Powder Technology, Vol.305, 652-661, 2017
Characterization of stressing conditions in mills - A comprehensive research strategy based on well-characterized model particles
Despite the abundant industrial use of various wet mills a detailed understanding of the mechanisms involved is far from being complete. During comminution stress distributions are applied to the individual particles of a processed suspension. In fact, the type of stressing and the acting stress energies are distributed. The distributions of acting stress energy and number of stress events per product particle are governed by the used mill and its operational conditions. Mill functions link the stress energy and stress number distributions to the operating parameters and are so far unknown. We introduce a new methodology to directly characterize the effective stress energy and effective stress number distributions within stirred media mills: Mechanically fully characterized spherical particles are used as particulate probes. The underlying finite element model for the energetic behavior of the probes during uniaxial compression is supported by manipulation experiments on the single particle level. The deformation behavior of individual particles and the respective changes of the particles' shapes are used to determine the stressing history of the particles and hence the stress energy and stress number distributions in the mill. Experimental limitations and prospects of the proposed methodology are outlined in detail. The new approach is comprehensively discussed for a lab-scale stirred media mill operated at exemplary process conditions. The transfer to other mills or unit operations, however, is straightforward. (C) 2016 Elsevier B.V. All rights reserved.