Screens can be used when achieving efficient separation of particles through dependence on differences between particle sizes with respect to any two dimensions. Assuming 100% screening efficiency, the separation results in a division of the feedstock into two size fractions per one practice. Also, Screens may be used to separate the feed stream into streams corresponding to three or more size classes.
Three types of screens are predominant: vibratory flat bed screen, the disc screen, and the trammel screen. Especially the trammel has proven to be effective and efficient for processing mixed waste and other mixtures where large flat particles and aggregate-type particles must be separated. Hence, it is widely used. In the case of size classification of source-separated materials, vibratory flat bed and trammel screens are feasible and used in a number of facilities.