The total amount of a medium transported through a cross section in a given time is called flow rate.
In mathematical formula, the letter Q can be found as representative of the flow rate.

The filling in injection molding is generally controlled by flow rate from the start of the injection phase until the switch over point is reached.
In this phase the machine keeps the flow rate on the set value.
Therefore dependent on the cavity volume the given flow rate results in a pressure profile.
Usually the screw moves forward until the given switch over point is reached. The movement can be done with different speeds (profile).

At the switch over point, the machine switches to pressure control until the end of packing phase.
This means that a given pressure is kept before the tip of the screw.
Based on that a flow rate is determined.

The flow rate it not only important regarding injection, but also for the coolant.
It decisively decides on the height of the Reynolds number and therefore on laminar or turbulent flow.
The possible flow rate depends on the respective cooling device and needs to be checked based on the pump curve.

Flow Rate in Injection Molding

Injection molding process: The flow rate Q is the amount of a medium, which flows in a given time through a cross section.

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This glossary of plastic industry is provided by PLEXPERT Canada Inc.