Surface Melt Fracture Onset Limits in Polyolefin Profile Extrusion
Surface melt fracture limits in polyolefin profile extrusion are governed by critical wall shear stress thresholds between 0.08 and 0.14 MPa at the die exit.
Weissenberg Rabinowitsch Correction
Meaning
Mathematical adjustments in rheology allow for the accurate calculation of shear rates for fluids that do not follow a simple linear flow model. The Weissenberg Rabinowitsch Correction is applied to data from capillary viscometers to account for the non-Newtonian nature of the material. It corrects the wall shear rate to reflect the true velocity gradient in the pipe.
This calculation is essential for polymer processing and food manufacturing.
Shear Rate
Measurements taken at the edge of a flow channel often underestimate the real speed of the fluid layers. By applying the Weissenberg Rabinowitsch Correction, engineers find the actual rate of deformation happening inside the material. This value is used to predict how the fluid will behave in an extruder or a pump.
Accurate rates lead to better product consistency.
Fluid Viscosity
Resistance to flow changes as the material moves faster or slower. The Weissenberg Rabinowitsch Correction helps in plotting the true viscosity curve across a range of speeds. Without this adjustment, the data would show an incorrect relationship between pressure and flow.
This curve is the fingerprint of the material’s processability.
Pipe Geometry
Dimensions of the tube and the pressure drop across it are the raw inputs for the formula. When the Weissenberg Rabinowitsch Correction is used, it takes the slope of the flow curve into account to fix the errors caused by the assumed parabolic velocity profile. This ensures that results from a small lab test can be scaled up to a production line.
It is a fundamental step in chemical engineering.