(270h) Investigation of Segregation Effect on the Packing Fraction for Density Estimation

Granular segregation is a commonly encountered problem during powder handling. Indeed, powders are polydisperse granular materials by nature. The size differences between particles can lead to various effects: small grains can percolate through the porous medium made by larger particles, the Brazil Nuts effect has the tendency to bring the large grains on the top of a granular pile under the influence of vibrations or a powder flow can unmix different species. While homogenous mixing can be time and energy consuming, the next steps of a manufacturing process can segregate the prepared powder mixture during conveying or packing due to inherent vibrations and flow encountered that lead to granular segregation.

Although granular segregation can be observed in manufacturing processes, powder mixtures are often assumed homogeneous for modelization and next steps. However, a segregated powder can lead to unwanted drawback. As an example, for medicines, the powder mixture must have a good homogeneity to guarantee a precise amount of active material and good mechanical properties. Another example is the density of concrete which is highly dependent on the homogeneity of the granular material inside the mixture.

The bulk density of a granular mixture is an important parameter that can influences properties of the final product such as its mechanical properties. We present experimental results on the bulk density of binary mixtures, made of two sizes of glass beads as model material. Different mixtures were prepared with different degrees of homogeneity by forcing the segregation and varying the proportion of small and large particles. For each mixture, the bulk density was measured by a tap density method with a GranuPack. The segregated mixtures are compared to the homogeneous ones to highlight the influence of segregation on the bulk density. A model [1] was developed to modelize the bulk density as a function of the spatial distribution of the two species in the packing. These results can be valuable in powder mixture proportioning and designing, considering the segregation impact.

References

[1] Pillitteri, S., Lumay, G., Opsomer, É. and Vandewalle, N., 2021. Forced segregation in binary granular mixtures. In EPJ Web of Conferences (Vol. 249, p. 02001). EDP Sciences.