High-speed mixer/granulators are used extensively for pharmaceutical granulation. They were developed from traditional planetary mixers to speed up the process and to reduce the number of pieces of equipment and separate process steps required. The machines have a stainless steel mixing bowl containing a three-bladed main impeller which revolves in the horizontal plane and a three-bladed auxiliary chopper (or breaker blade) which revolves in either the vertical plane or the horizontal plane. The main blade is designed to rotate at approximately 150–300 rpm and the high-speed chopper rotates at approximately 1500–3000 rpm.

Granule Formation Using a High-Shear Granulators

The unmixed dry powders are placed in the bowl and mixed by the rotating impeller for a few minutes. Granulating liquid is then added via a port in the lid of the granulator while the impeller is turning. The granulating fluid is mixed into the powders by the impeller. The chopper is usually switched on when the moist mass is formed as its function is to break up the wet mass to produce a bed of granular material. Once a satisfactory granule has been produced, the granular product is discharged, passing through a wire mesh, which breaks up any large aggregates, into the bowl of a fluidized-bed dryer.

High-Speed Mixer/Granulators Bowl Sizes

Like most modern process equipment, high-speed mixer/granulators are available in a wide range of sizes. These are often designed to have similar geometric and powder movement characteristics in an attempt to minimize scale-up problems when a product moves from development to production. Bowl volumes between 1 L and 1250 L are available. The weight of powder that each holds will depend on its bulk density and the optimum fill capacity (working volume) of each bowl. Bowls are manufactured from high-quality polished stainless steel.

Advantages of High-Speed Granulators

The advantage of the process is that powder blending, wet massing and granulation are all performed in a few minutes in the same piece of equipment. The process needs to be controlled with care as the granulation progresses so rapidly that a usable granule can be transformed very quickly into an unusable, overmassed system. Thus it is often necessary to use a suitable monitoring system to indicate the end of the granulation process (i.e. when a granule of the desired properties has been attained). The process is also sensitive to variations in raw materials, but this may be minimized by using a suitable granulation end point monitor.

Reference:

• Aulton, M. (2018). Aulton’s pharmaceutics, the design and manufacture of medicines. Edinburgh. : Elsevier.