How to measure flowability/caking

Stable Micro Systems' Powder Flow Analyser provides an accurate and reliable method for measuring the flow characteristics of powders. Powders with high flowability and low caking tendency are easier to store, transport, and process whilst inconsistent flowability can lead to dosing issues in manufacturing processes.

Understanding powder flowability is crucial for manufacturers to avoid problems like batch variation, caking during storage or transportation, and discharge issues from hoppers or bins. By measuring powder flow, manufacturers can optimise processes, prevent production issues, and maintain product quality.

Measuring powder flowability and caking using a Texture Analyser/Powder Flow Analyser offers insights into powder behaviour across industries like pharmaceuticals, food processing, and materials handling. Below are key applications:

• Pharmaceutical powder flowability testing: Evaluating the flowability of pharmaceutical powders used in tablet manufacturing by measuring the flow rate to ensure consistent dosing and uniform compression.
• Food ingredient flowability assessment: Assessing the flow properties of ingredients like flour and powdered spices.
• Caking tendency of powdered products: Evaluating the tendency of powders like instant coffee or powdered milk to cake by applying controlled force to break apart clumps and aggregates.
• Powdered chemical flow analysis: Assessing the flowability of powdered chemicals, such as fertilisers or catalysts, by measuring their flow rate dependence.
• Pharmaceutical powder caking evaluation: Testing the caking propensity of pharmaceutical powders during storage and transportation by applying compressive forces to simulate real-world handling conditions.
• Flowability of cosmetic powders: Evaluating the flowability of cosmetic powders, like face powder to ensure consistency.
• Materials handling powder flow assessment: Assessing the flow properties of bulk materials like cement powder used in construction by measuring their flowability during transportation.
• Powdered sugar packing evaluation: Testing the flowability of powdered sugar in packaging equipment by measuring the force required to break up lumps and ensure consistent product filling.
• Flowability of agrochemical powders: Assessing the flow properties of agrochemical powders, like pesticides, by measuring their flow rate dependence.
• Powdered food ingredient dispensing: Testing the flowability of powdered ingredients in bakery production by measuring the force required to discharge flavourings from dispensing nozzles.

In these examples, a Texture Analyser/Powder Flow Analyser applies controlled forces/distances or measures flow rates to quantify powder flowability and caking tendencies, helping manufacturers ensure process efficiency and product quality across various industries.

Cohesiveness is the tendency for particles of powder to cling together and agglomerate (form larger clusters of particles).

The PFA measures this cohesion characteristic by moving the blade in such a way as to lift the powder. A more cohesive powder will cling to itself and to the blade therefore reducing the force exerted on the base of the vessel. This is shown in the graphed data by a large negative force.

How to interpret the Powder Flow Analyser graph 

When measuring cohesion, the force vs distance/time graph typically shows a greater negative area under the curve as cohesion increases.  

From the graph you can observe/obtain the following:

• Cohesion Coefficient
• Cohesion Index 

Caking is the tendency of a powder to form large agglomerates during storage and transportation. The tendency of a powder to cake is closely related to its cohesiveness and generally a powder that is cohesive will also form a cake during the caking test. The strength of the cake will depend on a number of factors such as packing efficiency, particle to particle interactions and moisture content i.e. humidity. 

The blade levels the top of the powder column and measures its height. The blade then moves down through the column and compacts the powder to a pre-defined force (usually 750g). When it reaches this force, it measures the height of the cake and slices up through the powder. This compaction cycle is repeated four more times. The 5th time the target force is reached the blade slices through the compacted cake of powder formed at the bottom of the vessel. 

How to interpret the Powder Flow Analyser graph 

From the graph you can observe/obtain the following:

• Column and cake height ratios
• Cake strength work
• Mean cake strength force

Powder flow properties may change with increasing or decreasing flow speeds. For example, a powder may become more resistant to flow as it is forced to flow faster or indeed it may become more free flowing as the flow speed increases. This issue can lead to under/filling, for example, as a result of process changes to meet increase output demand.

The Powder Flow Analyser measures this characteristic by assessing the work needed to move the blade though the powder at increasing speeds. An evaluation of the flow stability of the powder is also made by comparing the work needed to move the blade though the powder at the start of the test compared to the work required to move the powder at the same speed at the end of the test.

The powder flow speed dependency (PFSD) test provides 5 sets of 2 cycles at increasing speeds. The downward parts of the cycles compact the powder and the upward stroke of the cycle uses a lifting action. Powders that flow freely will transfer very little resistance through the powder column in either a downward or an upward direction. Conversely, poorly flowing powders exhibit substantial amounts of force in either direction. 

How to interpret the Powder Flow Analyser graph 

From the graph you can observe/obtain the following:

• Compaction coefficients at each speed
• Cohesion coefficient
• Flow stability 

• Particle size, size distribution, and shape: Smaller particles and irregular shapes tend to increase cohesion and reduce flowability, potentially leading to caking. 
• Moisture content and migration: Higher moisture content can increase cohesion and promote caking, especially in hygroscopic materials. 
• Temperature variations: Temperature fluctuations can induce moisture migration, leading to localised caking. 
• Storage conditions: Extended periods of static storage can lead to particle consolidation and caking. 
• Consolidating load: Higher loads applied during testing can increase particle contact areas, enhancing caking potential. 
• Relative humidity: Ambient humidity directly affects moisture absorption or desorption in powders, influencing flowability and caking. 
• Surface properties: Particle surface roughness and chemistry affect inter-particle interactions and flow behaviour. 

The Stable Micro Systems Texture Analyser/Powder Flow Analyser excels in optimising flowability and caking measurements through its comprehensive approach and advanced features. It offers versatile testing capabilities, allowing for controlled flow measurement of various materials under gentle to aggressive conditions using a Powder Flow Analyser measuring characteristics such as cohesion, caking, bridging, and powder flow speed dependence.

Its superior engineering, featuring a true helix blade and high-precision data capture, ensures accurate and reproducible results. The system's flexibility allows for customisable parameters and multiple test types, providing a complete picture of powder behaviour.

This combination of comprehensive testing capabilities, advanced technology, and flexible analysis options makes it the ideal choice for industries seeking to refine product formulations and maintain quality standards in flowability and caking assessments across various materials and applications.