PACKING STRUCTURE OF POWDER COMPACTS

Abstract

The particle packing process is the major step in manufacturing of high-performance products and materials production in many industries. The shape and size of particles are the most important factors influencing the packing process. Therefore, in the recent years, there has been a growing interest in the investigation of packing structure of powder compacts containing non-spherically shaped particles. However, the thorough analysis of compact morphology is still limited. Thus, the main aim of the thesis work is to study the effects of various shapes of non-spherical particles and addition of non-spherical particles into spherical particles mixture on the packing microstructure of obtained compacts. The thesis reviews methodologies currently applied in the evaluation of packed compacts characteristics such as discrete element method, void size distribution and Voronoi tessellation analyses. Initial steps of creation of packed powder compacts employed DEM with superquadrics approachto generate non-spherical shaped particles. The provided two studies covered different simulation objects. The first samples are three specimens: pills, cylinders, and spheres of 45,000 particles in each compact with similar particles volume in order to focus on the packing structure analysis of shape effect. The second samples are four specimens of binary mixture of spheres (rfine:rcoarse 2cm: 4cm) with and without inclusion of fibers: ffine:fcoarse:ffiber 63:37:0, 62:37:1, 40:60:0, and 40:59:1. The results of first study analysis showed a trend of void size distribution among cross-sectional images normal to x and y with the dominance of small voids and uniform voids distribution for pills and cylinders compacts. However, symmetrical shape of spherical particles compacts affected to the small voids distribution in z direction in comparison with other two samples. Furthermore, the characteristics of constructed Voronoi diagram depicted voronoi cells volumes and surface areas. The pills compact showed the highest peak with narrower plot whereas cylinders compact had the lowest peak in the distribution of voronoi cell volumes. On the contrary, the distribution of voronoi cells surface area of spherical particles was with narrower plot and the highest peak due to construction of similar polygonal voronoi cells than for pills and cylinders. The second study had resulted in more uniform void size distribution for sample of large amount of fine spherical particles in binary mixture. Moreover, the addition of fibers contributed to generation of more packed compacts with small voids. The sample of 1%wt. of fibers, 62%wt. of fine and 37%wt. of coarse spheres demonstrated the smallest median size of voids 50 d = 0.795 mm and the most uniform voids distribution with sharpness index d10/d90 = 0.345. In conclusion, it was found that the non-spherical particles shape can significantly affect to the packing structure of powder compacts. The analyses of void size distribution and Voronoi tessellation can ensure more packed compacts with small-scale voids and smooth voronoi cells construction for irregular shapes of pills and cylinders than spherical particles. Likewise, the inclusion of non-spherical particles contributed to the formation of more packed compacts for ternary mixture of fine and coarse spheres, and fibers.