CAKING Analysis with the REVOLUTION

Cohesive particles in a powder can form larger agglomerated particles and clumps with material handling. This process can be intentional as in a granulation process or can be unintentional as in caking during storage. Either way a powder's quality is affected by the formation of these larger particles.

The REVOLUTION Caking Test can be used to study powders that exhibit particle size change during mixing, blending, transportation, production processing and/or storage. 

When a cohesive powder is stored, the powder's particles can join or stick together forming large agglomerated particles and / or clumps of particles.  The flow properties of this caked powder will change with the formation of these larger particles and clumps.  This caking process is studied by comparing a powder's flow properties in a rotating drum before and after storage.  Once your powder has caked, the REVOLUTION Caking Test can also test the strength of the caked particles by increasing the drum rotation speed to force high velocity collisions between the powder particles.  These collisions could cause the caked particles to break up. The caking software compares the results of the powder's properties after storage and after the increase in velocity to see if the powder remained in a caked state. 

Appropriate powders for the REVOLUTION Caking test include: food powders, cosmetics, pharmaceuticals, and other powders with caking potential. The caking analysis should be performed on any powder with caking tendencies where the existence of large particles should be minimized.

The REVOLUTION Caking Test has five process steps:  initial analysis, caking, caking analysis, de-caking, and de-caking analysis.  These steps are discussed below.     

Initial Step

The flow properties of a fresh sample are tested using the REVOLUTION Powder Analyzer .  These properties establish the initial nature of the sample before caking forces are applied to it.

 

Fresh Sample

Caking Step

The agglomeration or caking step is performed in process or in a caking test cell (off of the instrument) that allows pressure to be applied to the powder. The consolidating pressure can be applied for a short time or over a long period to simulate storage conditions. When the caking test cell is used, the entire sample is transfered to the Revolution sample drum after the caking period.

Analysis of Caked Sample

The flow properties of the sample after exposure to caking forces are tested using the REVOLUTION Powder Analyzer .  These properties establish the nature of the sample after caking forces have acted on it. This data is then compared to the data for the fresh sample to determine if the caking forces have changed the sample in any way.

 

Caked Sample

Example Result with Caking

In Figure A, the analysis shows a change in the avalanching behavior of the sample before and after it has been exposed to caking forces.  This indicates that agglomerated particles are being formed in as a result of the caking forces. The formulation of agglomerated particles or clumps typically decreases the avalanche power of the sample. If no caking occurred, the graphs for the two tests would be superimposed.

 

Figure A - Cumulative Power Spectrum - Fresh Sample Caked Sample

De-Caking Step

The de-caking step can be performed with the REVOLUTION Powder Analyzer or in the manufacturing process. With the RPA, the powder is rotated at a high fixed velocity for a set time to force particle collisions. The rotation speed and time of rotation of the de-caking process are set based on the process parameters. In the manufacturing process, a new powder sample is taken after de-caking process or material handling. The new sample is loaded into the test drum. 

De-Caking

Analysis of De-Caked Sample

The de-caking analysis will indicate if the clumps formed during the caking step break up with an increased rotation speed. This step is important for caking applications because if the powder formed large particles during the processing stage, it is important to know what force is required to break up these particles before packaging and storage.  The analysis is completed by determining the percentage of change in the statistical parameters from the caking analysis to the de-caking analysis.  

 

Figure B - Cumulative Powder Spectrum Caked Sample De-Caked Sample

In Figure B, the analysis shows change in the sample's avalanching behavior after the de-caking step. Based on this analysis, the conclusion is made that the aggregated material formed during the caking process has broken up into smaller particles during the de-caking step.  

In Figures C and D, the data for two different powders is presented;  one powder that exhibits strong caking behavior and one power that does not.  The data for the sample with no caking behavior has the data for the fresh sample, caked sample, and de-caked sample overlapping.

Figure C - Strong Caking

Figure D - No Caking