The computer-controlled Ring Shear Tester RST-XS.s can be used for:

  • Determination of powder flowability, e.g. for quality control, process optimization, or comparative tests.
  • Measurement of powder flow properties (compressive strength, internal friction, bulk density, compressibility, time consolidation, wall friction angle, etc.) e.g., for silo design for flow
  • Very small powder samples
  • Low stress tests
  • Support of attrition tests.

Advantages and highlights of the Ring Shear Tester RST-XS.s:

  • Easy operation of the tester and automatic evaluation of the test results by using specially suited computer software RST-CONTROL 95.
  • Variable stress level: The flow properties are measured at the same stress level which is relevant for the application of the results.
  • A new feature is the "Stress Walk" procedure, where with one specimen up to ten yield loci are measured in order to get a quick overview on the behavior of the powder at different stress levels.
  • Measurement of "caking" or time consolidation, respectively,  which is important if bulk solids tend to consolidate if they are stored at rest for a certain time interval). For storage under load the shear cell with the specimen can be removed from the tester. This allows to store the specimen in a climate cabinet, or oven. Further, the tester is not blocked and can be used for other tests.
  • Wall friction test (wall friction angle, wall yield locus). Wall material coupons can be prepared by the customer.
  • Various shear cell geometries (adjustment with respect to stress level and sample volume).
  • Appropriate device for measuring the flow properties of bulk solids which are hardly to test with other testers, e.g. very elastic products (plastics powder, saw meal) and very cohesive, moist or extremely fine-grained products (e.g. sludge, moist clay, carbon black).

Technical Data

  • Electric input: 24 V DC, 2 A (delivered with external power supply for 110 V to 240 V, 50 Hz / 60 Hz).
  • Measuring system for normal and shear force: load beams with strain gauges.
  • Measuring system for the sample height: inductive displacement transducer.
  • Internal amplifiers, A/D- and D/A-converters, communication with a PC via its serial communication port or USB port.
  • Normal force: Standard: max. 5 kg (ca. 50 N), i.e., a normal stress of approx. 20 kPa in the standard shear cell type XS-Mr, approx. 45 kPa in the smaller cell type XS-SV3 or XS-Sr.
  • Shear cell (dimensions of sample volume): Standard: inner diameter 32 mm, outer diameter 64 mm, height 13 mm (sample volume ca. 30 ml).
  • Other shear cells from 3.5 ml to 70 ml volume, wall friction cells, compressibility cell:  see here.
  • Shear velocity: ca. 0.025 - 15 mm/min (standard shear cell, mean specimen diameter).
  • Dimensions of the tester (ca.): width 320 mm, height 480 mm, front-to-back-size 385 mm.
  • Weight: ca. 23 kg.

RST-CONTROL 95 software for measurement and evaluation

The Ring Shear Tester RST-XS.s is  supplied with the RST-CONTROL 95 measurement and evaluation software. The software is to be installed on a PC (Microsoft Windows 7/8/10* operating system) that is connected to the ring shear tester via USB or RS-232. RST-CONTROL 95 controls the ring shear tester and, if required, automatically measures flow properties (yield loci), wall friction, compressibility, time consolidation, and more. RST-CONTROL 95 supports the preparation of the measurement with the help of step-by-step instructions, and it automatically evaluates the test results.

*) Microsoft Windows 7, Windows 8 and Windows 10 are registered trademarks of Microsoft Corp., USA

Options and Accessories

Generally, Ring Shear Testers RST-XS.s are delivered with a shear cell and a software package, so that different types of tests can be performed with this equipment, namely flowability tests (yield locus tests), and time consolidation tests (caking tests). For special applications, e.g. for time consolidation tests conducted on several specimens simultaneously, for wall friction tests, and for tests with very small powder samples we offer accessories as listed below.  

Shear cells

Shear cell XS-MrRing Shear Testers RST-XS.s are generally delivered with one shear cell type XS-Mr which is called the "standard shear cell". For coarser powders a larger shear cell, type XS-Lr, is available (data see below).

Shear cell XS-Sr (10 ml)If only very limited amounts of powder are available for testing, shear cell types XS-MV4, XS-Sr or XS-SV3 with specimen volumes of 3.5 to 10 ml can be used. The table below gives an overview.

Name Description
XS-Mr "Standard shear cell" with about 30 ml specimen volume, cross-section about 24 cm²
Maximum particle size depends on the type of powder and is about 1 mm for broad particle size distributions and 0.5 mm for narrow particle size distributions.
XS-Lr "Large volume": About 70 ml specimen volume,  cross-section about 46 cm²
Applicable for coarser materials than XS-Mr.
Lid provided with vanes similar to XS-Mr.
Maximum particle size depends on the type of powder and is about 1.5 mm for broad particle size distributions and 0.75 mm for narrow particle size distributions.
XS-Sr "Small volume": About 10 ml specimen volume,  cross-section about 13.5 cm²
Lid provided with vanes similar to XS-Mr.
Maximum particle size depends on the type of powder and is about 0.5 mm for broad particle size distributions and 0.25 mm for narrow particle size distributions.
XS‑MV4 "Small volume": About 9.5 ml specimen volume,  cross-section about 24 cm²
Lid and bottom rough, no vanes.
Maximum particle size depends on the type of powder and is about 0.5 mm for broad particle size distributions and 0.25 mm for narrow particle size distributions.
XS-SV3 "Very small volume": About 3.5 ml specimen volume,  cross-section about 13.5 cm²
Lid and bottom rough, no vanes.
Maximum particle size depends on the type of powder and is about 0.3 mm for broad particle size distributions and 0.2 mm for narrow particle size distributions.

Wall friction cells

Wall friction shear cell XS-WMWall friction cells are required for the measurement of the wall friction angle or coefficient of wall friction (friction between a bulk solid and a wall material). For the test, an annular wall material specimen ("coupon") is placed in the shear cell with the bulk solid specimen on top, i.e., the bulk solid is located above the wall material like on a hopper wall or a chute, which is absolutely necessary in order to avoid underestimating the wall friction angle in the case of segregating bulk solids.


wall material couponsWall material coupons can be made by the customer according to dimensions given in the tester's manual.

Name Description
XS-WM "Standard" wall friction cell, specimen volume about 20 ml, outer diameter of the wall material coupon about 75 mm.
XS‑WL0 Wall friction cell (low stresses) with specimen volume of about 30 ml,  outer diameter of the wall material coupon about ca. 88 mm

Low stress shear cells

Low stress shear cell XS-Lr0For the Ring Shear Tester RST-XS.s we offer a shear cell and a wall friction cell to achieve even lower stresses. Here the shear lid is attached to the loading rod ("hanging lid"). Fine resolution of measured stresses is achieved due to the large cross-sectional area.

Name Description
XS‑Lr0 Dimensions similar to XS-Lr (volume about 70 ml, cross-section about 46 cm², lid provided with vanes)
XS‑WL0 Wall friction cell with specimen volume of about 30 ml,  outer diameter of the wall material coupon about ca. 88 mm

Compressibility cell

The compressibility cell serves to determine the function of bulk density in terms of stress as accurately as possible. Due to the flat cylindrical sample space, the influence of wall friction is minimized.

Name Description
XS‑VM Compressibility cell (approx. 48 ml specimen volume, 64 mm specimen diameter).

Time consolidation benches

A time consolidation test examines how a bulk solid consolidates when it is stored at rest (e.g. in a silo or IBC). To measure this, the bulk solid specimen is first consolidated with the ring shear tester, then stored under constant load, and finally sheared to failure. All of this can be done automatically with the ring shear tester, without having to remove the shear cell with the bulk solid specimen from the tester. The disadvantage, however, is that the tester is blocked by this specimen. Therefore, the use of a time-consolidation bench for external storage is recommended.

When using a time consolidation bench, the specimen is consolidated with the ring shear tester, then removed from the tester and placed on a time consolidation bench. The consolidation stress is exerted on the specimen through weights. After the consolidation period is over (e.g., after some hours, a day or a week), the specimen is returned to the ring shear tester and sheared again to measure the strength of the consolidated powder. Thus, one obtains a quantitative result on the increase of strength during the consolidation time, which is known as "caking".  

Time consolidation bench XS-1CThe time consolidation bench with cover (type XS-1C) serves for the storage of one shear cell. The cover minimizes the contact of the specimen with the ambient atmosphere. The consolidation load is transferred to the powder specimen through a vertical loading rod provided with a disk, on which an appropriate amount of weights is placed.

Time consolidation bench XS-1OThe time consolidation bench without cover (type XS-1O) is provided with a special loading mechanism with counterweight. The counterweight compensates the weight of the loading mechanism, so that small consolidation loads can be exerted on the powder specimen.
The design without cover allows a more intensive contact between the powder specimen and the ambient atmosphere. This is preferable if the behavior of the powder in dependence on the ambient conditions has to be studied, e.g. by storing the time consolidation bench with the shear cell and the powder specimen in a climate cabinet.

Weights

For time consolidation tests in combination with the time consolidation bench (see above) weights are required for the adjustment of the consolidation load.

Available sizes:
2 kg, 1 kg, 0.5 kg, 0.2 kg, 0.1 kg.
Accuracy: min. +/- 1%
Dimensions: thickness 10 mm to 14 mm, other dimensions depend on weight.

Weights are available as set or separately.

Shear cell and driving axle for increased temperature consistency

Shear cell MTShear cell XS-MT was developed for the examination of samples at temperatures below or above room temperature. It is characterized by increased heat capacity (greater intrinsic mass) and reduced heat transfer to the environment. This means that a powder sample previously tempered with the shear cell can be examined with the RST-XS.s ring shear tester. The temperature change is significantly reduced compared to normal shear cells. 

Driving axle with exchangeable top partThe temperature change can be further reduced if, as in the picture with the shear cell, a (retrofittable) driving axle with exchangeable top part made of PTFE is used as shown in the picture above. The small picture shows this driving axle with top part made of stainless steel and above it the alternative PTFE top part.

In addition, tempered gas can be supplied with a protective cover (see below), in order to further improve the temperature constancy of the powder sample.

Protective cover for gas supply

Protective coverIf powders have to be tested at a specific atmosphere, e.g. in order to prevent change of moisture, or to reduce the risk of spontaneous combustion, the RST-XS.s can be provided with a cover around the shear cell (see image). The protective cover can be supplied with (inert) gas through a hose fitting for gas supply.

The protective cover is provided with openings for tie rod and push rod for shear force measurement, for the bar of the horizontal guiding system, and the loading rod of the normal load system. Since the openings must remain open during testing, it is necessary to supply gas permanently.

The protective cover can also be used to suck off gas from the space around the shear cell.

Technical modifications, misprints and errors excepted.