Incipient flow properties of two-component fine powder systems and their relationships with bulk density and particle contacts

The effect of incipient flow properties, such as cohesion and internal angle of friction, on the flowability of two-component fine powder systems is of great importance for controlling the process efficiency and quality of industrial products such as developers for electrophotographic (EP) printing devices. In this paper, we have studied the flow properties of model fine powders composed of glass ballotini (d(50)=69.4 mu m) and resin toners (d(50)= 6-8 mu m), using different mixing ratios of the components under a low normal consolidation stress (2 kPa) using a ring shear tester (RST). We have found that the dependence of the cohesion of the two-component mixtures on the mixing ratio can be reproduced by a linear superposition of the cohesions of each component weighted by the number of the three different types of interparticle contacts, which suggests that the bulk cohesive properties of fine powder mixtures are dominated by cohesion between particles and the number of each type of particle contacts in the system. Also, the frictional properties of the two-component mixtures are strongly related to the packing density of the mixture, and its dependence on the mixing ratio can be related to the densities of each type of particle contacts. Our results suggest that the dependence of the incipient flow properties of two-component fine powders on the ratio of the components can be predicted by measuring only the flow properties of each component and estimating the ease with which the mixture can be compacted. (C) 2012 Elsevier B.V. All rights reserved.