Mechanism of the onset of axial segregation in a rotating cylindrical drumfilled with binary granular mixtures

A phenomenon of axial band formation in a long rotating cylindrical drum fi lled with a binary granular mixture is described as a two-stage process. At the first stage, due to different mobility of the large and small particle s, a central core occupied by a small-size fraction is formed along the axi s of the dmm. The axial segregation, i.e., transverse band formation, is fo und to be associated with the instability of the radially segregated state caused by an asymmetry of the free surface of the granular material. This i nstability is caused by the difference in the repose angles of two granular fractions and deviation of the filling level of the drum from 0.5. [S1063- 651X(99)04308-1].