Principle

GranuDrum instrument is an automated powder tester to analyze the cohesion within the powder. It is based on the rotating drum principle.

A transparent drum cylinder is rotating around its axis half-filled with a sample of powder. The rotation starts and the drum will rotate at different velocities. A camera takes a snapshot during the rotation then the software can analyze the pictures stacked per speed. The analyses give the measurements for the cohesive index and flowing angle per speed. The cohesive index is only related to the cohesive forces between the grains. The average interface position gives the flowing angle and the dynamic cohesive index is measured from the interface fluctuation. The flowing angle is influenced by a wide set of parameters: the friction between the grains, the shape of the grains, the cohesive forces between the grains (VdW, electrostatic and capillary forces). The cohesive index is only influenced by the cohesive forces.

The user will have the following information:

• Flowability
• Cohesion
• Thixotropy – agglomeration, segregation, and attrition.
• Caking
• Aeration

The trend you will observe gives information on the way the powder behaves under a certain level of stress state or speed. If the speed increases in the rotating drum (and so the stress state) and the cohesive index increases as well we talk about a shear-thickening behavior, the opposite way we will talk about shear-thinning behavior.

A cohesive powder leads to an intermittent flow while a non-cohesive powder leads to a regular flow. Therefore, a cohesive index close to zero corresponds to a non-cohesive powder.

Applications

As said in the motivation, the GranuDrum powder tester is a must-have for a free-flowing process. The rotating drum has multiple applications in several fields.

In the pharmaceutical field, it is used for the mixer, formulation, optifiller, and tableting process analysis. As shown in an article in OnDrugDelivery (link) in a collaboration with DFE Pharma, you can relate the GranuDrum measurements with several key parameters in your process. The GranuDrum is useful for the formulations, you can determine how your blend behaves under a certain level of stress.

The relation between the recoater process and the cohesive index. You can thus have a predictive pass or fail test for your powders beforehand putting them in the machine. Here is a link to an application explaining the relation between the GranuDrum measurement and the spreadability. The GranuDrum powder tester is also used for the powder conveying in the printer. When you combine the GranuCharge and the GranuDrum you can have a complete picture of your cohesive forces.

Other fields use the GranuDrum for different applications as the food industry, the chemical industry, or the metal industry. You can find more information in the application notes.

In a nutshell, the GranuDrum powder tester is a must-have when you want to know more about your powders, whether you need a predictive test or a better general overview.