Atualmente a decrescente disponibilidade de carvões de excelente qualidade e seus preços elevados levam as coquerias a utilizarem carvões mais baratos e consequentemente com propriedades inferiores. Ao mesmo tempo, ocorre à necessidade de se manter as elevadas especificações de qualidade exigidas para o coque pelos altos-fornos. Nesse contexto, independente da escolha dos carvões a serem utilizados, o controle granulométrico dos carvões e misturas, realizado durante a britagem, pode manter ou até melhorar a qualidade do coque a ser produzido. O presente estudo teve como objetivo geral avaliar de que forma as propriedades dos carvões variam em relação a suas principais frações granulométricas após a cominuição, e estudar qual o efeito de diferentes distribuições de tamanhos de partículas sobre as propriedades de coques produzidos em escala de laboratório. Para isso, dois carvões coqueificáveis individuais e uma mistura foram amostrados, separados em frações granulométricas e caracterizados. Após a caracterização das matérias-primas, foram confeccionados coques em escala de laboratório, a partir de diferentes misturas de granulometrias para os carvões individuais amostrados. A caracterização dos coques foi realizada segundo análise imediata, textura, reatividade ao CO2 em termobalança, resistência a frio em tambor tipo I e microresistência. Os resultados obtidos da caracterização das matérias-primas mostraram que a cominuição dos carvões leva a concentrações de cinzas, matéria volátil e composição maceral em diferentes frações granulométricas produzindo alterações nas propriedades coqueificantes das frações granulométricas. O resultado da caracterização dos coques mostrou que cada carvão apresenta uma distribuição de tamanhos de partículas mais adequada, que irá gerar um coque de boa qualidade. Em termos de reatividade ao CO2, uma grande quantidade de partículas finas nas misturas levou a um aumento da reatividade dos coques produzidos. Além disso, a resistência mecânica foi mínima para as misturas grosseiras, enquanto uma mistura mais fina tendeu a produzir coques de resistência mecânica superior. / Nowadays, the decreasing availability of excellent quality coals and their high prices lead cokemakers to use cheaper coals, consequently with inferior properties. At the same time, there is the need to maintain the high coke quality specifications required for the blast furnace. In this context, independent of the choice of coal to be used, the particle size control of coals and blends, created during crushing, can maintain or even improve the quality of coke to be produced. The present study had as main objective to assess how the properties of coals vary in relation to its particle size fractions after crushing, and study what effect different particle size distributions can cause on the properties of coke produced in laboratory scale. Thus, two individual coking coals and a blend were sampled, separated into particle size fractions and characterized. After the characterization of raw materials, cokes were made on a laboratory scale, from blends of different particle sizes for an individual coals. The characterizations of cokes were done by proximate analysis, texture, thermobalance CO2 reactivity, cold strength in a CSR drum, and microstrength. The results of the characterization of raw materials showed that the comminution of coal leads to concentrations of ash, volatile matter and macerals on different size fractions, causing changes in coking properties of size fractions. The results of the characterization of the cokes showed that each coal used has a more suitable particle size distribution which will generate a good quality coke. In terms of CO2 reactivity, a large amount of small particles in the blend led to an increase of coke reactivity. Furthermore, the mechanical strength of cokes was sharply affected by coarse particle, while a blend with high fine proportion produced a coke with high mechanical strength.

Na produção de concreto estrutural, apesar dos avanços tecnológicos, ainda se utilizam de materiais in natura, o que vem ocasionando problemas ambientais e econômicos a cadeia produtiva. Um dos problemas está associado à extração de areia do leito de rios, motivo pelo quais os profissionais envolvidos com a tecnologia do concreto vêm buscando alternativas ao uso dessa areia na produção de concreto estrutural. Uma alternativa que vem sendo estudada, pela grande disponibilidade, é o uso de uma areia produzida a partir da cominuição de rochas, chamada de areia de britagem. Na região de Caxias do Sul existem grandes reservas de rochas de origem basáltica (Riodacitos), a partir das quais é possível se produzir esse tipo de areia. Neste trabalho foi avaliada a viabilidade de se substituir à areia natural por areia de britagem de rochas basálticas produzidas em cinco empresas mineradoras localizadas na região de Caxias do Sul. O estudo foi desenvolvido em três etapas: na primeira foram avaliadas as características das areias decorrentes da mineralogia e petrografia das rochas e do processo de fabricação nas mineradoras; na segunda etapa foram avaliadas as propriedades do concreto através do método de dosagem EPUSP/IPT; na terceira etapa, para comprovar a eficiência do método de dosagem, foram produzidos traços específicos para cada tipo de areia. Os resultados de caracterização demonstraram que as areias de britagem possuem características diferentes das da areia natural e que apenas duas das cinco areias avaliadas apresentam propriedades que permitem a sua utilização em concreto estrutural. As propriedades decorrentes do processo de fabricação, como a presença de material pulverulento, forma e textura dos grãos provocaram um aumento no teor de argamassa, o que influenciou diretamente no proporcionamento dos materiais constituintes. Os resultados para a avaliação das propriedades do concreto demonstraram que, para um mesmo traço, a resistência a compressão axial e o módulo de elasticidade são menores nos concretos produzidos com areias de britagem. Corrigindo-se os teores de argamassa e produzindo-se traços específicos para cada tipo de areia é possível produzir concretos com resistências desejadas. Apesar das diferenças encontradas nas propriedades das areias foi comprovado que as areias de britagem estudadas podem ser utilizadas na produção de concreto estrutural de cimento Portland, substituindo totalmente à areia natural. / Despite the technological advances on the structural concrete production, in natura materials are still used. This fact has been causing environmental and economic problems to the manufacturing chain. One of the problems is related to the sand extraction from riverbeds, this is the reason why professionals involved with concrete technology are searching for alternatives to the use of this type of sand in the structural concrete manufacturing. One alternative that is being studied in various parts of the country, because its large availability is a sand produced from the rocks´ comminution, called crushing sand. In the Caxias do Sul region there are large reservations of basaltic rocks origin (Riodacitos), from which it is possible to produce this type of sand. In this work, it was evaluated the feasibility of substitute natural sand for crushing sand from basaltic rocks produced in five mining companies located at Caxias do Sul region. The study was developed in three stages: on the first one, the features of the sand that arises from rocks´ mineralogy and petrography and from the mining manufacturing process were evaluated; on the second the concrete properties through the EPUSP/IPT dosage method were evaluated; on the third they were produced specific trace to each type of sand in order to verify the efficiency of the dosage method. The characterization results established that the crushing sand have different features IF compared with natural sand and that Just two out of Five evaluated sands presented properties that allow its use in structural concrete. The properties arising from the fabrication process, for example the presence of powder material, the grains´ shape and texture caused the raise of the plaster content, which influenced directly on the constituents materials proportioning. The results of the concrete properties evaluation showed that, for the same trace, the resistance to axial compression and the elasticity module are smaller in the concretes produced with crushing sand. If the plaster content is corrected and the specific traces are produced for each type of sand it is possible to produce concretes with desired resistance. In spite of the differences found on the sand properties it was proven that the crushing sand produced at the Caxias do Sul region can be used on the portland cement structural concrete production, replacing totally the natural sand used.

This master's thesis deals with construction concept, execution and final evaluation of the stress-strain analysis of the main parts of the coal crushing fan mill. The main thesis part describes the general issue and different types of coal crushing fan mill. Construction part of the thesis is focused on optimal design evaluation and strength analysis of spiral body case as well as fan mill beater wheel.

During this master thesis a crushing material composite was developed in order to determine if a specific design consisting of a pointy hard phase with a ductile phase in between can reduce the load needed to crush stone and therefor decrease the energy consumption during stone crushing. The steel hard phase (ASP 2012) was printed using an additive manufacturing method called selective laser melting (SLM). A process parameter optimization was performed in order to achieve a dense material and a pre-heated building platform was used to prevent cracking. The hard phase designs were printed and then filled with bronze (JM3 and JM7). The composites and steel references were tested by placing a stone on each sample and applying pressure until the stone broke. After the tests, the loads and the deterioration of the samples was analyzed. The results showed that it was possible to print the hard phase, but some defects like micro cracking were hard to eliminate entirely. Several methods were tested to cast the bronze but the most suitable during this project was melting of the bronze in an induction furnace with vacuum atmosphere. The results from the crushing simulations showed that there was a small difference between the references and the developed macro composites. The composites began to crush stones at lower loads than the references. Nevertheless, due to a large dispersion of the results a statistical difference could not be established.

This study uses dynamic centrifuge tests and three-dimensional (3D), nonlinear finite-difference analyses to: (1) evaluate the effect of soil-cement grid reinforcement on the seismic response of a deep soft soil profile, and (2) to examine the dynamic response of structures supported by shallow foundations on soft clay reinforced by soil-cement grids. The soil profile consisted of a 23-m-thick layer of lightly over-consolidated clay, underlain and overlain by thin layers of dense sand. Centrifuge models had two separate zones for a total of four different configurations: a zone without reinforcement, a zone with a "embedded" soil-cement grid which penetrated the lower dense sand layer and had a unit cell area replacement ratio Ar = 24%, a zone with an embedded grid with Ar = 33%, and a zone with a "floating" grid in the upper half of the clay layer with Ar = 33%. Models were subjected to a series of shaking events with peak base accelerations ranging from 0.005 to 0.54g. The results of centrifuge tests indicated that the soil-cement grid significantly stiffened the site compared to the site with no reinforcement, resulting in stronger accelerations at the ground surface for the input motions used in this study. The response of soil-cement grid reinforced soft soil depends on the area replacement ratio, depth of improvement and ground motion characteristics. The recorded responses of the structures and reinforced soil profiles were used to define the dynamic moment-rotation-settlement responses of the shallow foundations across the range of imposed shaking intensities. The results from centrifuge tests indicated that the soil-cement grids were effective at controlling foundation settlements for most cases; onset of more significant foundation settlements did develop for the weakest soil-cement grid configuration under the stronger shaking intensities which produced a rocking response of the structure and caused extensive crushing of the soil-cement near the edges of the shallow foundations. Results from dynamic centrifuge tests and numerical simulations were used to develop alternative analysis methods for predicting the demands imposed on the soil-cement grids by the inertial loads from the overlying structures and the kinematic loading from the soil profile's dynamic response. / Ph. D.

African copper PLC’s flagship is the copper producing Mowana mine located 129 km from Francistown in the North-Eastern part of the Republic of Botswana. The processing operation at Mowana is a standard flotation plant designed to produce copper concentrates from oxide, supergene, and sulphide ores. The expected average output of 16.2 tons per hour of copper concentrates has never been attained since plant commissioning. The major bottleneck has been established to be located around the crushing circuit of the Mowana production chain. The major hypotheses of this research are that performance in a crushing plant is adversely influenced by moderate and discrete changes in the process. The ultimate objective is to develop a dynamic process simulator, administered in Simulink/MATLAB® background, for application in the design of a control model utilising two crusher variables and a self-tuning control algorithm. In this research work, a process model describing the dynamic operation of an Osborn 57S gyrasphere cone crusher is investigated. Modelling of the Mowana crushing circuit is carried out by combining the steady-state and dynamic components of the crushing equipment in the Simulink/Matlab® environment. Eccentric speed (ES) and closed-side setting (CSS) are amongst the important inputs to the models. The rest of the inputs (crusher power, crusher cavity level, federate, pulley diameters, liner wear measurement, number of teeth of the pinion and bevel gear) are extracted from the data collected across the Mowana mine crushing circuit. While it has been demonstrated that the crusher CSS is the most influential controllable parameter, it has also been demonstrated that crusher capacity and power can be used effectively to optimise the circuit. The use of crushing power and cavity level control is suitable for the crushing circuit since the crushers are running on a constant ES and the CSS is set and reset manually. The outcome of the study presents an insight into the optimization of the Mowana mine crushing circuit through the design of a self-tuning controller for the cone crusher and for prototyping, parameters of a PID controller were determined in the Simulink/MATLAB® environment. The simulation involved the optimisation of the control model as a function of the cavity level of and the power drawn by the cone crusher. A self-tuning control algorithm at PLC and SCADA level of control was then tested. This formed the simulations and training platform. The outcome of the simulations carried out in this research needs to be validated against the real Mowana crushing process control upgrade. This will then inform the modifications and recommended crusher motor resizing exercise to be implemented. / Electrical and Mining Engineering / M. Tech. (Engineering: Electrical)

This dissertation is concerned with a type of energy absorption device made of thin-walled tubes. The tubes will undergo plastic deformation when subjected to an impact loading, and therefore absorb kinetic energy. It has been found that, if the surface of a tube is pre-folded according to an origami pattern, the failure mode of the tube can be altered, leading to a noticeable increase in energy absorption while at the same time, reducing the force needed to initiate plastic deformation within the tube. The main work is presented in four parts. First of all, an experimental study of a type of previously reported thin-walled square tube with pre-manufactured pyramid patterns on the surface has been conducted. Quasi-static axial crushing tests show that the octagonal mode, although numerically proven to be efficient in terms of energy absorption, cannot be consistently triggered. Secondly, a new type of thin-walled tubular energy absorption device, known as the origami tube, which has origami pattern pre-fabricated on the surface, has been studied. A family of origami patterns has been designed for tubes with different profiles. The performances of a series of origami tubes with various configurations subjected to quasi-static axial crushing have been investigated numerically. It is found that a new failure mode, referred to as the complete diamond mode, can be triggered, and both over 50% increase in the mean crushing force and about 30% reduction in the peak force can be achieved in a single tube design in comparison with those of a conventional square tube with identical surface area and wall thickness. A theoretical study of the axial crushing of square origami tubes has been conducted and a mathematical formula has been derived to calculate the mean crushing force. Comparison between theoretical prediction and numerical results shows a good agreement. Quasi-static axial crushing experiments on several square origami tube samples have been carried out. The results show that the complete diamond mode is formed in the samples and both peak force reduction and mean crushing force increase are attained. Thirdly, a new type of curved thin-walled beam with pre-manufactured origami pattern on the surface, known as the origami beam, has been designed and analyzed. A numerical study of a series of origami beams with a variety of configurations subjected to quasi-static lateral bending has been conducted. The results show that two new failure modes, namely, the longitudinal folding mode and the mixed mode, can be induced, and both reduced peak force and increased energy absorption are achieved. Finally, a number of automobile frontal bumpers, which have the origami tube and the origami beam as key components, have been designed and analyzed. Three impact tests have been conducted on each bumper. The numerical results show that both types of origami structures can perform well in realistic loading scenarios, leading to improved energy absorption of the bumpers.

Thesis (M.Dev.) --University of Limpopo, 2010 / Refer to document

Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water as the anti-solvent. Small crystals are produced by crystallization of the substance, and the crystals are agglomerated through the action of the bridging liquid. Different solvents: chloroform, toluene, heptane, pentane, cyclohexane, ethyl acetate and diethyl ether are chosen as bridging liquids, all being low soluble in water and showing good wettability for benzoic acid crystals. The influence of process conditions such as concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature on the properties of benzoic acid spherical agglomerates, are investigated. Different sets of experiments were accomplished to track how the properties of the particles gradually change during the normal spherical crystallization experiment. Other sets of experiments were performed to examine the influence of agitation and process time for agglomeration. The product properties such as particle size distribution, morphology and mechanical strength have been evaluated. The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10 N load cell. Compression characteristics for single agglomerates are compared with the data on bed compression. The present study shows that the bridging liquid has significant influence on the product properties, using diethyl ether and ethyl acetate no agglomerates are formed. Using any of the other five solvents (chloroform, toluene, heptane, pentane, and cyclohexane) spherical agglomerates are formed, as long as a sufficient amount of the bridging liquid is used. Using cyclohexane as bridging liquid at 5°C and toluene at 20°C the particles are larger compared to particles formed at other conditions. The highest particle fracture stress is obtained by using toluene as the bridging liquid at 5 and 20°C. Particle morphology depends on the bridging liquid used and the particles are completely spherical when toluene and pentane are used as bridging liquids. Different process parameters are found to have a significant influence on the physico-mechanical properties of the product. The range of operation for spherical agglomeration is relatively narrow and only at certain conditions spherical agglomerates are produced. With increasing amount of bridging liquid the particle size and strength increase and the morphology improves. Particle size decreases and the fracture force increases with increasing feeding rate, but the morphology remains unchanged. For all the solvents, the particle size and the fracture stress increase with decreasing temperature. For four of the solvents the morphology improves with decreasing temperature. For cyclohexane the result is the opposite, in that the particles are spherical at 20°C and irregular at 5°C. Spherical agglomerates of benzoic acid, both as single particles as well as in the form of a bed, have a high compressibility and low elastic recovery, properties that are favorable for direct tabletting. As the feed solution is supplied to the crystallizer the amount of benzoic acid that can crystallize actually does crystallize fairly rapidly. Hydrodynamics are responsible for bringing particles together for the agglomeration. Experiments reveal that during the gradual addition of the feed to the agitated aqueous solution, both particle size and particle number increases. It is clear from the experiments that not only further addition of feed solution leads to larger product particles but also continued agitation. Along the course of the process the properties of the particles change gradually but substantially. By continued agitation, the particle porosity decreases, density, strength gradually increases and also the spherical shape develops gradually. / QC 20110419

Für die Weich- und Mittelhartzerkleinerung von Primär- und Sekundärrohstoffen werden zunehmend Profilwalzenbrecher eingesetzt. Trotz relativ geringer Zerkleinerungsgrade zeichnen sie sich durch einen geringen spezifischen Leistungsbedarf, hohe Durchsätze, eine einfache Konstruktion und Instandhaltung sowie eine störungsfreie Betriebsweise aus und sind auch bei adhäsivem Aufgabematerial anwendbar. Trotz der Bedeutung dieser Maschinen gibt es bisher nur unzureichende Auslegungsmethoden. Die theoretisch begründete Modellierung der Zerkleinerung in markant profilierten Walzenbrechern ist deshalb Gegenstand dieser Arbeit, um dadurch die Dimensionierungsgrundlagen zu verbessern und Einsatzmöglichkeiten in der Hartzerkleinerung abzuschätzen. Dazu werden im Rahmen einer Systembetrachtung zunächst die wesentlichen Prozessparameter der Zerkleinerung ermittelt und die Bauarten von Profilwalzenbrechern klassifiziert (Kapitel 2). Die Darstellung der bekannten Berechnungsmodelle für die Hauptzielgrößen „Grenzdurchsatz“, „Produktgranulometrie“ und „Leistungsbedarf“ ist Gegenstand von Kapitel 3. Darauf aufbauend wird in Kapitel 4 ein neues, physikalisch begründetes Auslegungsmodell vorgestellt und das Untersuchungsfeld hinsichtlich der zu analysierenden Aufgabestoffart und Maschinengeometrie eingegrenzt. Die für dieses Modell erforderlichen Zerkleinerungstest- und Simulationsergebnisse werden in Kapitel 5 und 6 dargestellt, bevor die Arbeit in Kapitel 7 mit einer Zusammenfassung und einem Ausblick abschließt.