Liquid or solid: Can you measure powder flow behavior?
The paint and coatings industry has significant experience with rheology as it applies to the world of liquid, semi-solid, and powder-based materials. One interesting challenge confronting powder coating companies is that the science of flow behavior for measuring liquids is just the opposite for powders. The controlling parameter for liquids, known as shear rate, appears to be inconsequential when measuring powders. Consolidation stress is the control parameter that dictates powder flow behavior in gravity discharge from bins, silos, and intermediate bulk containers. This article reviews the test methods that are traditionally used by manufacturers to predict “flowability” of coating materials and then presents some new alternatives.
Viscosity is the primary property that manufacturers focus on to characterize flow behavior of liquid coatings. The simple definition for viscosity is “resistance to flow.” Science defines viscosity as shear stress divided by shear rate.