Taking the Cake: Anton Paar’s Powder Cell Measures Caking of Powders
The storage of powders and their subsequent discharge from containers create particular challenges in most powder-processing industries. A powder with good flowability can show impaired flow behavior after a certain storage time, after which discharging is only possible by hammering and pounding.
This effect is called caking, and it describes the time-dependent development of strong bonds between the powder particles (electrostatic bonds, bridging, mechanical form fit). This can arise from the constant pressure resulting from the self-weight of the powder or an externally applied force. Changes can then occur, for example, at the surface of the powder particles, leading to the development of new contact points and the formation of agglomerates and aggregates. These aggregates then become further consolidated, and the number and size of voids between the particles is reduced.
Usually caking is a non-desired effect, because it reduces the flowability of a powder, for example resulting in core flow. Often the application of a hammer is necessary, which is time- and cost intensive and can also impair the product quality. Thus, it would be advantageous to be able to identify caking in advance, and appropriately adjust process parameters to avoid its onset; for example, by adding anti-caking agents. We present here an easy, reliable and reproducible method for predicting and evaluating powder caking by using the Anton Paar Powder Cell.
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