Rheological Quality Control Limits in Polymer Extrusion Manufacturing
Polymer extrusion quality control limits require dynamic multi-point shear viscosity bounds at process shear rates to eliminate scrap and protect converting margins.
High Shear Processing
Meaning
Industrial mixing operations use intense mechanical forces to disperse or homogenize materials that are otherwise immiscible. Employing high shear processing is common in the production of polymers, paints, and specialty chemicals. It relies on a high rotor speed to generate the necessary fluid velocity gradients.
Energy Expenditure
Heat generation is an inevitable consequence of intensive mechanical dispersion. With high shear processing, the temperature of the mixture must be carefully controlled using cooling jackets to prevent the degradation of heat-sensitive active ingredients. This increases the total energy load of the plant.
Viscosity Reduction
Shear-thinning fluids experience a temporary drop in flow resistance when subjected to intense mechanical stress. This aspect of high shear processing enables easier pumping through narrow pipes and nozzles during the packaging stage. Once the stress is removed, the material returns to its high-viscosity state.
Equipment Wear
Rapid wear occurs on rotor blades and stator screens due to the high velocities involved. Regular maintenance and hard-facing of these components are required to maintain the efficiency of high shear processing over long production runs. Replacing these components during planned shutdowns prevents unexpected failures.
When abrasive materials are processed, the rotor-stator gap must be measured weekly, since even a fraction of a millimetre of wear will reduce the droplet-size reduction capability and result in a coarser emulsion that may separate in storage.