Shear cell rotational

Flowability If we re considering particles, powders, and other products that are intended to flow, then this is a very important consideration. These materials need to easily flow from bins, hoppers, and out of boxes for consumer products. Powder flowability is a measure-able characteristic using rotational shear cells (Peschl) or translational shear cells (lenike) in which the powder is consolidated under various normal loads, and then the shear force is measured, enabling a complete yield locus curve to be constructed. This can be done at various powder moistures to create a curve of flowability versus moisture content. Some minimal value is necessary to ensure free flow. Additional information on these devices and this measure can be found in Sec. 21, Sohd-Solid Operations and Processing. ... 

There are basically three types of shear cells available for powder testing (a) the Jenike shear cell, also known as the translational shear box (b) the annular or ring shear cell, also called the rotational shear box and (c) the rotational shear cell, which is a fixture of a powder rheometer. 

Alternatives to the Jenike shear cell are the annular shear cell and the rotational shear cell, also called the powder rheometer. It has been reported (Freeman and Cooke, 2006) that powder rheometers are reliable, fast, and give results comparable to standard methods based on the Jenike shear cell. The objective of the exercise is to compare the standard Jenike method for limestone CRM 116 powder with a method using a powder rheometer. 

A rotational shear cell instrument, such as the FT4 Powder Rheometer, equipped with a 48 mm rotational shear cell and a 30 mL shear measurement vessel. A batch of reference limestone powder (CRM 116), produced and sold by the Commission of European Communities. 

Freeman, R. E., Cooke, J. R., and Schneider, L. C. R. 2009. Measuring shear properties and normal stresses generated within a rotational shear cell for consolidated and non-consolidated powders. Powder Technology 190 65-69. 

Here, [L is the coefficient of internal friction, ( ) is the internal angle of friction, andc is the shear strength of the powder in the absence of any applied normal load. The yield locus of a powder may be determined from a shear cell, which typically consists of a cell composed of an upper and lower ring. The normal load is applied to the powder vertically while shear stresses are measured while the lower half of the cell is either translated or rotated [Carson Marinelli, loc. cit.]. Over-... 

The Jenike shear cell tester is classified as a direct shear tester that is capable of providing information on a solids cohesive strength as well as its wall friction properties. The tester allows us to measure the strength of a powder blend as a function of pressure applied to it. These are two main considerations when design a bin or hopper to ensure reliable material flow. The tester consists of a base, a moveable shear ring resting on top of the base, and a top cover lid (Fig. 7.3).61 The base is fixed while the lid rotates at a constant low rate. Powder blend is placed in the ring and base and a... 

The ring or annular shear cell, was developed by Carr and Walker as early as 1968. In recent years this tester has undergone a number of modifications. Peschl has developed an annular shear cell in which the sample and shear cell consists of a full circle. This contrasts to the earlier cells that have a band of sample on the outer portion of the circle. This was done to eliminate wall friction. It is also rotated very slowly, since at low speed, velocity variability becomes more negligible in the shear measurement. In this way a full ring can be utilized and speed differences in the outside and inside of the ring become negligible. 

FIG. 21-33 Exampl es of powder shear cells. Triaxial cells (a) Traditional triaxial cell h) true triaxial. Direct shear cells (c) Translational split, Collin (1846), Jenike (1964) d) rotational annulus, Carr and Walker (1967), Schulze (2000) (e) rotational split, Peschl and Colijn (1976), iShear (2003). From Measuring Powder Flowabil-ity and Its Applications, E G Associates, 2006, with permission.)... 

Fig. 7 Reprinted with permission from [111], copyright (2004), Institute of Physics Publishing. Confocal images (yz, 75p.mx56gm, 512x512 pixels-) of a colloidal fluid at various shear conditions taken in a counter-rotating cone-plate shear cell [111] see Sect. 2.3. The applied shear rates are 1.67,3.36 and 8.39 s (fop to bottom)-, the ratios ofthe applied cone to plate rotation speeds are 84, 129 and 175 (left to right). Graphs (a) and (b) show displacement profiles, y(z). measured from these images via cross-correlation of scanned lines. The appropriate profile is overlaid on each image (white curves). The velocity profiles (dy/dz) calculated from these displacement profiles are shown in the graphs (c) and (d). The particle diameter is 1.50 pm...

The so-called shear cells are used for direct shear tests, where the powder specimen is consolidated in the vertical direction and then sheared in a horizontal plane. There are basically two types of shear cells in use today the Jenike shear cell (sometimes referred to more generally as the translational shear box) and the annular (or ring) shear cell (the rotational shear box). As the equipment needed is highly specialized (and hence outside the scope of this Guide) and as manufacturers instructions are usually adequate, the following contains only an outline description of both the hardware and the test procedures. 

In annular shear cells which represent a commercial alternative to the Jenike shear cell), the shear stress is applied by rotating the top portion of annular shear box (see Fig. 18). These devices allow much larger shear distances to be covered both in sample... 

There is another type of shear cell, known as the ring cell or Peschl Shear Tester84. The cell is in the form of a full ring and is rotated like the annular shear cell. It is a very easy device for comparative measurements and another report from BMHB84,... 

Application of Shear Stress. The Rice University ROM-8 viscometer has been described previously (9). This apparatus permits volumes of 8 mL of fluid to undergo uniform shear stress exposure at readily quantifiable levels. For the present experiments, all surfaces coming into contact with leukocyte suspensions were coated with silicone (Siliclad), which had been demonstrated earlier to minimize or eliminate surface-mediated effects on PM Ns (2). The surface-to-volume ratio in the viscometer could be varied by a factor of three using different bobs. Effectively, the fluid volume was varied at nearly constant surface area. Increasing the surface-to-volume ratio increased the accessibility of the surface to cellular elements in the sheared fluid. Shear stress levels were 100 and 300 dyn/cm2 for the 10-min exposure, which had been documented previously to produce functional alterations in PM Ns. Control samples were placed into the viscometer for 10 min, but were not subjected to rotational shear stress. After exposure to the viscometer, cell suspensions were assayed without further delay as described in the next section. 

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