Nylon injection molding process

Machine condition of using an injection molding machine

Barrel temperature

Because nylon is a crystalline polymer, its melting point is obvious. The barrel temperature selected for nylon resins during injection molding is related to the performance of the resin itself, the equipment, and the shape factors of the product.

Too high material temperature is easy to cause a color change, brittleness, and silver wire of the rubber parts, while too low material temperature makes the material very hard and may damage the mold and screw. Generally, the minimum melt temperature of nylon 6 is 220°C, and that of nylon 66 is 260°C. Due to the poor thermal stability of nylon, it is not suitable to stay in the barrel at a high temperature for a long time to avoid discoloration and yellowing of the material. At the same time, due to the good fluidity of nylon, it flows quickly after the temperature exceeds its melting point.

Injection pressure

Nylon solution has low viscosity and good fluidity, but the condensation speed is faster, and it is prone to insufficient problems in products with complex shapes and thin wall thickness. Therefore, the higher injection pressure is still required, especially with glass fiber.

Usually, if the pressure is too high, the product will have overflow problems; if the pressure is too low, the product will produce defects such as ripples, bubbles, obvious fusion marks, or insufficient products. The injection pressure of most nylon varieties does not exceed 120MPA, generally 60-100MPA The selection in the range is to meet the requirements of most products. As long as the products do not have defects such as bubbles and dents, it is generally not desirable to use a higher holding pressure to avoid increasing the internal stress of the product.

Injection speed

For nylon, the injection speed is fast, which can prevent the ripples and insufficient mold filling caused by the slow cooling speed. The fast injection speed does not have a prominent effect on the performance of the product.

When the nylon resin is turned on, the nozzle temperature should be turned on first, and then the feeding cylinder should be heated. When the nozzle is blocked, do not face the nozzle hole to prevent the melt in the cylinder from being suddenly released due to pressure accumulation, which may cause danger. The screw must be emptied when the machine is stopped to prevent the screw from being twisted during the next production.

The wall thickness of the product, the flow length ratio of nylon is between 150-200, the wall thickness of nylon products is not lower than 0.8mm, generally between 1-3.2mm, and the shrinkage of the product is related to the wall thickness of the product. The thicker the thickness, the greater the shrinkage.

Exhaust, the overflow value of nylon material is about 0.03mm, so the vent slot should be controlled at 0.025