Rigidly-mounted roll mill as breakage tester for characterizing fine particle breakage

Abstract

Fine grinding based on compression stresses is an important industrial process step, which is often applied in mineral, chemical and pharmaceutical industries, for example by using stirred media mills. For this stress mechanism, several studies investigate how to predict the breakage behavior depending on process and formulation conditions by population balance modelling. Breakage rate and breakage function are essential to describe the evolution in particle size distribution over time. Hereby, the division in a mill and a material model has already been shown to be a successful approach for different mills. Especially for fine particles the determination of the breakage function is a particular challenge. In order to predictively model breakage characteristics of materials, such as the breakage function for different energies applied to break the material, it is required to develop a new method, which is easy, fast, and inexpensive to carry out. For this purpose, we present a newly designed breakage tester consisting of a rigidly-mounted two-roll mill. First, a recommendation for the use of a breakage tester is developed. In this step, the investigated machine parameters include the gap size, feed rate, and roller velocity. Furthermore, the influence of feed particle size on the resulting particle size distribution was researched. All tests have been conducted with soda-lime glass as a model material. Second, the applicability of different models for the breakage function, focusing on the tnt10-model, is demonstrated. The breakage can be predicted for new energy values and is in very good agreement with the experimental data. This new breakage tester allows the fast characterization of particle breakage in lower micron range.