Search Documents

This paper discusses the application of a computerised model based on genetic algorithms (GAs), called GenRel, for reliability assessment of underground mine hoisting systems. The purpose of this paper is to investigate whether GenRel can be applied to predict future failure data of a mine hoisting system based on historical records of failures. The incentive of selecting the GAs for prediction of failures is that GAs are a class of evolutionary algorithms which imitate the biological evolution procedures such as reproduction, selection, crossover and mutation. The reliability of mining equipment changes over time due to an array of factors (eg equipment age, the operating environment, number and quality of repair). These factors affect the equipment's failure patterns and have complex impacts on the equipment's reliability characteristics. The failure patterns are assumed to follow a biological evolution process, and thus GAs can be considered applicable in the modelling process.To conduct the reliability assessment, a study was carried out with historical failure data of hoists in the time period from January to December 2007. Two failure data sets of two mine hoisting systems were collected from two typical underground mines in Ontario, Canada, which are denoted as the NA mine and the SB mine. The failure data sets were prepared in the format of time between failures (TBF). Then, these data sets were entered in GenRel to generate predicted failure data sets for the period of January to March 2008. The paper discusses the statistical similarity of the actual failure data sets for the period of January to March 2008 with the predicted failure data set generated by GenRel in the same time period.

Dec 6, 2010

By A. Golshani, M. Oda, K. Suzuki, T. Takemura

Anisotropic behaviours of OhshimaOshima granite were investigated by carrying out uniaxial compression tests, together with observations of microcracks under an optical microscope. The elastic modulus tensor of Oshima granite at 10 per cent strength,E10, were calculated using theoretically formulation of elastic modulus tensor in terms of the second-rank crack tensor for pre-existing open microcracks. Furthermore, with the assumption of orthorhombic elasticity, the nine moduli of Oshima granite E10were determined by uniaxial compression test. Twenty-onemoduli of samples, calculated without assuming any symmetry, also showed orthorhombic features. Direction of the symmetry axes agreed well with the orientation of preexisting cracks. Comparison of crack tensor-based formulation results with the experimentally determined one show that the anisotropy of elasticity of Oshima granite is caused by pre-existing open microcracks, not by pre-existing healed microcracks and also crack tensor formulation can be used, as a first-order approximation at least, to describe the anisotropy of Oshima granite induced by pre-existing open microcracks. ZUSAMMENFASSUNG: Das anisotrope Verhalten des Oshima-Granits wurde mit Hilfe voneinachsigen Kompressionstests und durch die Betrachtung von Mikrorissen unter einem optischenLichtmikroskop untersucht. Das Elastizitätsmodul von Oshima-Granit bei 10 Prozent Kraft E10wurde berechnet, indem man die Formulierung des Elastizitätsmodultensors, ausgedrückt alsRisstensor zweiter Ordnung theoretisch auf bereits existierende Mikrorisse angewandt hat.Außerdem wurden die neun Module des Oshima-Granits unter der Annahme orthorhombischerElastizität E10mit einem einachsigen Kompressionstest bestimmt. Einundzwanzig Stichproben,die ohne die Annahme irgendeiner Symmetrie genommen wurden, zeigten ebenfallsorthorhombische Merkmale. Die Richtung der Symmetrieachsen stimmte mit der Orientierungbereits vorhandener Risse überein. Der Vergleich der Ergebnisse der auf dem Risstensorbasierenden Formulierung mit der experimentell bestimmten Formulierung zeigt, dass dieAnisotropie der Elastizität von Oshima-Granit von bereits vorhandenen offenen Mikrorissenverursacht wird, und nicht von vorhandenen vernarbten Mikrorissen, und dass dieRisstensorformulierung auch zumindest für eine Annäherung erster Ordnung benutzt werdenkann, um die durch vorhandene offene Mikrorisse induzierte Anisotropie des Oshima-Granits zubeschreiben. RESUME: Les comportements anisotropes du granit d’Oshima ont été étudiés en réalisant destests de compression simple, et en observant les microfissures au microscope optique. Le tenseurdu module d’élasticité du granit d’Oshima sous une résistance de 10 pourcents, E10, a été calculéen se servant de la formule théorique du tenseur de module d’élasticité basé sur le tenseur defissures de second ordre des microfissures ouvertes préexistantes. En outre, sur base del’hypothèse de l’élasticité orthorhombique, les neuf modules du granit d’Oshima ont étédéterminés par des tests de compression simple. Vingt et un modules d’échantillons, calculés endehors de toute hypothèse de symétrie, ont aussi montré des caractéristiques orthorhombiques. Ladirection des axes de symétrie correspondait bien à l’orientation des fissures préexistantes. Lacomparaison des résultats de la formule basée sur le tenseur de fissures avec les résultatsdéterminés expérimentalement montrent que l’anisotropie de l’élasticité du granit d’Oshimaprovient des microfissures ouvertes préexistantes, et non de microfissures préexistantes referméeset que la formule du tenseur de fissures peut servir, au moins comme première approximation, àdécrire l’anisotropie du granit d’Oshima marqué par des microfissures ouvertes préexistantes.

Jan 1, 2003

By M. Görnerup, A. Kapilashrami, Seetharaman. S., A. K. Lahiri

Simultaneous reduction and foaming of chromium-rich slag have been studied in a laboratory furnace equipped with X-ray image analysis. Reduction of the metal oxides by graphite generated CO, which caused the melt to foam. The slag composition continuously changed due to reactions and dissolution of lining. Gas generation rate, foam height, and gas bubble size were studied and correlated to slag composition. Viscosity increased significantly during the experiments due to a change in slag composition. Bubble sizes varied little during the progress of reactions but differed considerably for different slags. Bubble sizes were largest for V2O5 containing slag, which is contrary to the general understanding that the presence of strong surface active agents reduces the bubble size. The foaming index did not follow expected trends for bubble size and viscosity, suggesting that foaming index is not a suitable parameter for discussion of foams under dynamic conditions. Keywords: slag, foaming, dynamic conditions

Jan 1, 2004

Published experimental data on thermodynamic behaviour of cobalt-containing slags have been reviewed and used in validating a recently developed thermodynamic model. The results from the exercise show that the model provides a reasonably good description of behaviour of cobalt in multi-component slag systems. The models for cobalt containing slags, matte and oxide solid solution phases were incorporated into CSIRO?s multi-phase equilibrium (MPE) package, which was used to calculate the equilibrium distribution of cobalt between matte and slag phases under various conditions. The results agreed well with the experimental data. Furthermore, the good agreement between the calculation and the plant data indicates that the operating conditions of industrial smelting and converting processes are close to equilibrium. Two diagrams showing the effects of slag chemistry and SO2and O2partial pressures on the distribution of cobalt between phases were generated for conditions similar to smelting and converting processes. These diagrams provide some useful guidelines for developing new strategies to improve cobalt recovery.

Jan 1, 2004

By Mark DeSalvatore

Currently, at Caltrans, the Office of Structure Design is carrying out an extensive seismic retrofit program involving transportation structures throughout California. The goal of the retrofit program has been to upgrade existing transportation structures to meet the present seismic codes and anticipated loads that are generated during a seismic event Part of the retrofit program involves retrofitting existing structure foundations when required. To determine if the foundations of a specific structure need to be retrofitted, an engineering analysis of the existing foundations has to be done. If the engineering analysis of the structure foundations determines that the foundations will not meet the load carrying demands required by the structural engineer, the existing foundations are then retrofitted. The retrofit projects that require foundation modifications can be separated into two general cases. The first case comprises structures where the original designs will not meet the demands of the present seismic design code. In this case, the existing foundations are not capable of providing the load capacities the current seismic code requires. The second case consists of structures where the retrofitting of the superstructure will increase the required load carrying capacity of the existing foundations during a seismic event In this case, the anticipated load demands on the existing foundations are greater than the foundations are capable of providing. For either of the cases listed above, the present strategy for increasing the capacity of the existing structure foundation consists of installing tiedown anchors or large capacity piles to provide the required resistance to seisraically induced loads.

Jan 1, 1993

By Jorge Chira

INGEMMET realizó el proyecto “Estudio de los Recursos Minerales del Perú” con el objetivo de identificar las áreas prospectivas para propiciar actividades de exploración minera por parte de la empresa privada. Entre las funciones ejecutadas está la “Prospección Geoquímica Regional de Sedimentos de Quebrada”, donde se ha recopilado 5,636 muestras de sedimentos de quebrada, las que fueron analizadas por Au y 32 elementos a fin de elaborar posteriormente el Atlas Geoquímico del Perú. En ese sentido, el presente texto señala el uso del software para el tratamiento estadístico de los resultados a través del soporte técnico de la empresa GEOSOFT. Dicho software genera una tecnología confiable así como lo versatilidad para el manejo e interpretación de diversos datos. También se desarrolló el programa OASIS – MONTAJ; módulo CHIMERA con el cual se pueden manejar en forma exacta una gran cantidad de información geoquímica empleando controles de estándares y duplicados.

Aug 25, 2002

By O. F. Oxtoby, J. E. Olsen, M. W. Erwee, Q. G. Reynolds

"The extraction of molten products and wastes through smelting furnace tap-holes during the tapping process is a complex procedure involving many coupled thermophysical effects. Insight into the fluid flow behaviour in such systems can be gained by using computational mechanics tools to build highfidelity models of the fluid flow and other relevant physics. Previous work using such models indicates that the nature of the flow in the tap-hole, as well as operational parameters such as the tapping flow rate, depends strongly on the properties of the material being tapped and the geometry of the tap-hole channel. Additional complications arise when multiple fluid phases (for example, slag and metal) are present simultaneously, when porous coke beds hinder flow to the tap-hole entrance, and when the geometry of the tap-hole changes over time due to cycles of wear and repair. In the present work, challenges with the coupling of phenomena such as multiphase flow and porosity into computational fluid dynamics methods for tap-hole modelling are discussed in the context of electric furnaces used for ferromanganese production. Qualitative and quantitative results of computational models of flow through tap-holes are presented and compared as a function of material parameters to determine sensitivity effects, and in response to operational parameters to determine typical process behaviour over the duration of a tap. IntroductionPyrometallurgical production using electric furnaces accounts for substantial portion of the world supply of ferroalloys and other strategic materials (Degel et al., 2015). A range of different furnace designs may be used depending on the metallurgical process, with circular three-electrode submerged arc furnaces (SAFs) powered by alternating current being the most common for commodities such as ferromanganese and silicomanganese (Olsen, Tangstad, and Lindstad, 2007).As shown in Figure 1, manganese furnaces typically operate with a deep charge consisting of an upper layer of loose burden (onto the upper surface of which is fed solid raw material), a molten slag layer partially or completely filled with unreacted carbonaceous reductant (generally metallurgical coke), and a molten metal layer which settles to the bottom of the furnace due to its high density. The solid particles present in the slag and burden layers form porous beds which hinder the fluid flow of molten process material and gases inside the furnace (Olsen, Tangstad, and Lindstad, 2007).In order to remove material from the furnace during normal operations, a single tap-hole is built into the sidewall of the vessel near to the level of the hearth. Tapping involves removing both slag and metal phases through the same tap-hole channel, which makes tap-hole design, operation, and maintenance particularly complex. In the case of processes such as ferromanganese, which operate with no external gas injection or open arcs present at the furnace electrodes, flow of material out of the tap-hole is driven primarily by the hydrostatic pressure generated by the weight of the solid and liquid phases above the tap-hole."

Jun 1, 2019

By R. V. Ramani, C. J. Bise

INTRODUCTION Classification of coal seams as thin, medium, and thick is both subjective and relative and is more a reflection of the statistical mode of the thicknesses en- countered in a mining region. A geological factor more precisely understood as defined than thickness is the inclination of the seams to the horizontal, commonly referred to as the pitch or the dip of the seam. Thick and steeply pitching seams present far more challenges to the ingenuity of the mining men to devise methods for their extraction than the thick and less steeply inclined ones. In a marginal case, where a thick coal seam may be minable by surface or underground methods, the decision bears a close relationship to the technological developments in the mining scene. Near surface thick coal seams are a special gift of nature and are not as wide- spread as the ones that call for the application of under- ground methods. Recent advancements in surface mining equipment have made it possible to surface mine to great depths. Stripping ratios of 30: 1 (cu yd of over- burden removed per ton of coal) have been achieved. The extraction of thick seams which preclude the use of surface methods is the concern of this chapter. Specifically, the objective here is to outline the special technological factors in underground mining of thick coal seams and to illustrate through several case histories the methods that are practiced in the North American continent. For the purposes of this chapter, a thick seam is defined as one which is not readily minable with currently available equipment without modifications to the extraction method or the equipment. At the present time, a thickness of 4.8 m (16 ft) can be considered as the lower limit, although developments in equipment and methods can be expected to push this limit upwards. The data for the case histories were collected from two extended mine visits in 1975 and 1978, and from other published accounts of the mines visited. Reference is drawn particularly to reports by Bise, Ramani, and Stefanko (1976) and Rarnani and Kenzy (1979). THICK SEAM MINING METHODS The various methods of mining thick seams can generally be grouped into three major categories: full face methods, where the entire thickness of the seam is re- covered in a single pass; slicing methods, where the seam is extracted to its full thickness by horizontal or inclined slices either in an ascending or descending order; and caving methods, where the seam is undercut and the en- tire coal seam is recovered by caving the top coal into the excavated cut, or some variations of the basic sub- level caving method. As shown in Table 1, in each of these methods, the coal is removed by either room-and-pillar or longwall methods. Hydraulic mining and transport of the coal in open flumes or in pipelines are also practiced. Addition- ally, the void created by the removal of coal may be filled with a packing material (stowing) except in the caving methods. The pitch (dip) of the seam, particularly when it is greater than 0.26 rad (150), imposes severe operational limitations on mobile equipment. A more detailed general discussion of the methods can be found in Bise et al. (1976) and Vorobjev and Deshmukh (1964). Specific discussion on the many variations of the three basic methods can be found in the papers presented at the international symposia that were held in

Jan 1, 1982

By Michael Taylor, Thomas W. BoBo

Currently two of the most important characteristics of construction aggregates are (a) the particle size distribution (psd) and (b) the “shape” of the aggregate particles. The long established test methods and standards for these properties require substantial resources and most suppliers can take samples and conduct tests at intervals measured in days (psd) or even months (shape). Furthermore these tests require time: so the results are available only after material has been stockpiled or shipped. In the rare cases where problems are found the out-of-spec material has often been shipped to points unknown. There are substantial advantages to be obtained if the psd and other geometrical properties could be obtained from the material as it moves through the production processes and if the results could be reported back within seconds or minutes to Plant Control Managers. This paper describes a single on-line system used to evaluate production of crushed material in a production quarry. The system consists of an enclosure (containing the camera and lighting etc.) mounted over a production belt. Images are fed by fiber optic cable to a nearby control room where the data are analyzed; stored; displayed; and made available for integration into a process control system. Numerous forms of display can be created according to the needs of the producer. Once programmed by an automation engineer all functions of operation are fully automated. The system has permitted over 400 tests per hour with a feed back time less than 2 seconds. Sufficient geometrical measurements are made so that many different “shape” factors can be computed on a similar time scale. The paper summarizes the results from approximately 100 shifts of about 8 hours each and compares the imaging method with the current standard hand methods. Study of the data generated showed that, when combined with additional plant information, the system can be used to generate additional useful control information.

Jan 1, 2005

The outlook for suppliers of energy to the expanding economies of the Pacific Basin region is essentially positive, but particularly for exporters of high quality steam coal. This paper argues that economic growth in the Pacific Basin region has exceeded world economic growth for some years and that this will continue to be the case for the next decade at least. It looks briefly at the link between economic growth and energy demand and at the relationship between energy demand and the demand for electricity. Changing preferences in fuel mix for electrical generation in the region are noted and tentative forecasts made about variations in this mix. The pros and cons of various forms of fuel used to generate electricity are considered from the point of view of the consumer. Having concluded that steaming coal in particular is likely to become even more important as a generator of base load electricity, the paper looks at the opportunities this presents for exporters such as Australia, and touches on some factors that could prevent development of those opportunities. This paper will concentrate on electrical energy. For the purposes of this paper, the Pacific Basin refers essentially to Australia, New Zealand and the Asian countries bordering the Western Pacific. As a supplier, Siberia is not included because, although it has great potential, it is thought that problems of climate, infrastructure and political restructuring will delay the realisation of that potential until the next century. Although it deals with the Pacific Basin region, where many countries are industrialising rapidly from a predominantly agricultural base, it looks at the experience of mature industrial DECD economies where their experiences seem relevant.

Jan 1, 1990

By Will Hunt, Darren Thornton

In March of 2013, an undisclosed gold mine (MINE X), located in the Western United States, performed blast movement monitoring of three blasts occurring in one of two active pits. Blast Movement Monitors (BMMs) were placed in the bench before blasting, and located after the blast to determine vectors of movement. Using blast movement software, ore/waste boundaries were translated. These locations were compared to MINE X’s standard ore translation procedure, which consisted of moving polygon boundaries by 17.5 feet (5.3 m) in the burden direction of the blast hole pattern. This translation amount, identified by MINE X as “average” motion, had been ascertained by performing a previous blast movement study.

Jan 1, 2014

By G. S. Scott

Mine fires have occurred since the mining of coal was begun, and they are still occurring. The resulting economic waste may become considerable (219),3 especially if a fire is allowed to assume major proportions or to get beyond control temporarily. It is important, therefore, to act promptly whenever a fire is suspected and to have every action count. To do this effectively, it is necessary to know at the earliest possible moment and thereafter what is happening in a remote or inaccessible area. It is equally important to know before¬hand what may be expected as a result of any proposed combative measure. The logical method of combatting a fire demands the cooperation of both mining engineer and chemist. They should decide the course of action to be taken, drawing upon the mining engineer's intimate knowledge of the physical structure of the fire area, the cost and time required for proposed operations, and the probable efficiency with which they could be carried out, and upon the chemist's knowledge of the results to be expected therefrom.

Jan 1, 1944

By Alexandre Rizek Schultz

Esse projeto visou à substituição do sistema de controle instalado no laminador de barras e fio-máquina, por um novo e moderno sistema de controle. Este novo sistema irá controlar o laminador de barras e de rolos instalado na Usina da Vetorial, no Paraguay. Juntamente com a atualização do sistema de controle, a RUSSULA irá substituir os antigos e descontinuados conversores de corrente contínua VERITRON, fornecendo kit’s de digitalização e aproveitando os tiristores antigos, porem confiáveis. Na cabine central serão instaladas ferramentas para facilitar a operação do laminador e equipamentos, com novas telas de operação, sistema de aquisição de dados de alta velocidade, sistema de gerenciamento de intertravamentos, dentre outros. O PLC existente, um BBC Procontic, será inteiramente substituído por novos S7-1500, nova linha de PLC’s Siemens. O novo sistema irá possibilitar aumento de produtividade, diminuição de paradas, diminuição de perdas metálicas e maior confiabilidade no controle.

Oct 30, 2017

By Morgan L. Race, Matthew R. Glisson

"Most driven pile projects have plumbness limits from 0.25 in/ft (21 mm/m) to 0.5 in/ft (42 mm/m) to control bending stresses. For two projects, the project teams performed static load testing to evaluate performance of piles with sweep. One project, located in Grand Forks, North Dakota, used 9.625-inch (244-mm) diameter piles with a wall thickness of 0.395 inch (10 mm) and lengths ranging from about 130 to 160 feet (40 to 49 m). Measured pile sweep (lateral offset distance of the pile toe from the pile top) was between 12 and 17 inches (305 to 432 mm). Static load testing indicated that the piles could support the design load with axial deflection of less than 1 inch (25 mm) but only provided about 80 to 90 percent of the ultimate resistance at axial deflections of about 1.9 to 1.7 inches (49 to 43 mm), respectively. The other project, located in Shakopee, Minnesota, used 9.625-inch (244-mm) diameter pile but with a wall thickness of 0.352 inch (9 mm) and lengths around 50 to 90 feet (15 to 27 m). The measured sweep varied between about 20 and 63 inches (508 and 1,600 mm) for 9 of 214 piles driven at the site. Load testing indicated that these piles could provide the required design resistance with less than 0.3 inch (8 mm) of axial deflection and support the required ultimate resistance with about 0.5 to 0.6 inch (13 to 15 mm) to of axial deflection.INTRODUCTIONAnyone who has observed a significant number of piles has seen that, inevitably, the pile is not perfectly straight after driving. In spite of the best efforts of contractors, there are a whole host of reasons for piles to end up out-of-plumb or to have a curve, sometimes referred to as pile sweep. Most project specifications set limits for plumbness typically between 0.25 in/ft (21mm/m) and 0.5 in/ft (42mm/m) (USACE, 1991; PDCA, 2007; MnDOT, 2016; MoDOT, 2016). Closed-end pipe piles, including monotube or tapertube, are the only pile type that allow actual measurement of the final alignment of the pile.As Nadeem, et al. (2015) note, buckling failure of long, slender piles is the predominant mode of pile failure in soft soils. Pile sweep is just one source of buckling failure in long, slender piles. The nonlinear buckling analysis showed that increasing slenderness ratio and/or increasing degree of curvature decreases the loadcarrying capacity of a driven pile. Nadeem, et al. (2015) considered solid, steel pile with lengths from 24 to 66 feet (7.5 to 20 m), diameters from 9.75 to 26 inches (244 to 660 mm), initial bends from 2 to 6 inches (50 to 150 mm), and half- and quarter-sine shapes."

Jan 1, 2017

By Shahid Islam, Lucian Bogdan

Deep and large diameter drilled shafts use mostly bundles of Grade 60 (415 MPa) reinforcing bars as longitudinal reinforcement with rebar splices to make it longer. Lower Grade steel requires large number of bars which result in rebar congestion and difficulty in placing concrete. This leads to increased labor cost for fabrication and installation. By utilizing larger size and higher strength threadbar, the congestion of rebar can be reduced significantly and bundling of bars can be avoided. The lap splices are replaced with simple threaded couplers and end hooks are replaced with end terminators. Threadbar conforms to ASTM A615-15 and can be epoxy coated if required for corrosion protection. This paper describes an attractive value engineering of replacing Grade 60 (415 MPa) bundle of rebars with larger diameter Grade 75 (515 MPa), Grade 80 (550 MPa) and Grade 100 (690 MPa) threaded bars and threaded couplers in some specific drilled shaft projects in the USA. INTRODUCTION A drilled shaft which may also be referred to as drilled piers, caissons, cast-in-drilled-hole piles and bored piles is the key element to the foundation of massive structure. They are used for tall buildings, bridges and foundations for other applications such as retaining walls, sound walls, signs, or high mast lighting. Drilled shaft foundations are typically 3 to 12 feet (0.9m to 3.7m) in diameter cast-in-place deep foundation elements constructed in a drilled hole that is stabilized to allow controlled placement of reinforcing steel and concrete. Drilled shafts for transportation structures are commonly used to depths of up to 200 ft (61m) in the USA. Drilled shafts can be installed in a variety of soil and rock profiles, and are most efficiently utilized where a strong bearing layer is present. The reinforcing cage is typically lowered into position within the hole and then concrete placed through the center of the shaft, flowing from bottom to top through the reinforcement to fill the hole.

Jan 1, 2018

By Fábio Lerbach

Balanço Energético Global da Vallourec Sumitomo Soluções Tubulares do Brasil site Jeceaba em 2016, com os principais indicadores de consumo energético das áreas consumidoras. Além dos indicadores energéticos globais, o balanço apresenta os consumos específicos de cada insumo nas diversas áreas, permitindo a análise de cada setor da Usina, isoladamente. Destaca-se em 2016: - desligamento do AF em nov/2016

Jan 26, 2018

By Emmanuel Henry

Few industries are more challenged by technical, political and market uncertainty than the mineral industry. Technical uncertainty in mining projects concerns the volume and quality of the resource, the processing and metallurgical parameters, the production efficiency, etc. Political uncertainty can take diverse forms and includes possibilities of change in the taxation system, risk of expropriation and risk of social instability or war. Market uncertainty depends on the market structure of the commodity; price and demand volatilities are the most common sources of market uncertainty. Intensive feasibility studies including these uncertainties and risks are required before investing up to billions of dollars in the development of a new mine. Current feasibility studies are often based on a single (or very few) mean geological scenario and simplified price profiles along the life of the project. Yet, strategic decisions, for example, the level of investment in exploration and metallurgical studies, adoption of a flexible, but more costly, mine design and risk-sharing strategies are made at an early stage. Over the last twenty years, Real Option theory has emerged as a unifying framework enabling strategic planning under uncertainty (technical, political and market). Geological and market variances (second order statistics) are pivotal for proper uncertainty quantification. The present study explores the possible benefits of combining modern geostatistical tools and financial techniques for project management. More precisely, the following questions are examined: Is geological uncertainty really an issue? Can we combine geological and price uncertainties in a unifying Real Option framework? A simple example aimed at illustrating the concepts involved is presented.

May 1, 2003

By Gabriel Gonçalves Pessoa de Castro

O trabalho teve por objetivo produzir uma liga Al AA1070 com microestrutura ultrafina via prensagem por canais equiangulares. O processo empregou a rota C com 2 passes consecutivos a frio e acumulou uma deformação ?2 = 2,38. O material de partida é proveniente de um processo de laminação a quente na qual a microestrutura resultante era composta de grãos grosseiros com tamanho de grão de 14,5 ± 19,1 ?m e dureza de 31,1 ± 1,9 Vickers. Foi realizada a caracterização microestrutural com o auxílio das técnicas de microscopia eletrônica de varredura (MEV) e de difração de elétrons retroespalhados. O comportamento mecânico das amostras foi avaliado por ensaios de dureza Vickers, a fim de se determinar a energia armazenada durante os passes. Os resultados obtidos mostraram que o material de partida apresentou estrutura parcialmente recristalizada, decorrente do processo termomecânico de laminação. A deformação cisalhante severa que ocorre na interseção entre os canais durante o processamento via ECAP permitiu um intenso refinamento de grãos. O tamanho de grão após o 2° passe foi da ordem de 1,6 ± 1,7 µm. A dureza após o 1° passe quase dobrou em relação ao material de partida, mas praticamente se manteve no passe seguinte, sugerindo uma possível estabilidade. Pode-se concluir que ocorreu um considerável refinamento do tamanho de grão em função da elevada fragmentação e rotação da subestrutura após os passes de deformação.

Aug 8, 2018

By Larry: McAnuff Schneider, Edward Walter, Gordon Shaw, Daniel Grieco, Dennis Clark

During the 1998 Annual Conference of the International Society of Explosives Engineers (ISEE), the Seismograph Section established a subcommittee for the purpose of compiling a list of all regulations pertaining to limits imposed on ground vibration generated by blasting. The goal of this project was to determine the vibration regulatory levels being enforced, with the further intention of examining their scope, and uniformity. A secondary purpose was to evaluate the consistency of the existing regulations with the current scientific findings on structural response and damage potential.

Jan 1, 2001

By Luis Valentim, Terry Cousins

The goal of a mine is to produce ore at the lowest possible cost with due regard to safety of pemonnel and equipment. The mining process consists of a number of discrete operations such as planning, drilling, blasting,excavation, transportation and crushing. These processes are interrelated and cannot be considered as separate activities when optimising output and minimising cost. In order to optimise the global costs it may therefore be necessary to increase cost in one area such as blasting design and management beyond the norm.

Jan 1, 1998