Nylon PA612 is a high-performance polyamide material. Compared to common PA6 and PA66, it has lower water absorption, better dimensional stability, and excellent chemical resistance and wear resistance. Therefore, its injection molding process parameters need to be adjusted accordingly.
The following is a core parameter setting guide for the injection molding of Nylon PA612. Please adjust it according to your specific material grade, product structure, and mold design.
Core Principle: Drying is Half the Battle!
Before discussing injection parameters, the pretreatment of PA612 must be emphasized. Although its water absorption rate is lower than other nylons, trace amounts of moisture can cause hydrolytic degradation at high temperatures, leading to molecular chain breakage, resulting in reduced product strength, surface bubbles, silver streaks, and other defects.
- Drying Temperature: 80~90°C. It is strictly forbidden to exceed 100°C to prevent material agglomeration and oxidation yellowing.
- Drying Time: 4~6 hours (depending on hopper capacity and humidity).
- Dew Point: The dew point of the drying air should be below -30°C.
- Recommendation: Use a dehumidifying dryer and continue nsulation drying(heat preservation drying) on the machine’s hopper to prevent the dried material from re-absorbing moisture.
Detailed Injection Molding Machine Parameter Settings
1. Barrel Temperature
The melting point of PA612 is approximately 210~215°C. The barrel temperature setting is usually 20~50°C higher than the melting point.
- Rear Zone (Feed Zone): 220~240°C
- Function: Gently preheat the plastic and exhaust any possible residual air.
- Middle Zone (Compression Zone): 230~250°C
- Function: The plastic mostly melts in this zone. This temperature range is key to ensuring plasticizing quality and melt uniformity.
- Front Zone (Metering Zone): 240~255°C
- Function: Ensures the plastic is completely melted and provides a melt with uniform temperature for injection. This is the most critical temperature control point.
- Nozzle Temperature: 235~250°C
- Function: Slightly lower than the front zone temperature to prevent drooling (melt flowing out of the nozzle orifice automatically). A shut-off nozzle can be used.
Note:
- Excessively high temperature causes: Material decomposition (color darkening, bubbles, gas generation), severe strength reduction.
- Excessively low temperature causes: Poor plasticization, difficulty in injection, surface flow marks on the product, high internal stress.
- Recommendation: Use the lowest possible processing temperature on the premise of ensuring complete filling and good appearance.
2. Mold Temperature
The mold temperature decisively affects the crystallinity, dimensional stability, and internal stress of PA612 products.
- Recommended Range: 60~90°C
- Thin-Walled Products: It is recommended to use a higher mold temperature (e.g., 80~90°C) to improve melt flowability, reduce weld lines, and improve surface gloss.
- Thick-Walled Products: A slightly lower mold temperature (e.g., 60~80°C) can be used to shorten the cycle time and prevent sink marks.
- High Appearance Requirements: High mold temperature must be used to achieve the best surface quality.
- Mold Temperature Too Low: Leads to insufficient crystallization of the product, poor dimensional stability, large post-shrinkage and warpage, and high internal stress, making it prone to cracking.
3. Injection Pressure and Speed
- Injection Speed: Medium~High Speed.
- PA612 melt viscosity is sensitive to temperature and relatively less sensitive to shear. Using medium-high speed injection can:
- Fill the cavity quickly, preventing the surface from freezing too early.
- Reduce the visibility of weld lines.
- Achieve a smooth surface.
- For products with complex structures or thin walls, higher injection speeds may be required.
- PA612 melt viscosity is sensitive to temperature and relatively less sensitive to shear. Using medium-high speed injection can:
- Injection Pressure: 60~120 MPa (approx. 600~1200 bar)
- Use the lowest injection pressure possible on the premise of ensuring complete filling and good appearance.
- The holding pressure is usually 40%~60% of the injection pressure.
4. Holding Pressure and Time
This is key to controlling product dimensions, weight, and sink marks.
- Holding Pressure: Set to 30%~60% of the injection pressure.
- Holding Time: Mainly depends on the gate freeze time and product wall thickness.
- Core Principle: Holding should continue until the gate freezes. Too short a time leads to under-packing and sink marks; too long a time causes over-packing, difficulty in demolding, and high internal stress.
- Determination Method: The optimal holding time can be determined by the “Weighing Method“: Gradually extend the holding time; when the part weight no longer increases, that is the suitable holding time.
5. Back Pressure
- Purpose: To compact the melt, exhaust gases from the melt, and make plasticization more uniform.
- Recommended Range: 0.3~0.8 MPa (approx. 3~8 bar)
- Note: Back pressure should not be too high, otherwise it will prolong the plasticizing time and may cause material degradation due to excessive residence time in the barrel.
6. Screw Rotation Speed
- Recommended Range: Medium~Low Speed, recommended 50~100 rpm.
- Principle: Use low speed on the premise of ensuring uniform plasticization and not affecting the cycle time. Excessively high speed will generate excessive shear heat, which may cause local overheating and degradation of the material.
7. Molding Cycle
- Cooling Time: Mainly depends on the thickest wall section of the product and the mold temperature. Usually, sufficient time is needed for the product to cool and set properly so that it does not deform upon ejection.
Common Problems and Countermeasures
| Problem Phenomenon | Possible Causes | Solution Directions |
|---|---|---|
| Silver Streaks/Bubbles | 1. Insufficient material drying 2. Barrel temperature too high, decomposition 3. Back pressure too low, entrapping air | 1. Dry material thoroughly 2. Lower barrel temperature 3. Appropriately increase back pressure |
| Sink Marks/Voids | 1. Insufficient holding pressure/time 2. Injection speed too slow 3. Material/Mold temperature too high 4. Runner or gate too small | 1. Increase holding pressure and time 2. Increase injection speed 3. Appropriately lower material/mold temperature 4. Modify the mold |
| Prominent Weld Lines | 1. Mold temperature too low 2. Injection speed too slow 3. Poor venting | 1. Increase mold temperature 2. Increase injection speed 3. Improve mold venting |
| Brittle Product | 1. Insufficient drying or thermal degradation 2. Material temperature too low, poor plasticization 3. Mold temperature too low | 1. Check drying effect, lower barrel temperature 2. Appropriately increase material temperature 3. Increase mold temperature |
| Ejection Difficulties | 1. Holding pressure too high/time too long 2. Mold temperature too high, insufficient cooling 3. Insufficient mold draft angle or poor polishing | 1. Reduce holding pressure and time 2. Lower mold temperature or extend cooling time 3. Modify the mold |
Summary and Recommendations
- Drying First: The primary condition for successfully processing PA612 is strict and thorough drying.
- Temperature Strategy: Adopt a “medium-high material temperature, medium-high mold temperature” strategy to obtain the best fluidity and product performance.
- Pressure and Time: Use sufficient injection speed to ensure cavity filling, and optimize holding parameters using the “weighing method” to balance sink marks and internal stress.
- Step-by-Step Adjustment: Start with a median parameter value and make fine adjustments based on the actual molding situation (short shot, appearance, etc.). Change only one parameter at a time to observe the effect.
I hope this detailed guide is helpful to you! In practice, be sure to refer to the property sheet and data sheet provided by the supplier of the specific PA612 material you are using.