Ring shear testers

The weaknesses associated with the flow through an orifice and angle of repose measurements limit their application for powder flow studies and hopper designs. Consequently, several powder shear testers and methods that permit a more thorough and precisely defined assessment of powder flow characteristics were developed. Shear testers that measure the frictional characteristics of a powder bed under load yield valuable information with regard to powder flow in high-speed tablet equipment. A number of types of shear cell testers are available, but the most common types used in the pharmaceutical industry are the Jenike shear cell and the Schulze ring shear tester.61,62... 

Figure 7.4 Schulze ring shear tester annular trough.

TABLE 7.10 Classification of Powder Flow Properties Using the Schulze Ring Shear Tester... 

Schulze, D. Flowability and time consohdation measurements using a ring shear tester. Powder Handhng Process 1996, 8 (3), 221-226. 

Hausmann R. Bausch A. Bongartz C. 2 nn T. Pharmaceutical applications of a new ring shear tester for flowability measurement of granules and powders. In Proceedings of the 2nd World Meeting APGI/APV. Paris, May 1998 137-8. 

The limitations of the Jenike shear cell are that it is not very useful for measuring bulk solids with large shear deformations, e.g., plastic powders. The level of consolidation stresses required are inappropriate for pharmaceutical materials, and the quantity of material required is often beyond that available in the early stages of development. Alternative shear cells that have been used include annular shear cells (Nyquist and Brodin 1982 Irono and Pilpel 1982) and ring shear testers (Schulze 1996). 

Shear Tester Technique Ring shear tester 1.35 ... 

The issue of non-uniform shear travel in rotational testers can be minimi2ed if the test cell has an annular ring shape instead of a cylindrical one such as in the Peschl tester. While the irmer radius of the ring still has a shorter shear travel than the outer one. the difference is relatively small, particularly if the difference between the two radii is small compared to their average. This concept was developed a number of years ago by Carr and Walker [5]. In our experience, the early models of the device, while very robust from a mechanical standpoint, were too massive for delicate measurements. It also was difficult to clean the cell, particularly the lower ring. This form of ring shear tester uever achieved widespread use when compared to the Jenike cell. 

A similar concept with a number of engineering improvements has recently been developed by Schulze (Figure 5). The mechanism is much more sensitive than that employed by earlier ring shear testers, and the cell can be removed for cleaning and also for time consolidation testing. It is commercially available. Excellent correlation has been observed between the Schulze tester and the Jenike shear cell, as well as with more sophisticated research instruments. An automated version is available for situations where high productivity is required. As with the Peschl tester, testing times are about 1/3 of that required for comparable Jenike tests. 

Time dependent behaviour is well known for moist bulk solids like clay. For dry bulk solids a time dependent behaviour has always been neglected in practical applications. This is because an influence of any time dependent effect on the results obtained from the Standard Shear Testing Technique [1] has not been found yet. The typical devices used for shear testing are the Jenike Tester and the Ring Shear Tester. These devices deliver a shear stress in dependence of the applied normal stress which is not effected by the shear rate... 

Because neither the state of stress nor the state of strain are fully determined in the Jenike and Ring Shear Tester, in this paper a Biaxial Shear Tester has been used. Due to the design of this tester the complete state of strain and complete state of stress are fully determined. 

Experiments were performed using the same humid salt as used in [2], sheared in an annular ring shear tester. We present here a temporal study of its yield locus and of its cohesion. Two types of experiments have been performed, using the classical procedure of Jenike [1] where the shear stress is removed during the consolidation time, and relaxation experiments without removing the shear stress. In both cases, the dilatancy of the powder has been recorded in order to follow its compaction. 

The shear tests were performed using the annular ring shear tester (from Schulze SchiittgutmeBtechnik, D-38302 Wolfenbiittel) sketched on Figure 1. 

D. Schulze, Flowability and Time Consolidation Measurements Using a Ring Shear Tester, Powder handling processing, 8, (3), pp. 221, 1996. 

A free-flowing bulk solid Polypropylene (PP) lens shaped pellet was used. The bulk solid has a friction angle of wall friction angle of (pw = 15°, measured with a ring shear tester and the Jenike shear tester, respectively. The particle size of the bulk solid was about 3 mm. 

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