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By Rafael de Andrade Silva

O presente trabalho teve como principal objetivo estudar a evolução da recristalização em chapa de zinco, e para tal objetivo, chapas finas de zinco laminadas a quente foram sobrepostas e processadas pela técnica de deformação plástica severa conhecida como NECAE (Non Equal Channel Angular Extrusion). Em seguida, as amostras foram submetidas a um tratamento térmico de recozimento para recristalização com diferentes temperaturas e tempos de encharque. Para tal objetivo, foram utilizadas análises de microscopia óptica e dureza Vickers. De acordo com os resultados obtidos, observou-se que após o processamento via NECAE houve uma pequena fração recristalizada, e esta aumentou de acordo com o aumento do tempo e da temperatura de tratamento térmico.

Aug 16, 2017

By Matheus Fortes Stiborski

Este estudo descreve a aplicação de três métodos de cálculos teóricos pelos modelos matemáticos de Tafel e Sedlaczek, Siebel e Köster, com o objetivo de calcular o alargamento na laminação a quente de barras em aço AISI 1020 em um laminador tipo duo e definir quais dos modelos de alargamento se aproxima mais dos resultados obtidos experimentalmente. Foram utilizadas amostras com dimensões iniciais de largura (bo), 37,7 mm, altura (ho), 15,7 mm, e comprimento (lo), 300,00 mm onde se ajustou a luz dos cilindros para que fossem obtidas reduções aproximadas de 15% e 20% em altura. Os resultados obtidos indicam que o modelo de Siebel apresenta melhores resultados comparado com os valores experimentais.

Aug 16, 2017

By D. Steele, B. Ndlovu

"Adequate characterisation of clays is becoming increasingly important as operating mines move into areas of more complex ores. The processing therefore needs better mineralogical characterisation to identify problematic ores for better planning before issues arise. While a number of instrumental mineral characterisation methods are available, X-ray Diffraction (XRD) is widely recognised as perhaps the best technique for the identification and quantification of minerals, particularly clays. When an appropriate sequential and systematic sample preparation and treatment protocol is employed with instrumental XRD analysis individual clays can be uniquely identified, and the proportions of interstratified clays can also be quantified. The effect of sample preparation on the XRD analysis and identification of clays was investigated in this study. The results showed that sample preparation protocol is indeed critical to accurately analysis and characterisation of clays. For example, both dry grinding and micronizing affected the degree of crystallinity of kaolinite leading to the formation of reactive surfaces or changes in the physicochemical behavior. It was also found that the apparent degree of preferred orientation in platy minerals correlates directly with the amount of force/pressure applied during the preparation of backfilled powder samples. This work showed that manual preparation can produce highly variable peak intensities especially with minerals that show any preferred orientation. KEYWORDS Clay; XRD; kaolinite INTRODUCTION Clays are important in our life and they have numerous applications in modern world from cosmetics to environmental remediation. Therefore, clays have been extensively investigated for many years. Adequate characterisation of clays is becoming increasingly important as the mineral processing industry faces more complex mineralogy with the need for better mineralogical characterisation to identify problematic ores and plan accordingly. In most studies, X-ray diffraction (XRD) method has shown the unique capability to characterise mineralogy, especially for the fine grained size materials. The XRD technique is particularly diagnostic for clays. It is known that under ideal conditions, the peak intensities of an XRD diffractogram are proportional to the concentrations of individual minerals present in the sample. Hence, the qualitative mineralogical data obtained from XRD can be quantified, using either the internal or external standard methods. However, it is also known that clays are particularly sensitive to the influences of sample preparation method due to their physical characteristics (e.g. fine grain size, morphology, relative physical softness, crystallinity, thermal sensitivity) that could be destroyed by inappropriate preparation prior to the analysis. Thermal and mechanical treatment and grinding of clays can change their crystalline structure, and consequently, their characterisation results by XRD analysis. The behaviour of clays in grinding has been widely studied, especially for kaolinite (Miller and Oulton, 1970, Milocevic et al., 1992, Tomasevic-Canovic et al., 1992). With prolonged grinding time, the crystallinity of the clays can decrease (Filipovic-Petrovic et al., 2002). It has been shown that grinding may gradually cause the loss of hydroxyl ions of kaolinite (Gonzalez Garcia et al., 1991)."

Jan 1, 2018

By Cristovão Nery Giacomin

Foi desenvolvido um software para cálculo do balanço térmico dos fornos de reaquecimento de placas da Usiminas em Ipatinga. Ele realiza a busca automática de dados operacionais e das placas reaquecidas, valida, trata os dados e realiza os cálculos das parcelas de entrada e saída dos aportes térmicos para cada forno. Além disso, são calculados o rendimento, a eficiência térmica e o índice de ocupação dos fornos. O desenvolvimento foi realizado em ambientes visuais, com utilização de interfaces gráficas para fácil interação dos usuários com o software. A validação do software foi realizada pela comparação de resultados obtidos na busca automática com valores reais operacionais de balanços térmicos já realizados nos fornos.

Oct 30, 2017

By M. A. Amarante

Beneficiation studies were conducted on a Portuguese feldspar ore, in order to obtain final products capable of being used in the ceramic industry. A simple scrubbing operation is enough to break the lumps in the feed. The ore deposit contains ca 35 x 106tonnesfrom which, by screening, three main products could be obtained. This paper focuses on the beneficiation of the 500/74 µm fraction, which constitutes about 27% of the ore, assaying 9.42% Al2O3,equivalent to approximately ca 46% feldspar, with a mean iron content of 0.29% iron oxides. Magnetic separation and froth flotation testwork was carried out, in order to decrease the iron contamination and increase the feldspar content. Magnetic separation alone decreased the iron content of the feed to values between 0.04 and 0.08% iron oxides with an average yield greater than 90%. Flotation with HF, provided a feldspar recovery of 45?46% with a concentrate assaying 17.6% Al2O3. The use of H2SO4, gave a recovery of 35?36% of feldspar concentrate, assaying 16.1% Al2O3. However, economic and environmental advantages of using sulphuric acid may compensate for the lower mass recovery. The iron content of0.12% iron oxides in these concentrates, could be reduced to 0.04?0.05%, by further magnetic separation.

Jan 1, 1997

Henry LOUIS, London, England (communication to the Secretary) : Prof. Richards's paper has impressed me as highly valuable. Without entering upon any discussion of it as careful and thorough as it deserves, I venture to mention one or two points which a perusal of it has recalled to my mind in connection with my own study and practice of ore-dressing. I always mentally divide jigging into two phases: 1. A particle at rest on the jig-bed is lifted and carried upwards by the rising current of water, at an increasing velocity, which tends to a maximum. When the upward current is stopped, the particle continues to rise with rapidly diminishing velocity until it comes to rest. This completes the first phase. 2. In the second phase, the particle falls from its position of rest with an increasing velocity which tends again to a maximum, and continues to fall until the rising current of water has reduced its velocity to zero. This completes the second phase. The second phase will evidently be greatly modified by the effect of suction, as Prof. Richards shows; but I do not see that his experiments very clearly imitate the action of the second phase. And the brief intervals at the end of each phase, when the mineral particle, by reason of its acquired velocity, is still moving, though in opposition to the water-current, yet remain to be investigated. I feel especially, in Prof. Richards's paper, a difficulty which I have felt with regard to all similar previous investigations, namely, that the experiments deal with particles falling a long distance, when the velocity becomes uniform. I question whether this uniform maximum velocity is attained in actual jigging-practice. If so, it is certainly for a comparatively very small proportion only of each stroke. It seems to me that an investigation like that of Prof. Richards, but confined to the first 6 or 8 inches of fall only, and carried out with suitably delicate recording-apparatus, is what we

Jan 1, 1895

By M. E. Alam

In the present study, 1.1 volume percent of nano size copper was incorporated into pure tin using hybrid microwave sintering assisted powder metallurgy route. Microwave sintered samples were extruded both at room temperature and at 230 °C. Microstructural characterization studies were conducted on the extruded samples to investigate the distribution characteristics of secondary phase and grain morphology. Room temperature tensile test results revealed that hot extruded Sn-Cu samples exhibited higher strengths (~ 41%, in case of 0.2% yield strength and ~ 38%, in case of ultimate tensile strength) and ductility (~ 15%) when compared to room temperature extruded samples. On the contrary, the tensile properties of pure tin remained independent of extrusion temperature. An attempt is made in this study to correlate the effect of extrusion temperature on the microstructural evolution and tensile properties of Sn-Cu solder.

Jan 1, 2009

By Gustavo Ribeiro de Carvalho

O presente trabalho apresenta o projeto que propiciou melhores formas de controles internos possibilitando a redução do itinerário utilizado para o transporte de escória entre os Altos Fornos da Usina Presidente Vargas - UPV e a CSN Cimentos através da implantação de sistemas de controles de viagens por Validadores de Acesso, com a finalidade de viabilizar a utilização da melhor rota correspondente à menor distância entre as unidades operacionais e por consequência menor custo e impactos ambientais. A otimização do trajeto de escória possibilitou sinergia entre economia, meio ambiente e sociedade proporcionando ganhos financeiros e de produtividade. O projeto trouxe melhorias significativas, refletidas nos principais aspectos: Benefício financeiro com a redução dos custos contratuais com transporte interno de Escória; Inovação tecnológica que possibilitou controlar o registro de viagens por caminhão para melhor apuração da quantidade de viagens e maior confiabilidade dos desvios de estoques; Aumento da produtividade através da otimização do trajeto e aumento na performance de abastecimento da Cimentos; Redução mensal de 18 tCO2 eq. de gases do efeito estufa associado a economia média de 6600 litros do aspecto ambiental “consumo de recursos naturais” (Óleo diesel) com a otimização de 13.000 km.

Aug 17, 2017

By Jeffrey D. Winterton

Keywords: Copper, ion exchange, sulfonic acid, bis-picolylamine, ion exchange modeling, ion exchange kinetics As part of an investigation into the feasibility of using ion exchange resins to recover copper from aqueous waste streams generated during the manufacturing of semiconductor devices, the uptake of copper onto two ion exchange resins was investigated. The resins studied were DOWEX G-26, a standard gel type sulfonic acid resin, and DOWEX M4195, a macroporous chelating resin with a bis-picolylamine functional group. The equilibrium and kinetic behavior of the uptake of copper were investigated over a range of copper concentrations with constant sulfate concentration and different levels of acidity. The homogeneous structure of the G-26 resin yields equilibrium relationships that fit the Langmuir equation, and equilibration times of less than 30 minutes. The uptake behavior of M4195 is complicated by the need to absorb co-ions to maintain electroneutrality, resulting in uptake profiles that change character with increasing copper concentrations, and extended equilibration times.

Jan 1, 2005

By George Krauss, M. Cohen

The reverse martensitic transfomzation (i.e., the conversion of martensite to austenite on heating) was investigated in Fe-Ni alloys containing 30.5 to 33.5 wt pct Ni. The reversed austenite was found to be sufficiently distorted to exhibit marked differences in mechanical properties and to undergo recovery and re crystallization on further heating. In particular, the yield strength of the reversed austenite was as much as 2.5 times higher than that of the virgin austenite: with five cycles of the direct and reverse martensitic transformation, the yield strength was 2.6 times higher. There was an accompanying decrease in strain-hardening capacity and in stable ductility or uniform elongation. The recrystallization was observed to follow sigmoidal kinetics, but was characterized by an abnormal1y large temperature dependence which was evidently due to carbon segregation at the migrating grain boundaries. Upon recrystallization, the strength Properties reverted to those of the virgin austenite, but the ductility did not fully recover until the annealing temperature was further raised to dissipate the carbon segregation at the grain boundaries. The transformation of reversed austenite to produce second-generation martensite resulted in an unusually imperfect structure, thereby leaditg to additional strengthening. Horlleuer, the martensitic phase was much less responsive in this respect than was the austenite. MOST martensitic transformations are capable of undergoing a reverse transformation back to the austenitic phase on heating.&apos; This reaction, like the direct transformation to martensite on cooling, is usually athermal. In analogy with the Ms andMf temperatures for the martensitic transformation (where M, > Mf), the reverse transformation is characterized by the As andAf temperatures (where As<Af). It is well-known that the finish (Af) of the martensite-to-austenite reaction on heating may occur at a temperature where austenite is not stable relative to other phases in the equilibrium diagram.&apos; Reverse martensitic transformations have been found to influence the properties of the parent austenitic phase in a number of ferrous alloys. The austenite thus produced after one or more reversals is significantly altered in strength, microstruc-ture, diffusivity, and annealing characteristics compared to well-annealed, virgin austenite. The first detailed observations of such phenomena were made by Wasserman3 on an Fe-30 wt pct alloy. He found that the reversed austenite (i.e., austenite formed by the reverse martensitic transformation) was much stronger than the original austenite, and the second-generation martensite (i.e., martensite produced from the reversed austenite) was somewhat stronger than the first-generation martensite. On heating the reversed austenite, recrystallization occurred in a manner similar to that of a cold-worked metal; the Laue spots sharpened and the strength decreased.4 In recent years, Russian workers have shown considerable interest in these reverse martensitic transformations. Most of such investigations5-10 have been concerned with the stabilization of reversed austenite relative to subsequent martensitic transformation, and because of its unusual nature, this phenomenon will be discussed in detail elsewhere." On the other hand, the annealing behavior of reversed austenite and the attendant variation in properties have received little attention beyond the experiments of Wasserman.3,4 Gridnev eta1.,8 in one of the few such studies. followed the hardness change of reversed austenite as a function of time at three annealing temperatures. The marked strengthening of austenite achieved by the reverse martensitic transformation has been referred to as "transformation strengthening" by Wasserman3,4 and as "phase hardening" by Malyshev et a1.7,9,10 to differentiate it from hardening produced by cold working. Both groups of investigators noted that further strengthening of the austenite could be attained by repeated or cyclic transformations, but the first cycle resulted in the most pronounced effect. Evidence of the altered microstructure of reversed austenite has been reported by Maximova and Nikonorova6 and by Edmonson and KO.12 The former found that reversed austenite was much more sensitive to etching than the original austenite, and the latter authors observed a (&apos;ghost" structure resembling martensite in certain areas of the reversed austenite. Enhancement of the self-diffusion rate in reversed

Jan 1, 1962

By Carlos Alberto Perim

Durante o lingotamento contínuo de placas de aço, muitas vezes ocorre uma queda acentuada de temperatura ao longo do processo. Fatores como o tempo de lingotamento, o superaquecimento inicial da panela de aço, a presença de cascão na panela, entre outros, podem alterar significativamente a taxa de queda de temperatura, levando muitas vezes à interrupção prematura do lingotamento. Neste trabalho, será mostrado o desenvolvimento de um modelo de predição de temperatura ao final do lingotamento de uma panela de aço. Este modelo permite antecipar, com razoável nível de incerteza, a temperatura final do aço no distribuidor durante trocas de panela, de forma que forneça subsídios para a tomada de decisão sobre a interrupção do lingotamento, ou a antecipação de abertura de panela com retorno de aço. Desta forma, o índice de trabalho das Máquinas de Lingotamento Contínuo (MLC’s) da ArcelorMittal Aços Planos América do Sul seria maximizado, e com possível melhoria no Rendimento de Aço. O modelo se encontra em fase de implantação e validação na MLC#3, onde foram definidos parâmetros com critérios de decisão de interrupção/antecipação de troca de panela.

Aug 17, 2017

By E. Motica

Ores containing uranium and vanadium minerals have been mined from the Salt Wash Member of the Morrison Formation from many localities in the Colorado Plateau region since about 1900. The most productive deposits are in a relatively small area in Southwestern Colorado referred to as the Uravan mineral belt. The mineral belt is a narrow elongate area in which uranium-vanadium deposits in the Salt Wash have a closer spacing, larger size, and higher grade than those in adjoining areas. Pre- 1948 ore production from the mineral belt was 655,000 tons averaging 1.91 per cent V2O5 and 0.28 per cent U3O8. Production during the 1948 to 1964 period was 7,900,000 tons of ore averaging 1.46 per cent V2O5 and 0.27 per cent U3O8. The ore deposits occur principally in the uppermost sandstone unit of the Salt Wash. This unit consists of sandstone lenses formed by a system of aggrading braided streams flowing in an easterly direction generally normal to the mineral belt. These lenses, referred to as channels, are as much as one mile in width and average about 50 feet in thickness and can be traced for several miles along their courses. Areas favorable for one deposits are recognized principally by the following criteria: ( 1) a host sandstone thickness of over 30 feet, (2) the presence of carbonaceous material in the host sandstone, and ( 3) gray mudstones and clays associated with the ore-bearing sandstone. The ore minerals are believed to have been precipitated from laterally migrating solutions; there is no apparent genetic relationship between ore deposits and tectonic structural features. Exploratory and development drilling from the surface is conducted in three phases: first, wide-spaced drilling to find and outline favorable channels; second, moderate-spaced drilling in favorable ground to locate ore deposits; and third, close-spaced drilling to block-out ore. Long-hole drilling from underground stations is used to find and delineate extensions of ore bodies being mined. Due to intense production since 1948 from shallow deposits, best potential for new deposits exists in areas where the ore-bearing unit is 600 to 800 feet deep.

Jan 1, 1968

By G. Wendel

Uranium is a naturally occurring radioactive material in the earth?s crust. Geological processes have resulted in concentration of uranium into ore mined for its gold content in South Africa. This uranium is present in the form of discrete particles of uranium minerals, generally oxides, which are normally insoluble. Chemical and physical processes during gold mining and extraction, particularly when carried out in conjunction with uranium extraction and sulphuric acid manufacture, act on the uranium minerals and the radioactive decay products of uranium. This may result insignificant accumulations of radioactive materials in certain parts of the process. There are a number of naturally occurring radioactive materials in the earth?s crust, such as Uranium-235, Thorium-232, andPotassium-40. This paper focuses on Uranium-238, together with its decay products, and how they affect the gold mines. Water plays a significant role in the redistribution of radionuclides, both as a physical transport medium, and as a solvent in which chemical reactions take place.

Jan 1, 1998

By Ali Ebrahimi, Meena L. Viswanath, John F. Beech, Mustafa B. Erten, Ming Zhu

"Excessive deformation of a cantilever sheetpile wall can occur due to dredging, excavation, backfilling, or long-term creep behavior of soil. A buttressing berm constructed in front of the wall can be considered as a mitigation technique to prevent or decrease the deformation by increasing the passive earth pressure and thus improving the wall stability. The effect of the buttressing berm on the stability and deformation of a sheetpile depends on the berm geometry (i.e., the thickness/depth and the width) as well as the properties of the sheetpile and the adjacent soils. A parametric study was conducted using a conventional limit equilibrium method. Design charts were prepared to evaluate the effect of a buttressing berm and the soil friction angle on the wall stability and deformation. These charts can be used as a tool by geotechnical engineers to make a quick estimate of the required size of a buttressing berm in case of calculated or unexpected excessive deformation of a sheetpile. An analysis of the effect of a buttressing berm on the stresses and deformation of a sheetpile was also compared with the results from finite element analysis. The results of this comparison are discussed.INTRODUCTIONCantilever sheetpile walls are commonly used to support excavations. Sheetpiles are hot rolled or cold formed sections of steel made to interlock with adjacent sections to form a continuous structure providing lateral support. Sheetpile walls can be cantilever walls or anchored with tiebacks. To construct a cantilever sheetpile wall, sheetpiles are driven by pile drivers or vibrated in to a design depth sufficiently below the depth of excavation. Excavation can then proceed in front of the sheetpile wall, which resists the earth pressure loading from behind the wall. The design depth and geometry of the sheetpile wall depend on the soil conditions, the depth of excavation, and the tolerable deformation. In certain cases, when a small buttress of soil can be left immediately adjacent to the sheetpile wall, the required depth or geometry of the sheetpile wall can be reduced or adjusted, which can significantly decrease the cost of procuring and installing the wall. Such a buttress can also serve as a short-term or long-term remedy in case of observed excessive deformation in a constructed wall. Traditional methods of analyzing the stability of a sheetpile wall do not account for the passive pressure effects of this small buttress. In this paper, a parametric study was performed for a variety of soil types and wall and buttress geometries by implementing traditional limit equilibrium methods in commercial software and design charts were created illustrating the effect of a buttressing berm on sheetpile deflection. Selected cases were then modeled in a finite element software to compare the results with the traditional limit equilibrium method. The resulting design charts can be used as a tool by geotechnical engineers looking to reduce the design geometry of a sheetpile wall or address observed excessive deformation in a constructed sheetpile wall."

Jan 1, 2016

THE Institute met on Wednesday evening, May 22d, in the parlor of the Stanton House, Dr. T. Sterry Hunt, President, in the chair. The President delivered an introductory address on the Brown Hematite Deposits of the Great Valley, after which the following papers were read and discussed : Note on the Result of an Experiment with the Wheeler Process of Combining Iron and Steel in the Head of a Rail, by W. E. C. Coxe, of Reading, Pa. On the Jenks Corundum Mine, Macon County, N. C., by Dr. R. W. Raymond, of New York City. On Wednesday afternoon, previous to the opening session, the members who had already arrived in Chattanooga, were taken by the Local Committee to the works of the Roane Iron Company, and Chattanooga Iron Company, and then to the top of Lookout Mountain, where, at the request of the members present, Dr. Hunt described the geological and geographical features of the Chattanooga region, with the magnificent panorama spread out before them as a map. On Thursday morning an excursion was made by steamboat down the Tennessee River as far as Shellmound. Here cars were taken to the coal mines of the Dade Coal Company, where the members were courteously received by Mr. E. B. Wells, the Superintendent. After a trip through the mines the party partook of a collation provided by the company. South Pittsburgh, on the Tennessee River, was next visited, where the Southern States Coal, Iron and Land Company have a large blast-furnace plant in the course of erection. After conducting the party through the works, shops, etc., Mr. James Bowron, the manager, entertained the members with graceful hospitality at dinner. The second session was held on Thursday evening for the transaction of business. The President, Dr. T. Sterry Hunt, appointed Messrs. W. E. C. Coxe, R. H. Richards, and F. J. Slade, scrutineers, to examine the ballots for officers for the ensuing year.

Jan 1, 1879

By Allen F. Agnew

Geologic studies for the Federal and State governments in the Wisconsin-Illinois-Iowa zinc-lead district were begun in 1835, and subse¬quent surveys were made in the three states at in¬tervals until 1916, see Table I. The current study of the district, Fig. 1, by the U. S. Geological Survey was begun in 1942 in the hope that a systematic investigation would help in¬crease production of zinc and lead, then in ex¬tremely short supply. Major emphasis of the USGS program was on detailed mapping of the geologic structure and ore deposits. Preliminary maps and reports covering localities of intensive mining ac¬tivity have been published during the course of this study, Fig. 2. By 1950 the objectives of the study by the USGS were revised; 7Y2-min quadrangles of relatively unprospected localities as well as inten¬sively mined localities are now being mapped in Wisconsin. Since 1945 the investigation in Wiscon¬sin has been made in cooperation with the Wiscon¬sin Geological and Natural History Survey, and since 1951 the geologic mapping of areas of particu¬lar interest in Iowa has been performed in coopera¬tion with the Iowa Geological Survey. At intervals since 1943 the Illinois State Geological Survey has mapped the geologic structure and ore deposits of localities in the Illinois part of the mining district, see Fig. 2.

Aug 1, 1955

By J. E. McGill

The junior and small-scale mining sectors in South Africa play an important role in the livelihoods of numerous communities. Mining presents an opportunity, in the post-1994 democratic era, for many individuals to obtain access to much required empowerment and socio-economic development. These sectors are, however, not without numerous characteristics that pose problems for operators, legislators, and other role-players. Mining is inherently risky, with operators experiencing frequent difficulties and challenges throughout the life of mine. Opportunity exists, and needs to be enhanced, for junior and small-scale prospects and operations to include technical risk assessment techniques in documentation presented in search for funding, and in optimizing monthly planning and longer-term functioning. The focus here is to explore how the risk management cycle may currently be applied to a mineral resource suitable for exploitation by the junior and small-scale mining sectors. No management process can create additional value in the ground, but various available mechanisms can go a long way to quantifying the inherent risk that exists, highlighting the need to manage the risks and hopefully allowing the entrepreneur access to the intrinsic opportunities of the emerging mining sector in South Africa.

Jan 1, 2006

By J. Zou

With the increasing applications of the Chinese metal magnetic liners, the requirement for their technical specifications has become stricter and stricter. It is necessary to deeply analyse the metal magnetic liners in order to improve their reliability and economics. The key issue of metal magnetic liners is magnetic forces: their attractions to mill shell and protection layer. Mathematical models were developed using finite-element analysis software and systematic simulation analyses of the two most critical indexes of magnetic liners were performed to find out the most important parameters and their effect on the liner?s characteristics. The relationships between magnetic forces and installation gaps, thickness of permanent magnets and thickness of protection layer may be used to guide the design of metal magnetic liners for ball mills in order to achieve good economic indexes.

Jan 1, 2014

By James P. Connell

The American Concrete Institute defines "shotcrete" as "mortar or concrete conveyed through a hose and pneumatically projected at high velocity unto a surface." This definition thus includes what is traditionally known as "gunite," which is a pneumatically applied mortar. In mining practice, the term shotcrete is restricted to pneumatically applied concrete, and this differentiation will be used in this paper. In 1914, following the invention of the mortar gun in 1907, the then Chief Engineer of the U.S. Bureau of Mines, George Rice, developed the guntie process for underground test work at the bureau facility at Bruceton, Pennsylvania. After World War I, gunite was used extensively in American mines and was also utilized for underground civil works such as the San Jacinto Tunnel in California. The greatest development was In Europe where, as early as 1911, gunite was successfully used as an overlay for deteriorated tunnel linings. In 1951, the Swiss firm Aliva developed a pneumatic gun capable of handling coarse aggregate, thus making possible the first use of shotcrete at the Maggia hydropower development. Intially, shotcrete was used to reduce manpower requirements for forming; and placing conventional concrete. However, by 1954 Sonderegger was reporting that the structural advantages of shotcrete were derived from its flexibility and from the fact that it could be applied almost immediately niter the opening had been made. The incorporation of wire mesh into the shotcrete led to the New Austrian Tunnel Method, or NATM. The use of shotcrete in American mines has been implemented more recently. This delay seems to be due to previously unsuccessful experiences with gunite as a structural material and to the U.S. reliance on wood or steel supports in main line haulageways. The long experience with the apparently more substantial rigid supports led mine operators to be reluctant to the new and seemingly unrealistic lighter shotcrete support.

Jan 1, 1977

By Mario Rivadeneira B.

El presente texto señala la importancia del programa de seguridad industrial -en tanto representa la responsabilidad de la gerencia y complementa el interés y seguridad del trabajador-. El planeamiento de responsabilidad depende de cómo se desarrollen las operaciones de orden, limpieza, trabajos bien realizados, ausencia de accidentes y la eliminación de sufrimiento y perjuicio económico a la familia del trabajador. De otro lado, el cumplimiento de las normas de seguridad son bases complementarias de un programa moderno de seguridad, el cual es preparado por nuestra Sección de Seguridad Industrial, que forma parte del Departamento de Relaciones Industriales. Cabe mencionar que para desarrollar un exitoso programa de seguridad en la empresa, es necesario revisar siete elementos básicos que sirven de guia para la elaboración de un programa de actividades en un año cualquiera. Así como el desarrollo de la conciencia de seguridad, el entrenamiento, repetición, corrección son elementos que ayudan a controlar y reducir los accidentes de trabajo, como la voluntad y deseo de trabajar de los trabajadores.

Aug 20, 1963