Attritors

Attritors are stirred-media mills used for fine grinding and dispersion of materials in liquid media, and less commonly for dry milling. They employ a high-energy agitator inside a closed vessel with grinding media to reduce particle size and improve homogeneity. The term attritor originates as a trademark of Union Process to describe their stirred ball mills, though the name is often used generically for similar equipment.

In operation, grinding media such as steel, stainless steel, ceramic, or glass spheres are placed with the material and liquid (in wet systems) or dry powder (in dry systems) inside the mill. A shaft with arms or discs agitates the media at high speed, producing shear and impact that break particles. Milling can be configured as batch or continuous, and as wet or dry, depending on the material and process goals. The process favors materials that benefit from rapid size reduction and uniform dispersion.

Two common configurations are batch attritors, where charging and discharging occur in cycles, and continuous attritors, which feed material and discharge product continuously. Wet attritors are especially prevalent in pigment dispersion for paints and inks, as well as in ceramics and battery materials; dry attritors serve powders where moisture must be avoided.

Advantages include fast particle size reduction, narrow size distributions, and good control over dispersion with efficient energy transfer. Disadvantages can include higher capital and operating costs, wear of media and liners, and heat generation requiring cooling. Attritors are widely used in paints, inks, ceramics, electronics, and pharmaceutical-related grinding and dispersion processes.