For tablet manufacturing, there are many processes in which powder has to flow, for example from the hopper into the die. Characterising flow is important to ensure ease of handling. Merlin have a number of flow characterisation techniques to measure flowability of powders and granules. The most popular is shear cell testing.
Shear Cell Testing
Shear cell powder testing aims to measure how much energy is required to initiate powder flow, for example, from a silo or hopper into a receptacle.
Using a Schulze Ring Shear Tester (RST XS), we slowly apply horizontal stress to the upper layer of powder when the bottom layer is restrained from moving – the test is complete when the powder bed "yields”. The force applied can be changed to mimic the scale of the process of interest and predict how the material flows from small hoppers to large IBCs.
The ring shear tester is very useful in power testing as it is able to test materials that are poor flowing, free-flowing or require large shear deformations. We use the results to predict how formulations will flow in process equipment e.g. tablet press hopper.
Wall Friction Testing
We can carry out wall friction testing using the Schulze Shear Cell fitted with a XS-WM standard wall friction cell and a coupon manufactured of the wall material of interest. We can currently test against 304 2B Stainless Steel and 316 Stainless Steel surfaces. The friction of the hopper walls is also an important factor in flow behavior and rate.
Wall friction testing measures the change in flow from a polished surface. The angle of friction measured can be used to design appropriate hoppers for problem materials.
Related services and tests we offer include API characterisation, punch adhesion, manufacturing prediction and also bespoke testing.
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