PARTICLE SIZE CLASSIFICATION BY ADHESION.

Abstract

ALTHOUGH adhesion and its relation to particle size have been rather extensively investigated1–4, apparently no one has previously considered using the adhesion properties of small particles as a means of classification by size. It is shown here, however, that significant classification of dry powders, the particles of which are pre-dominantly less than 50µ in diameter, can be achieved for a number of powders with widely varying properties. The technique consisted of laying down a thin layer of powder on a moving solid surface such as a glass plate or a flexible continuous belt. This was accomplished either by moving the solid surface across a mass of the powder when the latter was readily dispersible or, when the powder required more energy for dispersion, by first dispersing it as an aerosol with a Wright dust-feed mechanism5 and then impacting it on to the surface. The solid surface with the adhered layer of particles then moved to a source of disruptive force which was actually either a vibrator or a jet of air. The larger of the adhered particles were dislodged and afterwards collected by vacuum filtration. Those particles remaining on the solid surface, finally, were removed by pressing a lint-free pad on to the surface and wiping them off.