Design and validation of an annular shear cell for pharmaceutical powder testing

An annular shear cell was constructed for powder flow testing, the influence of design and process parameters was characterized, and the results were compared with other flow methods. The shear cell was designed with interchangeable parts to mimic other shear cells. The texture of the powder-metal interface and the gap distance between the lid and side wall of the trough were varied, and the effects of shear rate, powder bed thickness, and consolidation times were tested. Shear parameters, such as cohesion, angles of friction, and flow factors, were measured for microcrystalline cellulose, anhydrous lactose, spray-dried lactose, mannitol, dibasic calcium phosphate dihydrate, anhydrous theophylline, and theophylline monohydrate powder. The results were then compared with the Carr index, mass flow rate, and flowability index. Design parameters such as surface texture and the gap distance significantly affected the shear call results, whereas for the process parameters studied, the shear rate, consolidation time, and powder bed height had a minimal effect on the shear cell results. Of the shear parameters obtained, the angles of friction best represented the known flow properties of powders and were in general agreement with those from other flow tests.