In this process stage, the crushed material can be further disintegrated in a cylinder mill, which is a cylindrical container built to varying lengthtodiameter ratios, mounted with the axis substantially horizontal, and partially filled with grinding bodies (e.g., flint stones, iron or steel balls).
A special development is the autogenous or semiautogenous mill. Autogenous mills operate without grinding bodies; instead, the coarser part of the ore simply grinds itself and the smaller fractions. To semiautogenous mills (which have become widespread), 5 to 10 percent grinding bodies (usually metal spheres) are added.
Mills classified as Ball mills, SAG mills and Rod mills.