Today's KNOWLEDGE Share : Filling at Constant Pressure

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Today's KNOWLEDGE Share

Historically, early injection molding machines would essentially be pressure controlled.

Many good parts have been made under such process control. So,it is not all bad !



However, note that when molding an end-gated fairly long part, a constant pressure fill translates into an ever decreasing melt front velocity, as the pressure drop builds up.

This in turns corresponds to a decreasing average temperature of the melt front along the flow.


Such a decreasing T will create an increasingly strong degree of molecular orientation when moving away from the gate. The part, especially when using semi-crystalline grades, will have a strong gradient of mechanical properties along the flow which could be as serious as showing good ductility near the gate and severe brittleness far from the gate.


source:Vito leo

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