Rheological Variation and Thermal Thermal Equilibrium in Polymer Processing
Melt temperature drift over 3 degrees Celsius shifts shear viscosity past structural tolerances, requiring active thermal balance before line acceleration.
Shear Rate Profile
Meaning
A spatial distribution velocity gradient describes how fluid layer velocity changes relative to flow channel walls during polymer extrusion or liquid pumping. Rheological modeling utilizes shear rate profile data to predict non-Newtonian flow behavior, shear thinning and wall slip in processing equipment. The profile governs fluid viscosity, shear heating and polymer chain alignment within die channels and pipes.
Analysis applicability ends where fluid flow halts and shear forces decay to zero.
Wall Shear
Maximum velocity gradients occur near channel walls where fluid friction exerts high shear stresses on flowing polymer. Mapping shear rate profile contours identifies high-stress zones where polymer degradation or melt fracture initiates. High wall shear increases viscous dissipation heat.
Viscosity Distribution
Non-Newtonian fluids experience localized viscosity reductions in high-shear regions across flow channel cross-sections. Characterizing shear rate profile variations enables accurate die design and pressure drop calculations for pseudoplastic materials. Supplier material data based on single-point shear testing fails to reflect polymer flow in complex die geometries.
Production flow prediction requires multi-point viscosity mapping across broad shear ranges.
Flow Stability
Sudden changes in channel cross-section disrupt velocity gradients and induce flow instabilities like sharkskin surface defects. Optimizing shear rate profile transitions smooths flow streamlines and prevents die swell anomalies during high-speed extrusion runs. Calling extrusion tooling ready without profiling shear distributions leads to surface defects on finished profiles.
Smooth velocity transitions maintain surface quality.