After injection, if the plastic parts are saturated with water (professionally called moisture treatment) such as soaking or cooking, to avoid plastic deformation and contraction.
Due to the high hygroscopicity and water sensitivity of PA66, it will degrade when containing trace amounts of water during heating, severely affecting the appearance and performance of the product. Therefore, moisture must be dried before molding. The drying method is related to the moisture content.
When the moisture content is less than 0.2%, it can be heated in hot air at 85°C for 4-5 hours; when the moisture content is greater than 0.2%, it needs to be greater than (115±5)°C. Vacuum drying for 4 hours is required to ensure sufficient drying and prevent oxidation. The method actually used in production is vacuum drying for 6 hours at a temperature of 110°C.
For PA66 plastic parts, humidity control treatment is also necessary.
The method is to quickly put the injection-molded plastic parts into hot water at 95-100°C for 1 hour, then let it cool naturally for 15-30 minutes, so that the plastic parts can absorb water in a short time.
Saturation can avoid slow absorption of moisture in the air and continuous size changes, which is conducive to reducing the internal stress of plastic parts and preventing brittle fracture. In addition, since high-temperature plastic parts are isolated from the air during humidity-controlled treatment, there is no need to worry about surface oxidation and discoloration.
Setting of barrel temperature
1. Because nylon is a crystalline polymer, its melting point is obvious. The selection of barrel temperature for nylon resins during injection molding is related to the resin's performance, equipment, and shape of the product.
2. Too high barrel temperature can cause color change, brittleness, and silver wire in the rubber parts, while too low barrel temperature can make the material hard and may damage the mold and screw.
3. The melting temperature of general PA6 is at least 220°C, and of PA66 is 250°C. Due to the poor thermal stability of nylon, it is not suitable to stay in the barrel at high temperatures for a long time, so as to avoid discoloration and yellowing of materials. At the same time, because nylon has good fluidity, once the temperature exceeds its melting point, it will flow quickly.
Setting of mold temperature
Mold temperature has a certain effect on crystallinity and molding shrinkage. The range of mold temperature is 80-120°C.
1. Choosing a high mold temperature can increase crystallinity, wear resistance, hardness, elastic modulus, and reduce water absorption, and increase the molding shrinkage of the product, suitable for thick products;
2. Choosing a low mold temperature can reduce crystallinity, good toughness, high elongation at break, and reduce shrinkage, suitable for thin products with good transparency.