How readily a powder moves under specified handling or test conditions.
Also called: powder flow; flow properties; free-flowing powder; cohesive powder.
Why powder flow depends on conditions
A powder may behave differently after settling, consolidation or aeration. Particle characteristics, moisture and stress conditions also affect its behaviour. A “free-flowing” label without the test and sample condition gives little basis for comparing reports.
A packing-based index measures one aspect of powder behaviour. It may not capture differences that matter during feeding or dosing, and results from a different material cannot establish how a supplement blend will perform.
Comparing powder-flow tests
Different observations, rather than interchangeable flow scores
Test or index
What the result describes
Important boundary
Angle of repose
The slope of a pile formed by a stated method
Pile formation differs from confined feeding.
Carr index / Hausner ratio
Packing change between loose and tapped states
An indirect density-based indication.
Flow through an orifice
Discharge through a defined opening
Opening geometry and powder condition belong with the result.
Shear-cell assessment
Resistance to the onset of flow after consolidation
A laboratory index characterises a sample under its test conditions. Feeding, packing and dosing in a filler involve additional demands, so assess the intended blend in its relevant material state and process.
Describe the observed problem as specifically as possible: interrupted hopper discharge, a stagnant region and dose variation point to different questions. A flow score alone cannot identify their causes.