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Rotating drum measurement in the pharmaceutical industry
This article will explain how the rotating drum measurement and the GranuDrum can be used in the pharmaceutical industry. What are the benefits of using new methods and how would you know if one test is relevant or not.
Can the rotating drum measurement be used for pharmaceutical processes and how?
Amongst all the powder characterization methods used in the pharmaceutical industry, the rotating drum measurement and more specifically the measure of the flowing angle and the dynamic cohesive index are fairly new. The lack of a standard to describe that method may scare some users, but, when it comes to R&D, new powder characterization equipment could give an advantage on product development and quality control improvement.
“The success or failure of a method depends on its ability to be a good proxy for a process.”
What is the GranuDrum?
The GranuDrum is an automated powder flowability measurement method based on the rotating drum principle. In this method, the powder flow is accurately analyzed at the air/powder interface without any compressive load. Measurements of the interface and its fluctuations are used to compute the flowing angle and the dynamic cohesive index.
The rotating drum geometry is appropriate for applications in many industries such as additive manufacturing, food, minerals, or chemical. But how does it apply to the pharmaceutical industry?
LEARN MORE ABOUT THE GRANUDRUM
How to fit the rotating drum measurement with a process?
First, one must understand the conditions in the rotating drum before fitting it with any industrial process. In the rotating drum, the stress fields are low, the powder is considered non-consolidated. The flow fields on the other hand are adjustable since the cell can rotate at a defined speed from 1 rpm to 70 rpm. Based on that observation, the rotating drum could bring new insights to any user trying to characterize powders in a process where the samples are unconsolidated and where the speed of the process is high or variable.
Many industrial processes are fitting this description like mixers, rotary presses, or optifiller stages in tableting machines for example. For all those processes the measure of the powder flowing angle and the dynamic cohesive index can bring new understanding and extensive knowledge on how the collective behavior of the powder will look like in that geometry.
Keep also in mind that while considering stress and flow fields, other process conditions could be worth taking into account. This is the case of environmental conditions. Indeed, temperature and humidity often have big roles in powder processability, and running the rotating drum measurement tests or any tests at temperature and humidity different from the one in the process may lead to irrelevant results. This is the reason it was critical while designing the GranuDrum to produce a cell that was airtight in order to control the humidity during the measurement but also to produce a stainless-steel test that allowed measurement at high temperature.
How could we bring the rotating drum measurement to the next step?
To predict powder behavior in complex geometry, new simulation tools were developed and now offer a way to understand how the powder will flow in certain processes. To use the simulation software efficiently, the numerical model of the powder must behave like the real powder would behave in the process. To this end, calibration is necessary, and just like in characterization, the calibration of the model must be performed with respect to the stress and flow field of the process.
The combination of simple geometry and precision makes the rotating drum a great candidate to calibrate numerical models with physical measurables by using the flowing angle and the dynamic cohesive index. Another way would be to export the raw picture and fit the powder/air interface in the GranuDrum with the powder/air interface in the digital twin of the GranuDrum. This method has the advantage to provide great accuracy and validating a model at different speeds.
In a few words
The rotating drum measurement and more specifically the GranuDrum is a new powder characterization method that would act as a good proxy for numerous pharmaceutical processes such as mixers, rotary presses, or optifiller stages in tableting machines. We can conclude that this method is relevant for the pharmaceutical industry and that its compatibility with numerical simulations will allow this instrument to become a must-have in any pharmaceutical R&D lab in the future.