Meaning
Measured against cavity cooling rates and runner heat dissipation curves, polymer solidification timing at the mold entrance defines the threshold where hydraulic pressure no longer affects part density. Dynamic study of gate freeze kinetics determines the minimum hold time necessary to prevent backflow of molten polymer into the runner system. Processing engineers use gate freeze kinetics to optimize cycle times while preventing sink marks and internal void defects.
Holding pressure applied after gate closure wastes energy and induces residual stress around the gate area. Precise determination of solidification kinetics ensures maximum part consistency without extending machine occupancy unnecessarily.
Solidification Rate
Gate dimensions directly dictate the heat transfer rate between molten resin and tool steel. Small pin gates freeze rapidly under ambient tool cooling, limiting hold time flexibility. Submarine gates with larger cross-sectional areas require extended pack phases to prevent void formation in thick wall sections.
Melt Backflow
Premature pressure release allows uncured polymer within the cavity to flow backward into the runner system. Cavity pressure drops sharply, resulting in volumetric shrinkage and dimensional variation across production lots.
Hold Calibration
Weight study protocols identify the exact moment gate freeze occurs by weighing parts molded under increasing hold times. Part mass plateaus once the gate solidifies completely.
