Meaning
Fundamental thermodynamic parameters describe the exponential increase in fluid viscosity resulting from elevated hydrostatic pressure during polymer processing. Calculation of the pizo-viscosity coefficient quantifies melt resistance to flow inside high-pressure injection mold cavities and runner systems. Polymer melts under hundreds of bars of pressure experience free volume reduction that compresses molecular chains together.
The governing relationship applies in ultra-high-pressure injection molding and thin-wall filling, whereas standard low-pressure extrusion ignores pressure-dependent viscosity effects.
Pressure Response
Hydrostatic pressure packs polymer chains together, restricting segment mobility and increasing flow resistance independently of temperature drops. Polymer melts characterized by a high pizo-viscosity coefficient exhibit sudden viscosity spikes near nozzle restrictors and thin gate entrances. Processors observing injection pressure spikes often misinterpret pressure-induced thickening as premature thermal freezing.
Correctly accounting for pressure sensitivity prevents misdiagnosing flow hesitation in long flow path molds.
Flow Modeling
Mold filling simulations incorporate pressure-dependent viscosity models to predict required clamp tonnage and injection pressure limits accurately. Omission of the pizo-viscosity coefficient leads software to underestimate fill pressure by up to thirty percent in micro-moulding applications. Accurate simulation prevents mold flashed edges and incomplete cavity filling.
Cavity Pressure
High pressure inside the runner system raises viscosity, requiring higher hydraulic pressure to maintain volumetric injection rate. Hydraulic pressure demands scale sharply when the pizo-viscosity coefficient is elevated. Molders must balance clamp force and injection speed to avoid exceeding machine pressure limits.
