Meaning
Solidification of polymer melt within the feed channel stops pressure transmission between the runner system and the mold cavity. Achieving gate freeze-off marks the transition where packing pressure no longer affects part weight or internal cavity pressure. As heat dissipates into the colder steel walls, the gate core transitions from viscous liquid to solid polymer, effectively sealing the cavity.
This thermal event dictates hold time requirements but does not control the initial filling speed of the injection shot.
Hold Time Optimization
Part mass stabilization indicates the exact moment when melt flow through the entrance channel ceases. Determining gate freeze-off involves weighing molded parts produced at incrementally longer hold times until part weight reaches a constant plateau. Setting hold time past this freeze point wastes cycle time, while short hold times cause volumetric sink marks and dimensional instability.
Gate Dimensions
Geometry dictates cooling rates within the narrow feed passage relative to main wall sections. Rapid gate freeze-off occurs when gate dimensions are too small, preventing adequate cavity packing and leading to excessive part shrinkage. Oversized gates extend cooling times unnecessarily, increasing total cycle cost and complicating gate vestige trimming.
Thermal Control
Mold coolant temperatures alter solidification rates within the runner system and entrance channels. Delaying gate freeze-off requires raising mold temperature around the gate area or increasing melt temperature, allowing extended packing pressure transmission. Conversely, lowering coolant temperatures speeds gate solidification, shortening cycle times for thin-walled parts.
