Estimation of the breakage function of a roller mill crushing quartzite

Abstract

Studies on the breakage function of roller mills are limited. The approach of using breakage functions adapted from other milling systems has been previously used to model the breakage of laboratory roller mills. However, in most cases this approach has been found to be inadequate because the assumption of normalization used for modelling other milling systems may not apply to roller mills. This study assumes the non-normalization of the model for roller milling. It aims to define the breakage function of roller milling of quartzite and to develop a predictive model for first breakage for a laboratory roller mill. Six size fractions of quartzite were prepared using a Jaw Crusher for primary breakage of a quartzite feed material. The product from the crusher was split into narrow size ranges using a sieve shaker. Each size fraction was in turn split into three samples, which were then fed separately to the roller mill, using a different roll gap for each sample. A breakage matrix for each roll gap size was then generated from the product size analysis of the sample. Using the cumulative passing and the milling ratio, the analysis of the three breakage matrices led to the definition of the breakage function. The coefficients of the breakage function were curve-fitted, in order to develop a predictive model. The results indicate that the assumption of non-normalization is appropriate for roller milling of quartzite rock. The breakage function follows a log-normal trend for all the feed size fractions used, and the coefficients of the breakage function can be fitted by polynomial functions of second degree of the feed size. Further research is needed to investigate the correlation of the breakage function and the product size.