Tumbling blender-mixer

Carefully identify at least 10 sampling locations in the blender to represent potential areas of poor blending. For example, in tumbling blenders (such as V-blenders, double cones, or drum mixers), samples should be selected from at least two depths along the axis of the blender. For convective blenders (such as a ribbon blender), a special effort should be made to implement uniform volumetric sampling to include the corners and discharge area (at least 20 locations are recommended to adequately validate convective blenders). 

Convection mixers use a different principle for blending. These mixers have an impeller. This class includes ribbon blenders, orbiting screw blenders, vertical and horizontal high-intensity mixers, as well as diffusion blenders with an intensifier bar. Scale-up considerations are similar to those for the tumble blenders. 

To ensure that specifications established for critical product quality attributes are met in a large-scale operation, the formulation and manufacturing process developed in the laboratory must be transferred to production and validated. It is necessary to start with a small scale in pharmaceutical research and development. Unfortunately, small-scale mixers necessary during the early development phase will not necessarily have the same characteristics as a commercial-scale mixer. Currently no mathematical techniques exist to predict the blending behavior of multicomponent solid mixtures therefore, experimental work to ensure the proper scale-up and transfer to the production facility is required. Consider the following process parameters for a tumbling blender during scale-up trials ... 

Tumble blenders also impart shear forces to the powders being blended as slip planes form between the walls of the blender and layers of the blend. The amount of shear force is often low for small-scale blenders, but can increase with increasing scale of the blending container. Because they tend to provide gentler blending and have less of an affect on the particle size of the materials being blended (compared to high shear mixers),... 

Materials introduced into the mixing unit (mixer or blender) are shifted in many ways by means of a fluidizing gas (fluidized bed mixer or pneumatic mixer), by mixer rotation (tumble blenders) or by the movement of some internal mixing mechanisms (ribbon, Z-blades, etc.) of the mixer (mechanical mixer). 

Industrial equipment. Rotating-shell mixers or tumbling mixers are shown in Fig. 3. Drum-type, cubical-shaped, double-cone, and twin-shell blenders with their axis of rotation horizontal to the center of the drum on its axis increase crossflow and improve the mixing action. Cubical and polyhedron-shaped... 

Fig. 11.13 Photograph of different tumble/growth agglomeration work modules that are attached to the all purpose drive stand of Fig. 11.12. (a) disc or pan agglomerator (b) coating pan (c) bowl blender (d) planetary bowl blender (e) double cone blender (f) cube mixer (g) high shear mixer (h) pug mill/kneader (courtesy Erweka, Heusenstamm, Germany).

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