Gate Freeze

Hold Time

Optimization of the cycle time depends on identifying the minimum holding time required to reach this solid state. Continuing to apply hold pressure after gate freeze has occurred does not add polymer to the cavity but increases the total cycle time and energy consumption of the machine. Conversely, releasing the pressure too early allows the molten core of the part to flow back into the runner, resulting in sink marks or voids.

Part Weight

Measurements of part weight plotted against holding time show a distinct plateau when the gate solidify. Below this limit, the part weight rises as the machine continues to pack more polymer into the cavity to offset shrinkage. Once the curve flattens, the gate is frozen and the moulder can safely end the holding phase to maintain high output.

Runner Design

Dimensions of the gate itself dictate how quickly this freezing point is reached. A small gate freezes rapidly, which shortens the hold time but can restrict the packing of thick-walled parts, leading to internal stresses. A larger gate allows for more prolonged packing but extends the required hold time, which increases the overall part cost.