In industries that handle powders on a regular basis it is very important to understand how a powder or granular material responds to pressure. In storage, the weight of powder in a container exerts pressure on the particles at the bottom. If the powder has good flow behaviour it will not consolidate and will flow out of the silo or hopper without sticking – this is very desirable. The longer a powder is stored for, the more likely it is to form a cake in its hopper and refuse to flow without further assistance.
A good measure of a powder’s flowability is the force required to cause it to flow. This can be calculated using the measurement of unconfined yield stress.
Unconfined yield stress is a simple technique that can be used to analyse the flow behaviour of many different types of powders and the change in this behaviour with different consolidation stresses and times. The measurement is made by filling a chosen weight of powder sample into a tube and a compression piston then applies a chosen consolidation force for a specified time. After consolidation, the tube is slid upwards above the consolidation probe and held up via a support disc before the probe moves back down to compress the freestanding column of powder which “yields”.
Formulae are built into Exponent software which are able to collect the required parameters and calculate the unconfined yield stress. Unconfined yield stress has little meaning as a measurement in itself as it depends on the consolidation stress (a powder more heavily compressed is likely to flow less freely and have a higher yield stress). The “flow factor” is therefore plotted and used to compare between samples instead. The larger the flow factor the more easily the powder will flow after any given consolidation pressure.
This assessment of powder characteristics is yet another measurement that the Texture Analyser can perform on powdered materials alongside the functionality offered by the Powder Flow Analyser.
We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.
Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.
For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.
The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is
available to measure and analyse the textural properties of a huge range of
food products. Our technical experts
can also custom design instrument fixtures according to individual
specifications.No-one understands texture analysis like we do!
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