity: PA66 readily absorbs moisture from air. Moisture-laden pellets undergo hydrolysis during processing, resulting in a decrease in molecular weight, a sharp deterioration in strength and toughness of finished product, and appearance of surface defects such as bubbles, silver streaks, and burn marks. Therefore, drying is a crucial and essential first step in PA66 processing.
Clear Melting Point and Crystallinity: PA66 is a semi-crystalline polymer with a well-defined melting point (approximately 260℃). Processing temperatures must be significantly above its melting point. Its crystallinity results in significant mold shrinkage (typically 1.5-2.0%), with distinct directionality, which must be carefully considered during mold design and process settings.

 

This is the first and most critical step in ensuring product quality.
Drying Temperature: 80℃ to 90℃. Never exceed 90℃, as this will cause surface of pellets to oxidize and turn yellow, or even clump.
Drying Time: 4 to 6 hours (depending on drying equipment and ratio of virgin to recycled material). Using a vacuum drying oven can shorten this time.
Moisture Content Requirement: Before injection molding, raw material moisture content must be less than 0.15%. For high-quality products, it is best to keep it below 0.1%. A moisture meter can be used for rapid testing.
Notes: Dried material should be used immediately or temporarily stored in an insulated hopper at a temperature above 90℃.
If exposed to air for more than 30 minutes, it needs to be re-dried.
A dehumidifying dryer is recommended for drying; conventional hot air drying is ineffective.

1. Barrel Temperature Settings:

Melt temperature range of PA66 is approximately 260℃ to 290℃. Actual setting should be adjusted based on product structure, mold, and material type.
Back Section (Feeding Zone): 260℃ to 275℃. Slightly below melting point, it is primarily used for conveying and preheating. Excessively high temperatures can easily cause bridging (material blockage).
Middle Section (Compression Zone): 270℃ to 285℃. This is primary plasticizing zone, ensuring sufficient material melting.
Front Section (Metering Zone): 275℃ to 290℃. This ensures uniform melt temperature for easier injection.
Nozzle Temperature: 270℃ to 285℃. Slightly lower than front section temperature to prevent drooling (spontaneous molten material flow). A closed nozzle can be used.
Important: Melt temperature must never exceed 300℃, as this will cause severe thermal degradation. Actual melt temperature measured by a thermometer is the most reliable reference.
2. Mold Temperature
Mold temperature significantly affects crystallinity, dimensional stability, appearance, and mechanical properties of PA66 products.
General Range: 60℃ to 90℃
Thin-walled products: High mold temperatures of 80℃ to 100℃ are required for filling and to minimize weld marks.
High Toughness Requirements: Using a low mold temperature of 40℃ to 60℃ can reduce crystallinity and improve product toughness.
High Rigidity and Dimensional Stability Requirements: Using a high mold temperature of 80℃ to 120℃ can increase crystallinity, enhance rigidity, heat resistance, and dimensional stability.
Recommendation: Use a mold temperature controller for precise temperature control. Excessively low mold temperatures can result in a rough surface, incomplete crystallization, and high internal stress; excessively high mold temperatures can extend cycle time.
3. Injection Speed and Pressure
Injection Speed: Medium- to high-speed injection is recommended. High-speed injection helps fill thin-walled cavities, reduces surface condensation, and makes weld marks less noticeable. However, for glass-fiber-reinforced materials, excessively high injection speeds can easily lead to fiber floats (surface exposure).
Injection Pressure: As long as cavity is filled, use medium-to-low pressure (typically 50-100 MPa). Excessive pressure will result in high internal stress and flash.
Holding Pressure and Time:
→Holding Pressure: Approximately 50%-80% of injection pressure.
→Holding Time: This is primarily determined by gate solidification time. This can be determined by weighing part: increasing holding time increases part weight; when weight stops increasing, optimal holding time is reached. Insufficient holding time can lead to shrinkage and sinking; excessive holding time or high pressure can lead to excessive internal stress and difficulty in demolding.
4. Screw Speed and Back Pressure
Screw Speed: 50-120 rpm. As long as melt is uniform, use a low speed to minimize shear heat degradation.
Back Pressure: 0.5 to 2 MPa. Appropriate back pressure can compact melt, expel bubbles, and ensure more uniform plasticization. However, excessive back pressure can increase shear, cause excessive temperature rise, and lead to degradation.
5. Molding Cycle
Cooling Time: This depends primarily on wall thickness and mold temperature. PA66 solidifies quickly, so cooling time is generally short.
Total Cycle Time: While ensuring part is fully cooled and set, minimize cycle time to improve efficiency.

 

Due to crystalline nature of PA66, internal stress may exist within part. Post-processing can eliminate this stress and further improve performance.
Annealing (Stress Relief):
Method: Place part in a hot oil, hot air, or vacuum oven at 90℃ to 120℃.
Time: 15 to 20 minutes per mm of wall thickness, but typically no less than 30 minutes.
Purpose: Eliminates internal stress, improves dimensional stability and toughness.
Moisture Conditioning (Moisture Balance):
Method: Place part in boiling water or a potassium acetate aqueous solution (boiling point 121℃).
Time: 2-4 hours (depending on wall thickness), until moisture equilibrium is reached.
Benefit: PA66 parts absorb moisture and expand in their operating environment. Moisture conditioning allows them to reach moisture equilibrium earlier, stabilize their dimensions, and significantly improve their toughness (transforming from dry brittleness to wet toughness).

Summary: Golden Rule of PA66 Processing
Dry, dry, and dry again! This is cornerstone of success.
Precise Temperature Control: Never allow material temperature to exceed 300℃. Set mold temperature according to product requirements.
Fast Injection and Slow Holding: Use medium-to-high-speed injection, medium-to-low holding pressure, and appropriate holding time.
Emphasis on Post-Processing: Based on product's intended use, choose annealing or moisture conditioning to optimize performance.