Search Documents

By Joaquim Luiz Monteiro de Barros

Com base na atual situação de restrição de disponibilidade e do custo da energia no Brasil, sistemas tipo Heat Pipe (tubos de calor) tendem a ser cada vez mais utilizados na recuperação do calor dos gases de exaustão nos processos de produção de gusa, para o pré-aquecimento de ar/gás, aumentando a eficiência energética global do sistema e reduzindo o consumo de combustível. Esta tecnologia agrega uma série de vantagens, quando comparada com os trocadores de calor tradicionais, pois possui um design compacto, transferência de calor uniforme em toda a área de troca térmica, alto grau de vedação, de forma a evitar o risco de vazamento e mistura/contaminação entre os fluidos quente e frio.

Sep 25, 2017

By Gandhi

Piled raft foundation under uniformly distributed vertical loads has been analyzed using Finite Element Method. The soil is considered to be linear elastic, isotropic, homogeneous. The raft,pile and the soil have been idealized with eight noded brick elements. Parametric study have been carried out varying pile length, soil modulus, raft thickness, and pile spacing. Design charts have been produced to achieve 50% load sharing between pile and raft for optimum design. Data available in literature is compared with the design chart results and found satisfactory.

Jan 1, 1996

By Gary R. Gavan

This report presents the results of a research project that gathered detailed information on the composition of the population of mobile equipment used in U.S. coal mines. A computerized data bank containing over 19,000 pieces of coal mine equipment in use in 1976 was prepared with a data retrieval program. Operator protective structure technology is reviewed; field problems experienced with ROPS are discussed.

Jan 1, 1978

By D S. Preece

The aim of the present work is to investigate the effects of shooting multiple explosive charges, in the same borehole, on the amplitude and frequency content of the generated seismic wave. The work also investigates the effect of the coupling medium used in the borehole on the quality of the generated seismic wave. The delay period between the shots is on the order of months and up to a year. The investigation utilizes a numerical modeling approach which is capable of modeling the detonation of explosives as well as shock and stress wave propagation in solids.

Jan 1, 2012

During the second quarter of 1983, the economic recovery showed further strength abetted by the performances of consumer spending, residential investment, and the slowing down of inventory reductions. Real gross national product (GNP) increased from the first to second quarter at an annual rate of 9.2 percent, compared with 2.6 percent from the fourth quarter of 1982 to the first quarter of 1983 and an overall 1.9- percent decrease in 1982. Total industrial production increased 1.8 percent in July, and productivity as measured by output per man-hour increased 1.3 percent between 1982 and the first quarter of 1983 (table 1). Especially noteworthy .was the performance of real consumer durable goods expenditures, which increased at an annual rate of 32.0 percent from the first to the second quarter (about half of the increase consisted of automobile sales) and real consumer spending, which increased between these periods at an annual rate of 9.7 percent. Residential investment increased at an annual rate of 76.1 percent between the first and the second quarters,1/ and private housing starts by about 38,000 units in both March and May.

Jan 1, 1983

By Catia Casagrande

O processo de pelotização foi desenvolvido com a finalidade de aproveitar as partículas finas e ultrafinas geradas nas operações de exploração e beneficiamento do minério de ferro. Entretanto para atender as usinas de pelotização, faz-se necessário utilizar a moagem para adequar as características de granulometria e superfície específica das misturas de minérios de ferro às especificações da produção de pelotas. Porém os moinhos possuem alto consumo de energia elétrica, elevando o custo operacional do processo de pelotização. Frente ao cenário atual, foi realizado o trabalho para estudar a substituição à moagem (área úmida) por processo de multi prensagens. Além disso, foram misturados os minérios de ferro com carvão, a fim de reduzir também o custo da moagem deste insumo. O objetivo principal foi quebrar as partículas de mistura de minérios de ferro e carvão, e avaliar os resultados de superfície específica e granulometria deste produto comparando com o processo padrão (moagem e prensagem). A prensa de rolos de bancada e as análises físicas e químicas foram realizadas para o desenvolvimento do trabalho. Foi concluída a possibilidade de atingir granulometria e superfície específica através de multi prensagens, atendendo o processo de pelotamento.

Aug 16, 2017

This is a sampling of the papers presented at the conference, the proceedings can be bought from the SAIMM The technique reported here involves measuring the air pressures generated within sealed boreholes located behind blasts. Results from twelve free face blasts in competent rock environments a represented. There were no instances of high pressure gas penetration, even at distances corresponding to less than one blast burden. Rapidly generated underpressures were measured in most holes, with the magnitudes of the peak pressures decreasing with distance behind the blasts. It has been proposed that the under pressures are the result of new volume created due to crack formation and overall rock mass dilation. The experimental evidence is consistent with this, including a correspondence of the onset times of the peak underpressures with the nominal firing times of the nearest blastholes. New post-blast cracks were observed when using borehole video cameras in the monitoring holes. A calculation of new volume produced within the monitoring holes is proposed as an indicator of damage. While the data exhibit considerable scatter, there is a power function dependence on scaled distance, which resembles that of typical vibration data. The data also lie within the normally quoted vibration regimes for rock damage and are consistent with measured extents of damage. It is concluded that this technique may provide an inexpensive and practical comparative measure of near-field rock damage due to blasting. It is further concluded that gas penetration is not a common phenomenon. Damage appears to be mainly attributable to the nearest blastholes and the control of charge mass in perimeter blastholes is emphasized for damage minimization.

Jan 1, 2000

By Tom Barry, Kameron Ray, Dr. Gavin Yuill

Imerys Talc, Yellowstone Mine in Montana faces significant geotechnical challenges such as poor wall quality and local instabilities. These instabilities are driven primarily by the characteristics of the rock mass, but are aggravated by drilling and blasting operations.

Jan 1, 2016

Atlas Copco Construction and Mining Australia identified a number of issues in regard to the skill levels, labour turnover and productivity of our service technicians. In 1994 we were experiencing a labour turnover rate of 42 per cent per annum amongst our technicians. Exit interviews were held with each individual and one of the major areas of dissatisfaction was the degree of product training provided on our equipment, compared to what is required to be competent across the range of our products. These tradespersons were prepared to accept the reduced remuneration that an OEM offers, for the benefit of comprehensive, professional training that, in theory, could be provided. The truth is that we were achieving approximately 40 per cent of our target for training hours because of the demands of field service, pre-deliveries, etc. So, the summary was the same as the industry was experiencing at that time because of skilled labour shortages, production demands, etc people were employed and thrown in at the deep end. A recipe for failure that will be successful every time.

Jan 1, 1998

By Segundo Velásquez, Enrique Mego, Robert Montes

La pila de lixiviación de minera Coimolache, después de 11 años de operación, actualmente cuenta solo con espacio para cargar mineral en el lift 18 a 150 m. de la geomembrana de base. Esta altura restringe la recepción de leyes pregnant en la poza PLS a 31 días por la velocidad de percolación, que se ha determinado en 5 m/día, considerando una humedad retenida de 10%; sumado a ello la calidad del mineral acarreado de los tajos Ciénaga y Mirador presenta contenidos de fino de hasta 60% m-1/8 en promedio, que perjudican la percolación de la solución cianurada a través de la pila de mineral.

Sep 30, 2022

The 53 countries that constituted Africa in 1992 accounted for a significant portion of total world output of a number of mineral commodities. However, the continent's total output for a number of major mineral commodities declined relative to the volume produced during 1991. (See tables 1 and 2.) The most conspicuous declines in mineral production from 1991 to 1992 were for cobalt and copper (declines of 28.6 % and 23.4 %, respectively), which could be partially attributed to mining and metal processing difficulties caused by political and economic disruptions in Zaire and for uranium (12 % drop), for which much of the continental production decline was ascribed to Namibian cutbacks in response to lower world prices. The severe regional drought also adversely affected the mineral industry in a number of sub-Saharan nations.

Jan 1, 1994

By R. J. Folic

Investigations of the vibrations of a pile in soil are performed on a dynamic model in the form of a prismatic bar of finite axial and flexural stifnesses with a discrete mass at its free end representing the cap. The soil is represented by a system of springs of constant and variable stiffnesses. Oscillation differential equations are derived by means of the Hamiltonian principle for non-conservative systems. The problem is reduced to a coupled system of two non-linear partial differential equations with corresponding initial-boundary conditions. Frequency equations of longitudinal and lateral linearized equations are formed. The paper determines natural frequenc­ies and oscillation modes. It separately examines longitudinal vibrations excitated by a hermonic force acting upon the pile cap, and lateral vibrations excitated by an impulse acting upon the cap. The results of the numerical processing are presented in respective diagrams in dimensionless form.

Jan 1, 2010

By R. L. Virta

Twenty-three companies mined kaolin in nine States in 2004. Production was estimated to be 7.6 Mt (8.3 million st) valued at $912 million, based on preliminary data. This was a slight decrease from 7.68 Mt (8.46 million st) valued at $939 million in 2003.Georgia was the leading producer state with an estimated 6.5 Mt (7.1 million st) in production. It was followed, in decreasing order of tonnage, by South Carolina, Alabama, California, Texas, Arkansas, Nevada, Florida and North Carolina. Georgia accounted for nearly the entire domestic water-washed, delaminated, and pigment-grade calcined kaolin production. Consumption Sales to the paper industry accounted for 49 percent of domestic sales and 64 percent of total sales. Other major markets for domestic sales were refractory products (10 percent), paint (5 percent), fiberglass (4 percent), catalysts (3 percent) and rubber (2 percent).Paper coating and filler markets accounted for about 87percent of export sales of kaolin.

Jan 1, 2005

By S. F. Fu

The Charkhan Salt Lake area of the Chaidamu Basin in West China is characterized by soft super-saline soils with very high contents of soluble salts. From the engineering point of view, these saline soils are saturated, liquid-plastic and moderately to highly compressible lean silty clay and clayey silt. In the natural state, their allowable bearing capacity is only 60-80 kPa. As to the saturated lean silty clay, liquifaction in case of an earthquake of intensity 7 on the Modified Mercalli scale is considered likely. In order to improve the geotechnicai properties of the saline soils, stone colomn stabilization by means of vibroflotation was performed. As the geotechnicai properties of the soils are closely linked with the amount and composition of the soluble salt content, saline water with chemical content similar to that of the saline soils was used as flush fluid in the course of hole-making and column-forming, with a view to keeping unaltered the amount and composition of the salts in the soils and thereby precluding reduction in or loss of their strength. Systematic monitoring on the behavior of the foundation soils before and after the treatment and comparison of the numerical data thus acquired have shown good technical results, testifying to the effectiveness of stabilization of soft superealine soils by vibroflotation. As a result of the treatment, the allowable bearing capacity was increased one to two fold, accompanied by elimination of the liquefaction potential.

Jan 1, 2010

By Eric E. Cather

Approximately 270,000 cu yd (20[0],000 cu m) of inferred subeconomic auriferous gravel resources were estimated in three Tertiary deposits in the Polk Springs study area (fig. 1 and table 1). These resources are exposed between tuff-breccia and lava flows of the Pliocene Tuscan Formation and Paleozoic or Mesozoic metamorphic rocks which suggests that although no deposits were identified in the other RARE II areas, they may be concealed beneath the Tuscan Formation. Difficulty in choosing drilling targets will make the likelihood of resource discoveries small. The development and production of these deposits would also be prohibitive under current economic conditions due to the thick covering of volcanic rocks. Recent stream gravels of Deer Creek in the Polk Springs study area contain enough gold to attract gold hobbyists; however, the stream gravels do not have sufficient volume to be considered a resource. Potential exists for additional auriferous gravels near the Occidental Mine in the Polk Springs RARE II area.

Jan 1, 1983

By H. Griesel

The overall supply of platinum is forecast to rise more than the demand, and market deficit will narrow somewhat, but is still substantial at about 480 000 ounces. Because of this deficit, the price of platinum is expected to remain high, not taking into account the impetus from funds and speculators. With this strong demand for platinum and the high price, platinum producers still need to initiate projects to not only sustain current production, but also expand output into the high demand. However, the rise in the platinum price does not entirely offset the drop in revenue due to the strong rand. Consequently, in the current economic environment, executives and managers are under extreme pressure to initiate only the highest yielding projects and implementing them successfully. During the initiation phase of a project, the cost of changing concepts is the least, and strategic project decisions are the most important. It is during this phase that the most value can be added to a project, therefore requiring inputs from highly skilled, creative and experienced people. This paper will discuss thought processes and paradigms during the initiation of projects that will assist project owners in the selection and initiation of successful and profitable projects. The project initiation process will also be discussed outlining selection models, risk analyses and funding considerations.

Jan 1, 2004

A wide range of materials are used in hydraulic backfilling operations and the pipeline flow behaviour of these mixtures varies considerably. It is shown that despite the large differences in constituent materials and flow behaviour, a common approach can be applied to analysing the flow of all hydraulic backfills. This is extended to include a rational design approach for backfill distribution systems. The use and limitations of pipe loop tests as a design aid is discussed. Backfill quality control is identified as a key area where improvement needs to be made to enhance the reliability of backfill system operation.

Jan 1, 2001

By Douglas Rudenko

Most engineers, mine operators, or contractors acknowledge the importance of having accurate subsurface information in order to plan a project or solve a problem. Conventional methods of exploring the subsurface such as augering, core borings, or test pits can provide information, but it is often costly and sparse. Geophysical methods offer an alternative to help supplement sparse information~ gathered through conventional exploration techniques.

Jan 1, 1998

Jan 1, 1989

By Karla Carolina Alves da Silva

Esse trabalho tem por objetivo, propor a utilização de um dispositivo, criado na UFPE, para estudar a fadiga funcional e mecânica num atuador de Ti-Ni com memória de forma. Inicialmente, fios de Ti-Ni com efeito memória de forma, com 0,89 mm de diâmetro, foram submetidos a um tratamento térmico de homogeneização por 24 horas a temperatura de 500ºC e têmpera em água a 25ºC. Posteriormente, os mesmos foram submetidas a calorimetria diferencial de varredura para obtenção das temperaturas de transformação. De posse desses dados, foram confeccionados atuadores com a forma de mola helicoidal. Utilizando o dispositivo proposto, esses atuadores foram submetidos às deformações cíclicas, com expansão total de 10mm, num banho térmico programável, a temperatura constante de 85ºC, na condição supereslástica, essa etapa é denominada neste trabalho de ciclo rápido. Com o objetivo de analisar o efeito dessas deformações cíclicas sobre as temperaturas de transformação e a capacidade de recuperação de forma dos atuadores foi realizada um segunda etapa, aqui denominada de ciclo lento. Nessa etapa, os atuadores foram solicitados à esforços de tração equivalentes a tensão de cisalhamento no fio de 70 MPa, dentro do intervalo de temperatura entre 15°C e 85°C, e tiveram o deslocamento e as temperaturas de transformação monitorados por um sensor LVDT e por um termopar respectivamente. Os ciclos rápidos e lentos são intercalados periodicamente. Dessa forma, observou-se a influência da ciclagem termomecânica na degradação do efeito de memória de forma.

Aug 16, 2017