Meaning
Determination of the exact time required for the molten polymer within the gate of an injection mould to solidify completely prevents material from flowing back out of the cavity when the holding pressure is released. This gate seal test establishes the optimum holding pressure time for a specific resin and part geometry.
Experimental Method
Molders perform this trial by starting with a very short holding pressure time and systematically increasing it in small increments while keeping other process variables constant. For each step, the weight of the molded parts is recorded and plotted against the hold time. The point on the graph where the part weight stops increasing indicates that the gate has frozen, meaning the gate seal test has successfully identified the threshold of solidification.
Optimization Yield
Running the process with a holding time that is shorter than the freeze-off time leads to sink marks, voids, and high dimensional variation. Conversely, excessive hold time beyond the freeze-off point needlessly extends the cycle time and increases energy consumption without improving part quality. Finding this balance ensures consistent part weight and dimensional stability across the production run.
Boundary Condition
Variations in melt temperature, coolant flow, or gate wear can shift the freeze-off point during a long production run. A datasheet value for gate freeze cannot predict these dynamic changes, which makes periodic testing on the active press necessary for high-tolerance components. This test is therefore a part-specific measurement rather than a general material property.
