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Viewpoint - good powder, bad powder
Powder flowability may appear to be a straightforward term describing how easily a powder flows, but with no units of flowability or reference database, how do we define it?
Generally 'good' and 'bad' are relative terms used to compare one powder with another. Tumble a cohesive powder and a non-cohesive one and it is clear which is the more free-flowing. Cohesive materials typically flow in agglomerated lumps, whereas each particle in a free-flowing powder moves independently. So we could define flowability as the extent to which particles move relative to their neighbours when powder is made to flow.
Observations show that a non-cohesive powder requires less force or energy to cause it to flow, so flowability could also be defined as the energy or work required to cause flow. Yet another definition might be the shear strength of the powder or its cohesion value.
These broad descriptions guide us when looking at how best to measure flowability, but more fundamentally, what do we mean by a 'powder'? Some thoughts on this in our next issue.
Reg Freeman, Managing Director |
