Meaning
Solidification of polymer melt within the restrictive entrance channel connecting an injection mould runner to its cavity prevents further mass transfer into or out of the moulded part. The occurrence of gate freeze establishes the boundary between dynamic cavity pressurisation during the packing phase and subsequent isolated cooling of the captive polymer mass. The measurement boundary applies specifically to the gate volume itself, terminating where the larger cross-sections of the runner system and the cavity interior remain molten.
Solidification Curve
Controlled experiments establish the precise freeze threshold by incremental increases in machine hold time, accompanied by analytical weighing of the resulting components. Component mass climbs steadily as prolonged packing force delivers supplemental resin to compensate for volumetric thermal shrinkage, until the mass reaches an absolute plateau. Once the gate freezes solid, additional hold time delivers zero mass gain, producing purely wasted cycle duration and mechanical wear.
Part weight fluctuations during unoptimised runs confirm incomplete gate seal.
Commissioning Audit
Factory acceptance trials require gate freeze studies across all operational tooling cavities to verify thermal consistency across the mould base. Suppliers frequently forecast elevated cycle rates by shortening machine hold times below the actual freeze point, which induces uncontrolled sink formation and dimensional shrinkage. Measuring gate freeze across low and high ambient machine cooling conditions confirms whether water jacket configurations sustain proper gate thermal balance.
Production yields plummet if tools are released with hold times truncated ahead of physical freeze, as cavity pressure drops induce reverse resin backflow into the runner system.
Thermal Management
Gate cross-sectional geometry and localised cooling channel routing dictate the exact instant of resin solid state transition. Pin gates and hot runner valve tips shorten the freeze window, whereas thick edge or tab gates sustain prolonged fluid channels that demand extended dwell times under pack pressure. High-conductivity mould copper alloys accelerate local heat extraction around the gate zone, narrowing the cycle threshold without changing part volume.
Variations in melt temperature between consecutive barrel charges shift the freeze point, introducing subtle part density drift under fixed machine timers.
