Several fields in chemical processing industries use grinding mills to process certain materials like minerals, food materials, and pharmaceutical and chemical products. These mills can also grind coarse materials into fine or ultra-fine powders. This article will discuss grinding mills in depth, including how they work and the different types available.
Mills break down larger solid materials into smaller pieces using a mechanical force called comminution. Comminution occurs when such a high level of stress, through pressure/compression or impact, is put on solid materials that their particles fracture. Comminution can include crushing, grinding, or cutting. Materials need to be brittle and elastic to be used in a mill. This changes the grain size, composition, and shape. The main purposes for using a mill is increasing the surface area of a material, manufacturing of a material to a specific size, and pulping materials to remove or separate contaminates or moisture. The 2 most popular types are fine and ultra-fine grinding mills.
Fine Grind Mills
A fine grinding mill can break down medium-hard to hard materials into a moderately fine powder. Materials must have a maximum particle size of 5-10 millimeters (mm) and a maximum Mohs hardness of 3-4. Any material larger or coarser could lead to excessive wear and tear or cause damage to the mill. This is because the mill uses a rotor at ultra-fast speeds, which is how materials are ground into smaller pieces. Also, materials that are heat-sensitive, meaning they have a softening or melting point above 70 degrees Celsius, cannot be used in a fine grinding mill. This is due to most of the motor’s energy being converted into heat between 50 and 60 degrees Celsius. In order for a fine grinding mill to successfully break down heat-sensitive materials, they or the mill would need to be cooled down first, which can lead to extra energy costs.
Ultra-fine Grind Mills
An ultra-fine grinding mill can break down soft to medium hard materials into an extremely fine powder. Heat-sensitive materials are ground by ultra-fine mills, because they have a water circulation jacket built in that keeps the grinding temperature low. A screw feeder is used to control the amount of material gets put through at one time. The mill uses air to sweep materials through a grinding contour where attrition and turbo combine to grind them to the right size. The powder is discharged into and collected from an opening in the bottom of the mill.