Injection pressure 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 pressure, the plastic melt enters the vertical flow path of the mold through the injection nozzle of the injection molding machine (for some molds, it is also the main flow path), the main flow channel, and the flow distribution. Road, and through the gate into the mold cavity, this process is the injection process, or called filling process. The existence of pressure is to overcome the resistance during the flow of the melt, or conversely, the resistance existing in the flow needs to be offset by the pressure of the injection molding machine to ensure the smooth progress of the filling process.
In the injection molding process, the pressure at the nozzle of the injection molding machine is the highest to overcome the flow resistance during the entire melt. Thereafter, the pressure is gradually reduced along the length of the flow toward the front of the melt, and if the inside of the cavity is well vented, the final pressure at the front of the melt is atmospheric pressure.
There are many factors affecting the melt filling pressure. There are three general categories: (1) material factors, such as the type and viscosity of the plastic; (2) structural factors, such as the type, number, and position of the gating system, the shape of the cavity of the mold, and the shape of the product. Thickness, etc.; (3) Forming process elements.