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MERCURY Scientific Inc

 

REVOLUTION Powder Analyzer 

 

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CAKING Testing with the REVOLUTION Powder Analyzer

Cohesive particles in a powder can form larger particles 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.

Caked Powder

Powder after De-Caking

When a cohesive powder is stored, the powder's particles can join or stick together forming large particles.  The flow properties of this caked powder will change with the formation of larger particles.  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 Granulation Test has five process steps:  initial analysis, caking, caking analysis, de-caking, and de-caking analysis.  These steps are discussed below.    

Initial Step

The initial step will indicate the powder's initial product characteristics by measuring the statistical analysis described below.  These initial parameters as seen in Figure A will be used as a comparison to the caking and de-caking analysis steps.  The software measures the powder's ability to granulate or cake during storage by comparing the initial granulation analysis to that of powder stored for a specified amount of time.  

Initial Process

Caking Step

The agglomeration or caking step is performed in process or in a special storage container (off of the instrument) that allows load to be applied to the powder. A powder sample is taken after the caking process and the new sample is loaded into the test drum.

Caking Analysis

The caking analysis indicates if the powder caked or clumped in the agglomeration step.  The analysis is completed by determining the percentage of change in the statistical analysis between the initial stage and the caking stage.  

Caking Analysis

In Figure A, the analysis shows a increase in the powder's avalanche power and time during the caking stage.  This change in power and time indicates that cakes are being formed during the caking step. The formulation of cakes causes the powder to avalanche less frequently and flow less freely.  In most caking applications, the user wants to know how much caking is occurring and how quickly the powder is caking.  In Figure A, the conclusion is made that this powder is caking in the caking process step.

Figure A- Cumulative Power Spectrum -  - Avalanche Time vs. Power - Initial Analysis (RED)  Caking Analysis (BLUE)

De-Caking Step

The de-caking step can be performed within the REVOLUTION Powder Analyzer or in the manufacturing process. Within the instrument, 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 Process

De-Caking Analysis

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.

De-Caking Analysis

In Figure B, the analysis shows an decrease in the powder's avalanche power and time. Based on this analysis, the conclusion is made that the granules formed during the caking process have broken up into smaller particles with the increased rotation speed in the de-caking stage.

Figure B -  Cumulative Power Spectrum - Avalanche Time vs. Power -  Caking Analysis (BLUE) De-Caking Analysis (GREEN)

In Figure C, the analysis shows the difference in the avalanche power and time between the powder's initial analysis, caking analysis and the de-caking analysis. In addition, a comparison is made between the results of the de-caking stage to the initial stage to see if the powder returns to its initial powder's characteristicsTherefore, the conclusion is made that the powder did in fact return to its initial powder characteristics. 

Figure C -  Cumulative Power Spectrum - Avalanche Time vs. Power - Initial Analysis (RED)  Caking Analysis (BLUE) De-Caking Analysis (GREEN)

In Figure D, the graphical analysis shows the volume the powder sample at the various stages - initial, caking and de-caking.  The volume of the caked sample is increasing during the process due to the rotating causing the clumps to break up.  After the de-caking process, the sample volume is significantly increased due to the reduction of caking and the introduction of air molecules within powder sample.

Figure D - Sample Volume Analysis  -  Time vs. Powder Volume - Initial Analysis (RED)  Caking Analysis (BLUE) De-Caking Analysis (GREEN)

In Figures E and F, the graphical analysis shows two different powders: one powder that exhibits caking behavior and one power that does not.

Figure E -  Cumulative Power Spectrum -  Avalanche Time vs. Power - Caking

Figure F -  Cumulative Power Spectrum  - Avalanche Time vs. Power - No Caking

Once the granulation test has been completed, the software will provide the user with the following statistical analysis for all three analysis steps: initial, agglomeration and de-agglomeration.   Please double click on any of the parameters for a brief measurement description.

 

Copyright of Mercury Scientific Inc      Revised March 2008     All rights reserved.