Shear cell test

The data listed above can be found by performing shear cell tests on the powder. 

Generally powders change bulk density under shear. Under the action of shear, for a specific normal load  

For a particular bulk density there is a critical normal load which gives failure (yield) without volume change. A powder flowing in a hopper is in this critical condition. Yield without volume change is therefore of particular interest to us in design. 

These yield loci characterize the flow properties of the unaerated powder. The following section deals with the generation of the powder flow function from this family of yield loci. 

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The range of application of shear cell testing methodology is seen in Tables 2-6. Table 3 relates the flow properties of mixtures of spray-dried lactose and bolted lactose. These mixtures, in combination with the excipients tested, cover a broad range of flow. Tables 4 and 5, for example, show lot to lot variations in the flow properties of several materials, and Table 6 shows the variation in flow properties of bolted starch, sucrose, and phenacetin at different relative humidities (RH). Figure 8 presents the yield loci of sucrose at four different consolidation loads. Also shown in the figure are the shear indices determined at each consolidation load. 

Select a deformation rate of 22.86 cm/min (9 inches/min) for the Wamer-Bratzler test. For the Kramer shear cell test or the wire cutting test, select a desired deformation rate. 

The applicability of the flow property test used is highly dependent on what the user is trying to capture. As an example, if there is concern that a certain batch of material may arch when transferred into a bin, a shear test may be the most comprehensive QC test. However, a quantitative test such as a shear test may require more time/resources to conduct than is practical, so faster test methods are often desired. One option is abbreviated shear cell testing (1). 

Shear cell testing of powders has its basis in the more comprehensive field of soil mechanics (Schofield and Wroth, Critical State Soil Mechanics, McGraw-Hill, 1968), which may be further considered a subset of solid mechanics (Nadia, Theory of Flow and Fracture of Solick, vols. 1 and 2, McGraw-Hill, 1950). The most comprehensive testing of the shear and flow properties of soils is accomplished in... 

The last set of tests includes solid indicizers pioneered by Johaim-son. These include the Flow Rate and Hang-Up Indicizers [cf. Bell et al.. Practical Evaluaton of the Johanson Hang-Up Indicizer, Bulks Solids Handling, 14(1), 117 (Jan. 1994)]. They represent simplied versions of permeability and shear cell tests. Assumptions are made with regard to typical pressures and wall frictions, and based on these, a... 

The technique of shear testing has traditionally been used to determine the shear behavior of consolidated powders. As discussed previously the Jenike shear cell testing is generally accepted as an established method for measuring powder flowability and standards based on it have been issued, both in Europe and the United States. Some disadvantages of the Jenike shear cell have also been mentioned. The process is extremely time consuming and tedious and correct consolidation of sample is difficult to achieve. It can be hardly used for all types of bulk solids due to its limited shear... 

The results of shear cell tests on a powder are shown in Figure lOWl.l. In addition, it is known that the angle of friction on stainless steel is 19° for this powder, and under flow conditions the bulk density of the powder is 1300 kg/m. A conical stainless steel hopper is to be designed to hold this powder. 

Shear cell tests on a powder give the following information ... 

Shear cell tests on a powder show that its effective angle of internal friction is 40 and its powder flow function can be represented by the equation [Pg.289]

Describe how you would use shear cell tests to determine the effective angle of internal friction of a powder. 

The hopper in question feeds a conveyor belt and periodically blocks at the outlet and needs to be encouraged to restart. The graduate makes an investigation on the hopper, commissions shear cell tests on the powder and recommends a minor modification to the hopper. After the modification the hopper gives no further trouble and the graduate s reputation is established. Given the information below, what was the graduate s recommendation ... 

Outlet - circular, fitted with 25 cm diameter slide valve Shear cell test data Effective angle of internal friction, <5 = 60°... 

Shear cell tests are carried out on a powder for which a stainless steel conical hopper is to be designed. The results of the tests are shown graphically in Figure 10E4.1. In addition it is found that the friction between the powder on stainless steel can be described by an angle of wall friction of 11°, and that the relevant bulk density of the powder is 900kg/m. ... 

Figure 10E5.1 Shear cell test data...

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