An experimental study on free-surface rolling segregation and correlations with angle of repose and particle sphericity

Abstract

Bulk solids commonly segregate when particles move on an inclined surface, often causing significant variations in content uniformity of particle properties such as size and species. Often called free surface rolling segregation, this is one of the most common segregation phenomena for powders and granules, where different sized and shaped particles become separated due to differential movement on the surface. Intensity of rolling segregation is widely understood to depend upon various factors including differences in particle size and shape as well as flow properties and densities. These influences have been studied and reported previously, but correlations between levels of rolling segregation and particle shape assessed by particle sphericity or sphericity ratio with consideration of angle of repose has not been investigated in detail.This is an experimental study of rolling segregation of one particulate material (calcium carbonate) with different particle size ranges; using a single material eliminates variations of influences not being studied, especially solid density. The influence of bulk and particle properties has been studied systematically, especially particle size distributions, angle of repose and particle sphericity. The segregation results show an increased trend with higher particle sphericity and especially sphericity ratio. Also, the results indicate higher levels of segregation with a low angle of repose, but little segregation when angle of repose is higher than 32 degrees. However, the authors caution that this angle of repose of 32° degrees should not be taken as a general indicator of a limitation of the susceptibility of blends to free-surface rolling segregation, for materials other than the one tested.