Fluid undergoes “shear” when a certain area of its surface is traveling with a different velocity relative to an adjacent area. A high-shear mixer uses a rotating impeller or high-speed rotor (or both) to create flow and shear. The tip velocity, or speed of the fluid at the outside edge of the rotor, will be higher than the velocity at the center of the rotor, and it is this difference in velocity that creates shear.
High-shear granulation is an effective way to turn powders into dense granules for tableting or coating. To create the granules, powders are added to the mixing bowl and the bowl is sealed. A large impeller rotates at slow speeds, spinning the powders into a vortex. After the powders are blended together, liquid is added to the product using a pump or pressurized container. A high-speed chopper tool located in the bowl shears the granules and removes air. The mixing continues until the desired granule size and density are achieved.