The gate open-time, is the time the melt takes to solidify. During this time, the thermal volume contraction of the cooling molding is evened out by the holding pressure, and the shrinkage of the molding is therefore minimized.
After the gate open-time has passed, the holding pressure can be switched off because, due to the solidified sprue, it can no longer be transferred to the mold cavity. Further extension of the holding pressure thereby no longer increases the weight of the molding but extends the cycle time unnecessarily.
The gate open-time is normally determined by extending the holding pressure time long enough until weight constancy of the molding has been achieved. Gate open-times are determined more rationally and precisely using the process data processing BMCS by means of the process data value ”sealing index”. The sealing index is calculated from the pressure transfer function between hydraulic and internal mold pressure and replaces traditional weight measurement.
A sealing index of 100 % indicates complete solidification of the melt in the injection mold and thereby marks the gate open-time.
