Knowledge about nylon modification and introduction to injection molding process
Modified nylon
Modified nylon is a type of engineering plastics. It is a granular product formed by using nylon raw materials as the base material and changing its physical properties.
The output of this type of product is modified according to the different needs of some manufacturers. Modified nylon generally includes:
Reinforced nylon, toughened nylon, wear-resistant nylon, halogen-free fire-resistant nylon, conductive nylon, fire-resistant nylon, etc.
1． Thermal properties: glass transition temperature (Tg) and melting point (Tm); high heat distortion temperature (HDT); high long-term use temperature (UL-746B); wide use temperature range; small thermal expansion coefficient.
2. Mechanical properties: high strength, high mechanical modulus, low latent degeneration, strong wear resistance and fatigue resistance.
3． Others: chemical resistance, electricity resistance, flame resistance, weather resistance, and good dimensional stability.
The output of such products is modified according to the different needs of some manufacturers. Modified nylon generally includes: reinforced nylon, toughened nylon, wear-resistant nylon, halogen-free fire-resistant nylon, conductive nylon, fire-proof Nylon etc.
Modified nylon has many properties, so it is widely used in automobiles, electrical equipment, mechanical parts, transportation equipment, fabrics, paper machinery, etc.
Nylon modification
1. Glass fiber reinforced PA
By adding 30% glass fiber to PA, the mechanical properties, dimensional stability, heat resistance, and aging resistance of PA are significantly improved, and the fatigue strength is 2.5 times that of the unenhanced one. The molding process of glass fiber reinforced PA is roughly the same as that without reinforcement, but because the flow is worse than before reinforcement, the injection pressure and injection speed should be appropriately increased, and the barrel temperature should be increased by 10-40°C. Since glass fiber will be oriented along the flow direction during the injection molding process, the mechanical properties and shrinkage will be enhanced in the direction of orientation, causing the product to deform and warp. Therefore, when designing the mold, the location and shape of the gate should be reasonable, and the process can be improved. After taking out the product, place it in hot water and let it cool slowly. In addition, the greater the proportion of glass fiber added, the greater the wear on the plasticizing components of the injection molding machine. It is best to use bimetallic screws and barrels.
2. Fireproof PA
Since fire retardants are added to PA, most fire retardants are easy to decompose at high temperatures and release acidic substances, which are corrosive to metals. Rubber gaskets, flanges, etc.) need to be hard chromium plated. In terms of technology, the barrel temperature must not be too high and the injection speed must not be too fast to avoid discoloration of the product and a decrease in mechanical properties due to decomposition of the rubber material due to excessive temperature.
3. Transparent PA
It has good tensile strength, impact strength, rigidity, wear resistance, chemical resistance, surface hardness and other properties. It has high transmittance, similar to finished glass. The finishing temperature is 300–315 ℃. Molding During finishing, the barrel temperature needs to be strictly controlled. If the melt temperature is too high, it will cause discoloration of the product due to degradation. If the temperature is too low, the transparency of the product will be affected due to poor plasticization. The mold temperature should be lower. High mold temperature will reduce the transparency of the product due to crystallization.
4. Weather-resistant PA
Add additives such as carbon black to PA to absorb ultraviolet rays. These greatly enhance the self-lubricity of PA and the wear on metal, which will affect the cutting and wearing parts during molding and finishing. Therefore, it is necessary to adopt a screw, barrel, rubber head, rubber ring, and rubber washer combination with strong feeding capacity and high wear resistance.
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