Theory of Compaction of Bulk Materials
- 97 Downloads
The mechanical properties of high pressure produced pellets depend on many factors. The most important factors are the type of wood, particle size, moisture content, the compaction pressure, the compaction speed, the deformation holding time, the punch diameter and the press temperature. Description of mechanical changes during high pressure compression of wood chips, the stress (σ)—deformation (ε) relationship are formulated by non-linear rheological methods, because the wood has a non-linear viscoelastic property. Consequently, during the compression process, the elastic modulus of wood chips greatly increases, and the resulted pellet at the end of the process suffers residual deformation. The amount of residual deformation determines the properties of a pellet, especially its density. This chapter gives a detailed overview of the rheological models and rheological equations, the non-linear compaction of bulk materials, some specific behavior of bulk materials with internal and external pores, general regularities of compaction and their energy requirements, pressure relations in the die-ring channel, similarity equation of the energy consumption of the pelleting process and the determination of channel length for a given pressure.