Classification of Materials and Types of Classifiers...

Classification of Materials and Types of Classifiers Size control of particles finer than 1 mm, are out of the practical range of conventional screens. Separation of such particles is carried out by classification. Classification implies the sorting of particulate material into different size ranges. It is a method of separation of fines from coarse particles and also lighter particles from heavier particles. The two product streams resulting from any classifiers are (i) a partially drained fraction containing the coarse particles, and (ii) a fine fraction of particles. Usually the principle of the classification is based upon the various densities, specific gravity, terminal falling velocities of particles in liquid and in air. 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. Classification is performed on the basis of the velocity with which the material particles fall through a fluid medium generally water or air. In view of the fact, that the velocity of particles in a fluid medium is dependent not only on the size, but also on the specific gravity and shape of the particles. In classifiers, use is made of the different rates of movement of particles of different sizes and densities suspended in a fluid and differentially affected by imposed forces such as gravity and centrifugal fields, by making suitable arrangements to collect the different fractions as they move to different regions. Based on their separation principles, classifiers are classified into two major types. They are (i) wet classifiers, and (ii) dry classifiers. Wet classification with hydro-cyclones using separation by centrifugal force typically covers the size range of 10 micrometers to 100 micrometers while wet classification with spiral classifiers using separation...