There are two methods of industrial sizing.
Screening is generally carried out on relatively coarse material, as the efficiency
decreases rapidly with fineness. Screening is generally limited to materials above about 250 microns in size, finer sizing normally being undertaken by classification. Industnal sizing is used in closed circuit with a crusher or a ball mill. For the large lump sizes coarse grizzlies made of rails or trommel (revolving) screens made of punched plate may be used. For finer material, screens are usually made of woven metal wire. The material that passes through the openings (apertures) of a particular screen is known as the undersize and material that remains on the screen is the oversize.
Classification: Classification is defined as a method of separating mixtures of mineral particles into two or more products according to their settling velocities in water, in air or in other fluids. Industrial classification may be carried out in different types of classifiers and these classifiers are; hydraulic classifiers, mechanical classifiers and cyclones. Basically they all work according to the principle that the particles are suspended in water which has a slight upward movement relative to the particles. Particles below a certain size and density are carried away with the water-flow, whereas the coarser and heavier particles will settle. In classification mostly we use wet cyclones(hydrocyclones) in which rapid spinning of the pulp centrifuges the solid particles.