Simple Physics of Powder Density in Gravity Discharge
22 Mar 2017
Ametek Brookfield has published a paper detailing techniques for analysing powder density.
Powder at rest can be deceiving. Spread out on a horizontal surface, the particles may look perfectly flowable because they move easily to the touch. Put the powder into a container and its behaviour in gravity discharge out the bottom may be something very different.
Powder particles unconstrained on a horizontal surface have plenty of open space between one another. They move freely at the slightest touch. When placed in a container, the self-weight of the particles on top pushes down on those below. Air between the particles is gradually squeezed out. Settling takes place as spacing between the particles moves closer. Consolidation causes bulk density to increase over time relative to the 'loosefill' condition when the powder was poured into the container.
One general observation is that powders which compress to less than half their original volume are prime candidates to have flow behaviour issues during processing. Is there a way to identify problem powders using this criterion? It’s one way to begin, but cannot be the sole test basis for making final judgement.
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