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By Aline Raquel Vieira Silva

A seleção e o emprego de materiais para serviços sob tensão e temperaturas elevadas envolvem diversos problemas e, portanto o estudo dos mecanismos de deformação plástica por fluência se torna extremamente desejável. Os aços ferríticos vêm sendo extensivamente usados na indústria, em componentes críticos de plantas petroquímicas e de geração de energia devido principalmente à sua elevada resistência à fluência. Em tais circunstâncias, a deformação por fluência é importante na determinação do tempo de vida do componente. Dentre os aços resistentes a altas temperaturas, a escolha pelos aços ferríticos Cr-Mo se destaca pela excelente resistência à fluência, tenacidade e resistência à corrosão, além de uma expansão térmica relativamente baixa, o que os tornam mais atrativos em aplicações com ciclos térmicos. O desenvolvimento desses aços ocorreu através de modificações na composição química, dando origem a diferentes gerações de aços com o objetivo de aumentar a resistência à fluência. A deformação por fluência até a ruptura varia com a temperatura, tensão e tempo de exposição devido à precipitação, alteração de morfologia e distribuição de precipitados. Visando compreender o desempenho dos aços ferríticos Cr-Mo em aplicações de alta temperatura a nível microestrutural, foi realizado o estudo dos mecanismos de deformação plástica por fluência desses aços, pertencentes à norma ASTM A-335, submetidos a tratamento térmico de 500ºC a 600ºC.

Aug 7, 2018

By Carolina Arriel Pedroso Dias

Neste trabalho, tiras de aço inoxidável duplex UNS S32205 foram laminadas a morno a 600°C com 60% e 80% de redução e, em seguida, foram recozidas a 1050°C durante 300 s. A tira como fornecida (laminada a quente industrialmente e recozida) também foi recozida para efeito de comparação. Avaliou-se o comportamento mecânico das amostras como fornecida, 60% e 80% por meio de ensaios de tração e microdureza Vickers, obtendo-se 779 MPa, 730 MPa e 807 MPa de limite de resistência a tração e 265 HV, 244 HV e 256 HV de microdureza Vickers para as três condições descritas, respectivamente. Outros ensaios de microdureza foram realizados ao longo da superfície do corpo de prova fraturado em tração, indicando um aumento da dureza nas regiões mais próximas da fratura. O aumento da dureza na região de estricção indicou o aparecimento da martensita induzida por deformação para as amostras laminadas a morno. Usando a derivada da curva tensão verdadeira em função da deformação verdadeira, (ds/de), avaliou-se o comportamento de encruamento do aço para as três condições. Juntamente com os exames por microscopia eletrônica de alta resolução e difração de raios X, buscou-se uma interpretação dos mecanismos de deformação plástica envolvidos no processo de encruamento. Em determinados estágios, observou-se uma mudança da inclinação para um regime estável, indicando a ocorrência de outros mecanismos de deformação plástica, diferentes do escorregamento de deslocações. A martensita induzida por deformação foi considerada responsável pelo aumento da taxa de encruamento do aço, i.e., por ser obstáculo à movimentação das deslocações e por postergar a formação da estricção.

Oct 30, 2017

By Thiago Cesar de Souza Pinto

Os teores de umidade (U) presente no minério de ferro, após o processamento mineral, se torna uma dificuldade para seu transporte marítimo à medida que este teor ultrapassar os limites de TML (Transportable Limit Moisture). O presente trabalho teve por objetivo a identificação dos mecanismos de secagem em concentrados de minério de ferro tipo sínter feed em unidade experimental de secador de bandejas em escala de laboratório. São apresentados e discutidos resultados em que os mecanismos identificados se revelam como água livre superficial e capilaridade, para a faixa de umidade de interesse (13<U<6%). Uma regressão não linear foi realizada identificando o peso das variáveis em estudo, permitindo assim um modelamento dos resultados de redução de umidade. O modelo apresentou boa aderência aos resultados experimentais com desvios menores que 10% entre os dados previstos e observados.

Aug 16, 2017

By Carlos Espinoza Zegarra

El presente trabajo describe el método de mecanización del sublevel caving realizado en la mina Yauricocha, donde se aplica a cuerpos que varían de de pequeños a medianos, irregulares o angostos a través del uso de Scoops. Así también el método puede ser usado en roca competente, así como en cuerpos que ya han sido parcialmente explotados como es el caso del cuerpo Cuye. Finalmente no es requisito fundamental que el mineral sea de resistencia muy mala, ya que al descubrir una superficie relativamente grande a través de varios bolsillos, el mineral cae con facilidad debido a la presión del techo aún sin usar explosivos.

Sep 12, 2005

By W. L. Wearly

El presente texto decribe el proceso de mecanización en la minería donde hay reducción del costo de mano de obra. Para elllo, se revisa la historia de este proceso desde el siglo XIX hasta la actualidadd (1970).

Sep 1, 1982

By Elipio Pérez Coronado

El presente texto señala la aplicación del método de corte y relleno ascendente y sus resultados obtenidos a partir de la mecanización de cuatro de las operaciones unitarias realizadas en la mina Atacocha. La aplicación de este método buscó contrarrestar la inflación sostenida en la empresa y asi el 46% del costo de tajo del relleno convencional sea reemplazado por el relleno hidráulico.

Nov 8, 1982

By Lenin Salazar Dulanto

La baja de precios en algunos minerales ha obiligado que las empresas mejoren su proceso productivo a través del uso de equipos de última tecnología en los procesos de mecánica, hidráulica, electricidad y electrónica, así como en la eficiencia en el corte y taladrado, extracción y transporte. Sin embargo, tanto el desatado y sostenimiento manual desarrollaron un estréss y desgaste de energía en el trabajador. En este sentido, el presente trabajo señala una nueva forma de realizar tales operaciones en el ciclo de minado de la empresa Milpo a fin de garantizar la seguridad física de los trabajadores y equipos.

Jul 31, 2003

By Néstor Deza, Kim Montes

En los últimos 20 años la operación minera en Antamina ha profundizado su tajo, el stripping ratio y la distancia de acarreo de desmonte, se han seguido incrementando para mantener la producción metálica. Tal como ocurre en las todas operaciones mineras de tajo abierto, se espera en los próximos años un incremento sustancial de la cantidad de desmonte a remover conforme se avance las siguientes extensiones de vida. En adición a esta situación, los recientes compromisos globales de reducción de emisiones de carbono exigen reducir progresivamente hasta eliminar el 100% la emisión de carbono, opuesto a lo requerido para seguir operando con métodos convencionales. Estos dos factores afectan la sustentabilidad en el largo plazo en todas las empresas mineras maduras como en el futuro de Antamina.

Sep 30, 2022

By Jesús Ortíz V

Si bien en 1974, las reservas del mineral duro y semiduro del yacimiento minero Cerro de Pasco resultaron apropiadas para el método Arch Bach, en cambio, sus niveles de producción no alcanzaron un mayor desarrollo. Es por ello que se optó por explotar los cuerpos de mineral suave a través del método de corte y relleno descendente (undercut and fill) cuya aplicación en la recuperación de pilares tuvo buena recepción. En este sentido, el objetivo del trabajo es mostrar las soluciones adoptadas en la mina de Cerro de Pasco al mecanizar el método de corte y relleno, con el fin de optimizar el método de minado, mejorar la eficiencia, recuperar los rangos de producción y reducir los costos.

Nov 20, 1978

By Carlos España Ch

El presente texto plantea la mecanización en la mediana minería como método de trabajo para el tratamiento de minerales y trabajos auxiliares. La ejecución de esta mecanización es de acuerdo al tipo de yacimientos de cada caso particular. En este sentido, la compañía minera Alianza S.A. es un ejemplo de este enfoque empresarial, así como las minas Hércules y Coturcán, las cuales implementaron la minería sin rieles, donde el desarrollo y preparación de las vetas se realiza por medio de rampas que puedan tener pilares de 200 mt.s de largo, posibilitando el uso del método de explotación mecanizado-fronton pilar e incrementando la productividad en comparación con las etapas de mecanización incipiente.

Oct 14, 1980

By Ralph Johnson, Philippe Gaultier, Loui Fauteux, Andrew Dasys

"This paper outlines the implementation of the Mechanic's Stethoscope from the earliest stages of development to the implementation at Brunswick Mining and Smelting. It details the cooperative efforts of personnel at Noranda Technology Centre (NTC) and Brunswick Mining & Smelting (BMS) during the technology transfer of the Mechanic's Stethoscope. It demonstrates how everyone worked toward a goal of developing a product that is accepted as a useful addition to the work environment.The Mechanic's Stethoscope is an underground vehicle diagnostic system consisting of computer hardware and software intended to assist mechanics in daily tasks. Its tools facilitate quick and easy access to any information required during the maintenance of an underground vehicle. Each tool presents vehicle condition data in a simplified manner. The additional information improves the mechanics understanding of the vehicle condition. The result is a healthier fleet of vehicles and faster diagnosis times.When introducing a computer based system into a traditionally non-computer oriented environment a concern is the acceptance of the system. This concern exists on many levels."

Jan 1, 1995

By A. S. Ratnayake, H. C. S. Subasinghe

In this study, we review the role of mechanical activation in the pyrometallurgical, hydrometallurgical, and electrometallurgical processing of titanium feedstock. Mechanical activation has been shown to decrease the activation energy of chemical reactions, thus enhancing process efficiency and product quality by reducing processing time and energy consumption. Pyrometallurgical processing is energy-intensive and time-consuming. Hydrometallurgy is costly, requires high-grade feed material, and generates toxic waste. Waste generation and process complexity are the major drawbacks of electrometallurgy and solvent extraction. Bioleaching via a mechanically activated pyrometallurgical process can be identified as an alternative method, but the lengthy processing time is the major disadvantage. Mechanically activated titanium concentrate can be used in a finely tuned combined metallurgical process to overcome the challenges and drawbacks in these technologies.

Aug 3, 2023

By B. Csoke

In a first stage of our investigations material properties of fly ash (three acidic and one alkaline type originating from combustion of various age coal) obtained from four various dumps have been characterized. In a next step systematic mechanical activation experiments??grinding??and measurements have been performed with various ashes to establish relations between grinding fineness (specific surface area), specific work input demand of grinding and activity. In a third phase utilization of a mixture of mechanically activated fly ash and lime for producing an independent binding composition has been assessed involving determination of interrelationship(s) between the degree of activation of fly ash, the lime concentration and the resultant strength of the obtained concrete. Finally, pilot size experiments were conducted and a test road section was built to explore possibilities for the production of suitable binding composition from the mixture of fly ash and lime as well as the applicability such mixture for road construction. After summarizing major achievements of the first and second stages of the work (history) the present study deals with the research conducted in stages three and four. Experimental results support the conclusion that the obtained binding material is suitable for construction of road bedding.

Jan 1, 2014

By T. C. Alex

Mechanical activation of gibbsite [?-Al(OH)3] is the theme of this paper. Industrially prepared gibbsite used in the study has a mono modal size distribution with a median size, d50=110 µm. Mechanical activation of this gibbsite has been carried out in a planetary mill at ambient conditions. Mechanical activated gibbsite samples are characterised in terms of particulate characteristics, structural characteristics and reactivity. As a result, of milling, mono modal size distribution of the unmilled gibbsite changes to a broad multimodal distribution. Size reduction has been sharp in the initial stages of milling; median size reduces to ~7 µm during 15 min of milling. Thereafter no decrease in median size is observed; rather it is found to increase gradually with further increase in milling time, indicating particle aggregation. Morphological studies of milled gibbsite have shown that the platelets forming the agglomerate are separated first; the separated platelets then undergo breakage. Aggregation of particles sets in the later stages of milling as a result of increased surface area and surface energy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies have clearly revealed the changes in gibbsite structure during milling. Analyses of XRD data show that the crystallite size of gibbsite decreases as the milling time progresses whereas its microstrain is found to increase. Accumulation of energy in the structure is the result in both cases. TEM micrographs with signs of defects leading to disordering of gibbsite structure complement the XRD results. Reactivity of milled gibbsite, decrease in its deydroxylation temperature and increase in alkali dissolution, is found to increase with mechanical activation. Increased reactivity of milled gibbsite is found to have a strong correlation with the BET specific surface area. Keywords: mechanical activation, gibbsite, alkali dissolution, thermal dehydroxylation, reactivity

Sep 1, 2012

By Rakesh Kumar, S. Mehrotra, T. Alex

"This paper, an overview of our recent findings on mechanical activation (MA) of minerals/materials, emphasizes the importance of sample genesis, mechanically induced/altered porosity and surface area, mineral interactions, glassy inorganic materials, surface alteration and zeta potential changes and, mechanically induced reactivity of solids. Materials investigated include Al-oxyhydroxides (gibbsite and boehmite), fly ash and granulated blast furnace slag. Planetary, attrition, vibratory and conventional ball mills are used for MA. Genesis of boehmite has been found to have a bearing on its behavior during MA. For example, BET specific surface area (SSA) of boehmite prepared by thermal dehydroxylation of gibbsite has decreased from 265 to 65 m2/g during 240 min of MA; in contrast, the SSA of hydrothermal boehmite has increased from ~2 to 36 m2/g. Mechanisms of surface area changes in the two boehmite samples differing in their genesis is explored. MA of gibbsite and its mixture with hematite/quartz using attrition milling has indicated that the presence of the second phase promotes amorphisation. Amorphous materials show signs of change in nature of bonding during milling as illustrated by MA of fly ash. Physicochemical changes during MA are not restricted to the bulk phase. The genesis of zeta potential changes in MA solids can be many; for example texture induced zeta potential changes as observed for gibbsite, while zeta potential changes during the milling of granulated blast furnace slag occur due to enhanced (possibly non-congruent) dissolution. Interesting manifestations of mechanically induced reactivity and its correlation with physicochemical changes are illustrated in terms of alkali leaching of boehmite and, hydration of MA slag. New findings reported here are associated with several open questions and are highlighted in the paper."

Jan 1, 2014

By Mohamed Y. Bakr, Aly M. Abdel-Rehim

The present work is related with mechanical activation of processing of Egyptian wolframite by simultaneous ball-milling and pressure alkaline leaching, to improve the recovery of tungsten from wolframite. The results show a total recovery of tungsten from wolframite (97.8- 98.7%) by simultaneous ball–milling and alkaline leaching at temperature 175-200oC. It is concluded that processing of wolframite by simultaneous ball- milling and leaching is mechanically activated and accelerated as a result of the grinding action of steel balls that caused the immediate rupture by continuous removing the product layer of the reaction ( sodium tungstate and iron and manganese hydroxides ) from reacting particle surfaces. This leads to the exposing of fresh and activated wolframite particle surfaces to alkaline leach solution and consequently the acceleration of the reaction of wolframite leaching .The results of the kinetic study 0f alkaline processing of wolframite and its mechanical activation show that the system is under kinetic control.

Jan 1, 2015

By H. M. Yang

Structural alteration of pyrophyllite during mechanical activation in a planetary mill was investigated by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. Mechanochemical effect markedly promotes the decrease in reflection intensities with increasing the grinding time. Prolonged grinding causes the pyrophyllite to become the amorphous structure. It can be indicated that pyrophyllite is very susceptible to alteration by grinding. Crystal size (d006) of pyrophyllite appears to be a limit after 2h grinding. IR spectroscopy analysis shows a little alteration in the bands of pyrophyllite after mechanical activation. The results indicate that the ordered structure of pyrophyllite is destroyed and lattice deformation occurs. Porous silica was then successfully prepared via leaching the mechanically activated pyrophyllite. Pyrophyllite was first ground for 6 h. Ground samples were subsequently leached with 4 M hy-drochloric acid at 80 °C for 2 h to produce porous silica with specific surface area of 188.1 m2/g, total pore volume of 0.18 mL/g and average pore size of 3.9 nm from N2 adsorption analysis. Otherwise, the porous silica obtained from direct leaching of the original pyrophyllite only has a specific surface area of 4.3 m adsorption analysis. 2/g and total pore volume of 0.03 mL/g. It is inferred that grinding is favorable for the formation of microstructure pores. It offers a simple and convenient route for the preparation of porous materials from natural minerals.

Jan 1, 2014

By George D. Haley

This report will be given in two sections. The first sec¬tion outlines techniques and equipment to form almond shaped fluorspar briquettes by means of briquet presses, and the second section outlines techniques of the balling disc. PART I - BRIQUET PRESSES Fluorspar has been briquetted for a number of years and the so called "peach pit" briquet is known to many steelmen. Present production is estimated at over 100,000 tons annually. Slide 1 shows an assortment of various sizes and shapes of briquettes. It is possible to form fluorspar into almost any configuration of briquet. For safety on the melting floor, pillow type briquets are preferred. Ease of mechanical handling and durability of the product are facil¬itated by an almond shape. The dimensions of the almond can vary from 1-in. to 1-1/2-in. in length, from 13/16-in. to 1-in. in width and from 1/2-in. to 1-in. in thickness. The type of equipment to pro¬duce almond shaped fluorspar briquettes is shown in Slide 2. Here we have a Komarek-Greaves and Company 300 ton briquettor equipped with almond rolls. This machine is capable of producing fluorspar briquettes at a rats of 30 tons per hour with power consumption of 35 hp per ton par hour.

Jan 1, 1969

By McDonough RJ

Mechanical agitation is the preferred system for Carbon-in-Pulp processes. Agitator design requires an understanding of the relationships between energy, shear and flow and the nature of shear rates and shear stress distribution in an agitated tank. Laser techniques are useful when studying these phenomena. The alternatives are open impeller agitation or draft tube circulation. Each has advantages and disadvantages but both require careful choice of impeller and system geometry. Overall the draft tube circulator is the more attractive in many cases. Open impeller agitators are designed in accordance with established procedures for mineral slurries taking due account of shear effects in tanks containing carbon. Preferred tank proportions are 1:1. Circulator design methods were developed in the alumina industry before being applied to CIP processes. Optimum draft tube diameter is critical to power requirements. The overall system must be designed as an axial flow pump operating in a closed circuit. Such a system exhibits quite characteristic behaviour which requires an impeller of varying pitch angle and aerofoil section for best stability and efficiency.' Tank height may be 2 or more times diameter. Resuspension of settled solids can be assisted by a series of slots in the draft tube. These slots have the secondary effect of stabilizing hydraulic behaviour and reducing installed power requirements.

Jan 1, 1982

By L. A. Weakly, D. A. Weiss, R. B. Crookston

A presentation of experience gained from using mechanical and conventional equipment for excavating shafts, raises, tunnels and other openings in various Colorado oil shale mining properties.

Jan 1, 1983