Meaning
State of complete thermal isolation between the runner system and the mould cavity occurs when the polymer melt in the gate area has fully solidified. Reaching a complete gate seal is necessary to ensure that the packed polymer does not backflow into the runner when the injection unit retracts or starts screw rotation. This state is reached after the holding pressure has been applied for a sufficient duration to allow the polymer to freeze across the gate’s cross-section.
The time to reach this state is a primary process variable for maintaining part consistency, especially in high-speed automated runs.
Weight Consistency
Variations in the weight of the moulded parts will occur if the hold pressure is terminated before the polymer has fully set. When the gate seal is not maintained long enough, the pressurized melt in the cavity flows backward, which reduces the final part weight and causes dimensional instability. Sourcing resins with a higher melt index can accelerate this backflow due to lower viscosity.
Cycle Optimization
Determining the exact moment of sealing allows the moulder to reduce the hold phase to the absolute minimum required. This prevents unnecessary hold time, which lowers the total cycle duration and improves the throughput of the moulding cell. Long hold times after sealing merely waste energy and extend the cycle.
Thermal Balance
Cooling rate of the mould steel around the gate area governs the time required to achieve a seal. Poor cooling line placement can lead to localized heat buildup, which delays the gate seal and forces the moulder to run longer cycle times. Correct cooling design is therefore essential for high-volume production runs.
