Where does the pressure of the injection mold come from?
2023-09-01
Injection pressure Cavity pressure refers to the melt pressure generated in the Mold cavity after the injection pressure passes through the pressure loss of the nozzle, runner, and gate. The pressure of the injection mold is provided by the hydraulic system of the Injection Molding system. The pressure of the hydraulic cylinder is transmitted to the plastic melt through the screw of the injection molding machine. Under the push of pressure, the plastic melt enters the vertical flow channel, main flow channel, and diversion channel of the mold through the nozzle of the injection molding machine, and enters the mold cavity through the gate. This process is called the injection molding process, or the filling process. The existence of pressure is to overcome the resistance during the melt flow process, or conversely, the resistance during the flow process needs to be offset by the pressure of the injection molding machine to ensure the smooth filling process. 
During the injection molding process, the pressure at the nozzle is the highest, as the first entrance of the melt into the mold requires high pressure to overcome the resistance encountered by the melt entering the flow channel. The pressure gradually decreases along the flow length towards the front end of the melt. If the cavity is well vented, the final pressure at the front end of the melt is atmospheric pressure. We know that when injection molds are used to inject products, the solution is transported to the injection nozzle through a spiral rod, and then through the injection nozzle, it is transported to the runner port and enters the mold cavity. The pressure generated by the head of the spiral rod during injection is the pressure of the injection mold, and the solution needs to be injected through pressure. If the injection pressure is too low, it can lead to insufficient pressure in the mold cavity, and the solution cannot smoothly fill the mold cavity. If the injection pressure is too high, it is easy to cause problems such as solution overflow and plastic deformation. Therefore, it is important to control the injection pressure during the Injection Process. The plasticizing pressure increases the internal pressure of the melt, enhances the shear effect, and increases the temperature of the melt due to the shear heating of the plastic. The increase in plasticizing pressure slows down the return speed of the screw, prolongs the heating time of the plastic in the screw, and improves the plasticizing quality; However, excessive plasticizing pressure also increases the reflux and leakage of the melt in the measuring chamber of the material barrel, reduces the conveying capacity of the melt, reduces the plasticizing amount, increases power consumption, and excessive plasticizing pressure can cause shear heating or excessive shear stress, making the melt prone to degradation. During the injection process, the injection pressure and melt temperature are interdependent. The combination of injection pressure and material temperature is required to achieve satisfactory results when the material temperature is high.
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