Bulk Solids Flow

Online, August 25, 2009 (Newswire.com) - The origins of bulk solids and powder flow properties testing were derived from soil mechanics. The original "shear cell" - or shear box, was design by Casagrande. This shear cell was rectangular, as knowledge in bulk solids and powder flow properties testing was limited at that time. Soil samples were easily prepared as rectangular as compared to other forms.

The rectangular shear cell was composed from a cell base, and a top-loading cover. The intention was a linear movement of the "loading cover" against the shear cell base, and the soil-sample shears in between the shear cell base and the loading cover. For soil samples, this method of shear test by Casagrande delivered acceptable results.

As knowledge and experience was gained, the Casagrande tester was introduced to determine bulk solids powder flow properties. However, unlike soil samples which have been consolidated for thousands of years, it was found that the samples of bulk solids and powders required to be consolidated in the shear cell, and the rectangular format was found to be less than ideal. This was due to the relatively unconsolidated state of powders and bulk solids compared to soils.

Experimentation and process requirements lead to a shear cell where powders can be more efficiently filled and consolidated. Early pioneer Jenike altered the square cell design of Casagrande, having a shear cell base ring and a loading cover. Operation of the Jenike shear cell remained a linear movement. In this revised design, the consolidation process occurred during the shearing process, until a stable shear stress was established. By experimentation, some powders too small in particle size were unable to reach a stable shear stress, making this design limited in effectiveness.