Meaning
Pressure loss rate represents a quantitative metric tracking the drop in internal mould force after the injection stage concludes. Cavity pressure decay provides a precise observation of how the cooling resin compacts within the tool volume while transition occurs from a fluid state to a solid state. This observation marks the boundary between effective packing and thermal shrinkage, defining the exact moment when the gates seal the part from the feed system.
Moulding Control
Operators utilize the measurement to detect flow restrictions or variations in viscosity that cause irregular wall thickness. Cavity pressure decay governs the set point for hold time in automated injection sequences to ensure complete solidification. An improper rate indicates thermal instability or a blockage in the nozzle which results in short shots or sink marks.
High decay values often signal that the polymer has not reached the necessary density because the packing phase ended too early.
Process Variation
Regrind blending increases the sensitivity of this measurement because the reduced viscosity shifts the moment of pressure loss relative to a virgin resin baseline. Moulders maintain a stable profile for cavity pressure decay to differentiate between machine repeatability and material batch shifts. Datasheet values regarding melt flow index provide a theoretical range, yet the recorded loss rate inside the tool confirms if the heat transfer matches the production requirement.
Tooling Impact
Effective pressure management prevents flash by ensuring the clamping force counters the internal load before the cycle finishes. Cavity pressure decay establishes the threshold for tool maintenance by linking structural leaks or worn seals to specific deviations in the pressure curve. Monitoring this variable prevents the production of parts with internal voids that compromise structural integrity.
