A colloid mill is a hydraulic shear producing device that is used to create something called an emulsification. An emulsification is the product of two different liquids that have different weights per volume. The two different weights create a suspension effect in the lighter liquid when it’s added to the heavier of the two.
The colloid mill works to substantially reduce the size of the suspended droplets, creating a mixture within the liquids that is much more uniform and complete. One application that requires the use of a colloid mill is the dispersion of solid particles within a liquid. The mill allows the solid particles to become so small that, rather than become suspended within the liquid, they seem to become a part of the liquid itself.
The process of colloid milling is done through the addition of the heavier liquid into the chamber of the mill that performs the shearing process. Once the heavier liquid has been added, the lighter material, whether it is a solid mass or a liquid of different viscosity, is added as the milling begins. When the milling portion of the function takes place, the materials are both stirred together within the mill at a high rate of speed. This makes the materials more apt to emulsification through contact with the mill’s teeth.
The mill’s teeth rotate in opposite direction of each other in some models. In other models, one tooth remains stationary while two opposing teeth are rotated within close proximity of the stationary one. This proximity draws both materials through itself as the teeth are rotated, which creates the amount of hydraulic shear needed to break both materials down far enough that they bond with each other on a molecular level.
One of the most common uses for a colloid mill is in the liquid-to-latex emulsion process. Latex paints must be mixed with solid pigments or oil-based pigments to achieve certain colors. Due to the dynamics of each substance used to create these tinted and colored latex paints, the only way to break the pigment particles down far enough to be emulsified into the latex to make colored or tinted paint is through the use of a colloid mill.
Another application in which colloid mills are used is in homogenization processes; however, these processes are done much more slowly than that of the emulsification process. The elements that are mixed with dairy products in order to make them safe for human consumption must be added while the product is still in liquid form. These elements are often added while the liquid milk is in large vats. The vats act as colloid mills, slowly turning the liquid over itself to thoroughly mix any secondary elements into it.