Whitepapers

Abstract

Throughout the process industries, manufacturers rely on high shear mixing to produce emulsions, dispersions and solutions. Many of today's chemicals, adhesives, pharmaceuticals, foods, plastics, coatings, composites and other products can no longer be made efficiently using traditional batch mixers such as propellers, turbines and saw-tooth dispersers. This can be attributed not only to new raw materials and formulations but also to the increasingly competitive market which puts a high value to process efficiency and lean manufacturing. The long mix times, multiple transfer steps, batch-to-batch variations and other issues that manufacturers were simply dealing with have become unacceptable. As a result, newer mixer designs such as inline high shear rotor/stator devices have become more in demand and have undergone significant developments in terms of features and functions.

This white paper presents some ideas for selecting the right inline high shear mixer for your process. The recommendations discussed in this paper are based on the company's collective experience as a mixing equipment provider to the process industries for over 170 years. Mixer testing and simulation trials are encouraged to confirm the suitability of a specific mixing strategy.

Introduction

Rotor/stator mixers, also called high shear mixers, are comprised of a rotor turning at high speeds within a stationary stator. As the blades rotate, materials are continuously drawn into one end of the mixing head and expelled at high velocity through the openings of the stator. The resulting hydraulic shear promotes fast mixing, breaks down solid agglomerates and reduces the size of suspended droplets.

Although high shear mixers were first developed as batch-style, top-entering mixing devices, they are now just as widely used in an inline configuration wherein they behave like a centrifugal pump. An inline rotor/stator mixer is not self-priming and thus requires static pressure (gravityfeeding) or positive pressure (pump-feeding) to introduce materials into the mix chamber.

Gravity usually feeds the product into the rotor/stator assembly since the mixer is typically positioned on the floor or on a platform below the liquid level. Most inline high shear mixer models will easily move materials up to around 10,000 centipoise (cP), depending on the formulation's shear-thinning properties. With an auxiliary pump, moderately viscous products can be processed in a rotor/stator mixer.