Ring Shear Testers

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Application and overview

Ring Shear Testers serve for the determination of flow properties of powders and bulk solids like pharmaceutical powders, flour, cement, soap powder, titanium dioxide, clay, sewage sludge, and others. Thus, a Ring Shear Tester may be called a powder tester, powder flow analyzer, bulk solid flow tester, or flow property tester, and sometimes it's called a shear cell tester or just ring shear cell. However, being a real shear tester, the Ring Shear Tester is a very accurate powder tester providing physical quantities to characterize powder flow. Results can be applied on product optimization, quality control, or characterization of powder flow, but also on quantitative design procedure like hopper design for flow.  Thus, our Ring shear testers are applied in a wide range of industry (e.g. Chemical Industry, Pharmaceutical Industry, Food Industry), and in universities and research institutions as well. 

The most important flow properties of powders and bulk solids are: Flowability, compressive strength, internal friction, time consolidation, wall friction, and bulk density. These are important (and physically-defined) quantities for the characterization of powders More about these terms you will find in an essay on this website (click here) and - somewhat shorter - on an information sheet which can be downloaded here as pdf file.

Typical applications for the ring shear testers are product characterization, quality control, comparative tests, and silo design.

An impression of the operation...

... of a Ring Shear Tester is given by the following example:

Small and large Ring Shear Tester

Small Ring Shear Tester: Ring shear cell XS-Mr

The principle of both Ring Shear Testers is the same: A powder or bulk solid specimen is contained in a ring-shaped (annular) trough, called the bottom ring, covered by an annular lid and subjected to a vertical load through the lid. The specimen is then subjected to a shear deformation by rotating the bottom ring relative to the lid. From the normal stress and the shear stress measured following different procedures a couple of quantities is determined, e.g., the unconfined yield strength (compressive strength), the flowability, the internal friction, the bulk density.

The major difference between the testers is the size of the shear cells. which determines the maximum particle size that can be tested. This limitation results from the conditions that a sufficient number of particles must be contained in the shear cell to obtain a continuum, i.e., a  "powder" or "bulk solid" instead of "some particles". 

If the materials to be tested do not contain particles greater than about 1 mm, the small tester is sufficient. If larger particles have to be tested, the large tester is preferable. Since the maximum particle size is the critical point, it is no problem to test very fine particles in the range of micrometers  or even nanometers in a large tester.

Large Ring Shear Tester: Shear cell M

The selection guide shows further criteria to identify the best tester for your application:

Ring shear tester RST Mk II  

RST Mk IIThe Ring Shear Tester Mk II, successor type RST-01.pc, is suited for all powders and bulk solids up to a particle size of 5 .. 10 mm (depends on particle size distribution). It performs the tests automatically, i.e. controlled by a Personal Computer and control software RST-CONTROL.

The RST Mk II is our most versatile tester due to the possibility of measuring powders and bulk solids with particle sizes from "0" to several millimeters. Thus, it is advantageous in areas where not only fine powders are to be tested, e.g., in silo construction and in the areas of food, feed, chemicals and raw materials.

Ring shear tester RST-XS.s   

RST-XS.sThe "small" Ring Shear Tester RST-XS.s is first of all an automatic flowability and caking tester for fine-grained powders. If is a bench-top device, much smaller than the RST Mk II, and serves as flowability and caking tester at many places, but is also used for the design of hoppers and silos.

The RST-XS.s is usually placed on a laboratory bench and is easy to operate. Because of the small required powder specimen (only about 30 ml for the standard shear cell, about 3.5 ml for the smallest shear cell) this tester can be applied also in industries where only small amounts of powder are available for testing, e.g. in Pharmaceutical Industry.

Why don't we call the Ring Shear Tester "powder rheometer"?

We deliberately do not use the designation "rheometer". A ring shear tester, or ring shear cell, is a shear tester. Shear testers for measuring the properties of powders and bulk solids originate from the scientific work of A.W. Jenike, the founder of modern bulk solids technology.

A good shear tester is optimized to have accurate control over stresses (e.g., applying a constant normal stress), and then to measure friction (or strength) as accurately as possible. In strength measurement, a powder or bulk solid is first  consolidated with the shear tester, then set to flow while the shear stress required to initiate flow is measured. This gives us information not only on flowability but also to the physical quantities required for quantitative hopper design (mass flow, no arching, no rathole formation), and also for structural silo design. 

In contrast to the typical rheometer, which is historically used to measure properties of fluids, e.g., viscosity, the shear rate plays a minor role in the shear tester.