Processing fine powders by roll press

• Role of trapped gas in roll compaction of fine powders is explored.
• Density of the solid is determined using Johanson model.
• Velocity of the solid is calculated from mass conservation.
• Gas pressure distribution is determined using Darcy’s law.
• Conditions of process instabilities are discussed.

The gas trapped into fine powders causes specific problems like feeding disturbances during roll compaction process. In this study, the gas flow and its effect on the rolling process are numerically investigated in the rolling direction, using Darcy's law and assuming the permeability as a function of both material density and particle size through Carman–Kozeny relationship. The solid properties evolution is based on the Johanson model, whereas the solid speed is determined from the conservation of the material mass.Computational results of solid properties and gas pressure distribution are presented by considering bentonite powder properties. According to material and process parameters, especially rolling speed and powder permeability, we discuss conditions for the escape of gas through the porous material during the process and stability conditions of the feeding at the rolls' entry.Beyond the simplicity of the model (1D), it allows for a better understanding of fine powders processing by roll press. It highlights the combined effect of the permeability of the powder and the rotating speed on the gas pressure, during roll compaction process.

Stability zones for processing fine powders by roll press (DPG=∂P∂xθ0/ρsg).Figure optionsDownload as PowerPoint slide