A rapid powder flow analysis and research service
We provide powder flowability measurements and a range of related powder rheology characterisation tests. Using our annular shear cell approach enables us to perform a series of measurements on a sample across a range of consolidation stresses to deliver the following studies:
- Flow Function
- Time Consolidation Test with Flow Function
- Wall Friction
Typical data outputs include:
• Flow Index
• Arching Dimension
• Rat-hole Diameter
• Hopper Half Angle
• Gravity Chute (Wall Friction) Angle
• Bulk Density Curve
Powder flowability dictates the storage, handling and transport of granular solids across a range of industries. Flow properties of powders can drastically influence the processing of materials such as:
- Food flavours, colours and coatings
- Spice blends, flours and starches
- Cheese and dairy products
- Pharmaceutical blends for tablet, capsule and granulation
- Building materials and cements
- Ceramics, minerals and clays
Powder Flow Function
Unlike liquids and semi-solids, powders display flowability that is dependent upon the applied consolidating pressure. As pressure is increased from, for example, the weight of a column of material in a silo, hopper or vessel, the yield stress of the material at the bottom increases, resulting in decreased flowability. By obtaining yield stress (known as the unconfined failure strength) across a range of consolidation stresses it is possible to generate a flow function such as those shown in the graphic below.
A powder that fails easily, even under a high consolidation stress, is signified by a shallow flow function and will prove to be a very flowable powder. In contrast, a powder that develops high shear strength, even under moderate consolidating stresses, displays as a steep flow function and will demonstrate poor flowability.
Time consolidation of powders
When left undisturbed powders will undergo time-consolidation to varying degrees. Time consolidation can lead to rat-holing in hoppers, bins and silos. A time consolidation study can reveal the propensity for a powder to gain strength and become problematic in this way.
Compression/compaction and relaxation studies on powders and granular solids
We have a custom compression cell that enables studies to be performed that deliver information on how a powder or granular solid behaves under compaction at controlled temperature and humidity conditions. Furthermore, on completion of a compression step the subsequent relaxation of the compacted mass can be monitored over time. The resulting compacted core can then be subjected to a uniaxial unconfined failure strength test.
In addition to these specialist measurements, more standard tests such as tapped density, Hausner ratio and Carr’s Compressibility Index can be performed.
Friction between a powder and a wall can significantly influence the flowability on hoppers, where, for example, high friction requires a steep wall angle to ensure flow and vice versa. Equally, high wall friction distributes the weight of a column of powder down the vessel walls rather than concentrating it on the material at the bottom. Wall friction tests can be performed with a sample powder against a range of materials.