Pore Stabilization in Cohesive Granular Systems

Cohesive powders tend to form porous aggregates which can be compacted by applying an external pressure. This process is modelled using the Contact Dynamics method supplemented with a cohesion law and rolling friction. Starting with ballistic deposits of varying density, we investigate how the porosity of the compacted sample depends on the cohesion strength and the friction coefficients. This allows to explain different pore stabilization mechanisms. The final porosity depends on the cohesion force scaled by the external pressure and on the lateral distance between branches of the ballistic deposit r_capt. Even if cohesion is switched off, pores can be stabilized by Coulomb friction alone. This effect is weak for round particles, as long as the friction coefficient is smaller than 1. However, for nonspherical particles the effect is much stronger.Comment: 10 pages, 15 figure

Material characterisation for discrete element modelling calibration

The accurate determination of the microparameters needed in a Discrete Element Method (DEM) simulation is essential to obtain reliable results. In this work the DEM model parameters sensitivity in three different laboratory tests (single particle drop test, uniaxial particle compression and rotating drum) are investigated with respect to parameter value changes. The DEM parameters are varied by ± 25% from standard values. Materials used are 3.0 mm soda lime glass spheres and 3.0 mm polyamide spheres. Drop test simulations were sensitive only to change in coefficient of restitution parameter. The single particle compression test indicates that mainly the elasticity parameters influence the numerical response, Young’s modulus and Poisson’s ratio respectively. The sensitivity analysis indicates that the dynamic angle of repose in simulations depends on static as well as rolling friction coefficients

Investigation of powder properties using alternating strain paths

Steady-state flow (ssf) of powders has been investigated using alternating strain paths, with precompacted powder samples sheared in alternating directions. The dependency of ssf on the level of precompaction is shown

Use of organic byproducts as binders in the roll compaction of caustic magnesia

This paper presents an improvement of the roll compaction process of dusty caustic magnesia carried out by using vinasses and molasses from the sugar beet industry as organic binders. The objective of this industrial study is to verify the possibility of increasing the particle size of the powdery raw material by granulation. It involved an instrumented pilot scale roller press (corrugated surface) to set the operating parameters and control the agglomeration process assessing the quality of the product established on a lot of final granules. As result, the effect of the addition of 5% (w/w) of binder by a spray nozzle atomizer on the caustic magnesia and the intensive mixing in a high shear mixer reduces notably the proportion of fines (by 30%) and increases significantly the rate of granules greater than 2. mm formed when the "moist powders" are compacted in the subsequent pressure agglomeration unit. This furtherance represents a process optimization strategy which increases the productivity and achieves a significant reduction in the quantum of failures. © 2012 Elsevier B.V. All rights reserved