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By DULUTH ENGINEERS' CLUB

DULUTH ENGINEERS' CLUB The engineers of Duluth, Minn., have taken the first steps to form a Duluth Engineers' Club by a meeting on May 20, at the Kitchi Gammi Club. At present, Duluth has no club embracing all engineers, although the environment is splendid for the growth of an engineers' organization. Within reasonable 'distance of Duluth are over 100 members of the four large national engineering societies, a number of members of the lesser engineering societies, and many non-member engineers. Until the Duluth Association of Civil Engineers was formed, four years' ago, these engineers had no common ground of meeting, and a force representing education, experience, and high ideals lay dormant. About 70 engineers were present at the organization meeting, and favorable responses were received from others who could not be present. F. E. House, President of the Duluth & Iron Range Railroad, outlined the objects of the meeting, calling attention to the importance of the engineer in all lines of activity in the war and the splendid qualities of American engineers in France. W. H. Woodbury outlined the plan, stating the three objects of the club as professional, social, and civic. Four plans of membership have been considered: First, an organization for all professional engineers, junior engineers, and associates, with .different status for each; second, an organization of members of the four big national societies; third, an organization of members and a limited number of associates; fourth, professional engineers, only, all on equal standing.

Jan 8, 1918

By G. R. Speich

RECENT studies by Smith and Olney,1,2 Olney,3 Greifer and Salli,4 Rys etal., and Olney and smith 6 have established that graphite is the first decomposition product to format the surface of hypereutectoid plain-carbon steels when they are austenitized in a vacuum or inert atmosphere and slowly cooled. This graphite evidently forms directly from the austenite and only at the surface of the specimen. The interior of the specimen is found to be free of graphite. The graphite layer can almost completely cover the specimen surface and the rate of its formation is markedly sensitive to the orientation of the austenite. The present work was undertaken to study this phenomenon further, especially with regard to the effect of temperature and austenite orientation. The material studied in this work was a high-purity iron-carbon alloy containing 0.88 pct C, 0.005 pct Mn, 0.016 pct Si, 0.005 pct S, and 0.002 pct P. Specimens were heat-treated in a commercial hot stage modified for rapid quenching.7 This permitted direct observation of the formation of the surface graphite. A vacuum of 10"" to 10-5 mm of Hg prevented oxidation or decarburization of the specimens. Specimens were austenitized for 30 min at 1100°C and quenched to a series of lower temperatures where they were isothermally transformed. Surface graphite was observed to form at 700°, 750°, and 780°C but not at 825°, 900° or 1000°C. Since the maximum solubility of austenite for graphite is 0.88 pct C at 800°C,8 surface graphite only forms at tem-

Jan 1, 1962

By F. Keeler, C. M. Craighead

Aluminum alloys containing magnesium and silicon are susceptible to strengthening and hardening by suitable heat-treatments, and they constitute a class of alloys of considerable commercial importance. Generally, they contain these two elements in the proportions required for the formation of the intermetallic compound Mg2Si, or an excess of silicon; no commercial wrought alloys are made with an appreciable excess of magnesium. The reason for not having excess magnesium is obvious from the results given in this paper, since it is shown that excess magnesium results in a proportional decrease in the solubility of Mg2Si. This is the eighteenthl of a series of papers from the Aluminum Research Laboratories dealing with the equilibrium relations in aluminum-alloy systems; most of the previous publications concerned binary aluminum-alloy systems; this is the fourth of a group pertaining to ternary aluminum-alloy systems. The work on this system was completed in 1930, but the results were not published because of the pressure of other work. Hanson and Gaylor2, in 1921, presented the results of an extensive investigation of the aluminum-magnesium-silicon system. Their results indicated that an excess of magnesium over the amount required to form the compound MgzSi caused a noticeable decrease in the solid solubility of MgzSi in aluminum. A more recent investigation3 in these laboratories showed that the solid solubility of MgzSi in aluminum was 1.85 per cent at 595' C. and decreased to 0.30 per cent at 300' C. The results of the latter investigation were used as the basis for the present work. The Present Investigation In the present investigation, a study was made of the effect of various amounts of excess magnesium upon the solid solubility of MgzSi in

Jan 1, 1936

By Allen Rogers

IT IS universal practice for corporations, at the end of the fiscal period, to call in a firm of chartered accountants to audit the books. The effect of this is to put an independent organization's seal of approval on the accounting of the business done by the management. Their report lets the stockholders know that the accounts rendered truly present the results of the year's business. This is as it should be; the average stockholder has no personal contact or even acquaintance with the managers of his enterprise and the approval of their stewardship by an indepen-dent agent is very desirable for maintaining confidence in their honesty and ability. But such an examination deals only with what may be called the arithmetic of the business; even the most elaborate audit, as the practice is at present, goes no further than to verify the items of the inventory. In other words, while checking up the entries showing the transaction's of the year and certifying to the correct-ness of the items of the balance sheet, such a report gives the stockholder no idea of the ability with which his affairs have been managed. If the profit and loss balance is satisfactory, as certified by the public accountants, he assumes that the management has been able; where it is not, he turns to the president's report and usually finds an explanation. Such an explanation never takes the form of admission of mis-takes in business judgment or of bad technical manage-ment. It could hardly be expected that it would. The stockholder is generally furnished, therefore, with a certificate of the honesty of his management, but never one of its ability. He does not worry about the latter as long as dividends come in; when they cease, his action generally finds expression in replacing the management. In other words, so long as profits are realized, he assumes the management to be good, even though its success is a matter beyond its control and better management would make larger profits. When there is no profit, the stockholders have no means of knowing whether it is due to conditions beyond the control of the management, as the annual report is sure to allege, or whether, by better management, profit is possible. Here is where the technical audit comes in.

Jan 6, 1922

By Oscar Lee

RESERVE Mining Co., owned jointly, by Armco Steel Corp. and Republic Steel Corp., controls 9% miles of magnetic taconite ore on the eastern end of the Mesabi Range lying between Mesaba and Birch Lake. The ore reserve which can be mined by open pit methods is conservatively estimated at 1.5 billion tons under a shallow, loose overburden requiring no rock stripping. Taconite now being mined is in the upper cherty horizon. It has been metamorphosed by the intrusion of gabbro and most of the iron oxide is altered to magnetite. The nonmagnetic portion of the iron is practically all in the form of silicate. The magnetic iron is finely disseminated through the rock and requires grinding -150 mesh for clean liberation of the iron oxide from the gangue.

Jan 5, 1954

By Robert H. Carpenter

Major trends in exploration geochemistry during the past year included an increased level of geochemical exploration by both government and private industry: greater sophistication in sampling, analytical and interpretive techniques: and increased activity on the part of universities and state geological surveys. The evolution of applied geochemistry in North America from a useful prospecting tool to an invaluable exploration method is largely due to efforts of the mining industry, the USGS and the Geological Survey of Canada. In the U.S., there has been a distinct reluctance on the part of universities to conduct research or to offer courses dealing principally with applied geochemistry. Most university geochemists have not been responsive to industry needs because government sponsorship of geochemical research in universities has been overwhelmingly in favor of theoretical, rather than applied research: and, because of the mistaken notion that exploration geochemistry is not sufficiently academic. A critical shortage of specialists in this field has resulted. Specialists in Exploration Geochemistry Needed Based on the response to a brief questionnaire sent to universities in the U.S. and Canada, there is some evidence suggesting a reversal in this trend. Graduate courses devoted to exploration geochemistry are currently being offered in geology departments at the following universities: University of British Columbia, Colorado School of Mines, University of Idaho, McGill University, University of New Mexico, Pennsylvania State University and the University of Utah. Other departments report that applied geochemistry is included in general geochemistry courses. A survey of recent publications suggests increased research interest in exploration geochemistry by university geologists.

Jan 1, 1970

By G. H. Ruggles

POPULAR opinion, as it might be termed, has always been of the trend that a flotation reagent added to the ball mill during grinding would be more thoroughly mixed with the pulp and for that reason more effective in the production of low tailing. That there are other effects, inimical to good flotation, when using so-called chemical reagents, is brought out by the series of tests outlined in Table 2. It was defi-nitely proved that if either the T. T. mixture (20 per cent thiocarbanalid-80 per cent orthotoluidin) or po-tassium xanthate were added to the ball mill the result-ing flotation concentrate would be lower in copper and higher in insoluble than the concentrate produced by adding these same reagents without the ball mill cir-cuit. With the T. T. mixture four sets of tests were made. The screen analyses of the flotation feed show that there was very little difference in the original grind-ing. When the T. T. mixture was added to the head of the flotation machine the flotation concentrate had a little over 61 per cent solids -200 mesh. If the mix-ture was put into the ball mill the flotation concentrate had but 40.7 per cent of the solids -200 mesh for one set of tests, and 49.0 per cent for the other set. With the mixture at the head of flotation the total concen-trate was high in copper (34.715 and 36.525 per cent) and low in insoluble (13.20 and 11.61 per cent). The assay of the concentrate when the T. T. mixture was introduced into the ball mill was what might be termed low in copper (29.389 and 30.833 per cent). In one of these 'sets of tests (periods 8 to 11, third column) the insoluble was high, 16.81 per cent. The other run (peri-ods 12 to 15, fourth column) for some unknown reason shows a low insoluble, 12.72 per cent. With similar grinding the addition of potassium xan-thate to flotation produced a concentrate having 62.8 per cent -200 mesh, whereas with the potassium xanthate added to the ball mill the flotation concentrate was very coarse, only 36.4 per cent passing 200 mesh. The difference in the total assay of the concentrate is remarkable ; 35.847 per cent copper when the xanthate went to flotation and 30.44 per cent copper when the xanthate was added to the ball mill; insoluble, 10.94 per cent in the former instance, as 22.15 per cent in the latter.

Jan 8, 1927

By D. A. Dahlstrom

THE necessity for slime elimination from valuable mineral and coal products has become increasingly significant within the past 5 years.1,2 Most of the mechanized mining and present beneficiation methods have resulted in larger tonnages of extreme fines, silts, and clay, commonly called slimes, processed by the preparation plant. Economics in turn have forced the plant operator constantly to lower the bottom size of effective beneficiation, necessitating an almost complete recovery of valuable solids regardless of particle size. When these important factors are considered, the need for an efficient slime removal method for fine solids becomes self-evident. Ordinarily slimes have been classified as ranging from 75 microns, or 200 mesh, down to colloidal dimensions of less than one micron. At the same time there is general agreement that the most troublesome slimes are primarily clays, silts and extreme fines, so that the actual top size may be placed at approximately 30 to 40 microns. This immediately restricts any desliming operation to classification, as screening or other methods would be both uneconomical and grossly inefficient at such dimensions. The liquid-solid cyclone has been recognized as one of the most efficient fine size classifiers available to the mining industry. Applications of cyclones to thickening, high efficiency solid recovery, degritting,

Jan 1, 1952

By H. B. Muller

Single stage autogenous grinding of run-of-mine ore was selected by Broken Hill South Ltd., parent Company of Cobar Mines Pty. Ltd. for the concentrator to treat 60,000 tons per four weekly period of copper and complex copper-lead-zinc sulphide ores from the C.S.A. Mine at Cobar, Australia. Ore is mined by mechanised horizontal cut-and-fill stoping and is prepared for grinding by crushing under- ground in a 60 in. x 48 in. jaw-crusher set at 5 in. closed side setting. The ore is reduced to 80% minus 76 microns in two parallel sections each of one 22 ft. dim. x 7 ft. long autogenous grinding mill, powered by a 1,250 H.P. motor, operating in closed circuit with a single stage 20 in. dim. cyclone. Broken Hill South's original concept of the concentrator required the maximum use of reliable instrumentation, centralised control, and the minimum of manning. To achieve this objective the control room, housing the process recorders, alarms, closed circuit television monitors and all the control equipment, overlooks the grinding and flotation sections, and the whole plant is serviced by a public address system. The grinding units and associated equipment are located in the open and are serviced with the aid of a mobile crane and a mobile hydraulically-operated liner lifting device.

Jan 1, 1970

By Jin Zigang

In China there are more than 30 coal fields menaced by karst-confined water. In the north and east of China there are many collieries which mine coal seams of the Carboniferous and Permian Systems, which are above the Ordovician limestone (general thickness is 500-600 meters). Ordovician limestone is full of karst fissures, contains a lot of water under high pressure (15-65 kg/cm2) near the commercial coal seams (20-80 meters), the water easily infiltrates the thin lime- stone at the point of the structure crevice, so water-irruptions from the floor are the main source of water-related disasters in these coal fields. According to the statistics there were more than 300 accidents of all kinds of water-irruptions from the floor in these fields since the beginning of their development. It is of great significance in developing coal production in the eastern part of China to solve the problem of safe mining of the seams menaced by the karst-confined water of the Ordovician limestone. The research on this subject consists of three parts: (1) investigating the geological structure and hydrogeological conditions of each mine of the mining area; (2) researching the mechanism of water-irruptions from the floor and proposing reliable methods to predict and monitor; (3) improving the mining system and proposing a mining plan with safety precautions against water-caused accidents. The chief task is to research the mechanisms involved and to discover the causes and conditions of the phenomenon. The authors have obtained some findings on this subject in the last five years, making use of the comprehensive observation and research system, which will be discussed under three headings.

Jan 1, 1984

By C. E. Meissner

THE need for a practical method of deciding upon new alloy steel analyses to widen its markets was the problem facing the Chrome Steel Works at the beginning of 1927. In addition to determining the physical properties of the alloys under consideration, it was necessary to test their value in service. Small melts of steel in a crucible, from which test specimens could be made, were insufficient to determine more than physical properties, therefore actual castings and ingots had to be made before the products could be placed in service. Furthermore, to save further experimental work, it was desirable that these heats should be made on a "pilot" basis; that is, actually duplicating regular open-hearth furnace practice. Therefore a one-ton (2000-lb.) acid open-hearth furnace was built. FURNACE DESIGN There are no special features in the design of this furnace. Standard acid open-hearth practice is followed, with the reproportioning of the dimensions necessitated by its small size; notably, a considerably increased length in proportion to width in order to get proper flame propagation. After the first heat was made it was found that the checkers were insufficient. The checker chambers were increased in size and the checker openings were made much smaller. The furnace was started late in March, 1927, and made 65 heats. Experimental work was then stopped until the data accumulated could be worked up and summarized. The run was resumed in November and the furnace is still operating, having made at this writing 60 additional heats. For the last series of runs, there was some rebuilding of both the furnace itself and the checkers. Slag pockets were added. Fig. 1 shows details of construction; Fig. 2, the, general appearance. All designing was done by the operating and engineering staff. Construction materials were those available around the plant. The reversing valve is a standard butterfly type taken from an old furnace.

Jan 1, 1928

By AIME

IRWIN W. ALCORN, present Chairman of the Petroleum Division, was born Sept. 5, 1899 at Marietta, Ohio, and moved with his family to Robinson, Ill., at the time of the early oil development there. This was in the days of the Star spudders, mud, mules, and Stanley steamers. Al graduated from Robinson High School after participation in basket ball, also attaining the captaincy of the football team of that school. He entered Missouri School of Mines and Metallurgy in 1918 and was ushered by the Army into the S.A.T.C. In 1920 he transferred to the Massachusetts Institute of Technology, later to return to receive his B.S. degree -in metallurgy at Rolla, also joining the AIME. On graduation, he worked for the Skelly Oil Co. at Cushing, Okla., shifting to the Moore Refining Co. at DeNoya, Okla., as superintendent of a small pipe-line system. After an interval of two years with the National Supply Co. in Tulsa, he joined the Independent Oil and Gas Co. of that city, and at various times was chief engineer of the Texas division, superintendent of the West Texas pipe-line system, chief engineer of pipe-line construction, and chief engineer of the refining division. Al organized the Company's production engineering department. In 1930 the Company was merged with the Phillips Petroleum Co. The depression was in and Al was out, 'as was true nine months later when the Smith Separator Co. whose chief engineer he had become, was liquidated. The next few years was spent with Oil Well Supply Co. as a subsurface pumping equipment engineer

Jan 1, 1948

By August Wendel

IT is a well-known fact to all Bessemer steel manufacturers using a blooming mill, that ingots show large cracks in the first few passes of the rolls, which, in the following ones, do not always roll up satisfactorily. This deficiency in the quality of the product is generally called " red-shortness," though, in the writer's opinion, mostly unjustly so. Different explanations for the said peculiarity are given by the leading authorities, each works selecting one element as a special scape-goat for the inferior quality of the ingot. The sulphur is generally first charged as being the principal cause of all mischief in this direction ; then, after ascertaining that sulphur is not higher than the average, and sometimes lower in the very worst heats, silicon has to bear its share of abuse. How and why silicon should affect the working qualities of the metal, the writer could never precisely learn, but is convinced that the doctrine of its pernicious influence is an established one with many. In cases where silicon failed to explain everything, resort was taken to calcium, aluminum, and some other known or unknown elements, without settling the difficulty; and lastly, when the skill of the chemist became exhausted, " practical men " came to the same conclusion, which many leading blast-furnace managers had arrived

Jan 1, 1876

By R. L. Brown, A. C. Fieldner

Committee it supports pioneering research on the development of a coal-burning gas turbine and through the Mining Development Committee it promotes research on a new type of continuous mining machine that operates without using explosives. Other organizations have contributed major publications on fundamental and applied coal research in the last two decades, including the Minerals Industries Experiment Station of Pennsylvania State College, the Illinois Geological Survey and University of Illinois, the University of West Virginia, the University of Michigan, the University of Alabama, the University of North Dakota, the Massachusetts Institute of Technology, the Koppers Company, the U. S. Bureau of Mines, and, in recent years, the Institute of Gas Technology. Engineering development work, which is included in the overall estimate of $20,000,000, is conducted largely by manufacturers of equipment, and this portion of the estimate is difficult to gage. It represents a large proportion of the estimate and probably is too small rather than too large. For example, the development of mobile coal-loading machines and continuous mining machines, outstanding in recent mining research, undoubtedly involved a high cost. Coal Mining From an economic point of view, the greatest research development in the coal industry obviously has been the growing degree of mechanization in mining. The percentage of underground-mined bituminous-coal output mechanically loaded has risen from 3 pct in 1926 to 67 pct in 1949. Coal operators and equipment , manufacturers have united in designing machinery. Loading machines of large capacity and astonishing flexibility are in common use. Shaking conveyors transport coal from producing faces to transfer points from which it may be carried long distances underground and on the surface; and in many mines rubber-tired shuttle cars carry the coal from the loader to the

Jan 1, 1952

By J. E. Forciea, R. W. Salmi

Operating and research personnel at U.S. Steel's Pilotac concentrator have evolved specifications for magnetic separators suitable for use in beneficiation of Mesabi magnetic taconite. These specifications were developed as a result of investigations into the operating and metallurgical problems at the Pilotac concentrator over a period of some ten years. This paper discusses primary magnetic separator specifications, but much of the information is also pertinent to secondary and tertiary magnetic separators. Of particular significance is the proposal of a new basis for specifying the magnetic field which includes consideration of both field strength and field gradient. Other areas of discussion include flowsheet service, operating conditions such as drum speed and pulp level, tank configuration, magnet strength including field gradient, sleeve bearing design, designation of corrosion resistant materials and other details that result in a metallurgically efficient machine that has low repair and maintenance requirements. The mechanical and metallurgical design of magnetic separators at the Pilotac plant, Minnesota Ore Operations, United States Steel Corp. has progressed from the original single-stage, belt-type machines to the present multiple-stage, drum-type units, In ten years of operation, the plant operating and research personnel, in consultation with manufacturers, have made design changes to improve mechanical, electrical and magnetic features to meet process needs as flowsheet designs developed and to incorporate new permanent magnet materials as they became available. Separator specifications were an end result of this effort. The latest specifications which were developed for the Minnesota Ore Operations' plant were not all-inclusive listings; they covered only those points indicated by plant experience. For example, magnet pole piece design and dimensions were not stated. The manufacturers were given freedom to use any design as long as the field pattern was as specified. The selection of the items to be included in the specifications was undoubtedly influenced by particular conditions at Pilotac such as composition of plant water, concentration characteristics of the ore, repair and maintenance facilities available and the research programs that had been conducted. Only the developments leading to the specifications for a primary or "cobber" magnetic separator are presented in this paper. However, the same general concepts are used to specify secondary and tertiary separators. The areas of interest discussed include flowsheet service, tank configuration, magnet design, bearings, materials of construction, and some minor mechanical details. FLOWSHEET SERVICE The primary magnetic separators in the Pilotac Concentrator flowsheet are located after the first stage of grinding as shown in Fig. 1.

Jan 1, 1965

By L. A. Bromley, R. L. McKisson

A high temperature calorimeter designed for use up to 1500°K is described and the theory of its operation presented. This calorimeter was used to measure the heats of formation of Na-Sn alloys ranging in composition from tin to Na2Sn. The values tend to support those reported by Kubaschewski and Seith. ONE method of obtaining the heat of formation of an alloy is to measure the heat of mixing of the elements at high temperature. The principal advantage of this method is that the desired quantity is measured directly, while in conventional room temperature methods the differences of the heats of solution of the elements and the alloy in a suitable solvent are measured. A method of improving the accuracy of the high temperature measurements, when the precision of the measurement is lower than that of the heat capacity values for the elements, is to add one component at room temperature to the other at the high temperature, so that part of the heat of reaction is dissipated in heating the cold component to the high temperature. Thus, only a fraction of the heat of reaction is measured, and a result of higher precision is obtained. The limitations of the high temperature technique are that volatile systems cannot be studied, and that many alloys melt at temperatures higher than those at which the calorimetric apparatus operates readily. Nevertheless, a calorimeter operating at 1500°K would be useful in investigating many of the lower melting alloy systems and the low melting mixed oxide systems. A unit designed for these applications was built and is described here. The Na-Sn system was chosen for investigation because the temperature involved, 880°K, would adequately test the operation of the calorimeter. Further, the data reported in the literature for the various alloys of sodium and tin differ markedly, and it was hoped that this investigation would help to fix the values of the heats of formation in this system. Design of Apparatus A detailed discussion of the considerations involved in the calorimeter design is given by Mc-Kisson and Bromley,' and a brief summary follows. Fig. 1 shows a sectional view of the calorimeter. The inner graphite chamber is maintained at constant temperature by means of the circulating molten tin bath in which it is submerged. The tin is contained in a graphite vat. This unit comprises a thermostat whose heat capacity is about 7000 cal per "C. The main heating element consists of a machined graphite spiral with a room temperature resistance of about 1/2 ohm. These parts are separated from the powdered carbon external insulation by the cage, a cylindrical graphite chamber. The electrical insulators and separators, the auxiliary heater spool, and the loading tube liner are made of sintered alumina. The tin vat stirrers, the sample stir-rer, the melt thermocouple well, and the power leads are made of molybdenum. The auxiliary heater is wound with molybdenum wire and serves to compensate for the heat loss up the loading tube. All of the individual components in the high temperature region of the calorimeter will withstand at least 2000°K, and the various contacting materials should easily withstand 1500°K. The external container for the insulating carbon powder is a copper shell upon which copper tubes are soldered to serve as cooling coils.

Jan 1, 1953

By Walter M. Stephen

MODERN developments in alloy steels have been so rapid and diverse that engineering practice has scarcely had time to re-appraise all items of past experience wherein conclusions became axiomatic under conditions that no longer apply. A case in point is the wet screening of abrasive ores within the fine range still looked upon as belonging exclusively to classifiers. By virtue of the development of stainless steels (18 per cent Cr, 8 per cent Ni), it is no longer true that classifiers are more economical than screens in closed circuit with large-tonnage ball or rod mills at 65 or even 100 mesh, provided a selective overgrind of the higher-gravity constituents of the ore is not desired. Wet screening of ores is a highly corrosive as well as an abrasive operation, because of the inevitably high degree of oxygenation of the water. Screen cloth of ordinary or spring-steel wire almost at once becomes pitted arid covered with a film of corrosion products, which causes rust-blinding of fine-mesh screens and offers high frictional impedance to the flow of ore particles. On the other hand, the well-known properties of stainless steel enable it to maintain a bright surface, and so to eliminate blinding either by ore particles or by corrosion products. That a large-tonnage mill grinding hard ore to 65 mesh can be operated economically in closed circuit with screens instead of classifiers has recently been demonstrated at the Copper Cliff concentrator of the International Nickel Co.; in the test to be described, a 6 ½ by 12 ½ -ft. Marcy rod mill ground from 625 to 820 tons of ore per day to approximately 65 mesh, operating in closed circuit with three 4 by 5-ft. Hum-mer screens, without any classifier. Stainless-steel cloth gave an indicated life of several months. There was no difficulty with blinding, yet dilution and spray water could be controlled so that screen undersize averaged not less than 40 per cent solids. In contrast, ordinary carbon steel was pitted and blind with rust within 40 hours.

Jan 1, 1938

By R. S. Shoemaker, D. L. Harris

Past investigations into the possibility of concentrating the low-grade iron ores of the Gogebic Range in Wisconsin have been hampered by the complex association of the constituent minerals. In part the problem arises from the fact that the iron occurs essentially as two minerals, hematite and goethite, having nearly the same chemical composition but exhibiting different physical properties. Individual grains of these minerals are usually so small that the ore must be ground to a size finer than 325 mesh if substantial liberation of the minerals is to be secured. Appraisal of beneficiation tests on this iron ore requires, therefore, some method of determining quantitatively the contents of constituent minerals in the various products of the beneficiation. Because of the chemical similarity of the two iron minerals, chemical analyses do not provide a means of differentiation. Although the minerals are different physically, they are both opaque and friable, and as the ore must be ground to a very fine size for liberation to be secured, quantitative microscopic methods of analysis are extremely difficult at best. In an effort to overcome these analytical problems, a quantitative X-ray diffraction analysis method has been developed at the University of Wisconsin for the research program on iron ore beneficiation.

Jan 5, 1955

By Jed H. Mosgrove, Paul M. Budzak

INTRODUCTION Good mine ventilation starts at the drawing board. A coal mine will either be adequately ventilated or not, depending upon how good a job was done in the planning. Poor planning will not only result in inadequate ventilation, but may also lead to low productivity. A mine foreman cannot achieve high productivity while trying to maintain 4.2 m3/s (9000 cfm) of air at his last open crosscut. PLANNING What will provide adequate ventilation? A rule of thumb in laying out a coal mine is to provide enough entries in the main entry system to keep air velocities at 2.5 m/s (500 fpm) or less; at this rate of flow, good ventilation may be expected. The intake and return air courses of a coal mine do not improve with age. Entries will deteriorate, ribs will slough, roof will fall, and clutter will accumulate. The resistance offered to air travel will continue to increase with each passing year. Providing enough airways for the present and the future cannot be emphasized too strongly. In order to better appreciate good planning and bring it into better focus, assume a hypothetical mine has the following features: entries 1.5 m (5 ft) high and 6.1 m (20 ft) wide; one intake and one return entry; the mine development is 4.8 km (3 miles) from the intake and upcast ventilation shafts; and the ventilation requirement is 141.6 m3/s (300,000 cfm) . Air travel of 4.8 km (3 miles) into a mine and the same distance back to the fan is not unusual. However, to do so with one intake and one

Jan 1, 1981

By Glenn S. Wyman

CHUQUICAMATA, located in northern Chile in the Province of Antofagasta, is on the western slope of the Andes at an elevation of 9500 ft. Because of its position on the eastern edge of the Atacama Desert, the climate is extremely arid with practically no precipitation, either rain or snow. All primary blasting in the open-pit mine at Chuquicamata is done by the churn drill, blasthole method. Since 1915, when the first tonnages of importance were removed from the open pit, there have been many changes in the blasting practice, but no clear-cut rules of method and procedure have been devised for application to the mine as a whole. One general fact stands out: both the ore and waste rock at Chuquicamata are difficult to break satisfactorily for the most efficient operation of power shovels. Numerous experiments have been made in an effort to improve the breakage and thereby increase the shovel efficiency. Holes of different diameter have been drilled, the length of toe and spacing of holes have been varied, and several types of explosives have been used. Early blasting was done by the tunnel method. The banks were high, generally 30 m, requiring the use of large charges of black powder, detonated by electric blasting caps. Large tonnages were broken at comparatively low cost, but the method left such a large proportion of oversize material for secondary blasting that satisfactory shovel operation was practically impossible. Railroad-type steam and electric shovels then in service proved unequal to the task of efficiently handling the large proportion of oversize material produced. The clean-up of high banks proved to be dangerous and expensive as large quantities of explosive were consumed in dressing these banks, and from time to time the shovels were damaged by rock slides. As early as 1923 the high benches were divided, and a standard height of 12 m was selected for the development of new benches. The recently acquired Bucyrus-Erie 550-B shovel, with its greater radius of operation compared to the Bucyrus-Erie 320-B formerly used for bench development, allowed the bench height to be increased to 16 m. Churn drill, blasthole shooting proved to be successful, and tunnel blasts were limited to certain locations where development existed or natural ground conditions made the method more attractive than the use of churn drill holes. Liquid oxygen explosive and black powder were used along with dynamite of various grades in blast-hole loading up to early 1937. Liquid oxygen and black powder were discontinued because they were more difficult to handle due to their sensitivity to fire or sparks in the extremely dry climate. At present ammonium nitrate dynamite is favored because of its superior handling qualities and its adaptability to the dry condition found in 90 pct of the mine. In wet holes, which are found only in the lowest bench of the pit and account for the remaining 10 pct of the ground to be broken, Nitramon in 8x24-in. cans, or ammonium nitrate dynamite packed in 8x24-in. paper cartridges, is being used. This latter explosive, which is protected by a special antiwetting agent that makes the cartridges resistant to water for about 24 hr, currently is considered the best available for the work and is preferred over Nitramon. Early churn drill hole shots detonated by electric blasting caps, one in each hole, gave trouble because of misfires caused by the improper balance of resistance in the electrical circuits. Primarily, it was of vital importance to effect an absolute balance of resistance in these circuits, the undertaking and completion of which invariably caused delays in the shooting schedule. Misfires resulting from the improper balance of electrical circuits, or from any other cause, were extremely hazardous, since holes had to be unloaded or fired by the insertion of another detonator. The advent of cordeau, later followed by primacord, corrected this particular difficulty and therefore reduced the possibility of missed holes. After much experimentation, the blasting practice evolved into single row, multihole shots, with the holes spaced 4.5 to 5 m center to center in a row 7.5 to 8 m back from the toe. Sucti shots were fired from either end by electric blasting caps attached to the main trunk lines of cordeau or primacord. The detonating speed of cordeau or primacord gave the practical effect of firing all holes instantaneously. Double row and multirow blasts, fired instantaneously with cordeau or primacord, proved to be unsatisfactory in the type of rock found at Chuquica-

Jan 1, 1953