Wind-Tunnel Classifier for Sand and Silt

Abstract

Methods of of sorting granular material according to particle size have long claimed the interest of a number of professions. Sieves are widely used as a means of laboratory analysis, and on a large scale are well adapted to commercial sizing of gravel and crushed stone. However, sieving becomes less satisfactory for quantity separation as the material decreases in size, and it is particularly difficult to obtain well sorted separates with sieves finer than 200 mesh; furthermore, large variations in the shape or density of particles may cause undesirable complications. These difficulties are largely overcome in hydraulic separation, either air or water being used as the distributing medium. Such methods have reached their highest development in the abrasive and mining industries, but the various patented devices developed by them are generally designed for specific separations on a commercial scale. The increasing need for a simple, dependable, and inexpensive classifier has become particularly apparent in the sediment-research laboratory, where a w1de assortment of sand and silt separates is required in sufficient quantity for experimental investigation. As has been demonstrated at the Pasadena laboratory of the Soil Conservation Service, U. S. Department of Agriculture, artificial mixtures of any desired type can readily be prepared from a series of well-sorted separates differing in average diameter by a small increment. Since the material required by this laboratory includes sizes finer than 200 mesh, and since it is used exclusively in hydraulic experiments, a method of sorting based on settling velocities has been developed, with equipment constructed at low cost in the laboratory shop.