Special Subject: Forefront of fundamentals and applications of advanced powder processing
Rheometry of Cohesive Powder Flow
2020 Volume 63 Pages 3-12
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2020 Volume 63 Pages 3-12
Powder processing and manufacturing operations are rate processes for which the bottleneck is cohesive powder flow. Diversity of material properties and sensitivity to environmental conditions, such as humidity and tribo-electric charging, make its prediction very challenging, but highly desirable particularly when addressing a powder material for which only a small quantity is available. Furthermore, in a number of applications powder flow testing at low stress levels is highly desirable. Characterisation of bulk failure for flow initiation (quasi-static) of such powders is well established. However, bulk flow parameters are all sensitive to the speed with which the powder is sheared, but in contrast to quasi-static test methods, there is no shear cell for characterisation of bulk flow parameters in the dynamic regime. There are only a handful of instruments available for powder rheometry, in which the bulk resistance to motion can be quantified as a function of shear strain rate, but the challenge is relating the behaviour to the physical and mechanical properties of the constitutive particles. A critique of the current state of the art in rheometry of cohesive powder flow is presented, reviewing features of a number of widely used instruments.
