Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Steven Y Liang; Committee Member: Chen Zhou; Committee Member: David G Taylor; Committee Member: Min Zhou; Committee Member: Shreyes N Melkote.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 76-79).

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1930. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed November 19, 2009)

IsaMill is a stirred type mill used in mineral industry for fine and ultra-fine grinding. The difficulty in obtaining the internal flow information in the mill by experimental techniques has prevented the development of the fundamental understanding of the flow and generating general methods for reliable scale-up and optimized design and control parameters. This difficulty can be effectively overcome by numerical simulation based on discrete element method (DEM). In this work a DEM model was developed to study particle flow in a simplified IsaMill. The DEM model was validated by comparing the simulated results of the flow pattern, mixing pattern and power draw with those measured from a same scale lab mill. Spatial distributions of microdynamic variables related to flow and force structure such as local porosity, particle interaction forces, collision velocity and collision frequency have been analyzed. Among the materials properties of particles, it is shown that by decreasing particle/particle sliding friction coefficient, the particle flow becomes more vigorous which is useful to grinding performance. Restitution coefficient does not affect the particle flow significantly. A too low or too high particle density could decrease grinding efficiency. Although grinding medium size affects the flow, its selection may depend on the particle size of the products. Among the operational variables considered, the results show that fill volume and mill speed proved to be important factors in IsaMil process. Increase of fill volume or mill speed increases the interaction between particles and agitating discs which results in a more vigorous motion of the particles. Among the mill properties, particle/stirrer sliding friction plays a major role in energy transfer from stirrer to particles. Although there exists a minimum collision energy as particle/stirrer sliding friction increases, large particle/stirrer sliding friction may improve grinding performance as it has both large collision frequency and collision energy. However, that improvement is only up to a critical particle/disc sliding friction beyond which only input energy increases with little improvement on collision frequency and collision energy. Reducing the distance between stirrers or increasing the size of disc holes improves high energy transfer from discs to particles, leading to high collision frequency and collision energy. Among the different stirrer types, the energy transfer is more effective when disc holes are present. Pin stirrer shows increased collision energy and collision frequency which also result in a high power draw. Using the DEM results, a wear model has been developed to predict the wear pattern of the discs. This model can be used to predict the evolution of the disc wear with the time. It is shown that energy transfer from discs to particles are increased when discs are worn out. An attempt has also been made to analyze the microdynamic properties of the mill for different sizes. It is shown that specific power consumption and impact energy are correlated regardless of the mill size and mill speed.

No description available.

No description available.

IsaMill is a stirred type mill used in mineral industry for fine and ultra-fine grinding. The difficulty in obtaining the internal flow information in the mill by experimental techniques has prevented the development of the fundamental understanding of the flow and generating general methods for reliable scale-up and optimized design and control parameters. This difficulty can be effectively overcome by numerical simulation based on discrete element method (DEM). In this work a DEM model was developed to study particle flow in a simplified IsaMill. The DEM model was validated by comparing the simulated results of the flow pattern, mixing pattern and power draw with those measured from a same scale lab mill. Spatial distributions of microdynamic variables related to flow and force structure such as local porosity, particle interaction forces, collision velocity and collision frequency have been analyzed. Among the materials properties of particles, it is shown that by decreasing particle/particle sliding friction coefficient, the particle flow becomes more vigorous which is useful to grinding performance. Restitution coefficient does not affect the particle flow significantly. A too low or too high particle density could decrease grinding efficiency. Although grinding medium size affects the flow, its selection may depend on the particle size of the products. Among the operational variables considered, the results show that fill volume and mill speed proved to be important factors in IsaMil process. Increase of fill volume or mill speed increases the interaction between particles and agitating discs which results in a more vigorous motion of the particles. Among the mill properties, particle/stirrer sliding friction plays a major role in energy transfer from stirrer to particles. Although there exists a minimum collision energy as particle/stirrer sliding friction increases, large particle/stirrer sliding friction may improve grinding performance as it has both large collision frequency and collision energy. However, that improvement is only up to a critical particle/disc sliding friction beyond which only input energy increases with little improvement on collision frequency and collision energy. Reducing the distance between stirrers or increasing the size of disc holes improves high energy transfer from discs to particles, leading to high collision frequency and collision energy. Among the different stirrer types, the energy transfer is more effective when disc holes are present. Pin stirrer shows increased collision energy and collision frequency which also result in a high power draw. Using the DEM results, a wear model has been developed to predict the wear pattern of the discs. This model can be used to predict the evolution of the disc wear with the time. It is shown that energy transfer from discs to particles are increased when discs are worn out. An attempt has also been made to analyze the microdynamic properties of the mill for different sizes. It is shown that specific power consumption and impact energy are correlated regardless of the mill size and mill speed.

Thesis (M.Eng.)--University of Wollongong. / Typescript. Includes bibliographical references: leaf 131-135.

Size-reduction of materials is an important operation in many chemical industries. The purpose of size-reduction are: (a) for specific mesh size product; (b) grinding for release, or unlocking grinding for purposes of surface exposure or locked-in products for chemical or physical attack; (c) specific surface grinding for product; and (d) size modulus, where limited mesh size is needed for specific processing operation. Size-reduction is accomplished by (a) impact, (b) differential movement of adjacent surfaces and (c) by the combination of both. Most size-reduction of a combination of both, whereas swing hammermill grinding is due mainly to impact. Rittingers’ and Kicks’ laws are empirical formulas which do not make an attempt to resolve the forces as applied to grinding into their component parts. Possibly the application of the component forces as applied to impact grinding would give a key to the multiple factors controlling size-reduction. If this can be worked out, the general formula might be obtained that would apply to all phases of size-reduction. The purpose of this investigation is to study the factors as applied to swing hammermill grinding; also, to determine if it is possible to formulate an equation which will hold for the size reduction of various materials. / Master of Science

As a prerequisite to producing super-clean coal with any physical coal cleaning process, such as microbubble flotation, the feed coal must be micronized to liberate the finely disseminated mineral matter. The stirred ball mill is regarded as one of the most efficient devices for micronizing coal. Using a five-inch batch mill, the optimum operating conditions have been determined in terms of media size, feed size, media type, stirring speed and percent solids. The rates of breakage determined with monosized feeds are compared on the basis of specific energy consumption. It has been found that a 20:1 ball size/particle size ratio gives optimum grinding conditions. With the fine particle sizes obtained using stirred ball milling, as well as other fine grinding techniques, a growing concern has been generated regarding the accuracy of these size distributions. An automated technique has been developed in which a complete mass balanced size distribution can be obtained using an Elzone® 80XY particle size analyzer. A computer program is used to blend the data from successively smaller Orifice tubes, as well as, to determine the weight percent of material in a particle size distribution finer than the lower detection limit of the analyzer. This result is then used to correct the distribution for the missing fine material. / Master of Science