Flowability assessment of weakly consolidated fine powders

Flowability of powders is generally evaluated using the methodology proposed by Jenike, which is often referred to as the shear testing methodology. The shear testing methodology approaches the powder testing with a two-stage procedure; consolidation or pre-shear where a powder sample is sheared under a defined normal stress and attains the steady state when it shears at constant powder volume and shear stress; followed by a shear to failure where the powder’s strength is measured by shearing the sample under a reduced normal stress. There are many handling scenarios in industry in which the powders might not be subjected to flow regimes leading to critical shearing states, such as in dosing, filling and small-scale silos/hoppers for storage and discharge. Where the internal shear of the powder is limited during powder flow in these situations, and the powder may not achieve steady-state deformation conditions, it is plausible that the Jenike method of flowability assessment may not apply. The present study attempts to characterise the flow properties of fine cohesive powders, considering the possibility of powders to be partially consolidated or at un-steady state conditions. The study utilized the Schulze Ring Shear Tester to characterize flowability of two cohesive powders at steady and partially consolidated states and the discrete element method (DEM) technique was used to model the particle interactions, a coarse-grained meso-scale DEM model was developed and calibrated using experimental data. The study shows that the flowability depends on the state of consolidation or the deformation state of the powder.