The purpose of the pressure drop test of the injection molding process and "pressure limitation"

Pressure drop test of the plastic molding process

In the injection molding process, pressure changes are closely related to the quality of molded products. Therefore, evaluating the pressure in different stages of filling and the pressure change history of the plastic cavity during the injection process is helpful to study the influence of the rheology of the material in the cavity and other process parameters on the cavity pressure and product quality.

The purpose of the pressure drop test: is to evaluate the pressure loss at different stages of filling. This usually includes the machine nozzle, vertical runner, main runner, secondary runner, gate, and filling end.

What is the "pressure limitation" in the injection molding process?

The molding process should not use the maximum pressure of the machine. For example, if the maximum pressure of the machine is 180 Bar, then the maximum pressure required for filling should not reach 180 Bar. If this is the case, it means that the screw needs more pressure. The set injection speed is reached, but it cannot be reached due to pressure limitations. This situation is called "pressure limitation".

Generally, the injection process should not exceed 90% of the maximum pressure of the machine. In the pressure drop curve that is made, if the pressure is "limited" or more than 90% of the machine pressure, find the steeper section of the pressure curve and try to reduce the pressure loss here. For example, in the picture on the right, the pressure drop of the secondary flow channel is very large, which means that a lot of force is needed to promote the flow of plastic in this section. Enlarging the diameter of the flow channel in this section will help reduce the pressure.