Mechanical agitator granulators as the name implies are granulators that by virtue of agitator speed, sweep volume, or bed pressures, generate relatively lower shear which has implications on the operating conditions and resultant granule properties. Mechanical agitator granulators can also be referred to as low shear granulators.
During granulation process, the active compound and other excipients are combined with a binder solution to form granules with a fixed composition through rotating low-shear forces via low-power-per-unit-mass with addition of a liquid.
Mechanical agitator granulators are generally characterized by;
The subclasses of wet low-shear granulator/ mechanical agitator granulators are primarily distinguished from one another by the geometry and design of the shear inducing components. Granulators which operate by mechanical agitation include the following;
Shear is induced by either rotating impeller, reciprocal kneading action, or convection screw action.
Ribbon blender popularly used as a dry mixer can serve as a very reliable granulator if a dry paste is formulated for the machine. The following is worthy of note when using a ribbon or paddle blender as a granulator;
The two popular ribbon or paddle blender used as granulators are;
Planetary mixers which are mainly used to mix medium viscous to high viscous media can also be used as granulating equipment. When used as a granulator, planetary motion of the mixer is generated by rotating the agitator off an assembly in a direction opposite to that of the rotation of the agitator assembly as it moves around the bowl. Despite the representations of planetary by different commercial names, like Hobart granulator, kitchen Aide granulator, etc, they still have the following basic makeup;
Planetary mixer tends to be better of mixing drying powders in a horizontal plane than in a vertical plane and so may require a distinct dry blending step prior to wet granulation.
Orbiting screw blender which is mainly used for dry mixing of powders when modified is used as a very gentle granulator mixer. The following modifications along with a chopper in the sidewall make orbiting screw blender an effective granulator for powders, slurries, suspensions, and pastes;
Sigma blade mixer is a compressive granulator designed for kneading, mixing, and homogenizing wet, pasty and high viscous materials. The two sigma shaped blades which sit horizontally and parallel at the bottom of the mixing trough rotates in opposite directions at different speeds.
This rotatory movement of the blades causes the material to be moved from blade to blade and from end to end generating /resulting in a figure-eight pattern of movement that produces a thorough powder mix. When used as a low shear granulator, the sigma blade mixer is proceeded by a dry mixer and the unit generates liquid added to the powder during granulation which facilitates the formation of uniform granules with binder matrix and good binder distribution.