Injection pressure refers to the pressure exerted on the plastic melt by the top of the plunger or screw. Its function is to overcome the flow resistance during melt flow filling process during injection, so that the melt has a certain filling speed; after the cavity is filled, the melt is compacted and backflow is prevented. The injection pressure depends on the type of injection molding machine, the type of plastic, the structure of the injection mold, the temperature of the injection mold, the structure and size of the pouring system, and the shape of the plastic parts.
In general, the injection pressure of plastics with high viscosity is higher than that of plastics with low viscosity; the injection pressure of thin-walled, large-area and complex-shaped plastic parts is high: the injection mold has a simple structure and the gate size is large, the injection pressure is low; the plunger Injection pressure is greater than screw injection machine: barrel temperature, injection mold temperature is high, the injection pressure is low. Because there are many factors that affect the injection pressure and the relationship is more complicated, before the formal production, the injection trial molding is started from the lower injection pressure, and then the increase or decrease is determined according to the quality of the plastic part, and finally the reasonable injection pressure is determined. After the melt fills the cavity of the injection mold, it still needs a certain time to hold the pressure. In production, the holding pressure is equal to or less than the injection pressure. When holding pressure is high, plastic parts with higher density, smaller shrinkage and better mechanical properties can be obtained, but the residual stress in the plastic parts after demolding is larger. , It will cause difficulty in demoulding.

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