High Shear Rheology Calibration Thresholds for Recovered Polyolefin Industrial Blends
Calibrating high-shear capillary rheology via Bagley and Weissenberg-Rabinowitsch corrections prevents off-spec polyolefin lot processing failures.
Weissenberg-Rabinowitsch Correction
Meaning
Capillary rheometry mathematical transformations convert apparent shear rates measured in circular capillary dies into true wall shear rates for non-Newtonian polymer melts. Weissenberg-Rabinowitsch correction accounts for velocity profile blunting caused by shear thinning behavior inside die flow channels. The calculation delivers accurate viscosity data required for numerical flow simulation and injection mould cavity filling analysis.
Application applies strictly to steady, fully developed laminar flow of non-Newtonian fluids in circular tubes or slits.
Shear Adjustment
Shear thinning fluids flow with flatter velocity profiles than ideal Newtonian fluids, increasing actual shear rate at die walls. Applying the weissenberg-rabinowitsch correction increases calculated wall shear rate, preventing gross underestimation of shear stress and fluid viscosity. Datasheet viscosity curves rely on this mathematical adjustment to reflect true shear thinning behavior across multiple decades of shear rate.
Regrind additions alter the power law slope, changing magnitude of necessary rate corrections.
Rheological Accuracy
True shear rate values ensure correct calibration of non-Newtonian fluid models used in mold filling simulation software. Accurate flow models prevent miscalculating gate pressure drops during tool design.
Flow Assumption
Wall slip or yield stress violates basic velocity gradient assumptions of the correction equation. Uncorrected slip phenomena lead to overestimation of true fluid shearing rates.