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By D P. Obeng, L Reemeyer, R Holmes

The Zinifex Century Mine employs a large number of Detritor mills for fine and ultra-fine grinding to liberate silica and sphalerite at 80 per cent passing 7.5 microns before final zinc flotation. A joint project between CSIRO Minerals and the Zinifex Century Mine was carried out to evaluate the Detritor mill performance. Plant surveys were conducted around the Detritors in conjunction with laboratory tests. The survey data showed that the Detritors in the ultra-fine milling circuit performed well. They reduced a feed F80 sizing of 46 microns to a product P80 sizing of 7.5 microns at a gross energy consumption of 37.2 kWh/t. Scale-up of ultra-fine milling Detritors was studied using a 0.55 kW laboratory batch unit and a 355 kW full-scale Detritor by processing Century zinc concentrate with 1 mm sand media. The results indicated that the 0.55 kW laboratory mill underestimated the energy consumption of the full-scale Detritor by about 20 per cent for a product P80 of seven microns. The performances of a horizontal IsaMill and a vertical Detritor were compared as ultra-fine milling devices for processing Century zinc concentrate. The experimental data demonstrated that, when using the same grinding media, the energy efficiency of the two mills is similar despite the difference in mill designs. The Detritors used for regrind duty at the Century Mine performed poorly when processing feed at 80 per cent passing 88 micron. The energy consumption was high and the product size distribution was broad with particles above 100 microns in the feed unbroken and particles below ten microns overground. A coarser ceramic media of 3 mm was therefore tested in a laboratory Detritor to process the regrind Detritor feed as an alternative to the 1 mm Colorado sand used at the Century Mine. The ceramic media reduced the energy consumption significantly and produced a narrower product size distribution, which is more desirable for the downstream flotation process.

Jan 1, 2007

By M. Gao

The Zinifex Century Mine employs a large number of Detritor mills for fine and ultra-fine grinding to liberate silica and sphalerite at 80 per cent passing 7.5 microns before final zinc flotation. A joint project between CSIRO Minerals and the Zinifex Century Mine was carried out to evaluate the Detritor mill performance. Plant surveys were conducted around the Detritors in conjunction with laboratory tests. The survey data showed that the Detritors in the ultra-fine milling circuit performed well. They reduced a feed F80 sizing of 46 microns to a product P80 sizing of 7.5 microns at a gross energy consumption of 37.2 kWh/t. Scale-up of ultra-fine milling Detritors was studied using a 0.55 kW laboratory batch unit and a 355 kW full-scale Detritor by processing Century zinc concentrate with 1 mm sand media. The results indicated that the 0.55 kW laboratory mill underestimated the energy consumption of the full-scale Detritor by about 20 per cent for a product P80 of seven microns. The performances of a horizontal IsaMill and a vertical Detritor were compared as ultra-fine milling devices for processing Century zinc concentrate. The experimental data demonstrated that, when using the same grinding media, the energy efficiency of the two mills is similar despite the difference in mill designs. The Detritors used for regrind duty at the Century Mine performed poorly when processing feed at 80 per cent passing 88 micron. The energy consumption was high and the product size distribution was broad with particles above 100 microns in the feed unbroken and particles below ten microns overground. A coarser ceramic media of 3 mm was therefore tested in a laboratory Detritor to process the regrind Detritor feed as an alternative to the 1 mm Colorado sand used at the Century Mine. The ceramic media reduced the energy consumption significantly and produced a narrower product size distribution, which is more desirable for the downstream flotation process.

Jan 1, 2007

By J. M. Jimenez, G. D. Schena, A. J. Cazorla

A full-scale Deister column was operated in parallel with the conventional cleaning bank of cells and a pilot Jameson cell in parallel with the conventional rougher cells. Flotation column performance was appreciably enhanced by use of an improved washing system and an internal launder. The performance of the rougher bank of cells, Jameson cells, cleaner cell bank and column were described by simple linear functions. These allowed calculation of overall circuit recoveries and evaluation of alternative circuits. An evaluation procedure based on a financial criterion is demonstrated with a simplified example, illustrating how revenues and operating margins are often of more concern than concentrate grade and recovery

Jun 18, 1905

By Charles G. Kemsley

MR. C. R. WHITTEMORE: It is interesting to note that the mining industry is making increased use of alloy steels for drilling. They will undoubtedly lead to greater footage at lesser cost. Mr. Kemsley states that, for use in hard ground, the shanks are brought to a hardness of 435 to 440 Brinell by heating them to approximately l,800°F. It seems to me that this temperature is excessively high-it is considerably above the critical point of the steel. The only effect of such a high temperature is to lessen considerably the impact resistance of the steel. The possibilities of an oil quench, followed by a tempering draw which does not lessen the hardness of the steel too much but increases its toughness, might well repay further study; also the temperature control, a factor which depends on the composition of the steel. However, service results are undoubtedly the best criterion of practice. MR. KEMSLEY: I would like to point out that the steel is not quenched at 1,800°F. After heating to this temperature, it is laid aside to cool gradually; this high temperature is necessary to produce the required hardness by simple normalizing-cooling in still air. We all know that ideal conditions for hardening steel demand salt baths and furnaces with automatic temperature control, but for most companies the cost of such equipment having sufficient output capacity is prohibitive. The end we are trying to attain is to make good drills at a cost that will be within the means of any mine.

Jan 1, 1942

By Y. Ichihara, H. Matsumoto, K. Itakura, H. Eguchi, G. Deguchi, K. Sato

Mechanical data from a rockbolt drilling machine, such as torque, thrust, revolution and stroke, are useful for understanding the geological and geomechanical conditions around roadways and hence selecting the optimum bolt type and density. Laboratory experiments showed that the level of torque or thrust reflects differences in rock type, with separation of strata and cracks appearing as a specific pattern. Algorithms of neural networks based on adaptive resonance theory and back-propagation were used to extract the pattern and estimate the location of discontinuities. For field testing in an underground coal mine, a prototype data acquisition system was attached to a portable drilling machine. Several sets of logging data from one locality were combined to construct a two-dimensional model of the strata, from which the slope angles of discontinuity faces could be estimated

Jun 19, 1905

By Y. El-Mossallamy

The piled raft foundation was extensive applied in the last two decades in different soil conditions e.g. in soft to stiff clay as well as in medium to dense sand and even in highly weathered rock. The piled raft is now applied not only to control the foundation settlement but also to minimize the required raft thickness to reach the most economic foundation design. An innovative application of the piled raft is its special adjustment to cases of foundations with large load eccentricities or very different loaded parts of buildings to avoid the need of settlement joints, which are especially complex below ground water table. Recently, the piled raft is applied for foundations of highway and railway bridges with special serviceability requirements regarding the allowable total and differential settlement as well as tilting. Actually numerical analyses are the mostly used design methods for piled rafts. For all day design practice a simple and modest design method is highly needed -at least in the first design stage- to check the feasibility of the piled raft on the specific project conditions. In this paper, a general overview on the recent innovative applications of piled rafts in Germany will be presented in a short overview. The results of the simple design method will be discussed and compared with the results of more enhanced numerical methods.

Jan 1, 2006

By Shirley F. Colby

The past 40 years have seen the sand and gravel industry grow from small roadside pits and holes in farmers' back yards to giant corporations selling millions of tons of sand and gravel each year and owning plants representing huge capital investments in land and equipment. The days hen a man could "work out" his taxes by providing the materials for nearby roads are gone forever. In addition to the hundreds of privately owned and operated plants, Government agencies operate sand and gravel pits and plants to supply aggregates for the tremendous road-building and public-works programs in progress during the past few years. EXPANDING PRODUCTION In 1940 the send and gravel industry produced almost a quarter of a billion short tons valued at more than 110 million dollars. This compares with less than 2 million short tons worth 1 1/2 million dollars produced in 1902. The practice of screening sand and throwing away the gravel in the early days of the industry's growth has stopped, and in 1940 gravel constituted two-thirds of the total production. In 1906, the first year in which sand and gravel were reported separately gravel accounted for only one-

Jan 1, 1942

By Fernando Antônio Corrêa

O processo de soldagem híbrido LASER- GMAW, comumente designado por HLAW (Hybrid Laser Arc Welding), foi concebido há bastante tempo, mas só recentemente começou a ser aplicado industrialmente. Nesse trabalho foi feita uma avaliação do seu desempenho na soldagem de chapas de aço C-Mn com 10mm de espessura. As juntas produzidas foram avaliadas por meio de ensaios de impacto Charpy-V e mapeamento de microdureza Vickers, além da caracterização microestrutural. Também foram realizadas, medições dos níveis das tensões residuais introduzidas na junta soldada pelo processo híbrido, comparativamente com o processo GMAW robotizado. Os resultados da avaliação de desempenho do processo híbrido mostraram uma maior produtividade em relação ao GMAW robotizado. As propriedades mecânicas da junta soldada se mostraram compatíveis com os requisitos do material de base.

Oct 30, 2017

Mining is a fundamental activity on which modern society and the world's economy are entirely dependent. Mining investors, large and small, invest on an international scale, frequently being active in several countries.   Prior to committing investment to new countries, the prudent investor will consider the risk involved by analysing a number of physical, financial, administrative and political parameters that impact on the potential financial returns it is seeking. This paper considers these risk factors in relationship to New Zealand and six competitor countries. The conclusion is that for reasons largely within the control of our politicians, New Zealand is a high risk country for mining investors.

Jan 1, 1993

By Charles Janin, HENNEN JENNINGS

Many articles have been written on the general principles and details of gold dredging, a but it is not possible within the limits of this paper to recapitulate them, and it is thus necessary to assume some knowledge of this literature by the readers of this paper. Although the purpose of this paper is to describe gold dredging in Montana, a brief mention of some early appliances used in New Zealand, Australia, and California may serve as a world-connecting link in our consideration of the development of gold dredging. DREDGES EARLY USED IN NEW ZEALAND, AUSTRALIA, AND CALIFORNIA. Spoon dredges operated by hand were tried in New Zealand on rich spots in the Clutha River with some success as early as 1865. A dredge of this kind is shown in Plate I, A. In 1870 a modification of the spoon, operated by steam and being thus a primitive steamshovel dredge, was worked in New Zealand. Steam-shovel dredging was attempted in California as early as 1888 and 1893, and with some success in later years. The elevator gold dredge with endless bucket chain was put into operation in New Zealand in 1882. Plate I, B, illustrates a type of this dredge operated by current wheels. Plate II, A, shows a steam-operated dredge of this class, also started in 1882. In 1897 R. H. Postlethwaite, connected with the Risdon Iron Works, San Francisco, introduced the dredging practice of New Zealand into California. The first dredge built sank in the turbulent current of the Yuba. The second at Oroville, owned and operated by W. P. Hammon, proved effective and was the start in California of successful gold dredging. Since then the growth of the golddredging industry in California has been so rapid that the gold output from dredges in that State exceeds that of all other States in the Union, and, in fact, of any other country of the world, the value of the gold produced in California by dredging from 1897 to the end of 1914 having been about $71,000,000.

Jan 1, 1916

Humankind's interest in measurement of human physical strength probably dates to the first humans. At that time, life was truly a struggle in which the fittest survived. To a great extent, fittest meant strongest. Interestingly, current interest in human physical strength in the workplace stems from 1970-1980s vintage research demonstrating that persons with adequate physical strength are less likely to be injured on physically demanding jobs. Survival in many modem workplaces may still be a case of survival of the strongest. There is, however, a flip side to this issue - that persons with limited strength are more likely to be injured on "hard" jobs. To address this problem, we can apply what we know about physical strength to job design. "Hard" jobs can be redesigned to be within the physical strength capability of most people. Since physical strength is important to these jobs, we must find ways to quantify it through testing. This publication concerns human physical strength testing. Its purpose is not to recommend any particular type of testing, but rather to describe the types of testing available and their uses. It is up to each individual user of strength testing to decide which testing technique is most appropriate for his or her particular application. This booklet discusses four types of strength testing: isometric, isoinertial, psychophysical, and isokinetic. Human Strength Before describing the different types of strength measurement, we must define the term "strength" and explain the concept of strength measurement. Strength is defined as the capacity to produce force or torque with voluntary muscle contraction. Maximum strength is defined as the capacity to produce force or torque with a maximum voluntary muscle contraction.(1,2) These definitions include some key words that must be explained. A voluntary muscle contraction is "voluntary." When a person's physical strength is measured, only the effort the person willingly puts forth at the time is measured. Thus, when we test a person's "maximum strength," we are not measuring his or her actual maximum, but some lesser value representing what he or she is comfortable expressing at the time with the existing equipment and environmental conditions. Interestingly, when researchers startled persons being tested (e.g., by setting off a starter's pistol behind them), they have found significant increases in measured strength.(3) It has been hypothesized that the lower strength displayed during normal testing provides a margin of safety against overloading and damaging muscle tissue. The test equipment and the tested person's familiarity with the process also influence the "voluntary" strength output. The interface between the tested person and the test equipment is particularly important. A poorly designed interface induces localized tissue pressures that vary from uncomfortable to painful. In this situation, testers are measuring voluntary discomfort tolerance - not strength. It is important for strength researchers to keep the "voluntary" nature of their data in mind when they are designing their equipment and protocols.

Jan 1, 1998

By Renpei Yoda

An investigation was conducted to develop columbium alloys with e1evated-temperature strengths higher than those exhibited by more common commercial columbium alloys, and attention was given to improving the oxidation resistance and ease of fabrication. Additions of carbon, aluminum, and chromium were made to some columbium-base alloys, and their effects on workability, recrystallization, oxidation resistance, and mechanical properties at elevated temperatures were explored. The additions were made to take advantage of (1) solid solution strengthening, and (2) precipitation hardening. Three alloys displayed good high-temperature properties with relatively good oxidation resistance at 1,000° C, and tensile strengths from 26,000 to 32,200 psi at 1,400° C. When the properties of these alloys were compared with those of commercial alloys, B-66 and FS-85 (1),4 the outcome was favor-able for the alloys studied in this investigation.

Jan 1, 1967

By M. Tangstad, H. Brun, P. Calvert, A. G. Lindseth

In 1999, Eramet bought the ferromanganese plants in Porsgrunn and Sauda (Norway) and Marietta (USA). With an ownership in the Comilog mine, the plants will operate with a high amount of Comilog ore. The properties of Comilog ore are reviewed and compared to a number of industrial operations. Important ore properties are chemical and mineralogical analyses, CO reactivity and mechanical strength. The advantage of Comilog ore is its contribution to lower energy and coke consumption. However, special precautions must be taken regarding the amount of fines and water introduced in the furnace, as Comilog ore is more porous compared to other Mn ores.

Jan 1, 2004

By N. O. Gray, John Henderson

Hydrogen-reduction data for naturally occurring single crystals and Prepared polycrystals of dense hematite have been presented. Results cover the temperature range 400o to 1000oC, for particles from ten sources, ranging in size from 0.07 to 10 mm and in shape from spheres to cylinders, cubes, and thin slabs. A consistent pattern of behavior has been demonstrated for single crystals and the reduction mechanism shown to be temperature-dependent. Below 579oC reduction is a simple topochemical process but at higher temperatuves it is complex and occurs in two distinct stages. Prepared particles from these laboratories behave in a similar manner to the single crystals. Data from two investigators showing topochernical reduction of Prepared particles above 575°C are inconsistent with that for other dense hematites. It is concluded that topochenzical reaction should not be used as a model for generalized rate expressions for dense hematites. SINCE 1958, McKewan1-6 has brought to prominence a simple concept of dense hematite reduction. This model is that oxygen is lost from a hematite particle undergoing reduction only from an oxide-iron interface that recedes in such a way that the oxide remaining retains the original shape of the particle, i.e., reduction occurs topochemically. An adjunct to this concept is that any intermediate oxides in the transition from hematite to iron only form thin layers so that oxygen cannot be lost from the particle without movement of the oxide-iron interface. Further, the rate of oxygen loss from the particle is said to be proportional to the area of the receding interface so that the iron layer grows linearly with time and the over-all reduction process can be described by the equation where ro and do are the initial particle radius and density, respectively, R is the fraction of the original oxygen lost, i.e., the fractional reduction, at time t, and K is the rate constant. The idea of an underlying simplicity in hematite reduction is attractive because it gives a tractable basis from which general theories of hematite reduction can be developed and it has received wide support,7-14 based mainly on the large amount of data13 that can be fitted to Eq. [I]. However, despite the fact that this equation has been derived for dense materials, the bulk of the data that have been used to test it13 have been for materials of only about 90 pct of theoretical density (5.26 g cm-3) or less, so that its generality for dense hematites has not been demonstrated. In any case, as will be seen, adherence of reduction data to Eq. [1] does not necessarily imply that reaction occurs topochemically. In this work only data for hematites approaching theoretical density are considered and it will be shown that in only one study besides McKewan's is topochemical behavior observed over the whole range of temperature investigated. For the majority of materials a linear rate of interface advance is observed to complete reduction only when wustite is not a stable intermediate phase in the transition of hematite to iron, i.e., at temperatures below about 575°C. Above this temperature, reduction is an exceedingly complex series of reactions that takes place in two distinct stages and it is only in the first stage that reaction in any way resembles a topochemical process. This means then that, far from representing general behavior as has commonly been supposed, topochemical reaction for dense hematites is only a particular behavior that may be observed under some circumstances. EXPERIMENTAL Hydrogen-reduction data have been collected and cross-checked in these laboratories by three techniques, weight loss, collection of water evolved in the reduction reactions, and direct metallographic examination. Details of these techniques are discussed elsewhere," where it is shown that results obtained by the three methods are in close agreement. The weight-loss method, by which most of the results were obtained, consisted of hanging the sample in a platinum mesh basket from an Ainsworth Model AV-AU-1 vacuum recording balance inside a vertical l 1/4-in.-ID alumina tube furnace. Dry deoxidized hydrogen was flowed downwards through the tube at 2 to 4 liters min-1 (stp). Single crystals from two sources and artificial oxides from three sources have been examined. The single crystals were from hematite deposits at Yampi Sound, Western Australia, and Brazil, the latter being obtained from Gregory, Bottley and Co., London, U.K. The "Yampi Blue" crystals were hand-picked from washed, magnetically concentrated, sized fractions, -200 mesh BSS (mean diameter ca 0.07 mm) and —36 + 44 mesh BSS (mean diameter ca 0.4 mm) while 10-mm cubes were cut from the Brazilian crystals with a diamond saw. The starting materials for the prepared particles were hematites designated, respectively, "Specpure Iron Oxide", Laboratory No. S639 from Johnson Matthey & Co. Ltd., London, U.K., "Calcined Ferric Oxide" from B.D.H. Laboratory Chemicals Division, Poole, U.K., and "Pigment Grade Oxide", EPR-50, from C. K. Williams & Co., Easton, Pa., U.S.A. Approximately spherical particles were prepared from the artificial oxides by rolling the material, moistened if necessary, in a glass jar, and cylindrical compacts approximately 10 mm in diam and of approximately equal height were pressed in a steel die at 200 psi. These spheres and cylinders were subsequently fired in oxygen for 20 to 100 hr at 1370°C. The

Jan 1, 1967

By J. F. Neill, O&apos

The manganiferous schists occurring in the vicinity of Kings Mountain, North and South Carolina, suggest significant tonnages of potential submarginal ores. Although some reconnaissance work in connection with these deposits has been reported, no recent information has been published. Evaluation of the schists as a possible domestic manganese resource has not always adequately considered the fact that the manganese content occurs quantitatively both as oxide and as the silicate, spessartite. The Bureau of Mines investigation herein reported includes preliminary studies to indicate the extent of manganese oxide mineralization and to deter-mine the amenability of the material to sulfur dioxide leaching. The field reconnaissance studies suggest a resource containing in one area an average of 6.4 percent manganese as oxide. The procurement of depth information was beyond the scope of the investigation.

Jan 1, 1962

By Maryam Sadeghi, Jonathan Roy, Claude Bazin

"The operation of mineral processing equipments is intimately related to the mineral composition of the ore. However unit performances are usually characterized in terms of metal contents or recoveries as this data is easier to obtain than the mineral contents. This paper describes a method that combines the operations of material balancing and estimation of the mineral contents of the ore. The estimated mineral contents can be used for process analysis and diagnosis of operating problems.IntroductionThe ore that is feeding a concentrator is made of minerals that condition the energy requirements for the ore comminution and the performances of the subsequent separation circuit. Indeed a change in the mineral composition of the ore may lead to lower grinding mill throughput as well as lower recovery or grade of the economical products. Despite this relationship is recognized the mineral composition of the ore is seldom measured or estimated to provide regular information for the diagnosis of operating problems. Some methods such as the QEM-SCAN (Whiten, 2008; Lamberg and Vianna, 2006) are available to measure the concentration of the minerals in ore samples but the method is time demanding and plant operators usually base their evaluation of the plant performances on chemical assays of metals or elements since this data is easier to obtain from ore samples.Usually samples of the streams of mineral processing plants are collected on a daily basis to be assayed for strategic elements. The obtained concentrations are balanced to produce coherent data with the material conservation constraint and then used to characterize the day to day operation of the plant in terms of recovery of valuable metals and grades of the marketable concentrates. The behavior of contaminant elements can also be monitored from this data allowing the operators to explain for instance a lower zinc concentrate grade by a more important contamination of iron. However such diagnosis is only partial as the contaminant element can be transported by different minerals. Indeed the iron contamination of a zinc sulfide concentrate may be caused by an inadequate depression of pyrite or due to another iron carrying mineral. A possible way to answer the question is to determine the concentrations of the various minerals in the ore and produced sealable concentrates. Since measuring the mineral contents of the ore could be a demanding task one should consider to estimate this data from the daily chemical assays of the sample collected on the main streams of the circuit. Some authors have already investigated the problem. Whiten(2008) described a method to estimate the mineral contents of an ore sample. Lamberg and Vianna(2006) proposed a method to do a sequential mineral reconstruction followed by a material balance. Few of these methods account for the mass conservation of the reconstructed mineral contents."

Jan 1, 2016

By J. H. East

"INTRODUCTION Diesel locomotives have been used successfully in underground mines of Europe for 18 years, and much has been written on the technical details of the design of these machines and the safeguards provided by the manufacturers. The actual conditions under which' the Diesel locomotives are used have not been publicized as well and consequently are not well-known. In 1945 the writer observed numerous Diesel locomotives working underground in coal and metal mines of several European countries and was favorably impressed with the practical approach to the safe use of this- type of equipment.Recent statistics showing the number of Diesel locomotives in use are not available now because of the World War, but the extent to which this type of mine locomotive was used immediately before the war is indicated by table 1, which classifies the number of locomotives used in several countries according to the type of power, such as compressed air, Diesel, and electric.Mining conditions observed by the writer in the European countries are very different from those in most coal-mining districts of the United States. The surface plants are larger and are permanently constructed of brick or concrete; numerous coal beds are worked through one shaft; the crosscut rock tunnels or levels, driven to intersect the coal beds, are lined with brick or concrete blocks where needed instead of timber; the coal beds dip more steeply and are not as thick as in most fields of the United States."

Sep 1, 1946

By E. C. Foster

The project objective of this contract is to design, develop, and demonstrate a dust collecting system for auger head miners, used in coal seams 40 inches or less in height, which will reduce respirable dust below the limits established by the Federal Coal Mine Health and Safety Act of 1969. This system was to be incorporated into 3 Wilcox Mark 20 continuous miner. In order to accomplish this, the objective was divided in three main areas. First: To develop a dust control system which would remove by isolation, respirable dust from the face area and areas where miners work. Second: To develop a dust scrubbing system to remove and collect float dust before the air reaches the return airway. Third: To reduce the overall noise levels to which the miners are exposed.

Jan 1, 1974

By M. L. Trépanier

"Engineering and technical services are supplied by the Engineering Department, located at Thetford Mines, Quebec, approximately 60 miles southwest of Quebec City. The department serves the three operating mines in the Thetford area, the Asbestos Hill mine at Putuniq, Nouveau Quebec, and the Nordenham plant at Nordenham, West Germany. The Engineering Department is responsible for supplying the following services. 1. Administration and coordination of capital projects. 2. Engineering, design and drafting services for in-plant changes or improvements. 3. Preparation of geological plans for mine planning and ore reserves determinations. 4. Short-, medium- and long-term mining plans. 5. Rock mechanics studies and monitoring. 6. Grade control monitoring. 7. Environmental control engineering and construction. Details of the organization and services rendered will be the basis of the paper."

Jan 1, 1976

By Luiz Augusto Ferreira de Campos Viana

O processamento de aços ARBL (Alta Resistência Baixa Liga) para fabricação de bens de capital de dimensões avantajadas pode sobrecarregar máquinas operatrizes de indústrias do setor metal-mecânico. Uma rota alternativa para processamento deste material é a conformação do mesmo a temperaturas elevadas (processamento "a morno"), para redução de seu limite de escoamento e consequente diminuição do esforço nos equipamentos. Entretanto as propriedades mecânicas destes materiais devem ser mantidas após seu retorno à temperatura ambiente. Neste trabalho um aço ARBL temperado e revenido foi submetido a 1, 3, 5, 7 e 9 ciclos térmicos, com a soma do tempo de todos os ciclos térmicos igual a 10 horas e temperatura de 580°C. Em seguida ensaios mecânicos de tração, impacto em corpos de prova Charpy-V e dureza Vickers foram executados. A caracterização microestrutural e análises fratográficas dos corpos de prova de tração e impacto foram realizadas por meio de microscópio eletrônico de varredura (MEV). A análise microestrutural revelou o coalescimento de partículas de cementita em todas as amostras. A resistência mecânica dos corpos de prova submetidos a 1, 3, 7 e 9 ciclos caiu. A energia absorvida no ensaio de impacto aumentou para estas amostras. O corpo de prova submetido a 5 ciclos térmicos apresentou endurecimento secundário. A fratografia de todos os corpos de prova ensaiados a tração revelaram fratura dúctil. O mesmo ocorreu para os corpos de prova submetidos ao ensaio de impacto, exceto para os corpos de prova submetidos a 5 ciclos térmicos. Em nenhum dos casos ocorreu descaracterização do material com quedas nos limites de resistência a valores inferiores aos especificados pelo fabricante.

Aug 16, 2017