How particle density affects dry-powder classification, according to Hosokawa Micron

Firing Industries Ltd. supplies many processing solutions by Hosokawa Micron, including equipment for dry-powder classification. Bulk-solids classifying machines use a variety of different technologies, and their effectiveness depends on the material characteristics, the target particle size, and how the material will be used. Particle density has an important effect on classification of dry powders. Sometimes, material particles are uniform in size, but differ in densities, so some particles are heavier than others, so screeners cannot classify the material, since particles fit through the same-sized screen openings and remain mixed.

Cyclones and other machines

This is why different classification mechanisms are required to separate material by particle density. Among the machines that Hosokawa Micron manufactures are cyclones, which use vortex airflow to separate material into fine and coarse fractions. A highly economical solution for many classification applications, a cyclone safely and efficiently handles many materials with consistent production yields. It delivers a minimum of 95 per cent collection efficiency when classifying particle sizes greater than ten microns. Cut point and collection efficiency are determined by dimensions, outlet-tube diameter, air velocity, material load, and other parameters.

Elutriation classifiers work according to Stokes’ Law, which expresses the settling velocity of small spherical particles in a fluid medium. They use this force relationship to separate low-mass or low-density particles from high-density or high-mass ones. A user can control which particles rise and fall to determine the cut point by adjusting the classifier’s opening parameters. But elutriation can have issues classifying particles with a uniform size but varying densities, or uniform particle density but different surface areas. Elutriation classifiers are best recommended for particle sizes from 0.3 to ten millimetres that cannot be sieved effectively because of their differing characteristics.

Dynamic air classifiers by Hosokawa are also available from Firing Industries. These units employ the principles of elutriation, drag force, and centrifugal force to separate material into coarse and fine fractions. They classify a broad range of materials with particle sizes from three to 100 microns, achieving high production yields and efficiencies.

To learn more, contact Firing Industries’ application-sales engineers at or (877) 688-0974.

This entry was posted in Uncategorized.