Numerical analysis of density-induced segregation during die filling

In this study, segregation behaviour of binary granular mixtures with the same particle size but different densities during die filling in the presence of air was investigated using a combined discrete element method (DEM) and computational fluid dynamics (CFD) approach, in which the kinematics of particles was modelled using DEM, the motion of air was analysed using CFD and a two-way coupling of the particles and the air was incorporated. The depositions of powder from stationary and moving shoes into the die cavities of different geometries were simulated and the corresponding segregation behaviours were analysed. It has been found that, for die filling from a stationary shoe, the concentration distributions of the heavy and light particles along the die width mainly depend on the initial spatial distribution of the granular mixture in the shoe. For die filling from a moving shoe, a low concentration of light particles on the leading side of the die (referring to the direction of the shoe motion) is observed for die filling with a square die, in which the process is dominated by nose flow. The density difference can cause segregation along the die depth with a low concentration of light particles at the bottom. The presence of air enhances this segregation tendency by resisting the flow of light particles into the bottom of the die and causes a higher concentration of the light particles at the top. Finally, the segregation index, defined as the volume weighted root-mean-square deviation in the content of light particles, was introduced to quantify the degree of segregation in the horizontal and vertical directions. It has been found that the degree of segregation is determined by the presence of air and also the powder flow pattern.

Graphical abstractA coupled DEM/CFD method which incorporates a two-way coupling of particles and air is used to investigate density-induced segregation of binary mixtures during die filling in air. Results show that the presence of air resists the flow of light particles and promotes the segregation with a depletion of light particles at the bottom of die cavity. The segregation behaviour also depends on powder flow patterns.Figure optionsDownload full-size imageDownload as PowerPoint slide