PA46 is a high-crystallinity, high-melting-point high-temperature nylon with outstanding mechanical strength, heat resistance and dimensional stability. It features extremely high hygroscopicity and a narrow processing temperature window, so its requirements for injection process, equipment and mold adaptability are far higher than ordinary nylon. Improper processing will easily lead to product defects, material degradation or performance damage. To ensure the qualification rate and quality of PA46 molded products, strict full-process control is required from raw material pretreatment, equipment selection, temperature control, mold design, parameter adjustment to defect troubleshooting and post-processing, following material characteristics and avoiding common processing errors. The detailed precautions are as follows.
1. Raw Material Drying Control
PA46 has much higher hygroscopicity than conventional nylon, and excessive moisture is the main cause of processing defects. Undried raw materials will cause silver streaks, bubbles and material hydrolysis degradation, greatly reducing product strength. A dehumidifying dryer is mandatory, with dew point controlled at -30 to -40°C; ordinary hot air drying is invalid. Set drying temperature at 100-110°C for 4-5 hours, with material thickness no more than 50mm to avoid uneven drying. The moisture content must be below 0.02% before molding. If production pauses over 30 minutes, seal and keep drying the residual materials; materials exposed to air over 30 minutes need re-drying to prevent secondary moisture absorption.
2. Injection Machine and Screw Selection
PA46 requires high wear resistance and temperature control accuracy of equipment, especially for glass fiber reinforced grades. A bimetallic alloy screw is recommended, with length-diameter ratio 18:1-22:1 and compression ratio 2.8:1-3.2:1, ensuring full plasticization and reducing fiber breakage. The check ring must be well sealed to prevent melt backflow. Barrel temperature control accuracy should reach ±1.5°C, and the nozzle needs independent heating to avoid drooling and blockage, ensuring stable continuous production.
3. Processing Temperature Control
The melting point of PA46 is about 295°C, with a narrow processing range close to its decomposition temperature, so gradient heating is required. Barrel temperature: rear section 280-290°C, middle section 290-305°C, front section 300-315°C, nozzle 305-315°C; reinforced grades can be slightly higher but not exceed 325°C. Mold temperature is 80-140°C, preferably 120°C, which balances crystallinity, dimensional stability and molding cycle. Actual melt temperature should be 300-315°C: low temperature causes poor plasticization, while high temperature leads to material degradation and blackening.
4. Mold Design and Ventilation Optimization
PA46 melt solidifies quickly, so runner and gate sizes should be 15%-20% larger than ordinary nylon molds to reduce pressure loss. Vent grooves with depth 0.02-0.03mm should be set at weld lines, flow ends and wall thickness mutations; vacuum ventilation is applicable for complex products. The cooling system must be uniform to avoid warping, with draft angle no less than 1.5°, polished mold surface and balanced ejection mechanism to prevent product cracking or sticking.
5. Injection Process Parameter Control
Follow the principles of fast filling, short holding pressure and low back pressure. Adopt medium-high injection speed to ensure full mold filling; reduce speed for reinforced grades to avoid fiber breakage. Injection pressure is 80-150MPa, adjusted by product structure. Holding pressure is 60%-80% of injection pressure, lasting 5-15 seconds until the gate solidifies, to avoid excessive internal stress. Back pressure is 7.5-10bar, screw speed 50-100rpm, cooling time 15-40 seconds based on wall thickness. Material residence time in barrel shall not exceed 5 minutes; clean the barrel with PE before long-term shutdown to prevent carbonization.
6. Common Defect Troubleshooting
Silver streaks and bubbles are mostly caused by insufficient drying, high temperature or poor ventilation, solvable by re-drying, lowering temperature and optimizing vents. Short shots result from low temperature, insufficient pressure or small gates. Sink marks are due to inadequate holding pressure or uneven wall thickness. Warping is caused by uneven cooling or high internal stress, which can be improved by optimizing cooling and annealing. Glass fiber exposure can be fixed by lowering injection speed and raising mold temperature.
7. Post-Processing and Production Safety
Anneal products at 80-100°C for 1-2 hours then slow cooling to eliminate internal stress and improve dimensional stability. Monitor moisture content, temperature and process parameters in real time during production. PA46 releases slight irritant gas at high temperature, so keep the workshop ventilated and take anti-scald measures.
