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By Fun-Den Wang

This report presents theoretical studies and experimental work dealing with the detection of dangerous roof and pillar conditions in underground mines through measure¬ment of temperature differences on the surface of the mine opening. The theoretical work is directed at modeling the circumstances where a loose slab of rock might be detected. The experimental work provides input data for the theoretical models. At the beginning of the project, little was known by the authors of the conditions that would permit detection of a loose slab of rock or coal by measuring the surface temperature differences. The U.S. Bureau of Mines had found that there were detectable surface temperature differences on the roofs and pillars of mines. The Bureau contracted with Colorado School of Mines to measure temperature profiles around mine openings in an effort to learn if the temperature differences they had detected were directly related to loose pieces of roof and pillar rock. The Bureau was principally interested in learning if loose rock could be found in coal mines by measurement of surface temperature differences with an infrared thermometer.

Jan 1, 1972

By Frank Firmstone

When in charge of the Glen don Iron Works, the importance of good methods of filling was forcibly brought to my attention, and it occurred to me that the first step toward the discovery of the best plans was the accumulation of exact information as to the distribution actually effected by various chargers; also, that something could be done in this direction by careful measurements in the furnace, to be afterwards recorded for comparison on drawings. The figures shown herewith have been prepared from such measurements, and nearly all of them refer to Glendon, where the fuel used was anthracite and the ore-mixture about threequarters of New Jersey magnetic ores and one-quarter of brown-ores from the vicinity of the works. Every occasion furnished by the blowing-in of furnaces was utilized, but the data accumulated rather slowly in this way; and, opportunity oEering to make special trials at no great expense, the figures from 2 to 7 were thus obtained. The trials were made by dumping a hopperful (6 barrows) of material at once into the furnace, and, when all the fuel of a round (12 barrows) had been put in, the profile of the upper surface was obtained by stretching a steel tape across the top on a diameter and at a known height. By measuring down from this with a graduated rod, the profile was easily obtained with sufficient accuracy, especial pains being taken to get correctly the crests of the ridges and the bottoms of the hollows, as many intermediate points being included as seemed necessary. This was repeated on another diameter when there was occasion. The same course was followed for the limestone and ore.

Jan 1, 1899

By M. Wu, A. Kharicha, J. Bohacek, A. Ludwig

"During the horizontal spin casting of rolls, vibrations and mould deformations seems to have a significant effect on the final quality of the product. Sources for vibrations can be found in the poor roundness and a static imbalance of the chill itself. The bending of the mould axis is also considered. Both, vibrations and axis bending, are used as an input for CFD simulations of the flow dynamics of the liquid metal inside the rotating cylinder. The aim is to study the feedback of the free surface behavior in terms of wave propagation and various wave shapes. Introduction The horizontal spin casting process (HSC) is a casting process that has several advantages over the traditional gravity casting processes. Centrifugally cast products have a high degree of metallurgical purity and homogeneous microstructure. A significant gain is observed for the rupture strength, the rupture strain, and the Young modulus. These properties naturally depend on the centrifugal force and thus, the best mechanical properties can be found at the largest distance from axis of rotation. However proper selection of the angular frequency has to be done in order to prevent the so-called ""metal rain"" i.e. metal droplets can fall down from the upper part of the cylinder due to a too weak centrifugal acceleration. In the same time excessive speeds can lead to the appearance of longitudinal cracks caused by the hoop stress in the initially solidified layer. From empirical knowledge other parameters have important influence on the casting products, it includes the pouring temperature, the pouring rate, the mould coating etc. Recently the presence of natural or forced vibrations have been identified as possible additional factors to be taken into account [1-2]."

Jan 1, 2012

By P. C. Hollick

Two marine diamond deposits on concession 2b off Namaqualand along the South African Coast, have been systematically mined over the past year by the mv Moonstar. The two deposits, Smith?s Ulcer and Wedge Point Basin, are comparable in morphology, straddled the same water depths and have similar geology yet have given very different recoveries when compared to their respective grade models. These differences are best ascribed to the different style of mineralisation observed within the two deposits which has been directly controlled by the bedrock morphology. The smith?s Ulcer deposit has been formed in a metagreywacke bedrock displaying a strong north-south trending foliation which dips steeply to the west. Consequently the mineralisation is confined to narrow north-south linear trends with limited lateral extent (less than 5m) making extraction extremely difficult and somewhat variable. RE factors (recovered grade versus estimated grade) for this deposit range from 0.5 to 1.1. The Wedge Point Basin deposit is formed in a micaceous metaquartzite with a conjugate southwest northwest joint set, the southwest lineation being the more prominent, and structural foliation dipping gently to the west. The resultant style of mineralisation is confined to basinal features defined by topographical lows and is fairly lateral in extent (in order of 50m). Extraction of the mineralisation from this deposit is less arduous with recoveries more uniform, RE factors are frequently in the range 2 - 3. This style of mineralisation is more in line with what is to be expected from marine alluvial deposits, the nugget effect of diamond concentration being responsible for the high RE factor. The long narrow linear trends observed in Smith?s Ulcer demonstrably require a specialised approach in successfully sampling, modeling and ultimately mining.

Jan 1, 1998

A. 0. ASHMAN, Palmerton, Pa. (written discussion *.).-Mr. Newcomb's paper has interested me greatly, as I have had numerous experiences along this line. I do not think enough emphasis can be put on his warn-ing to keep platinum couples free from contact with quartz tubes, as silica shows a tendency to alloy with platinum to a surprising degree even at low temperatures. I have frequently had evidence of silica contamination in a perfectly good tube, in which there was seemingly no possibility of a reducing atmosphere. This is rather important as it seems to be common practice to insulate, as well as protect, the wires by means of- capillary silica tubing, thus allowing the entire wire to be in contact with the silica. The best way to mount a couple in a silica protecting tube is by means of double-bore porcelain insulating tubes, the protecting tube being slightly longer than the couple so as to leave a space between the couple and the end of the tube. In this way there is no possibility of contamination from silica. In no case should silica capillary tubes be used to insulate platinum wires. Mr. Newcomb states that there is still much to be desired in pyro-meter protecting tubes; this is in keeping with my experience. From a practical standpoint there is not a satisfactory pyrometer tube on the market for high temperatures; with all clue respect to the many improve-ments and good work recently done in this line. I believe that the whole future development of pyrometry is dependent on the development of suitable refractories. With suitable refractories, for example, Darling's1 work with liquid couples could be developed to a practical basis, making possible the use of base-metal couples to replace platinum.

Jan 12, 1919

NOW continuing with the preparation of the moulds I say that it is necessary to give the greatest attention to the differences of the clays as well as to the differences of those things that you wish to mould; and to know that every concavity in the mould produces a convexity and every convexity a hollow following the shape of the original pattern that you have. The pattern should be a body of a harder mated than the thing [78] you wish to mould with and of a substance that is not swollen or disintegrated by moisture. Its archetype may be of marble, bronze, lead, or any other metal, or also of wood, wax, tallow, gypsum, sulphur, or other plaster compositions-in short, of whatever you may have or whatever succeeds best for you, depending on whether the works are large or small and easy or &cult to mould. If you wish to cast them in bronze, you must mould them with loam, covering them with it and then drying it. There are some things in which it is enough to form only one part, such as half- or bas-reliefs. These are easy if they have no undercuts. Some other patterns that are easily handled are formed in two halves, or in three or four pieces, if they are of a hard material. There are also moulds for large statues, which, if one desires to make them of bronze, are first made of wax according to the ordinary procedure. I have in mind to describe every one of these processes in their own place. There are like- wise some moulds that are difficult to make, like scenes on a plane to which figures in full relief are attached, or twisted ornaments or other detached things that cannot be withdrawn from the mould without break-

Jan 1, 1942

By Paul Delottinville, Maynard Hall, Henry Hillier

"An expert system application for supervisory control and optimization of the indurating process at the Iron Ore Company of Canada (IOCC) has been developed and installed in closed-loop. Prior to the installation of the expert system, the indurating machine was rebuilt and the instrumentation revamped. A Foxboro I/A Distributed Control System (DCS) was installed for regulatory control, and a new control strategy configured. The modernization of the regulatory control has resulted in significant improvement in both production rate and product quality. Expert system control was implemented in September 1996. Preliminary indications are that the expert system has further improved the consistency of product quality, enhanced fuel efficiency and increased productivity. The expert system considers both wet and dry sections of the circuit, and its optimization scheme is driven by pellet tumble index and compression strength. Statistical Process Control (SPC) rules were implemented in the expert system as part of the quality analysis and control scheme. The expert system application was developed and delivered using the Comdale Expert Optimizer (CEO), and has been in continuous closed-loop control since its installation. The system development and implementation is described, and preliminary benefits are presented..... IntroductionIn early 1996 the Iron Ore Company of Canada (IOCC) contracted Comdale Technologies of Toronto to develop and implement a real-time expert system for optimizing the indurating pelletizing furnace at our plant location in Labrador City, Newfoundland.The decision to install the expert system has been timely. Like many other resource-based industries in increasingly competitive markets, IOCC recognizes the need to find ways to improve the efficiency of our production process and ensure that product quality is maintained at the highest levels. With the Labrador City plant producing 11 million tons of iron ore pellets annually, implementing the best technology solutions to meet these objectives is critical."

Jan 1, 1998

ANDES, lying south of Chuquicamata and north of Braden on the western slope of Chile's cordillera, can best be described as a big well-managed copper-mining enterprise without any peculiarly outstanding features. In point of copper produced, since output started in 1927, it ranks fifth among the Porphyries, being exceeded only by its two Chilean contemporaries and by Utah Copper and Morenci in the United States. Even so, there is little to distinguish it from other properties. It does not have the phenomenally rich ore (better than 2 per cent copper) that characterizes Braden; and it is not in the same class as Chuquicamata whose ore has the excellent tenor of around 1.7 per cent, nor has it Chuqui's immense tonnage of proven ore reserves and potential ore resources. One might say the operations are standard in that there are no basic or radical departures from established practice. A letter from New York supplying me with sundry pertinent facts for which I had asked, makes this comment regarding the answer to one inquiry: "omitted because it is the ordinary equipment found in any well-run mine." The substance of that remark applies generally to the other operations, plants, and facilities. One interesting fact that helps explain this situation should not be overlooked. Until the "new" Morenci in 1942, Andes was the last of the Porphyry copper mines to come into production. It did not do much pioneering because other companies had, of necessity, charted the way in many particulars. The company was organized by the Anaconda Copper interests in 1916 to take over a, group of claims held under option by William Braden who, a few years earlier, had interested

Jan 1, 1957

By M. A. Mallinger

A series of laboratory tests was conducted to determine the limits of practicability in regulating the weights of various cement slurries. It was found that slurry weights of 12 to 19 lb per gallon could be obtained by adding bentonite to decrease the weight and barytes ore to increase the weight. It was also found that barytes ore was not usable in all cements. LIGHTWEIGHT CEMENT SLURRIES INTRODUCTION During the drilling and completion of oil wells the magnitude of the hydraulic pressures exerted on certain formations is critical. In many cases considerable care must be exercised to prevent drilling mud weights from becoming too high, and in those wells where loss of circulation is a problem, the use of normal weight cement slurries will generally result in lost returns during casing cementing operations. While mud weights can easily be controlled, it is necessary to exercise care in the selection of weight reducing additives for cement slurries in order that slurry weights may be reduced sufficiently to prevent the loss of a large portion of the cement to the thief formations without seriously affecting the setting properties of the cement. EXPERIMENTAL RESULTS An extensive search revealed that a large number of materials .that might have been otherwise practicable as a weight reducing additive were not acceptable for use with oil we cements because the imposition of pressure on the slurries caused the additive being tested to be compressed or to absorb water from the slurries, resulting in negligible decrease in the slurry weight. This search for lightweight additives disclosed that bentonite, a material very commonly used for reducing the weight of drilling muds and cements, produced the best results without undue harmful effects on the properties of oil well cements. It was found that there was a limit to the amount of benton-

Jan 1, 1950

W. ROWLAND Cox,* New York, N. Y. (written discussion?).-The process described by Mr. Malcolmson undoubtedly represents a great stride toward conservation of our natural resources. Without discussing the subject from an economic standpoint, I wish further to emphasize the fundamental principles of the Smith process in order that its economic value may be fully appreciated. The process is essentially a means of producing an ideal fuel, as regards its combustion qualities, by the removal of the so-called volatile matter from the coal, in the form of byproducts, which have value for other purposes far in excess of their fuel value. In other words, coals which contain. large amounts of gas, tar, and ammonia, and are not suitable for domestic or industrial fuel, or for treatment in byproduct coke ovens or gas retorts; because they possess poor coking qualities, can he prepared for commercial use by the. Smith process with a very high degree of efficiency. Much work has been done along this line, both in this country and in Europe, in developing a means of preparing coal, as the economic advantages have long been recognized. To the best of my knowledge, the Smith process is the only one that has proved its commercial adaptability. Distillation of coal at 900° to 1000° F. (480° to 540° C.) yields a large amount of tar and oils. The residue of the distillation, however, is a very friable semi-coke, wholly unsuitable for use as a fuel, unless it can be charged directly into a byproduct gas producer. The problem which confronted the inventor was then to convert this carbon residue into a commercial product, and it is in this step that the Smith process has overcome the obstacles which prevented a number of other methods from becoming commercially practicable.

Jan 10, 1918

THE millng methods employed in the Mount Lyell Mining and Railway Company's mines are, perhaps, less known to the milling world than those of other important districts, due to the geographical remoteness and isolation of the Mount Lyell field,but they present many features which are unusual, and should be of interest to the mining engineer. Typical mining is carried out on an open-stope system, details of which are the result of local experience and evolution, and of which the outstanding feature is that the ground is so worked as to be largely self-supporting by virtue of domical form given to the stope roofs. It is locally termed "rill" stoping,' but differs widely from what is generally understood by that designation, chiefly in that the "rill" or slope is developed in every direction from a central focus, and not merely in directions followllig the strike of a lode or ore-body whose longitudinal dimensions are very much greater than its width. Such terms as "donie stoping" or "arched-back stoping" would be more appropriate and descriptive.The company's active operations' at the present time extend to the Mount Lyell and North Lyell mines, and, though the fundamental principles of stoping methods are the same in each, the dissimilarity of the ore-bodies, both in nature and mode ofoccurrence, necessitates considerable variation as to details to meet the respective conditions. The Mount Lyell pyritic body lends itself to the adoption of the .system in its simplest and almost ideal form, and a description of stoping in this mine willserve best to illustrate it, while later reference to details of practice in the North Lyell mine will indicate how it may be varied to meet more difficult circumstances.

Jan 1, 1915

By Sylvain Castonguay, Sylvain Pilon

"Operator competency is an important factor in the safe and successful operation of today’s complex processes. Competent process unit operators deliver superior performance and results. In greenfield projects, operator competency is particularly critical, as the lack of specific operations experience must be offset with proven practical knowledge and skills to avoid mistakes that can cost millions in terms of start-up delays, production losses and equipment damage. It is, therefore, important to know precisely what competencies are required for a project or site, and what any gaps in operator competency need to be addressed and improved. The success of plant commissioning, start-up and sustainable operations is directly tied to operator competency. The significant investments required for new projects, the exploitation of more challenging ore bodies, and the increasing complexity of plant operations have placed renewed emphasis on the need for competent operators. Furthermore, many large capital projects are being developed in remote regions, often with ties to the delivery of social benefits for the local population in terms of jobs, training and other development opportunities. While automation and processing technologies have helped do more with less, indicators now point to a bottleneck in human performance limiting operational results.Automation industry development in managing abnormal situations, including solutions for simulation and operator training, has produced applications to provide customized and flexible training methods. This paper will discuss tools to automate the operator competency process in order to guide trainers to effectively teach, measure, control, provide feedback, and monitor operator skills. Today’s competency management solutions can be effectively applied throughout the course of an operator’s professional life, as a guide to hiring new operators, for developing competencies to support operations, and also to develop and refine best practices and share lessons learned."

Jan 1, 2016

By J. R. Long, E. T. Hayes, R. S. Dean, F. S. Wartman

THE production of titanium in 15-1b. lots and with a purity sufficient to be consolidated into ductile metal, as described in a previous paper,1 has provided adequate material for a study of the : physical properties of titanium and a more thorough examination of its working qualities. Data on the physical properties reported in that paper were obtained on metal fabricated by a fixed procedure, standardized for the purpose of control of the reduction, and are representative only of material fabricated under those conditions. There are many possible variables in the working schedule, which will have significant effects on the properties of the finished material; and since the previous working methods were not necessarily the best, an investigation of the fabrication of titanium by other methods was undertaken. In this work the consolidation of the powder by pressing and sintering was conducted essentially as outlined in the report cited' and all efforts were centered on fabrication methods for those powders and the properties produced by them. Hardness, density, microstructure, and tensile properties were determined at various stages in the working and annealing; and resistivity measurements were made on a few bars and drawn wire. [ ] CONSOLIDATION OF THE POWDER The screen analysis of the available titanium powder is given in Table I. No attempt was made to alter the size distribution from that noted because this powder, although coarse by normal powder-metallurgy standards, produced acceptable compacts suitable for the present work. Because of their large specific surface, finer powders are more contaminated by oxygen and produce harder compacts, which are difficult to work. The powder as produced is soft, compresses in a normal fashion, and exhibits very little tendency to adhere to the die surfaces. Unlike aluminum and magnesium powders, it can be readily pressed without the use of die lubricants. When compacted at so tons per

Jan 1, 1946

By G. A. Kosick, M. Freberg, L. A. Kuehn

"Highly variable and higher than forecast lead miff feed grades were problems experienced at the Polaris Concentrator. Limited flotation capacity and poor operating flexibility prevented the plant operators from overcoming these difficulties, and resulted in grades and recoveries which were lower than necessary.Two column cells were integrated into the lead circuit in an effort to give the operators the tools they required to achieve the best grades and recoveries possible, regardless of the miff feed grade. Installation of the column cells increased lead concentrate grade from 76% to 79.3% Pb, and increased lead recovery from 9/% to 91.3% Pb.This paper reviews the design, development and operation of column flotation cells in the lead circuit at the Polaris Mine.IntroductionThe Polaris Concentrator was constructed in 1980 on a barge in Trois Rivieres, Quebec, and towed to its pre sent location on Little Cornwallis Island, Northwest Territories, about 1450 km from the North Pole. The plant presently treat s about 2800 mtpd of new feed with average feed grades of 3010 Pb, 13% Zn and 5% Fe. Current production averages 36 000 tonnes of lead concentrate and 220 000 tonnes of zinc concentrate annually.The barge design and min e location dictated that the concentrator .be compact with very little unused floor space. As a result, flexibility was limited in terms of expanding the plant.Mill feed grades were highly variable and above forecast and the lead flotation circuit was found to be under capacity. This caused continued overloads in the lead cleaning circuit, resulting in low concentrate grades and recoveries. It was evident that an increase in lead flotation capacity and flexibility was necessary. The existing floor space did not allow for the installation of additional conventional flotation cells, but one alternative was the installation of column cells."

Jan 1, 1988

By J. R. Long, R. S. Dean, F. S. Wartman, E. T. Hayes

The production of titanium in I5-lb. lots and with a purity sufficient to be consolidated into ductile metal, as described in a previous paper,' has provided adequate material for a study of the physical properties of titanium and a more thorough examination of its working qualities. Data on the physical properties reported in that paper were obtained on metal fabricated by a fixed procedure, standardized for the purpose of control of the reduction, and are representative only of material fabricated under those conditions. There are many possible variables in the working schedule, which will have significant effects on the properties of the finished material; and since the previous working methods were not necessarily the best, an investigation of the fabrication of titanium by other methods was undertaken. In this work the consolidation of the powder by pressing and sintering was conducted essentially as outlined in the report cited' and all efforts were centered on fabrication methods for those powders and the proper- ties produced by them. Hardness, density, microstructure, and tensile properties were determined at various stages in the working and annealing; and resistivity measurements were made on a few bars and drawn wire. Consolidation of the PowdeR The screen analysis of the available titanium powder is given in Table I. No attempt was made to alter the size distribution from that noted because this powder, although coarse by normal powder-metallurgy standards, produced acceptable compacts suitable for the present work. Because of their large specific surface, finer powders are more contaminated by oxygen and produce harder compacts, which are difficult to work. The powder as produced is soft, compresses in a normal fashion, and exhibits very little tendency to adhere to the die surfaces. Unlike aluminum and magnesium powders, it can be readily pressed without the use of die lubricants. When compacted at 50 tons per

Jan 1, 1946

By J. R. Long, E. T. Hayes, R. S. Dean, F. S. Wartman

The production of titanium in I5-lb. lots and with a purity sufficient to be consolidated into ductile metal, as described in a previous paper,' has provided adequate material for a study of the physical properties of titanium and a more thorough examination of its working qualities. Data on the physical properties reported in that paper were obtained on metal fabricated by a fixed procedure, standardized for the purpose of control of the reduction, and are representative only of material fabricated under those conditions. There are many possible variables in the working schedule, which will have significant effects on the properties of the finished material; and since the previous working methods were not necessarily the best, an investigation of the fabrication of titanium by other methods was undertaken. In this work the consolidation of the powder by pressing and sintering was conducted essentially as outlined in the report cited' and all efforts were centered on fabrication methods for those powders and the proper- ties produced by them. Hardness, density, microstructure, and tensile properties were determined at various stages in the working and annealing; and resistivity measurements were made on a few bars and drawn wire. Consolidation of the PowdeR The screen analysis of the available titanium powder is given in Table I. No attempt was made to alter the size distribution from that noted because this powder, although coarse by normal powder-metallurgy standards, produced acceptable compacts suitable for the present work. Because of their large specific surface, finer powders are more contaminated by oxygen and produce harder compacts, which are difficult to work. The powder as produced is soft, compresses in a normal fashion, and exhibits very little tendency to adhere to the die surfaces. Unlike aluminum and magnesium powders, it can be readily pressed without the use of die lubricants. When compacted at 50 tons per

Jan 1, 1946

By X Yang, B Wang, L Liu

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. The Huoqiu iron ore field in north-west Anhui province is located in the south-east margin of the North China Craton and hosts large iron resources. Orebodies are hosted in Neoarchean amphibolite facies metamorphic rocks, forming silicon-iron bands from north to south. The area is dominated by an Early Precambrian basement consisting of Neoarchean grey gneisses, amphibolites and metasediments. The gneisses are similar with assemblages of Trondhjemite-Tonalite-Granodiorite in compositions and intercalated with amphibolites. Igneous zircons from gneisses and amphibolites have U-Pb ages of 2.86 and 2.75 Ga respectively, which are interpreted as the crystallisation ages of their protolith. Zircons from amphibolite and gneiss have eHf(t) values of 2.4–15.5 and -3.0–1.5 respectively. The tDM2(Hf) model ages of the gneiss range from 2.87 to 3.14 Ga, which is consistent with tDM1(Hf) ages of amphibolite (2.84–3.16 Ga). The U-Pb-Hf isotopes thus confirm that the gneisses were generated by partial melting of amphibolite. Two granites produce two group Hf isotopic compositions. The older one (1916 ± 42 Ma) has eHf(t) values and tDM1(Hf) ages of -9.4–3.4 and 2.24–2.71 Ga respectively, whereas the younger one (1823 ± 41 Ma) shows a large variation in eHf(t) values of -18.1–12.5 and tDM1(Hf) model ages of 1.73–2.92 Ga. Geological and geochemical characteristics indicate that the Huoqiu banded iron formations are a Superior-type iron formation rather than an Algoma-type as previously considered.CITATION:Yang, X, Liu, L and Wang, B, 2015. Study on the Huoqiu banded iron formation, West Anhui Province, East China , in Proceedings PACRIM 2015 Congress, pp 649–656 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By Edwin R. Phelps, Charles W. Porterfield

BACKGROUND OF SURFACE MINING Surface mining refers to the process of removing the material (over- burden) overlying a coal seam and exposing the coal so that it can be loaded out and conveyed by trucks or other methods to the preparation plant or other facility. Surface mining has not always been important in the coal industry. In the early 1900s, almost all of the coal mined in the United States was mined by underground methods. In 1900, about 192 Mt (212 million st) of bituminous coal were mined and less than 1% was mined by surface methods. The development and use of larger equipment has allowed surface mining to gain prominence throughout the years. Table 1 shows the total production of coal by mining method in the United States for ten-year periods since 1920 and indicates the growth of surface-mined coal production. Surface mining will undoubtedly continue to account for a large percentage of the coal production in the US for many years because: 1) The capacity of surface mining excavators has continued to in- crease. Today, mining companies are using shovels (see Fig. 1) which are able to move up to 137.6 m3 (180 cu yd) in each bite and draglines (see Fig. 2) which move up to 168.2 m3 (220 cu yd) in each bucketful. 2) Increasing tonnage from the thick western coal seams is being produced by surface mining methods. 3) Surface mining has normally had lower costs and a better safety record than underground mining. 4) Surface mining normally recovers a much higher percentage of the coal reserve than can be recovered by underground mining. 5) Some coal measures can best be extracted by surface mining

Jan 1, 1981

By Robert S. Archer, L. W. Kempf

It is now well known that the structure of aluminum-silicon alloys can be refined in a rather remarkable manner, with consequent improvement of physical properties, by certain treatments applied to the molten metal shortly before casting. The differences between the treated and the untreated alloys are so marked that special terms are used to distinguish them, the untreated alloys being referred to as "normal" and the treated alloys as "modified." The first practical method of accomplishing this result was that of A. Pacz,1 which consists in treating the molten metal with a salt flux of which the active ingredient is sodium fluoride. The result can also be brought about, and in a more economical manner, by the addition of small quantities of metallic sodium (or potassium) to the molten alloy shortly before casting.2 The action of the Pacz flux evidently consists essentially in the production of free sodium by the reaction of sodium fluoride with aluminum. The changing of a normal alloy to a modified alloy is referred to as "modification" and any process for accomplishing this result is a "modifying" process. Modified aluminum-silicon alloys were introduced several years ago, and it has been demonstrated both in the laboratory and in commercial practice that it is no simple matter to produce castings having the maximum or nearly the maximum properties which under favorable circumstances can be obtained. The alloys are rather sensitive to small changes in chemical composition, and the modifying process must be carried out in a very particular manner to obtain the best results. Extensive experimental work has been carried out in the laboratories of the Aluminum Co. of America with the object of determining the conditions that must be observed to make these alloys of the greatest possible value. It was necessary to learn how to control the modifying process

Jan 1, 1926

By Robert Mehl

THE purpose of this investigation was to prepare high-purity iron-carbon alloys, to determine as precisely as possible the A3(GOS), the Acm(SE), and the A1(PSK) transformation temperatures in the meta-stable iron-iron carbide system (up to 1.4 per cent C), and to study the influence of carefully controlled and constant rates of heating and cooling (1/8 to 2° C. per minute) upon the transformation temperature and upon the resulting microstructure. Apart from the general metallurgical importance attending the completion of such a task, it will be noted that highly precise transformation temperatures are of interest and importance in the thermodynamic study of this system1. Several determinations of the iron-iron carbide diagram have been made. These suffer generally from the low purity of the alloys used, and from the application of methods of investigation of low sensitivity. Attempts to compare and weight the many data available in an effort to construct as accurate a diagram as possible have, in the main, been unsuccessful. In general, the wide differences in the results of different workers, the lack of complete analytical data, the omission of important details relating to the heat-treatment of the alloys, and the meager description of the methods of investigation applied, render such a process of averaging nearly meaningless. It may be seen from the summaries by Epstein2 and Körber and Oelsen1 that variations as great as 30° C. exist in the reported data on the A3 temperatures in iron-carbon alloys. For-tunately, the A3 temperature in pure iron is now known to be 910° C. ± 1° C.3 The best recent work on iron-carbon alloys is that of Esser4 on hypoeutectoid steels and that of Sato' on both hypoeutectoid and hyper-eutectoid steels.

Jan 1, 1937