(110c) Up Scaling the Isamill with the Enhanced Stress Model
For Nano grinding in stirred media mills an enhanced stress model was introduced, which enables the prediction of optimum stress conditions different mill designs, sizes and materials on basis of geometrical data and material values as input parameters [3-6]. Therefore the median stress energy is used for different mill sizes and geometries, which could roughly be calculated by geometrical data of the mill. Besides the prediction of the optimum grinding conditions, with less experimental work the prediction of specific energy input for a given set of parameters and a determined product quality could be realized. This model was used for lab scale mills (grinding chamber volumes below 2 L) and especially for nano applications where the stability and rheology of the suspensions plays a major role.
Within this work the model is applied for the scale-up of a fine grinding process in a more industrial scale. Therefore experimental work was carried out at a 4 L and a 20 L IsaMill with dolomite as a model mineral. For both mills the classical optimization way with the stress energy curves was realized by the variation of the process parameters grinding media diameter and stirrer tip speed.
The ISA-mill has a special separator at the rotor to keep the grinding media away from the sieve. This separator transfers back lifting forces to the grinding media, which lead depending on the process parameter to heterogeneous grinding media distributions [7-9]. This grinding media distribution has a strong influence on the mill operation in terms of grinding efficiency, production rate and mill wear for instance. [8-9].
Besides the experimental work the enhanced stress model was proofed for this fine grinding process with those bigger mills in comparison to the results of lime stone grinding in a small lab scale mill (0.5 L). Therefore different parameters like the median stress energy or the different energy transfer factors were calculated. The experimental work was used for the proof of the validity of the model as well as a few selected results for the determination of parameters for the model.
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