Casson models, viscosity measurements

For a food whose flow behavior follows the Casson model, a straight line results when the square root of shear rate, (y), is plotted against the square root of shear stress, (cr) , with slope Kc and intercept Kqc (Figure 2-2). The Casson yield stress is calculated as the square of the intercept, ctoc = (Kocf and the Casson plastic viscosity as the square of the slope, r]ca = The data in Figure 2-2 are of Steiner (1958) on a chocolate sample. The International Office of Cocoa and Chocolate has adopted the Casson model as the official method for interpretation of flow data on chocolates. However, it was suggested that the vane yield stress would be a more reliable measure of the yield stress of chocolate and cocoa products (Servais et al., 2004). 

Besides the Brookfield viscometers, the Haake rotoviscometer, PKIO MlO/PKl 2 Cone, Casson Model is used to measure viscosity at shear rates of 0.4—30 second . This instrument is used alone or in combination with a Brookfield viscometer for SMT adhesives. The equipment is used not only to measure viscosities, but also to provide flow properties in the form of graphs of shear stress versus shear rate. 

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