Determination of processing data: Gate open time

The gate open time is the time the melt takes to solidify in the injection mold.

During this time, the thermal volume contraction of the cooling molding is compensated by the holding pressure and the shrinkage of the molding is therefore minimised. Once the gate has been sealed, the holding pressure can be switched off because it can no longer be transferred to the mold cavity due to the solidified sprue. A longer holding pressure time would simply extend the cycle time unnecessarily rather than further increasing the weight of the molding.

The gate open time is normally determined by gradually extending the holding pressure time until the weight of the molding is constant. A more rational and more precise way to determine the gate open time is to use the “sealing index” in the MCS system for process data processing. The sealing index is calculated from the pressure transfer function between the hydraulic pressure and the cavity pressure and replaces the traditional weight measurement. A sealing index of 100% indicates complete solidification of the melt in the injection mold and marks the end of the gate open time.