Apparent particle density, compression

There are three definitions needed to accurately describe this process. (1) Compaction is the compression and consolidation of a two-phase (particulate solid/gas) system by the application of an external force (2) compression causes an increase in the apparent density (or a reduction in volume) by the displacement of air and (3) consolidation is defined as an increase in mechanical strength due to particle-particle interaction [1,2]. 

The effective density of a particle is the particle mass divided by the volume of liquid it displaces (Archimedes density). Its true density is the particle mass divided by the volume it would occupy if it were compressed so as to eliminate all the pores and surface fissures. Its apparent density is its mass divided by its volume, excluding open pores but including closed pores. 

Three major quantities are used in P/M the bulk density of the loose iron powder (e.g., 3000 kg.m for water-atomized powder) which is lower than the apparent density due to air space. After compression, the compressed density doubles to about 6000 kg.m Finally, after sintering, the fusion that occurs between particles increases the steel s density to a density approaching the theoretical density or pore-free density. Three types of iron powders are available commercially. 

---