Grindability Test Modelling, Measurement and Mill Fringerprinting

Publication Reference: 
Author Last Name: 
Jin Y. Ooi, Li-Ge Wang, Jian-Fei Chen, Jin Sun
Report Type: 
Research Area: 
Size Reduction
Publication Year: 
Publication Month: 
United States

Executive Summary

Milling is commonly deployed in many industrial sectors for intended particle size

reduction. In this project, we aim to develop a robust methodology to link material

grindability with particle dynamics in a mill in order to provide an innovative step--

change in mill fingerprinting and optimization. This involves characterizing the stressing

events that prevail in a milling operation and establishing material grindability in the

context of the stressing events. The material grindability will require a detailed study of

the fundamental fracture and breakage mechanisms of individual particles under different

loading regimes, and how they relate to the mechanical properties and the final size

distribution. This will provide the fundamental scientific basis for developing appropriate

grindability measure capable of analysing particle breakage subjected to particle impact,

compression, and shear etc. pertaining to a milling process, which in turn will provide the

basis for an improved particle breakage model calibrated against the defined grindability.

The centrifugal impact pin mill has been selected as the first mill to be studied for this

project, in collaboration with Hosokawa Micron Ltd. The work performed in Year 4 of

the project is summarized here. UPZ100 pin mill experiments were conducted with the

effect of rotary speed and feed rate examined. Six parameters including particle size

distribution, median product size, relative size span, bond’s grinding energy, size

reduction ratio and specific surface area are chosen to characterize the milling results. In

particular, the relationship between relevant parameters is investigated. The grinding

energy approximately follows a linear relationship with the size reduction ratio. The

alumina particle requires more grinding energy as compared to the zeolite particle. The

population balance modelling (PBM) is used to predict the product size distribution in the

milling impact tests. As indicated by the general form of PBM, it shows that two

functions, i.e. selection and breakage functions have to be considered. The capacity of

PBM is exemplified by predicting product size distribution in the impact pin mill

considering two simple selection and breakage functions. The coupling framework of

PBM-DEM is presented considering the deficiency of PBM, which forms the platform

for the follow-on work.