Whether used for dry powder mixing, granulation, melt coating etc., high-shear mixers offers a number of advantages over other types of mixers and granulators. This includes most importantly the possibility to process particle types which are difficult to process in other equipment. Furthermore high-shear mixers can spread highly viscous binders and are capable of producing small granules of diameters less than 2 mm. When used to granulate particles into agglomerates such granules typically have a denser and compact structure than e.g. agglomerates produced in fluid beds. High-shear mixers are commonly found in the pharmaceutical, agrochemical and detergent industries.
High shear granulators in general fall into two classes, being horizontal mixing and vertical mixing, and can be either continuously operated or batch operated. High-shear granulators use an impeller to vigorously agitate the powder and produce high-density granules. Impellers typically rotate at high speed (between 100 and 1500 rpm) on either a vertical or horizontal axis to create the agitation required for granulation. Typically, a secondary smaller impeller, called a chopper, is used. This rotates at much higher speed (around 1500 rpm). The role of the chopper in granulation is currently a matter of debate: it either fractures larger agglomerates or causes growth of smaller agglomerates, depending on the feed properties, operating conditions and the geometry of the mixer, impeller and chopper. Binder addition to high shear granulators can be in the form of a liquid spray through nozzles or by pouring through lances. For melt granulation, binder can be added as a solid to a preheated high shear granulator.
For many years and still to a certain extent currently, high shear granulation design and process optimization remains an essentially empirical process. In general, the majority of literature is concerned experimentally with the role of material properties and process conditions on the properties of the product granules. Seydlitz United Consultants offer consultancy in both vertical and horizontal high-shear mixers, both batch and continuous and most importantly with focus on both product properties and process conditions.