In Mold Pressure Sensing Architecture for Multi Cavity Tooling Setup
In-cavity piezoelectric pressure sensing setups in multi-cavity tools decouple fill control from hydraulic drift to minimize scrap and verify part density.
Runner Shear Variance
Meaning
Rheological imbalances in melt distribution systems produce non-uniform shear histories across symmetrical flow paths. Processing engineers monitor runner shear variance to identify temperature and viscosity discrepancies between center and outer cavity channels. As polymer flows through runner channels, high shear rates near channel walls generate localized viscous heating, creating hot low-viscosity outer layers.
High-speed flow splitting at runner intersections distributes these thermally non-uniform layers unevenly into down-stream cavities. Multi-cavity tools experiencing this phenomenon exhibit variations in fill rate and volumetric shrinkage despite geometrically balanced runner lengths. Correcting shear imbalances requires specialized runner geometry modifications to homogenize melt temperatures.
Melt Imbalance
Fluid layers experiencing maximum shear stress migrate toward specific runner walls during laminar flow. Unmanaged runner shear variance forces higher-temperature material into inner cavities while cooler material fills outer cavities. Cavity pressure curves reveal significant filling time delays between balanced runner branches.
Viscosity variations caused by uneven shear heating induce differential molecular orientation across multi-cavity tools.
Part Variation
Dimensional discrepancies between parts molded in inner and outer cavities stem directly from unequal filling pressures induced by runner shear variance. Higher melt temperatures in specific cavities increase volumetric shrinkage, leading to reject parts.
Melt Rotation
Re-orienting melt layers using melt flippers or specialized geometric inserts homogenizes temperature profiles across sub-runners. Melt rotation eliminates runner shear variance by mixing high-shear outer layers into the core flow.