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Dynamic ball indentation for powder flow characterization

Tirapelle, Monica, Santomaso, Andrea C. and Hare, Colin (2020) Dynamic ball indentation for powder flow characterization Powder Technology, 360. pp. 1047-1054.

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In industrial processing and manufacturing, characterizing the flowability of particulate solids is of particular importance both for reliable powder flow and for a consistent production rate. Shear testing is the most widely used method for powders subjected to moderate or high stresses, and under quasi-static conditions. However, this method is not suitable for measuring the powder flow properties occurring in dynamic systems, such as powder mixers and screw conveyors. In this study, the rheological behaviour of powders at high shear rates has been evaluated by the ball indentation method. The technique, which simply consists of dropping a ball onto a cylindrical bed of previously consolidated powder, directly measures the material hardness, which is related to the unconfined yield stress by the constraint factor. The impact of the ball on the bed is recorded with a high-speed camera to determine velocity and penetration depth. The hardness against the strain rate is considered for four different materials. Because of their difference in particle size, and by using a range of drop heights and a range of indenter densities, the intermediate regime of flow has been fully analyzed. Although hardness is constant in the quasi-static condition, it results to be strain rate dependent in the intermediate regime of flow. Finally, a predictive correlation that allows the operator to choose the best operating conditions for achieving the desired flow regime is proposed, and the unconfined yield strength of the materials is inferred.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Chemical and Process Engineering
Authors :
Tirapelle, Monica
Santomaso, Andrea C.
Date : 15 January 2020
DOI : 10.1016/j.powtec.2019.11.009
Copyright Disclaimer : Copyright 2019 Published by Elsevier BV
Uncontrolled Keywords : Powder flowability; Powder rheology; Dynamic flow; Intermediate flow regime; Ball indentation
Depositing User : Diane Maxfield
Date Deposited : 13 Jan 2020 12:54
Last Modified : 09 Nov 2020 02:08

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