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By D. R. de Fontaine

By computing the values of the resolved shear stress for a great many orientations of the tensile axis on all 12 (111) <110> slip systems, Taylor and Elam&apos; were able to map out a stereogram of slip systems, given here, Fig. 1, in Diehl&apos;s notation (see, for example Hauser and Jackson&apos;). The purpose of the present note is to derive such a stereogram by mathematical reasoning and to give a simple method of defining the system with highest resolved shear stress for any direction of the tensile axis, thereby eliminating tedious computation of the Schmid factor. Let the tensile axis, of direction cosines [xyz], make the angles 0 and relative to the slip plane normal [HKL] and the slip direction [hkl] respectively. Fig. 2 shows a simple cubic cell whose edges define a Cartesian coordinate system. Let A be a unit vector of origin 0 supported by the tensile axis. Its end point [xyz] then lies on a sphere of unit radius, on the positive hemisphere of which the planes z = 0, x = y, y = z limit the so called primitive triangle of a standard [loo] stereographic projection. For any point of this triangle, the following hold: 0«2 «y *sx « 1 [l] Now, for given [xpz], the most highly stressed system will be the one for which the following expression of the Schmid factor has the largest possible value: (HKL) belonging to the form (111) and [hkl] to the form <110>, the denominator on the right hand side of Eq. [2] is equal to 1.fi.a. The unknowns H, ... h, . . . can now be determined by correctly distributing +1 and -1 to H, K, L, and +1, -1,O to h,k, 1 giving the numerator of Eq. [2] its greatest positive value (the angles 0 and cpare chosen acute) subject to the condition: Hh+Kk+Ll = 0 [3] since the slip direction must lie in the slip plane. Condition [3] can be satisfied only by having one of its terms vanish and the other two equal to +1 and -1. Taking the case of the tensile axis lying in the primitive triangle, x2y, z and therefore Hh will be chosen equal to +1 with H = h = +1 in order to retain a maximum of + signs. There remain two alternatives: either 1 = 0 or k = 0. 1) take 2 = 0 Then Kk = -1 and the numerator of [2] becomes: Retaining a maximum of + signs gives L = k = +1 and becomes: 2) take k = 0 Then L1 = -1and, likewise, the numerator of [2] becomes: xz - z2 + xy + yz [5] But the difference [5] - [4] can be written: (y - z)(x+y +z) [6] positive or zero by virtue of [I]. If [6] is positive (y > z), then the largest possible value for the numerator of [2] for any xyz inside the primitive triangle is given by [5], i.e., for: That is to say, the active slip system corresponding to an orientat:~on of the tensile axis inside the primitive triangle is:

Jan 1, 1962

By C. M. McKinney

This report presents analyses of crude oil from most of the fields in the United States producing 2,500 barrels per day or more. The purpose of the report is threefold : 1) To present detailed analyses of crude-oil samples from as many al possible of the important fields in the United States. On January 1, 1947, there were 340 fields producing 2,500 barrels & day or more. Analyses for 283 of these fie1ds are presented. Fifty-seven fields have been omitted because the Bureau of Mines did not have analyses or the crude oils being produced. As one sample was not representative of the promotion from several of the fields, two analyses are given for each field of this kind. (2) To compile these analyses, many of which have not been published previously in a single report. Since the publication of Bulletin 291 in 1928, there has been no report showing analyses of crude petroleum from fields throughout the United states, but a number of separate reports according to area or state have been issued. Many of these are out of print. (3) To provide a means of ready comparison of the properties of crude oils from different areas of the United states.

Jan 1, 1948

By Breno Totti Maia, Rubia Teodoro Silva, Daniel A. G. de Carvalho, Aline Lima da Silva, Gilvan Nascimento de Souza

Para a maior eficiência na técnica conhecida como Slag Splashing, empregada com fins de manutenção e reparo de refratários de convertedor LD, a escória deve apresentar características apropriadas em termos de viscosidade e fração de sólidos. No presente trabalho, desenvolveu-se uma metodologia híbrida, combinando a utilização de padrões para a caracterização visual de escórias na planta, baseada em critérios de atribuição de notas, com a simulação termodinâmica usando o software FactSage para determinação das fases presentes na escória, quantificação de fração de sólidos e cálculo da viscosidade efetiva. A metodologia proposta permite identificar os quadrantes ideais de viscosidade efetiva, fração de sólidos e teor de ferro total, de modo que se possa garantir escórias com notas altas, apresentando qualidade apropriada para o processo. Os resultados indicam que as escórias com nota 3 (ótima) são obtidas nas seguintes condições: temperatura de fim de sopro de 1690-1720ºC, viscosidade efetiva na faixa de 0,070-0,650 Pa.s, fração de sólidos de 13-22%, teor de ferro total na escória de 14-17,5%..

Oct 1, 2019

By João Paulo Vilano de Castro

O processo termomecânico de laminação controlada seguido de resfriamento acelerado permite obter aços de elevada resistência mecânica e tenacidade e excelente soldabilidade, com o emprego de menores adições de elementos de liga, além da exclusão de tratamentos térmicos posteriores. Com a aquisição do sistema de resfriamento acelerado pela Usiminas, CLC, diversos aços vêm sendo desenvolvidos. Este trabalho apresenta a caracterização microestrutural e mecânica relativa à fabricação do aço API 5L X80, utilizando resfriamento acelerado. Foram avaliados os resultados de dois projetos de liga, Nb-Cr-Mo-Ti e Nb-V-Ti, com a laminação terminando no campo intercrítico. O aço Nb-V-Ti foi processado, também, com a laminação concluída no campo austenítico. Em todos, os testes a resistência mecânica e a tenacidade atenderam aos requisitos especificados pela API 5L. Embora a microestrutura dos aços tenha sido distinta em função das suas condições de processamento, a laminação do aço Nb-V-Ti no campo austenítico foi mais vantajosa em consequência de ganhos em produtividade e estabilidade operacional.

Aug 16, 2017

By Mark Eisner

ONE&apos;S JOB is the watershed down which the rest of one&apos;s life tends to flow write the Lynds in the first pages of their classic social study, "Middletown in Transition." Certainly engineers will confirm this statement after a check among those in their own profession with whose lives they are at all familiar. I have no hesitancy in acknowledging the truth of their observation for the men and women who are engaged in the profession of the law. It has been often remarked that American public life is overrun with members of the law profession. The highest public office in the land, that of President. has been occupied by lawyers almost to the exclusion of citizens of any of the other professions. Twenty-two Presidents of the United States out of the total of 31, were members of the bar. For the most part, members of Congress, the governors of the states, the state legislators and the mayors and other local leaders, men who occupy important positions of responsibility and public trust, have had legal training. Now this fact is no mere accident. Those who were fitted for the "job" of the practice of the law are favorably placed with respect to their participation in public life. Thus public service and public office is the watershed down which the "lawyer&apos;s" life tends to flow.

Jan 1, 1940

By J. D. de V. Louw

Introduction Zircon is a natural occurring mineral and may exhibit natural low level radioactivity. It contains trace levels (90 to120 pCi/g and 110 to 115 pCi/g respectively or 3.3 to 4.4Bq/g and 4.1 to 4.3 Bq/g) of naturally occurring radioactive uranium and thorium. This mineral is often found in a suiteof minerals (rutile, ilmenite and monazite) Due to the overlap in physical properties of monazite (containing 4–7% thorium) with some of the zircon (slight magnetic susceptibility) it often contaminates the zircon, adding to the levels of thorium in the product. Hazards associated with the products from zircon and its processing is inhalation of respirable dust (generated by milling) containing radioactive uranium and thorium which may cause cancer of the lungs. Legislature regulates the transport, use, workplace environment exposure and storage of radioactive material. In America the general regulation for the unlicensed use of low levels of radioactive materials limits the concentration to 500 ppm (U plus Th). Europe (IAEA) specifies a limit of10 Bg/g (Bequerels per gram) on the parents for transport only which is a higher level of U+Th. Companies selling into these markets need to comply with these regulations and certification is therefore required, not only of the major constituents determining the price, but of the U and Th levels as well. Exceeding the limits for U and Th may result in material being returned to the country of origin. However, for the analyst the requirement is to analyse for these elements throughout the production process as well as the analysis of the ‘tails’ that is returned to the mine area. This requires a wide range of concentration to be analysed. Methods of analysis A wide variety of methods exist for the analysis of U and Th in a range of matrices. (Table I) All these methods have been used with varying degrees of success in terms of accuracy. Overall precision for the different techniques varies from 5 to 25% relative. Time to produce results from these methods vary from a few minutes to several days. The Production Chemist is expected to produce between5 and 10 analyses per hour for process control purposes. A suitable technique that fits this requirement is X-Ray Fluorescence. Both Wavelength Dispersive (WDXRF) and Energy Dispersive X-Ray (EDX) instruments are suitable. X-Ray analysis in general has a few major advantages over competitive techniques. •It is fairly simple to set up and interferences are known and easy to correct •It has multi-element analysis capabilities •Clean spectral lines for U and Th (in zircon specifically) •Uncomplicated and easy to measure background •Low detection limits (3 to 5 ppm) •A very high degree of precision •Sample preparation is uncomplicated and fast (pressed powders and fused beads). In Zircon (ZrSiO4) processed sands the matrix is constant(>99% ZrSiO4) and the background is thus essentially constant. A typical set up for the analysis of U and Th by WDXRFis given below: X-Ray Tube Tungsten (W) Target, 2.5 to 3kW operated at 50mA/50kV Crystal LiF200 (or LIF220 for higher resolution) Analytical Lines (2?)U La1,226.14Th La1,227.47 Detector Scintillation Counter Analysis time, depending on the concentration can vary from as little as 20 seconds up to 5 minutes. Standards As with any other comparative technique XRF analysis relies heavily on the quality of the standards used. Assuming proper set-up and operation of the instrumentation as well as consistent sample preparation, accuracy is determined by the quality of the initial calibration standards. A search for the available zircon certified reference materials (CRMs) shows that there are only a few CRMs

Jan 1, 2003

By K. Schonert

Jigging is a separtion process that has already been described by Agricola in 1556. Fine size material is normally treated in a hutch jigging process, in which the heavy particles are penetrating the jigging bed and are recovered in the hutch. In this process, a ragging consisting of the same or higher specific gravity particles is inserted upon the screen. The ragging is used mainly as a valve to maintain a constant upward flow of the water. Since the heavy particles should pass easily into the hutch, the ragging particles are up to ten times larger than the maximum feed size (1). In the fine size range - 1 mm the performance of jigs is mainly insufficient; some of the low density particles percolate the ragging while the hutch water flow prevents the fine heavy particles from entering the bed (2). By giving a thin layer of particles, which posesses a density sensitivity in case of certain adjustment of flow conditions, directly on the screen, the precision of separation can be increased. Stroke length and frequency have to be adjusted to give this filter layer a homogenous porosity between 60 and 70% during the pulsion phase, and the "en masse" lifting of the bed, as it is known in jigging of coarser material, has to be prevented (3). In this case, the jig cycle is only of minor influence.

Jan 1, 1987

By Dennis Dolinar

In this National Institute for Occupational Safety and Health (NIOSH) investigation, numerical modeling is used to evaluate the degree the pillar strength is increased with a rectangular pillar over a square pillar. Three-dimensional models are developed with pillar sizes and geometries typical of underground limestone mines in the United States. Physical properties for the models are based on geotechnical surveys of nearly 30 underground limestone mines. To examine the effects of pillar length on pillar strength with the modeling, a parametric study was conducted where the pillar width was held constant while the length and height were varied resulting in width-to-height ratios ranging from 0.5 to 1.5 and width to length ratios ranging from 1 to 6. There are two aspects to pillar strength and failure. At relatively low stresses, pillars can fail as a result of geologic structure. At greater depths and sufficient extraction ratios, the pillars can also fail as a result of the vertical stresses exceeding the pillar strength. The effects of increasing pillar length regarding both strength aspects are presented in this study. Equations were developed for the increase in pillar strength with both height and length based on the model results. The results from these equations were compared to those from previously developed empirical equations for rectangular pillars. For the more slender limestone pillars with a width-to-height ratio below one, there is little increase in pillar strength for length-to-width ratios above 2 and almost no increase with length for a width-to-height ratio of 0.5. Only with the more squat pillars is there a significant improvement in strength with length. The gain in pillar strength with length for the pillars is explained by the change in the ratio of the area of the pillar affected by the ends to the area of the pillar. For the squattest pillar, the change in strength is also affected by an increase in pillar confinement along the central length of the pillar as the pillar transitions from a square to a long rectangular pillar. With geologic structure, added pillar length can significantly improve the pillar strength, depending on the strike of that structure with respect to the long pillar axis.

Jan 1, 2007

Gold mining in Australia and globally has a long and variable history. In recent years, due to ongoing public concern over long-term environmental impacts, the mining industry globally has been moving towards a more sustainable framework, presented as the æMining, Minerals and Sustainable DevelopmentÆ (MMSD) framework at the Johannesburg Earth Summit in 2002. There are a number of fundamental issues and concerns with assessing the sustainability of mining. Firstly, long-term trends show that ore grades for almost all metals and minerals will continue to decline (some rapidly so), increasing waste rock is being produced due to the trend towards large-scale open cut mining and more complex ores are now commonly being developed. The impact of these trends on the resource intensity, or unit cost, of gold production is of major concern as it could lead to an increase in energy, water and reagent consumption and greenhouse emissions per unit gold produced. A detailed compilation of these fundamental sustainability indices for gold mining has been undertaken, and is presented with respect to indices over time, ore grade and ore throughput. A clear observation is that the resource intensity of gold mining is extremely sensitive to the ore grade, with energy, water and cyanide consumption and greenhouse emissions rising significantly as ore grade decreases. Based on the gold ore resources at operating mines and other known gold deposits, it is most likely that the average gold ore grade will continue to decline, leading to increased resource intensity and consequent environmental impacts (assuming no breakthrough new technologies occur). These findings are of major importance to understanding the sustainability of gold mining. The final judgement of the sustainability of gold mining therefore must take into account the sensitivity of the ore grade in the resource intensity of gold production.

Jan 1, 2007

By T. J. Goff, G. M. Denton

Mintek has developed the EnviroplasTM process for the treatment of solid wastes from the metallurgical industry, especially steel plant dusts, without requiring agglomeration to produce inert slag and at the same time recover metal values such as nickel, chromium and zinc. The products that are generated in the plasma-arc process are usually a metal and a non-toxic slag, which are tapped from the furnace in liquid form. The metal is mainly composed of chromium, nickel and manganese. During the production of stainless steel between 30 and 70 kg of dust and fine waste is generated per ton of steel. Mintek has successfully processed around 1000t of AOD/EAF dust on a toll treatment basis in order to recover the contained Cr and Ni. The metal produced contained 18.5 per cent Cr, and 5.5 per cent Ni. All slag samples tested conformed to US EPA regulations for disposal. The chromium and nickel recovery to metal was 90 and 98 per cent respectively, on a once through basis i.e. no baghouse dust recycle. Slag tapping temperatures varied between 1650°C and 1750°C. The average actual energy requirement excluding furnace heatlosses of smelting steel plant dust with anthracite as reductant was 1.36MWh/ ton of dust. The total mass of feed reporting to the off-gas stream was 10 per cent. The average ZnO content of the fume was 35.5 per cent.

Jan 1, 2004

By L Zhang

The Chinese coal industry is the largest coal producer in the world. The total production in I995 was 1.28 bnt. On the way towards introducing a market economic system, this mature industry is facing major challenges. The main problems are a large surplus of manpower, shortage of current assets and capital, low productivity, high casualties and a huge deficit. This paper discusses the present situation and the future developments in the Chinese coal industry. The current policy can be stated as ‘rapidly developing the state collieries and improving the village and private mines; integrated development to achieve an economic operating scale and encouraging a diversified economy; rapidly exploiting and developing in the North west and South west; promoting productivity and efficiency; welcoming multi-sources and types of investment; setting up coal exchange markets; and the careful control of resources and the environment'.

Jan 11, 1996

By Craig R. Barrett

The influence of the stress dependence of the dislocation density on the overall stress dependence of The steady-state creep rate is discussed. Experimental measurements of dislocation densities and creep rates jor an Fe-3.1 pct Si alloy tested over a wide range of stress are presented which indicate a close correlation between the two quantities. EXPRESSING the stress dependence of high-temperature steady-state creep rates has been the subject of numerous investigations over the past decade. From these investigations have emerged a few general equations which fit most of the available data reasonably well. Garofalo 1 has proposed that for a wide range of stress and temperature the creep rate, i, can be expressed by a relationship of the form: where A, ß, and n are temperature-dependent and is the applied stress. Eq. [I] gives a stress dependence of a at low stresses and exp(nßo) at high stresses, both consistent with experimental observation where n = 5. A number of other investigatorshave proposed a similar expression where: where m and w are in general functions of temperature. Theoretical justification for Eqs. 111 and [2J comes from two different approaches, theories based on dislocation glide3-5 and theories based on the balance between work-hardening and recovery.&apos; Dislocation glide theories predict where p is the mobile dislocation density and V is the activation volume. In order for Eq. [3] to predict a on stress dependence at low stresses with n = 5, it is necessary for p to be a strong function of stress, about proportional to u3 or u4.436 Recovery models of creep start with the general expression:&apos; where r is the recovery rate and h is the work-hardening rate, and then employ a detailed model to determine the stress dependencies of r and h. As example, weertman2 has described a model based on pile-up hardening which results in an expression similar to Eq. [2] with m = 2 and p = 2.5. A recent, seemingly more general approach suggested by McLean is to use Friedels dislocation network growth expression to calculate the stress dependence of r. This model predicts r = p 3,2 and, as h is taken to be a relatively weak function of stress, the stress dependence of i should be about proportional to p3, 2. Once again, it is required that p be a strong function of stress to yield i This recovery model is by no means complete as the stress dependence of network growth is calculated in the absence of an applied stress meaning that r should probably be a stronger function of stress than given by p3, 2 and also some recent work by Mitra and McLean8 suggests that the stress dependence of h may be as large as Because of the importance of the stress dependence of p in determining the overall stress dependence of the strain rate it seems reasonable to examine this relationship in some detail. Measurements made on dislocation densities present during high-temperature steady-state creep generally obey the following relationship a =o0 + aGVWp [5] where uo is usually called a friction stress, a is a numerical constant about equal to unity, G is the shear modulus, and b is the Burgers vector. Depending on the magnitude of uo, data obeying Eq. [5] can give rise to a range of stress dependencies of p. For example, if we assume that the expression where 6 is some constant, adequately represents the stress dependence of p over a range of o, then from Although Eq. [6] obviously breaks down when u 5uo for uo 6 can vary over a wide range of values. In particular, if u > a, > 0 then 6 will be greater than 2. As an example the data of Ishida and McLean are plotted in Fig. 1 showing excellent agreement with dynes per sq cm) and also showing good agreement with a p cc u3 dependence when plotted on a log-log basis. As oo increases 6 tends to increase and correspondingly the stress dependence of the predicted creep rate should also increase,* as-

Jan 1, 1968

By Alfred Weiss

At the end of the first decade of digital computing in the minerals industry, geostatistics in North America was still in its infancy. This was in contrast with the rest of the world where the technique of kriging was already widely practiced. By the end of the 1970s, there was increasing awareness among practitioners of its potential. But it was not until the late 1980s that geostatistics was universally applied and accepted. This was due, in large measure, to contributors at Applications of Computers and Operations Research in the Minerals Industry (APCOM) symposia. Such an evolution in new computer methods could again be observed at APCOM 26.

Jan 1, 1996

Jan 1, 1967

By THOMAS G. FEAR

THE COAL DIVISION started its share of the annual meeting Monday morning with a study of coal classi fication. A. C. Fieldner was in the chair. The report of the tellers of the ballot for division chairman, stating that Thomas G. Fear had been elected to that office, was read by M. D. Cooper. Mr. Fear acknowledged the honor in a few words. In reviewing the history of the Coal Classification Committee the chairman pointed out that this was its third symposium, the last previous one having been held at the 1930 Annual Meeting. Throughout its work the com¬mittee has had the active cooperation of the Canadian workers who are interested in the subject which should result in a uniform scheme of classification in Canada and the United States. F. E. Lathe, of the National Research Council, Ottawa, abstracted the first two papers of the session entitled "Determination of the Alkali-Soluble Ulmins in Coal," by Edgar Stansfield and K. C. Gilbart, and "Moisture Determination for Coal Classification," by the same authors. The third paper "Condition of Water in Coals of Various Ranks"&apos; was presented by its author, A. W. Gauger. Written discussions of these papers were presented by H. C. Porter and Gilbert H. Cady. In the oral discussion which followed, W. T. Thom, Jr., brought out the advisability of considering age as a factor in classification. Mr. Fieldner favored retaining bed moisture as a partial classification basis, stating that a review of many coal analyses revealed a remarkable consistency in this item in samples from a given mine particularly where the moisture content was not high. Mr. Porter pointed out that the structure and porosity of coal often have much to do with its moisture content and that these vary in different parts of a seam, particularly in anthracite. Mr. Gauger expressed doubt as to whether the Stansfield method gives the true moisture content of coal, which is needed for classification purposes.

Jan 1, 1932

By I. S. Servi, N. F. Graves

THE etch-pit technique has long been used to reveal low-angle boundaries and, in general, the distribution of dislocations in high-purity metals. Often this technique is amenable to quantitative computations,&apos; but generally is affected by some degree of uncertainty because etch pits can be nucleated not only by dislocations, but also by inclusions and surface imperfections. In the case of high-purity zinc, Gilman&apos; reported that etch pits were produced only after adding 0.1 atomic per cent of cadmium to the crystals and aging at a proper temperature. In the course of a study of low-angle boundary behavior in zinc crystals, etch pits were produced in 99.999 pct zinc without resorting to intentional contamination, by etching in a 50:50 HNO3H2O solution. The technique consists of etching until the heat of reaction brings the solution to a boil, and in displacing the etchant rapidly with a stream of cold water, thus avoiding staining. The undesirable features of this technique are the heating effect and the removal of a considerable amount of material. A high polish is obtained if staining is controlled properly; therefore, the etch pits appear very clearly and with excellent contrast when observed under dark field illumination. This is especially helpful for cursory examinations at low magnifications. Several observations were made on zinc crystals of square cross section, having one face parallel to the basal plane and one edge parallel to a slip direction, Fig. l(a). When such a crystal was bent about 2" over a glass die and annealed at 390°C, a sharp boundary was formed only in the inner portion of the crystal. Near the two prismatic faces, perpendicular to the basal plane, the boundary was always branched into many lower-angle boundaries, Fig. 1(b). Attempts to move the main boundary by applying a shear stress to the specimen invariably resulted in curving the boundary, the branched ends remaining pinned in their original location, Fig. 1 (c). The prismatic face, when etched as indicated in the foregoing, revealed the existence of numerous (sometimes up to 30) fine boundaries, nearly parallel to each other. Pre-existing lineage boundaries, generally parallel to the direction of growth, were barriers to the formation of polygonization boundaries and interrupted the continuity of the substructure, Fig. 2. Twin

Jan 1, 1959

Most people are familiar with Euclidean dimensions: zero for a point; one for a line; two for a plane; and three for a volume. Howeverbobjects are not actually Euclidean, but lie somewhere between Euclidean æend-membersÆ with a non-integer fractal (or æfractionalÆ) dimension. The fractal dimension D is a measure of the relative importance of large versus small. Consider the trace of a coastline on a map. It has a fractal dimension (1 =D =2) somewhere between a line (dimension = 1) and a plane (dimension = 2). The more tortuous the coastline, the higher the fractal dimension, and the closer it becomes towards a plane. The concepts of fractals and spatial geometry can be applied to a wide range of geologicaVmining problems as well as than those dealing with space. One commonly quoted fractal relation is the log-log relationship of ore-grade and tonnage. Until recently, we have never been able to define or measure spatial-geometry, but new developments in mathematics have provided a means by which to quantity and apply it to our problems.

Jan 1, 1992

By Antônio Carlos Aguiar Gagno Junior

O Sistema de Controle de Equipamentos de Radiofrequência (SCER) nasceu a partir de uma demanda da área de Telecomunicações com o objetivo de minimizar as interferências dos diversos equipamentos emissores e receptores de ondas de rádio existentes em todo o perímetro da Usina ArcelorMittal Tubarão. Anterior ao sistema, todo o cadastro, controle e alocação destes equipamentos era feito em planilha Excel, mantida pela área de telecomunicações. Todas as verificações para liberação da instalação/configuração do equipamento a ser instalado eram feitas manualmente, com auxílio de equipamento analisador de espectro de frequência. Com a implantação do SCER, as fragilidades do controle manual foram supridas, trazendo o diferencial de cálculos automáticos de interferências feitos pelo sistema em função dos parâmetros de ajuste de cada equipamento, da sua abrangência e localização geográfica. Através de uma interface Web, os usuários podem não só controlar os equipamentos, fabricantes, modelos e aplicações, como também visualizar em mapas, com georreferenciamento, as áreas da Usina em que estes equipamentos atuam, bem como alterar os polígonos e perímetros de alcance e abrangência das áreas.

Aug 16, 2017

By Ivan R. Jankov

No setor industrial no mundo todo, são exigidas as emissões cada vez mais restritivas. Nas plantas onde o Precipitador Eletrostático já está instalado, a solução com o melhor custo-benefício para reduzir as emissões de material particulado abaixo de 20 mg/Nm3 é com o Filtro Híbrido. Esta tecnologia consiste em combinação dos princípios de operação de um Precipitador Eletrostático (utilizado na entrada do sistema), com uso de campo elétrico para separação de material particulado do fluxo gasoso, e de um Filtro de Mangas (utilizado na saída do sistema), com uso de tecido para retenção de material particulado. Salienta-se que a viabilidade de implementação do Filtro Híbrido depende da configuração original do Precipitador Eletrostático (i.e. altura das placas, número de campos, largura da carcaça) que determina o espaço disponível para mangas, bem como as velocidades máximas do gás dentro da carcaça. Na indústria siderúrgica, este tipo de retrofit já é utilizado em planta de sinterização, mas também é aplicável para despoeiramento de fornos de cal e de plantas de pelotização.

Oct 30, 2017

By Maurice Grieves

The great majority of shafts constructed today are still excavated by drilling and blasting, a method which changed very little in over 100 years until the introduction of the mechanical lashing unit and cactus grab by the South Africans, which enabled muck to be removed as fast as massive hoisting systems could handle it and resulted in very rapid rates of sinking. Record breaking month&apos;s performances were achieved at -Hartebeestfontein No. 4 shaft, October 1960-337.1 m; Western Reefs No. 4 shaft, October 1961-340.7 m; and Buffelsfontein eastern twin shaft, March 1962-381.2m. The method was very labor-intensive, requiring a crew of over 60 workers at the shaft bottom during the drill cycle. Safety precautions were strict, but in the drive to achieve rapid advance, cases of personal injury were still somewhat high because of the large number of people engaged in this potentially hostile environment. The South African method, as it came to be referred to throughout the rest of the world, was adopted in the United Kingdom in the late 1950s in a modified form with greatly reduced manpower and nonsimultaneous sinking and lining, which was insisted on by the British Mines Inspectorate. In that instance, it was successfully used to sink the 7.3-m-diam concrete-lined shafts at Kellingley to 770 m depth, with rates of advance of over 90 m/month achieved, a British record at that time. During the sinking of the 1.15-km-deep twin shafts at Boulby potash mine in the UK in 1970, the method was again used, but for the first time ever in Britain exemptions from the mining code permitted the use of crash beams, crash doors, jack catches, and semi-simultaneous sinking and lining techniques. New British shaft sinking records of over 120 m/month were achieved in both shafts. Similar equipment and techniques were used in the early 1970s to sink several deep shafts in Canada, notably Creighton #7 and the Con zinc mine at Yellowknife in the NW Territories. Today, this equipment is standard for deep shafts in the US and the rest of the world. However, with the tremendous escalation in mining labor costs, the impact of health and safety legislation, and environmental regulations, coupled with a very real shortage of miners willing to work in this exposed situation it was apparent that an alternative to the labor-intensive conventional method of shaft construction had to be found. Recognizing the trend is inevitable, one or two major German shaft sinking contracting firms began to take a fresh look at full face boring techniques applied to tunnels and raise bored shafts. The results were most encouraging. Tunnel drivage techniques using moles had developed considerably from Colonel Beaumont&apos;s original channel tunnel machine circa 1880 to the superbly engineered Priestley machine selected to cut the British side in 1975 and the double shielded Robbins Grandori borer on the French side of the English Channel. Full face tunnel machines were being successfully used to drive uphill in inclined shafts in Austria and Switzerland. At Mapprag in Switzerland, the Demag mole drove the first (intentional) vertical transition and curve, and then went on to successfully complete the 730-m-long penstock shaft at an inclination of 35°. In Austria, the Wirth mole drove the Kaprun Glacier ski-lift railcar tunnel at record breaking rates of 457 m/MONTH (best 30 m/d) through green schist at an inclination of 29° for a distance of 3.35 km while the Hydro tunnel at Sarrelli in Switzerland was being driven by the Robbin&apos;s mole at an inclination of 35°. Simultaneously, extremely promising results were obtained using large assemblies of cutter discs on raise borer heads, such as the 4.87-m-diam X 460-m-deep shaft raised by Teton for Jim Walter Resources Inc. Bearing in mind that most mine shafts in the future (unless in exceptionally competent rock) will require some form of lining, and the trend will be toward deeper shafts as the more easily accessible mineral deposits become exhausted, it was seen that normal raise boring had definite limitations in vertical accuracy, in the limitation imposed by the drill string on the available torque that could be applied to the cutter head, and in the risk of collapse of the unsupported shaft rock wall in friable or jointed and fissured ground, since it is not possible to apply any form of temporary support until the permanent lining is being installed. A further problem was the economics of installing a subsequent lining, necessitating setting up a headgear and hoisting arrangement approaching in size that required for conventional drill and blast sinking and lining. Because of the economics, German contractors opted for a phased transition from drill and blast to the full face, rodless, out of the solid shaft mole, by starting off with a down-the-hole shaft boring machine -without a drillstring-but using a pilot hole to get rid of the muck.

Jan 1, 1982