Nylon (PA) injection molding performance parameters

2020-12-07 21:32:24

1. Nylon (PA) is a crystalline material. It has a high melting point during injection molding, a narrow melting temperature range, and poor thermal stability in the molten state. When the melting temperature exceeds 300°C and the residence time exceeds 30 minutes, decomposition will occur.

2. Nylon (PA) material has strong moisture absorption performance. It must be preheated and dried before injection processing, and the water content must not exceed 0.3%. After the plastic absorbs moisture, the fluidity decreases significantly, and defects such as bubbles and "silver wires" will occur. Plastic parts with high precision requirements should be treated with humidity control.

3. Nylon (PA) has good fluidity and is prone to overflow. When a screw injection machine is suitable for injection molding, the screw should have a non-return ring and be heated by a self-locking nozzle.

4. PA material has a large shrinkage range and shrinkage rate during injection molding, and it is prone to shrinkage, dents, deformation and other defects, so the general injection molding conditions should be stable.

5. The cooling rate of the melt has a significant effect on the structural performance of the crystallinity plastic parts, so the mold temperature must be strictly controlled during injection molding, and the wall thickness of the plastic part is generally selected within the range of 20-90°. If the temperature of the material rises, the shrinkage will increase and flash will easily appear. The injection pressure is selected according to the type of injection machine, the material temperature, the shape and size of the plastic part, and the mold casting system. The injection pressure is high, easy to flash, small shrinkage, and strong directionality; low injection pressure, dents and ripples are easy to occur. The molding cycle is selected according to the wall thickness of the plastic part, and the thickness is longer. The thinner is shorter. In order to reduce shrinkage, dents, and shrinkage holes, low-temperature molds and low-temperature materials should be used. If the resin viscosity is small, the injection, high pressure and cooling time should be long, the injection pressure should be high, and white oil release agent should be used.

6. The injection mold gating system increases the cross-sectional size of the runner and gate, which can improve the shrinkage and dent phenomenon.

7. The main runner of the injection mold should have a cold slug hole and an exhaust system.