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In the course of the research projects of the Department of Process Engineering of the University of Miskolc the empirical breakage functions of several crushers (jaw, gyratory, cone and hammer crushers) were determined by measurements under operating or pilot-plant (laboratory) conditions. A method was developed to optimize the crushing technology. An appropriate computer algorithm was developed...
The solution of the dynamic population balance model (PBM) of a closed grinding network consisting of a mill, sump, and cyclone is problematic. The fact that the dynamic PBM model equation solution to the Inverse Problem for grinding systems is degenerate or underspecified is demonstrated. Two numerical solution approaches to the Inverse Problem are used. These are: (1) providing additional constraints...
Fluidized bed jet mills are used for the dry comminution in the μm range. The application of the jet mill ranges from deagglomeration purposes to grinding of hard materials. This indicates the wide field for the usage of this grinding technique. The comminution effect is based on particle-particle impact in expanding gas streams. A dynamic classifier is integrated in the fluidized bed jet mill...
LKAB has started the construction of a new concentrator at Kiruna, with a capacity of 5 Mtpy. The flowsheet of the new grinding circuit is technically innovative and critical because it entirely relies on ore breakage properties. It includes primary fully autogenous closed circuit grinding and secondary pebble milling. A critical size class of the magnetite ore is extracted from the autogenous...
According to a generally accepted principle, the data describing test conditions should be always sufficiently complete to enable the reader to repeat the experiment. However, it is not quite an exception if a technical report on or a scientific publication of results of grinding tests carried out in lab-scale tumbling mills omits most relevant data (e.g.: total mass of the mill charge) in favour...
In stirred ball mills, the specific energy input during comminution is the most important parameter influencing the product fineness. In order to get further information about the distribution of the local specific energy in the grinding chamber, the flow pattern in the chamber was calculated numerically. The calculations are restricted to a stationary operation of a stirred ball mill in the absence...
A considerable body of experimental data now exists on laboratory- and full-scale high pressure rolls which indicates that they offer considerable energy savings over conventional mills such as ball mills. It has been proposed, from experimental data obtained largely from studies on minerals, that the product size distributions from such rolls can be normalised and that a linear relationship is demonstrable...
Development work of laboratory test methods is presented for autogenous grinding, done in cooperation between Outokumpu Mining Services and Technical Research Centre of Finland. The test methods and their developed applications are described and the main results are discussed. The possibilities to use the test results in planning of pilot plant trials and in the design of full scale autogenous comminution...
Systems optimization is an exciting new tool for improving the performance of existing comminution plants while incurring minimal capital expenditures and producing high rates of return. The goal of this approach is to achieve significant performance gains without installing new equipment or replacing older, less efficient equipment. Thus, rates of return can be much higher than the historical rates...
In rotor impact mills soft and semi-hard materials up to Mohs hardness of 3-4 can be ground without excessive wear at the grinding elements. The fineness of the grinding products depends to a great extent on the impact velocity. Other parameters such as the geometry of the grinding zone have to be considered as well. Especially for the ultra fine grinding an improved two stage rotor impact mill...
A model was developed for interparticle breakage considering especially the influence of the feed particle size distribution. Based on experimental results with particle beds consisting of narrow size fractions, a consistent description of the breakage behaviour of a material can be achieved in terms of the fraction of broken particles and the breakage function, both depending on the particle size...
Within the crushing process, significant improvements in capacity and crushing product are obtained by the reconstruction of the secondary and tertiary crushers. The total energy consumption is reduced considerably. Optimal crushing product is obtained by using the adequate crusher construction and power with minimum operation costs and maximum equipment utilization. Comparing the operation efficiency...
The investigation into wet grinding, with the forced movement grinder, RSK LAB 10-25 MATTER PARTNER proved the efficiency of this grinder. The essential parameters are the rotor and the feeding speed. The population balance method showed that the coarse particles display a first order grinding reaction and a non linear grinding according to time duration while the finest particles don't display...
Centrifugal air classifiers, or classifiers with some sort of centrifugal field, are used in classifying particulate materials in the cut size range between a few hundred microns to below one micron. The sharpness of cut in these devices depends on adequate dispersion of the feed material and the maintenance of identical forces on the particles, regardless of their position, in the classifying zone...
At Boliden Mineral's Aitik concentrator approx 16 Mtpy is milled in five parallel fully autogenous grinding circuits. The original maximum throughput control strategy lead to overruns of the primary mills. Tests showed peak throughput at mill power lower than max power. The peak power varies due to variable ore grindability implying a need for continuous adjustment of the millpower setpoint. The...
The fracture of solids is accompanied by such physical and chemical phenomena as emissions of electrons, ions, photons and molecular particles. The understanding of the mechanisms of all these processes is impossible without the knowledge of the uvenil fracture surface (UFS) temperature. In this research the temperature of UFS of glassy polymer polymethylmethacrylate (PMMA) was measured in time range...
A dynamic model for a semiautogenous grinding mill is developed in the standard dynamic system form of state and state-output equations and the resulting model is analyzed with this perspective. The model is based on results obtained under stationary conditions using a pilot SAG mill and communicated in an earlier paper. From the point of view of the state equations, these results constitute sub-models...
High-pressure particle-bed comminution, using double roll machines (Roller Presses), has become state of the art for grinding cement clinker, blast furnace slag, cement raw meal, kimberlite and some other bulk solids. There was some reluctancy in introducing the process in ore preparation plants. Newly developed wear protection measures, particularly the ''stud lining'', in connection with some other...
The problem of wear in high speed impact mills is serious. In impact mills the processes of wear and fragmentation occur simultaneously. Most of the parameters influencing wear also influence milling efficiency. On special testing rigs, modeling the conditions of work in real mills, the main laws of the process were investigated. In this paper special attention is paid to the influence of impact...
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