Powder flow test types
A complete reference to powder characterisation tests – covering the Powder Flow Analyser and Texture Analyser working together as a single instrument platform.
| No single test defines powder behaviour but a combination of Texture Analyser and Powder Flow Analyser provide a complete powder and product characterisation capability that no standalone powder flow instrument can match. |
The Powder Flow Analyser sits directly on the Texture Analyser to operate – so every PFA customer automatically has both testing capabilities available from day one.
PFA tests characterise how your powder behaves in motion: dynamic, conditioned testing sensitive to speed, aeration, consolidation history, and flow instabilities.
Texture Analyser tests characterise how your powder resists, deforms, and fails under load: controlled static testing that measures compaction strength, cake breakability, shear failure, and penetration resistance.
Test types
Cohesion
When powders resist flow initiation, bridge, or stick despite appearing free-flowing.
Cohesion at 4 speeds
When a change in behaviour is suspected to be linked to process speed, but there is a need to isolate the cohesive component.
Caking
When powders form lumps, set up during storage, or fail to discharge cleanly after rest.
Powder Flow Speed Dependence
When powders behave differently as process speed or throughput changes.
Compressibility
When packing, settling, or density changes affect filling, forming, or storage performance.
Consolidation and caking
When restart after storage is unreliable or requires mechanical intervention.
The complete powder characterisation reference
The tables below covers every test available across both instruments. Both instrument sections include a Custom tests row for bespoke method development.
Powder Flow Analyser
| Test type | Key parameters/outputs | Typical issues it helps with |
|
Cohesion (1 speed) |
Cohesion Index (work done during lifting phase at a defined speed) Bridging Factor |
Bridging and arching Poor hopper or bin discharge Sticking to equipment Batch-to-batch flow variabili |
|
Cohesion at 4 speeds |
Cohesion Index at four speeds Compaction coefficients Flow Stability |
Sensitivity to process speed changes Unstable flow during dosing or mixing Scale-up risk assessment |
|
Powder flow speed dependence (PFSD) |
Compaction coefficients across speeds Cohesion coefficient at reference speed Speed Sensitivity Ratio Flow Stability |
Conveying and feeding problems at higher speeds Speed-dependent segregation, attrition or aeration Dosing drift and flow instability |
|
Caking |
Column height ratios Cake height ratios Cake Strength Mean Cake Strength |
Caking during storage or transport Cake strength after consolidation Difficulty emptying packs, bins or silos |
|
Powder Consolidation and Caking |
Work to break consolidated cake after defined load and time |
Flow failure after storage Consolidation under self-weight Delayed or incomplete discharge Restart problems after rest |
|
Compressibility |
% Compressibility % Relaxation Stiffness % Elastic Recovery |
Tablet and capsule filling behaviour Packing and settling during storage Blend and formulation optimisation Density changes after handling |
|
Bulk density |
Conditioned bulk density (g/ml) Available from all tests using the split vessel |
Fill weight variation Pack size optimisation Supplier and material grade comparison |
|
Custom Controlled Flow tests |
User-defined work, force, distance and stability metrics |
Special processes Novel powders R&D screening Bespoke method development |
Texture Analyser
Available on the same instrument when the PFA attachment is removed.
| Test type | Key parameters / outputs | Typical issues it helps with |
| Uniaxial Powder Compression |
Force-distance or stress-strain response Yield point Work of compression |
Compaction behaviour and tabletability screening Powder bed strength under static load Formulation development |
| Powder Penetration / Hardness |
Peak force Resistance to probe penetration |
Surface crusting and hard layers Capping behaviour Resistance to penetration after storage |
| Powder Shear / Failure |
Shear force Failure force Energy to failure |
Inter-particle strength under static conditions Cohesion at rest Break-up and flow initiation behaviour |
| Cake Strength / Break test |
Maximum break force Work to fracture |
Mechanical strength of cakes after storage Handling robustness Breakability during reprocessing |
| Custom powder tests | User-defined force, distance, speed, time or energy metrics |
Novel powders Non-standard processes Bespoke method development |
Bulk Density
Determined on every test that uses split vessels which create a precisely defined, conditioned powder volume, ensuring repeatable and meaningful density measurements relevant to packing, dosing, and filling operations.
Using a split vessel, all of the above test types can measure Bulk Density within the test routine which provides a parameter of great interest to powder testing.
A split vessel allows the accurate preparation of a precise volume of conditioned powder which is weighed and subsequently bulk density is automatically calculated.
Create your own test
Controlled Flow technology enables the sample to be physically displaced in many different ways.
The test settings of blade path angle and blade tip speed determine the mode of Controlled Flow achieved within a sample column. Once programmed, the Test Settings can be exactly repeated test after test.
The Test Settings can be optimised to show the maximum differentiation between similar products, or to imitate the process or storage handling conditions, experienced by the product.
Precision manufactured rotor blades (optimised patent applied design), and test vessels ensure that Powder Flow Analysers always provide identical controlled flow conditions when completing the same test programme.
Nothing surprises us more than what experienced users want to investigate. That is why for Research and Development needs we allow the flexibility for you to not only customise the test projects that we provide but also for you to completely create your own test protocols to test in a different way or analyse your data to collect additional parameters.
FAQs about powder flow analysis tests
I'm not sure which tests my powder needs – where should I start?
The Quick Test is a good first step. It runs two conditioning cycles and three test cycles at a single speed, giving an early indication of compaction and cohesion behaviour in under five minutes. It won't replace the fuller tests, but it helps you understand your powder before committing to longer runs.
Which powder flow analysis test should I start with?
It depends on the type of problem you’re seeing. If you’re mainly concerned with powders sticking, bridging or refusing to discharge, start with the Cohesion test. If the issue is powders forming hard lumps during storage, the Caking test is more relevant. Where problems appear when line speeds or conveying rates change, Powder Flow Speed Dependence (PFSD) is usually the best starting point.
Do I need to run all the tests for every powder?
Not necessarily. Many users focus on one or two tests that are most closely linked to their process issues. For example, a manufacturer might use Cohesion and PFSD for hopper discharge and conveying problems, while a tabletting process might rely more on Compressibility and Bulk density. Once you understand which tests are most sensitive to your powders and processes, you can build a routine test set around them.
How do the cohesion and caking tests differ?
The Cohesion test mainly looks at how the powder behaves under relatively gentle slicing and lifting, focusing on how easily it moves and how strongly particles stick together during flow. The Caking test deliberately compacts the powder column several times to form a cake, then measures how strong that cake is and how easily it breaks apart. In simple terms, cohesion is about flow resistance, while caking is about strength after consolidation.
When should I use the Powder flow speed dependence (PFSD) test?
Use PFSD when your process involves changing speeds - for example variable-speed feeders, conveyors, augers or different line speeds during production. Some powders flow well at low speed but become unstable, segregate or suffer attrition at higher speeds. PFSD tests show how compaction and aeration behaviour change with speed, helping you choose safe operating windows and spot materials that are especially sensitive.
Why measure bulk density and compressibility as well as flow?
Bulk density and compressibility link flow behaviour to packing and filling performance. Bulk density affects how much product goes into a pack or cavity at a given volume, while compressibility (often expressed as a Carr Index equivalent) shows how much a powder compacts under load. Together, they help you understand fill weight variation, settling during storage, and how powders will behave when granulated, tabletted or packed.
Can I run cohesion, PFSD and caking on the same sample to save time and material?
Yes – the three tests can be run sequentially on a single sample in around 18 minutes, ordered from least to most destructive (cohesion first, then PFSD, then caking) so results remain as representative as possible. This is particularly useful when sample quantity or test time is limited. It's not recommended for powders likely to segregate or attrit during testing, and it's worth reading the help file for each individual test before running the sequence for the first time.
Can I design my own powder flow analysis tests?
Yes. The Powder Flow Analyser uses a Controlled Flow approach, where blade angle, direction, speed and the number of cycles can all be programmed. You can start from the standard cohesion, caking or PFSD projects and then adapt them – or create new methods – to mimic specific process steps or stresses. This is particularly useful in R&D when working with novel powders or unique handling conditions.
