High shear mixers are used to emulsify, homogenize, disperse, grind and/or dissolve components of a mixture that is too difficult, expensive, or time consuming to be processed by ordinary mixers.
These machines operate by shearing the mixture composed of a dispersed phase and a continuous phase. During the shearing process, the dispersed particles or droplets are reduced to smaller sizes making it easier to be dissolved and combined creating a homogenized, continuous phase.
The two main parts of a high shear mixer are the rotor and the stator. This assembly is known as the mixing head or generator. The region between the rotor and the stator, known as the shear gap, is where the mixture is being sheared.
An emulsion is created when two immiscible liquids are mixed, such as oil and water. Aside from being hydrophobic, oils are lighter than water which enables them to float on the surface. To homogenize this mixture, the dispersed droplets must be broken down into smaller ones preventing their natural separation.
A suspension is different from an emulsion where the dispersed particles are solid. The function of the high shear mixer is also to break down the dispersed solids into smaller particles.
Particle size reduction and granulation are other two functions performed by high shear mixers. High shear mixers can help bind components into larger and denser agglomerates. These agglomerates are then broken down into finer particles until the target size is attained.
There are four types of high shear mixers: batch, in-line, powder injection, and granulators. Batch and in-line high shear mixers are the two main types, while the other two are modifications. Batch high shear mixers can process large volumes in a shorter period. In-line mixers, on the other hand, are less prone to contamination and can be controlled effectively.
Powder injection high shear mixers are a modification of the first two wherein a vacuum system draws in the powdered components directly into the mixing head to facilitate better mixing.
High shear granulators mix fine powdered products by using a binder liquid to form large agglomerates. These agglomerates are then broken down into granules with the desired particle size.
Equilibrium mixing is the point where additional effort by the mixer does not change the properties of the product.