THE CONVERSION OF SEDIGRAPH SIZE DISTRIBUTIONS TO EQUIVALENT SUB-SIEVE SCREEN SIZE DISTRIBUTIONS

In many industrial applications a major part of the data on size distr ibutions uses screening to define size, whereas an important part of t he size distribution information is determined using sub-sieve size an alysis. It is necessary to have an accurate method of converting one t ype of data to the other. A technique is presented for conversion of S edigraph size distribution data to equivalent screen size. The techniq ue consists of first characterizing the material by determining the Se digraph size distribution on a sample of the powder carefully wet-scre ened to lie between 270 and 400 mesh (53-38 mu m) and fitting the data by a log-normal or log-logistic distribution function to give mu and sigma or mu and lambda values characteristic of the material. The Sedi graph size distribution of a sample of less than 400 mesh powder scree ned from the total sample can then be converted to an equivalent scree n size distribution by a back-calculation technique, using the charact eristic parameters of the material in a constrained search program. Th e technique is illustrated by application to data taken around an indu strial grinding mill. (C) 1998 Elsevier Science S.A.