Rotor-stator mixers are single-shaft mixers with an impeller rotating in close proximity to a stationary housing. They are used to rapidly break apart solid particles in a liquid, or to emulsify a liquid into liquids. The impeller or rotor mechanically imparts high-shear forces to the ingredients. With rotor-stator mixers, clumps of particles are also broken apart by the hydraulic shearing forces generated as they are ejected through openings in the stator into the rest of the batch. In addition, rotor-stator mixers are effective at chopping coarse particles such as rubber or flake resin. The stator directs the flow and confines the particles while the rotor imparts shear.
Product specifications for rotor-stator mixers include media type and operating capacity. There are three choices for media type: liquid, liquid with suspended solids and powder or granular. Media viscosity, a measure of a fluid’s thickness, is important to consider when choosing rotor-stator mixers for processing liquids or liquids with suspended solids. As a rule, thicker materials require more energy for mixing, homogenizing, or blending. In terms of operating capacity, volume capacity and feed rate are important parameters. Capacity is the volume of product that a rotor-stator mixer can accommodate. Feed rate is the volume that can be processed over a given period of time.
Rotor-stator mixers differ in terms of operating configuration. Devices are designed for industrial or laboratory use, and there a variety of choices for mounting style. Rotor-stator mixers have batch or continuous-process modes. Batch mixing is the simplest mode of operation. The rotor-stator mixer is filled with a medium and mixing is allowed to proceed. When the mixing has finished, the contents are emptied for downstream processing. The mixer is then cleaned and refilled, and mixing begins again. With continuous-feed rotor-stator mixers, the sample being mixed is continuously added and mixed fluid is continuously removed. The device can be run for long periods of time without being shut down.
Additional specifications for rotor-stator mixers include mixer location, mix rate and motor speed, operating temperature and pressure, and application. There are four choices for mixer location: in-line, top entry, side entry, and bottom entry. In-line mixers are mounted on the process line. Top-entry devices are mounted through an entry port at the top of the process material tank. Conversely, bottom-entry mixers are mounted through an entry port at the bottom of the process material tank. Normally, side-entry rotor-stator mixers are mounted through a nozzle on the side of the tank or chest. The nozzle is near the bottom of the tank so that mixing is possible at reduced liquid levels during filling or emptying.