Application of Ring Shear Testers, Examples


In the 1960's, when shear testers for powders and bulk solids, especially the Jenike Shear Tester, were introduced, they were intended to be used first of all for silo design. For silo design mechanical properties are required which characterize the flow behaviour sufficiently accurate. Only on the basis of safe and reliable data it can be predicted, for example, what minimum size the outlet of a silo must have to avoid arching.

Thus a shear tester is an appropriate instrument for characterizing the flow properties of a powder. However, the Jenike Shear Tester requires a very routined operator, because it is not easy to operate, and a test (yield locus test) requires typically one to two hours.

In contrast to this, our modern computer-controlled Ring Shear Testers offer automatic testing and evaluation, whereby they are very easy to operate, and the duration of a yield locus test is only some minutes (e.g. 15 minutes), whereby the operator is required only for setting up the test and emptying the shear cell after the test (< 5 minutes).

RST-XS

This unique combination of accuracy and easy operation has lead to the fact that our Ring Shear Testers, e.g. the RST-XS (see Image), are mostly applied as "powder tester" or "flowability tester". The goals of our customers are manifold, e.g. the comparison of powders, the optimization of products, or quality control of raw materials or products. Some of our customers have developed product-specific test procedures.

Ring Shear Tester
RST-XS

In the following examples and test results are presented, which should give you an idea where to apply our Ring Shear Testers. If you have questions regarding a possible application, please do not hezitate to contact us.

Example:
Product optimization by adding a flow aid

An important quantity, which is measured with the Ring Shear Tester, is the flowability ffc. The flowability is a measure for the effort required to initiate flow. The larger the flowability is, the better a powder flows. To find out the effect of a flow aid on the flowability, mixtures of the powder with different flow aid concentrations have been prepared and then tested with a shear tester.

In the diagram to the right the flowability ffc of the product is plotted vs. the concentration of the flow aid (a very fine powder). The red curve shows the instantaneous properties, whereby the blue curve shows the properties after 22 hours storage at rest (e.g. storage of the product in a silo or a container).

One can see clearly that the flowability after the 22 hours storage at rest is smaller. This shows that the product shows a pronounced time consolidation effect. Time consolidation is also known as "caking".

The flowability shows a maximum at a flow aid concentration of 0.55%, i.e. this flow aid concentration yields the best flowability. An increase of the flow aid concentration beyond 0.55% has a negative effect on the flowability.

Further application examples:

  • Quality control: Ensuring a product with good dosing behaviour by limitation of the range of flowability.
  • Quality control: Ensuring a product which has a sufficient flowability even after storage at rest over a long period of time.
  • Investigation of the influence of the particle size distribution on the flow behaviour.
  • Investigation of the influence of the storage temperature on the tiome consolidation effct (caking).
  • Optimization of production processes regarding good flowability of the products..
  • Optimization of the powder composition for homogenous filling of the dies of a tablet press.


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Last updated: July 18, 2003