Apparatus and method to screen materials having different sizes and/or density

摘要

Apparatus to screen materials (11) having different sizes and/or density, comprising a plurality of screening rollers (16) arranged parallel to each other and each having the outer surface shaped in such a manner as to define a plurality of protruding elements (22) alternated to corresponding grooves (24). The screening rollers (16) are arranged in such a manner that the protruding elements (22) of each roller are inserted, more or less deeply, into the grooves (24) of an adjacent roller. The screening rollers (16) define a screening plane which is divided into one or more fractions (F1, F2, F3), one adjacent to the other, in each of which the relative screening rollers (16) are separated from each other so as to define a gap (25) of a determinate value, different from that of the other fractions. In the field of each of the fractions (F1, F2, F3) at least one screening roller (16a) has the protruding elements (22) reduced, beveled or rounded so as to obtain zones (30) with a section of passage which is locally greater, without varying the interaxis between the screening rollers (16a) and hence the gap (25).