Shear Cell Measurements

A powder s strength increases significantly with increasing previous compaction. The relationship between the unconfined yield stress/, or a powder s strength, and compaction pressure is described by the powder s flow function FE The flow function is the paramount characterization of powder strength and flow properties, and it is calculated from the yield loci determined from shear cell measurements. [Jenike, Storage and Flow of Solids, Univ. of Utah, Eng. Exp. Station Bulletin, no. 123, November (1964). See also Sec. 21 on storage bins, silos, and hoppers.]... 

Shear cell measurements offer several pieces of information that permit a better understanding of the material flow characteristics. Two parameters, the shear index, n, and the tensile strength, S, determined by fitting simplified shear cell data to Eq. (6), are reported in Table 2. Because of the experimental method, only a poor estimate of the tensile strength is obtained in many cases. The shear index estimate, however, is quite reliable based on the standard error of the estimate shown in parenthesis in Table 2. The shear index is a simple measure of the flowability of a material and is used here for comparison purposes because it is reasonably reliable [50] and easy to determine. The effective angle of internal... 

An analysis of the experimental errors associated with shear cell measurements indicates that, in general, neither the standard deviation nor the percent... 

The angle of repose of a powder blend, effective angle of internal friction (EAIF) from shear cell measurements, and the mean time to avalanche (MTA) in powder cohesivity tests are useful for assessing the flow of a tableting mixture at various scales (15 18). 

The prediction power of the shear cell measurement for powder flow as judged by tablet weight uniformity is shown in Figure 2. Discrepancies, especially among powders with good flow, are observed. 

In general tensile strength is not used alone to predict flow. Danjo et al. utilized tensile strength measurement, shear cell measurement, and Carr s flow factor to investigate the effect of particle shape on powder flow. 

Hiestand, E.N. Wilcox, C.J. Shear cell measurements of powders proposed procedures for elucidating the mechanistic behavior of powder beds in shear. J. Pharm. Sci. 1969, 58, 1403. 

Ramachandruni H. Hoag S. Application of a modified annular shear cell measuring lubrication of pharmaceutical powders. Thesis research directed by School of Pharmacy. University of Maryland, 2000. 

Nyquist, H., and A. Brodin. 1982. Ring shear cell measurements of granule flowability and the correlation to weight variations at tabletting. Acta Pharm. Suec. 19 81-90. 

In view of the experimental errors normally affecting shear cell measurements and the amount of personal judgement required to draw Mohr stress circles tangential to a curved yield locus, there is always some uncertainty in the flow function derived from the Jenike-type shear yield loci method. A direct measurement therefore offers considerable advantage and, besides possibly giving better accuracy, may prove to be more rapid and reproducible. 

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