Nylon's special properties make it widely used in automobile, electronic and electrical equipment, mechanical structure, sports equipment, textile and so on. However, with the miniaturization of automobiles, the high performance of electronic and electrical equipment, and the process of lightweight mechanical equipment, the demand for nylon and performance requirements have gradually increased. Therefore, the modification of nylon is particularly important.
Nylon modification precautions：
1. Barrel temperature setting
Because nylon is a crystalline polymer, it has an obvious melting point. The barrel temperature selected during injection molding of nylon resin is related to the performance of the resin itself, the equipment, and the shape factor of the product.
Excessively high material temperature can easily cause discoloration, brittleness and silver threads in plastic parts, while too low material temperature can make the material very hard and may damage the mold and screw.
Generally, the minimum melt temperature of PA6 is 220℃, and that of PA66 is 250℃. Due to the poor thermal stability of nylon, it is not suitable to stay in the barrel at high temperature for a long time to avoid discoloration and yellowing of the material. At the same time, because nylon has good fluidity, it flows quickly after the temperature exceeds its melting point.
2. Setting of mold temperature
Mold temperature has a certain impact on crystallinity and molding shrinkage. The mold temperature ranges from 80 to 120°C.
Choose high mold temperature, high crystallinity, increased wear resistance, hardness, and elastic modulus, decreased water absorption, and increased molding shrinkage of the product, which is suitable for thick products;
Choose low mold temperature, low crystallinity, good toughness, high elongation and reduced shrinkage, which is suitable for thin products with good transparency.
If the wall thickness is greater than 3mm, it is recommended to use a low-temperature mold at 20~40℃. For glass reinforced materials, the mold temperature should be greater than 80°C.
Temperature control of molds where the wall of the product is thin and difficult to form or requires high crystallinity. If the product requires a certain degree of flexibility, cold water temperature control is generally used.
3. Wall thickness of product
The flow length ratio of nylon is 150 to 200, and the wall thickness of the product is not less than 0.8mm, usually 1 to 3.2mm. Moreover, the shrinkage of the product is related to the wall thickness of the product. The thicker the wall thickness, the greater the shrinkage.
4. Exhaust
The overflow value of nylon resin is about 0.03mm, so the vent slot should be controlled below 0.025.
5. Runner and gate
The gate hole diameter should not be less than 0.5t (t is the thickness of the plastic part). With submersible gates, the minimum gate diameter should be 0.75mm.
6. Glass fiber filling range
During the molding process of nylon, lowering the mold temperature, increasing the injection pressure, and lowering the material temperature will reduce the shrinkage rate of nylon to a certain extent, making the product more prone to deformation due to increased internal stress. For example, the shrinkage rate of PA66 is 1.5% to 2%, and the shrinkage rate of PA6 is 1% to 1.5%. After adding glass fiber additives, the shrinkage rate can be reduced to about 0.3%.
7. Use of recycled materials
It is best not to exceed three times to avoid discoloration of the product or a sharp decline in physical and mechanical properties. The application amount should be controlled below 25%. Too much will cause fluctuations in process conditions. The mixing of recycled materials and new materials must be dried.
8. Safety instructions
When starting up the nylon resin, you should first turn on the nozzle temperature, and then heat the barrel. When the nozzle is blocked, do not face the nozzle hole to prevent the melt in the barrel from being suddenly released due to pressure accumulation and causing danger.
9.Use of release agent
Using a small amount of release agent can sometimes improve and eliminate defects such as bubbles.
10. Post-processing
Heat treatment is required after the product is formed.
The product should be moistened after molding.
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