ABSTRACT
Compressibility and compactability of a powder are influenced by the flow properties, and in the microscale, by the adhesion forces between particles. These properties of bulk materials can be analyzed using a shear cell. And the strength of the agglomerate – here the compressed powder – can be determined by shear test. The compression can be described by compression rate, compression function and specific compression work Tomas (2004). For the correlation between bulk density or agglomerate density ρb and the characteristic stress during steady-state flow or average pressure σM,st only five material parameters from powder mechanics are used: the bulk density ρb,0 for a loose packing without any compaction, the isostatic tensile strength σ0 for the loose packing, the angle of internal friction ϕi, the stationary angle of internal friction ϕst and the compressibility index n. The so-called compression rate describes a compression increment (Kawakita & Lüdde, 1970; Mort et al. 1994), which includes the compressibility index n as the characteristic for volume reduction of a cohesive powder:
The physical basis of this comfortable expression was shown in previous paper Tomas (2004). The compression function describes the relationship between the applied pressure and the agglomerate density. The
compression function can be obtained by integrating the compression rate Equation (1)
and the mass related or specific compression work is obtained by an additional integration of the reciprocal compression function Equation (2).
