Cavity Balance
Pressure Drop
Process Window
Gate Seal
Cooling Study
Theory of Pressure Drop

As plastic flows through the different sections of the machine and the mold, because of drag and frictional effects there is a loss of the applied pressure at the flow front of the plastic. Additionally, as the plastic hits the walls of the mold, it begins to cool increasing the viscosity of the plastic requiring additional pressure to push the plastic. The skin of plastic that is formed at the walls decreases the cross sectional area of the plastic flow that also results in the pressure drop. The molding machine has a limited maximum amount of pressure available to push the screw at the set injection speed. The required pressure to push the screw at the set injection speed should never be more than the maximum available pressure. In this case the process becomes pressure limited. During process development, knowing the pressure loss in every section helps in determining the overall pressure loss and the sections where the pressure drops are high. The mold can then be modified to reduce this pressure drop and achieve a better consistent flow.



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