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 tests capable of analyzing particle breakage subjected to particle impact, compression, shear and abrasion etc. pertaining to a milling process, which in turn will provide the basis for an improved particle breakage model calibrated against 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 3 of the project is summarized as below.
UPZ100 pin mill experiments were conducted with the effect of rotary speed and feed rate examined. Conceptual design of instrumented pin was trialed in laboratory and its mechanical response was explored in both static and dynamic loading. An inverse analysis scheme has been developed and validated for determining force and angles from strain measurement on an instrumented steel pin. With the finding of the significance of tangential component of impact velocity, a new breakage model was proposed based on a mechanistic approach assuming that lateral crack accounts for the chipping mechanism. The new model was then assessed and compared with other breakage models which demonstrates that the new model is superior in predicting both normal and oblique impact regimes for the range of velocities studied. DEM simulations of single particle breakage were conducted to study the damage ratio arising from the velocity regimes pertaining to an impact mill. A recently developed new DEM bond contact model [15] was utilized considering axial, shear and bending behaviour of bond. 2
The breakage pattern of chipping and fragmentation under low and high impact velocity was successfully reproduced in DEM.