Search Documents

THE National Coal Association held its annual meeting at Cleveland on Nov. 14-16, 1928, having changed the time from the spring to the autumn to avoid conflict with the great number of meetings ordinarily held in the spring. Institute members were \\yell to the fore in its activities, the president, E. C. Mahan (who was reelected for another term!, C. E. Bockus, treasurer, and the secretary, H. L. Gancly, being A. I. M. E. members, as are many of the directors. At the first session, our past president, S. A. Taylor, presented a 1;aper which is reprinted in part herewith. At the Thurs- day session W. D. Brennan presided, Walter Barllum led the discussion on membership, and Otis Mouser led the discussion on taxation. In the afternoon, J. P. Williams, Jr., led the discussion on research. Rembrandt Peale presided at the annual dinner in the evening. At the concluding session on Friday resolutions were adopted, among them one in which the Association "reaffirms its attitude toward proposed Federal legislation affecting the bituminous coal industry by saying that it opposes legislation which would seek to single out this industry for regulatory action. This particularly applies to such bills as S4490."

Jan 1, 1928

By F. C. Bond

Since the Third Theory of Comminution was presented eight years ago (I) it has found increasing use in crushing and grinding problems. The practical utility of its wok index equation is quite generally acknowledged (2). However, its theoretical basis has been questioned in at least three technical articles (3) (4) ('). The purpose of this paper is to present experimental proof that it is scientifically correct. Particles under compressive stress are strained and deformed. They absorb strain energy, and when this locally exceeds the breaking strength, a crack tip forms. The surrounding strain energy flows to the crack tip, which rapidly extends and splits the rock, releasing the strain energy as heat. The initial energy flow causes additional crack tips in highly strained areas. If the compression is rapidly applied by impact, crack tips may form before the strain energy has reached equilibrium in the particle, thus decreasing the total work input required for breakage. The energy necessary to break is essentially the energy necessary to produce crack tips, since the energy necessary to extend the cracks to breakage is already present as strain energy in the deformed particles. After breakage nearly all of this energy appears as heat. The crack length cannot be measured directly. However, in particles of regular and similar shape the crack tip length is considered as equal to the crack depth, or crack extension necessary to break, so that the crack length equals the square root of one-half of the surface area. The Third Theory states that the useful work done in crushing and grinding is directly proportional to the total length of the new cracks formed. It can be confirmed by showing that a constant work input produces a constant length of new cracks when reducing the same material to different product sizes. This is done in the present paper on a wide variety of material. The constant work input was supplied by one revolution of the 12" x 12" laboratory ball mill used in making grindability tests by the Allis-Chalmers method (12) (13) The new crack lengths produced per mill revolution were measured from all available grindability test results at 28, 35, 48, 65, and 100 mesh on fifteen different ores, and were found to remain substantially constant for each ore at all mesh sizes. A new technique is used for the measurement of crack lengths. Size distribution plots of the mill feed and product are made by the Third Theory method (9) and the crack lengths are obtained from these plots by the procedure described in the present paper. The energy input required to produce a unit length is of fundamental importance in the size reduction of brittle solids. The crack length Cr is expressed in centimeters per cubic centimeter of solid material. It bears a definite relationship to the external surface area of the crushed or ground solid. A uniform particle shape must be assumed before the surface area and crack length can be evaluated. In this paper it is assumed that the relationship between the surface area and the particle volume of a particle d microns in diameter is the same as that of cube d microns on a side. The external surface areas of particles with a cubical breakage probably agree approximately with this rule, and correction factors can be applied when physical measurements of the surface areas are available for comparison. However, the assumption of equivalent cubes has been found satisfactory for most calculation purposes. Assuming equivalent cubes, one cubic centimeter of particles d microns in diameter will have a crack length Cr of v30.000/d centimeters, and a surface area of 60,000/d square centimeters. The specific crack length is thus equal to the square root of one-half the specific surface area. Where Sa is the surface area in square centimeters per gram and Sg is the specific gravity of the ground solid, then Cr = vSg . Sa/2 = 173.2/ vd (1)

Jan 1, 1961

By E. H. Rose

IN a year of sober reflection and stocktaking after the mineral-squandering spree of World War II, the role that beneficiation of low-grade must henceforth play in American mineral industry has become unmistakable. From the volume of research and development progress in mineral engineering during 1946, mineral dressers evidently have ample resoluteness to meet the challenge. Perhaps ,the most conspicuous trend of the year was the renascence of interest in gravity concentrating methods and more serious effort than ever before to make them effective in finer size ranges down to 200 mesh. This has been forced by the problem in iron ores where the low value of the product will not support a high flotation reagent cost, however good flotation pilot plant results may have been and however well the acute problem of variable feed may be met. The race is on between rabbit flotation and tortoise gravity methods and a surprising amount of betting money is being laid on the tortoise which already is showing previously unsuspected talent for speed. Mostly, however, a wait-and-see attitude prevails during the present preliminary heats. As evidence of the latter, two magnetic plants are now on the boards for magnetic taconites on the eastern Mesabi to establish a reprieve against the time when nonmagnetic taconites must be addressed. Incidentally, these operations will force the blast-furnace issue on preparation of fine material since a minus-100-mesh grind is contemplated.

Jan 1, 1947

By Charles H. Fulton

The process of crushing ore in cyanide solution was first used at the Crown mine, New Zealand, in 1897, by Mr. F. R. W. Daw; and, two years later, Mr. John Hinton tried it experimentally at the old Dakota plant, Central City, South Dakota. To Mr. Hinton belongs the credit of introducing this important modification in the Black Hills, this being its first successful application in the U. S., and its results have been so satisfactory that it has become established as the proper manner in which to treat the dense oxidized siliceous ores of this district. Five mills are now crushing ore in cyanide solution, namely, the Horseshoe, 120 stamps (60 in operation); the Dakota, 30 stamps; the Maitland, 40 stamps; the Hidden Fortune, 60 stamps; the Lundberg, Dorr & Wilson, one 6-ft. Monadnock roller-mill; and several others intend to adopt this practice. The dry-crushing process still holds its place for the treatment of the more porous and open siliceous ores; and two mills continue to dry-crush dense siliceous ores. Character of the Ores. The occurrence of the ores of the Cambrian strata in the northern Black Hills has been frequently described.' In practice they are classified, according to their appearance, into " red " and " blue " ores, the former being oxidized and the latter unoxidized. At the present time, usually the red ores only are treated at the mills, although occasionally small quantities of blue ore, which have become intimately mixed with the red in mining, are included. Generally the extraction of values by the direct treatment of raw ore is from 70 to 75 per cent. for red ores, and from 25 to 50 per cent. for blue ores. The ores consist mainly of a siliceous matrix containing, as a +1SOUTH DAKOTA SCHOOL OF MINES, RAPID CITY, SO. DAK.

Jan 1, 1905

Iowa Geological Survey, Des Momes, Ia. George F. Kay, State Geologist A list of publications will be sent upon request Most of the papers of the Survey have been published in the Annual Reports, issued since 1892. Separates of the many papers in the Reports may be had for postage, except where they are out of print, and except for vol 1 (1892), 2 (1894) and 14 (1903), where no separates are to be had. Thirty-five Annual Reports have been issued up to and including vol 35 (1929). A charge, plus postage, is made for vols, 4, 5, 7, 8, 9, 10, 28 and 33, others will be sent free upon request, plus postage on from 2 to 6 pounds Space prohibits giving more than a general picture of some of the contents; vols 4, 5, 7, 8, 9, 10, 11, 12, 13, 15, 16, 20, 27, 32, contain, among others, papers on the geology of Iowa, by counties Vol. 19 (1908), 6 lb , contains a number of papers dealing with the peats and coals of Iowa, and has bibliographies of those subjects Vol 22 (1912), 6 lb , contains an annotated bibliography of Iowa geology Vol-24 (1913), 6 lb , contains the analyses of 16 Iowa coals Vol 28 (1917, 1918), price $1 50, 4 lb , completely covers the subject of gypsum in Iowa, and has a bibliography of the sub¬ject. Each volume carries an administrative report and a review of mineral production for the period covered In addition, Technical Paper 2 (1930), Studies of Iowa coals, will be sent free upon request Also a geological map of Iowa, and maps of Iowa showing the distribution of the glacial drift sheets throughout the state, have been issued and are available

Jan 1, 1933

By J. Elmer Thomas

The evolution of the oil business is one of the great industrial romances of modern times. First used as a medicine, then as a lubricant, then as an illuminant, and finally as a motor fuel, each change in its principal usage caused large increases in consumption. Producing Successes The producing branch of the industry responded ably to the demands made upon it. Never was there a famine, rarely any threat of scarcity, and stored inventories were gradually accumulated to form comfortable working stocks. Originally an erratic and hazardous undertaking, the discovery and development of oil fields has made such strides as to classify now as a science. When storage stocks were low, production in close balance with consumption, and demand trending sharply upward, considerable concern was expressed over future needs. Price was very responsive to fluctuations in supply under those conditions, and quotations for crude and refined oils exhibited wide swings. A very different situation exists today. Consideration of the statistics only since the war will show how recent has been this change. In the 10-year period from 1918 to 1927 inclusive, we produced in the United States 6,100,000,000 bbl. of crude and imported 900,000,000 bbl., our total supply being 7,000,000,000 bbl. The consumption was 6,600,000,000 bbl., thus adding to stocks 400,000,000 bbl., an accumulation of somewhat less than 6 per cent. of the total supply. During that period virtually every field was promptly developed as soon as discovered and nearly every well in the country was producing at full capacity. With the maximum production of the wells required to take care of the rapid increases in consumption, with storage stocks moderate and proven reserves very slight, the producing division of the industry acquired a tempo not needed now. Potential Surplus Today the situation is vastly different. The economic consumption is about 2,700,000 bbl., with current production slightly in excess of that.

Jan 1, 1930

Mine Transitman.-Engineer, about 30 years of age, experienced in coal mine underground surveys. Must be good draftsman and possess sufficient personality to get results from the men. Location, Illinois. No. R 419. Coal Mining Engineer: Coal mining engineer of proved ability for position of manager f high-grade bituminous coal property. Location, Canada. No. R 427. Chemist or Metallurgical Engineer.-Chemist or metallurgical engineer for special library work. Man with scientific training with the ability and education -of a young instructor in a university. Duties would consist of working out a new method of indexing scientific information, more particularly in obtaining information for use of a Committee on the Heat Treatment f Steel. Location, Washington, D. C. No. R 470. Topographical Draftsman.-Civil engineering training and topographical and surveying experience. Unmarried man, under 40 years of age. Knowledge of Spanish not necessary. Discharged army or navy man preferred. Location, oil fields, Mexico. Salary, $5 per day, living and traveling expenses. No. R 483. Mechanical Draftsman.-Engineering training, familiarity with drawings of pumps, piping, etc., need not necessarily be a designer. Unmarried man, under 40 years of age. Discharged army or navy man preferred. Location, Mexico. Salary $5 per day with living and traveling expenses. No. R 484. Engineer Translator.-Engineer of Portuguese nationality who has received his technical training abroad, and has been filling engineering positions in this country, to translate material for catalogs of an engineering character. No. R 486.

Jan 5, 1919

By Paul Berggreen

LIST OF PUBLICATIONS In the Bibliography titles of publications are replaced by corresponding symbols in this list. American A-1. Transactions of the American Institute of Mining Engineers, New York. A-2. Journal of the New York Microscopical Society, New York. A-3. Journal of the Franklin Institute, Philadelphia, Pa. A-4. The Metallographist, Boston, Mass. A-5. The Electrochemical and Metallurgical Industry, New York. A-6. Bulletin of the American Institute of Mining Engineers, New York. A-7. The Iron Trade Review, Cleveland, Ohio. A-8. The Journal of Physical Chemistry, Ithaca, N. Y. A-9. The Physical Review, New York. A-10. Van Nostrand's Electric Engineering Magazine, New York. English E-1. Proceedings of the Institution of Mechanical Engineers, London. E-2. Journal of the Iron and Steel Institute, London. E3. Proceedings of the Institution of Civil Engineers, London. E-4. Journal of the Chemical Society of London, London. E-5. Philosophical Magazine, London. E-6. Proceedings of the Royal Society of Edinburgh, Edinburgh., E7. Carnegie Scholarship Memoirs, London. E-8. Proceedings of the Royal Society of London, London. E-9. Chemical News, London. E-10. Philosophical Transactions of the Royal Society of London,, London. E-11. Transactions of the North-East Coast Institution of Engineers and Shipbuilders, Newcastle-on-Tyne E-12. Iron, London. E-13. Nature, London. E14. English Mechanic and World of Science, London.

Jan 6, 1914

By R. C. FLEMING

G OLD MINING is enjoying a real revival in the West, and a considerable portion of the production is coming from small properties. The large mining companies of the world get most of the publicity, but in the last year the small gold property has often proved a more attractive field for the mining engineer looking for something to do. Old mines have been re- opened, prospects have been more closely examined, and many properties that were out of the running with the high commodity and labor costs of two or three years ago, have recently been making money for their operators. An interesting phase of this activity is the operation of so-called one-man mines. The west is dotted with these small properties, without the resources or reserves to warrant large-scale operation, but which return a living and often something over to one or two men who under- stand mining and simple methods of treatment.

Jan 1, 1932

C. H. MATHEWSON, New Haven, Conn. (written discussion *).-In a recent discussion of Dr. Jeffries' paper on tungsten,1 J. C. W. Humfrey,2 after taking exception to certain of the author's ideas relative to the cohesion of A and C metal, expresses the opinion that future research is likely to develop a method of preparing tungsten possessing "mechanical properties in line with those of other metals." The present paper by Dr. Jeffries begins with a determination of comparative properties of tungsten, copper, and iron, in which much dissimilarity is apparent, and ends with a coherent explanation as to why much of this dissimilarity is natural and inevitable, thereby supplying theoretical means for visualizing the changing properties of metals in general, once certain fundamental facts are known. The author's reasoning is primarily from the standpoint of the amorphous theory and his principal achievement is the development of an idea f differential cohesion according to conditions of temperature, etc., between A and C metal (which was first plainly suggested by Rosehain and Ewen, in their papers on Intercrystalline Cohesion of Metals) along with associated ideas, so as to give us a really useful working theory. I have come rather reluctantly to believe in the amorphous theory, or some theory admitting a modification of the ordinary crystalline phase so as to permit differential properties within the conglomerate, mainly because in no other way does it seem possible to account for observed changes of properties with temperature, etc. The very best illustration f the competency f the amorphous theory in this respect is seen in this and other recent papers by the author. All fractures through normal or healthy metal that have been preceded by deformation are supposed, by Dr. Jeffries, to take place either through the amorphous phase or at certain boundaries between amorphous and crystalline material; his reference to fractures, both members of which are similar in appearance and do not reveal a preexisting coarse-grained structure because of a coating of amorphous metal, indicates his preference for the former interpretation.

Jan 5, 1919

By W. G. Lidman, H. J. Hamjian

' I HE fabrication of many materials from powders involves a sintering process. A mass of powder will sinter because of the excess free energy over the same mass in the densified state caused by the higher total surface area of the powder. An understanding of the kinetics and mechanism of sintering should assist in improving the properties of such materials. The present investigation conducted at the NACA Lewis laboratory deals with the sintering of chromium carbide. Dry sintering (sintering at a temperature below the melting point) was divided into two stages by Shaler:' the first stage, during which the particles preserve much of their original shape and the voids are interconnected, and the second stage, during which densification occurs and the pores are isolated. The mechanism of forming interfaces between particles, or welding together of particles, has been investigated by Kuczynski2 and may be described by any one or a combination of the following mechanisms: viscous flow, evaporation and condensation, volume diffusion, or surface diffusion. The mechanism by which pores are closed or eliminated (densification) during sintering, is of interest. Grain growth observed during sintering may be attributed to the variation in the surface energies of individual grains, causing some grains to grow at the expense of others. Grain boundary migration occurs presumably by a diffusion process, therefore the rate of grain growth would be expected to increase exponentially with increasing time and temperature. Thus, for practical sintering times of less than 1 hr, a certain minimum temperature may exist at which major structural and property changes will occur. Densification and kinetics of grain growth during sintering under pressure of chromium carbide were investigated to provide additional information which will aid in describing more accurately the sintering process and the mechanisms involved. This material was selected for this study because of the current interest in high strength, oxidation resistant refractory materials, such as carbides, which are sintered to produce solid, dense materials from powders. Sintering under pressure is a process where the heat and pressure are applied to the compact simultaneously, specimens for this work were prepared by sintering under pressure at different temperatures and for various time periods. Experimental Procedure Preparation of Specimens: Chemical analysis of the commercial chromium carbide used in this investigation was as follows: Cr 86.19 pct, C 12.14 pct, and Fe 0.2 pct. X-ray diffraction powder patterns gave characteristic diffraction lines of Cr3C2 crystal structure. Powder particle size was determined microscopically and the average initial particle size was 6 microns with 85 pct between 2 and 10 microns. Specimens sintered under pressure were formed in graphite dies3 heated by induction. Sintering temperatures were measured with an optical pyrometer by sighting into a 3/8-in. hole drilled 1 in. deep at the midsection of the graphite die. A load of approximately 1 ton per sq in. was applied to the powder. The die assembly was heated in 20 min to the highest temperature (2500°F') at which no increase in grain size could be observed, and less than 2.5 min were required to heat from this temperature to the maximum temperature (3000°F). Sintering temperatures and times for the specimens of this investigation are indicated in Table I. Analysis of Specimens: Specimens polished with diamond abrasives were etched to reveal the grain boundaries with a 1:1 mixture of 20 pct potassium hydroxide and 20 pct potassium ferricyanide heated to 160°F. Representative areas of each sample were photographed at 1000 diameters. The largest diameters of all well-defined grains were measured, but only the measurements of 15 of the largest grains were averaged in order to determine an index of grain size on the assumption that they were among the first to begin growth. Densities were determined from differential weighing of the samples in air and water. The reported density values are considered correct within ±0.01 g per milliliter. Results and Discussion Metal compacts have exhibited grain growth when sintered at temperatures about two-thirds of the absolute temperature of their melting point.' Grain growth also occurs during the sintering of chromium carbide and is illustrated by the micrographs shown in Fig. 1. These micrographs were prepared from specimens sintered for 90 min at temperatures ranging from 1371°C (2500°F) to 1648°C (3000°F). Average grain size and density measurements of specimens investigated are presented in Table I. The relationship between grain size and sintering tem-

Jan 1, 1954

By P. B. Liebermann

THE resistance to motion offered by mine cars is caused principally by: Rolling friction, flange friction, bending rails, bearing friction and wind resistance. With proper construction and with a fair amount of attention and care, that is, under favorable conditions, the first three items cannot be greatly improved. The wind resistance ordinarily is negligible on account of the slow speeds commonly used. The bearing friction, however, is a variable item, depending upon the design, the bearing material, the lubrication, the location (whether in wheel-hub or on car-body) and the alignment. Under the most favorable conditions the bearing friction will reach a lowest possible value. By the development of a successful anti-friction mine-car bearing this lowest value has been improved to such an extent as to affect the whole system of mine haulage. After being satisfied of their durability and certainty of operation, any investigation into the advantages of anti-friction bearings for mine cars will have to be based upon reliable information as to the saving in power of such bearings. While numerous tests have been made in this direction, the results have not always been convincing, principally because of the rather crude methods that were employed. These crude methods are the main cause of the wide variations existing in regard to the exact amount of the frictional resistance. Frequently an ordinary spring balance is used and the pull necessary to move a certain car or train of cars is obtained by a number of readings. Such spring balances necessarily have a coarse graduation and the continuous vibration and fluctuations to which they are subjected make them highly dependent upon the individual observer. Further, they must be frequently calibrated. Sometimes these tests were made without regard to acceleration, speed or even grade.

Jan 6, 1916

By Arnold Hague

In the short time allotted to me* I can only hope to present to you a brief sketch of the main geological features of the country which you are about to visit. My remarks must, of necessity, be more or less incomplete, as my desire is not so much to elucidate any special problem connected with the many interesting geological questions to be found here, as rather to offer such a general view of the region as will enable you, during your five days' trip through the Park, to understand clearly something of its physical geography and geology. The Yellowstone Park is situated in the extreme northwestern portion of the Territory of Wyoming. Its boundaries, as determined by the original Act of Congress setting apart the Park, are very ill-defined. At the time of the enactment of the law establishing this national reservation, the region had been but little explored, and its relation to the physical features of the adjacent country was but little understood. Since that time, surveys have shown that only a narrow strip, about two miles in width, was situated in the Territory of Montana, but it was also found that a still narrower strip extended westward into the Territory of Idaho. The question of properly establishing the boundaries, -based upon our present knowledge of the country, is now before Congress, and an Act has already passed the Senate, proposing to make the northern boundary coincide with the boundary between Wyoming and Montana, and the western boundary coincide with the Wyoming and Idaho line. The Act under consideration extends the southern boundary of the Park to the 44th parallel of latitude, carrying the area of the reservation southward nine and one-half miles. The eastern boundary is made to coincide with the meridian of 109' 30') adding a strip of country about twenty-four and one-half miles in width along the entire eastern side of the Park.

Jan 1, 1888

By George A. Laird

THIs old and once famous district played, through its enormous production of silver and gold, an important part in the history of the State of San Luis Potosi. According to a pamphlet prepared under the direction of the Governor of the State, Sr. Don Blas Escontria, and presented to the visiting members of the Institute during the Mexican meeting of 1901, this district is situated 20 km. east of the city of San Luis Potosi, in a range of mountains of moderate height, extending 135 km. N. and S., and 16 km. E. and W.; and the mineralized area hitherto developed is about 600,000 sq. m. The history of the district, as given by the record dated 1778, and formerly kept in the Sail Francisco convent, says that it was discovered in 1575 by Sr. Don Pedro Irarte, and adds that the city of San Luis Rey de Francisco de1 Potosi received its name (in allusion to the famous Potosi mines in Bolivia) by reason of the remarkable productiveness of its gold- and silver-mines in the first period of their exploration, during which they paid to the Crown, as quintos (the fifth part of the product), $97,000,000, as appears from the accounts of the royal treasury. The amount of the quintos paid during the " bonanza period " of 80 years was $72,000,000. The larger sum first mentioned probably represents a longer series of years. But either will suffice to indicate the great wealth of the mines. In 1663, the decadence of the industry began with the caving-in of several mines, concerning which the record of 1778, already cited, says, in substance, that on Good Friday one of the owners in the enterprise, in view of the unfavorable prospect of a lawsuit in which he was engaged, set fire to the timbers supporting the underground galleries and workings of the Sail

Jan 1, 1905

By R. Bainbridge

THE Consolidated Mining and Smelting CO. of Canada Ltd. has operated a lead smelter at Trail, B. C., for many years. In order to take advantage of metallurgical advances, as well as to improve materials handling methods, this company, commonly known as "Cominco," commenced planning a program of smelter revision and modernization some years ago. The first stage of this program involved the design and construction of a new blast furnace gas cleaning system. The selection of equipment, the design of facilities, and preliminary operating details of this system will be dealt with in this paper. The essential problem was to clean and collect 100 tons of dust daily from 153,000 cfm* (12,225 lb per min) of lead blast furnace gas which varied in temperature from 350º to 1100°F. Because it was desired to collect the dust dry, either a Cottrell or a baghouse cleaning plant was to be selected. Comin-co's many years of experience with both systems provided a background for choosing the most satisfactory installation. All information pertinent to the two methods of dust recovery was carefully investigated, and it was decided to replace the existing equipment with a baghouse. Very briefly, the reasons for this decision were as follows: 1—A baghouse installation would be practical because the SO2 content of the gas was low and corrosion would not be a problem if the baghouse operating temperatures were held sufficiently above the dew point. 2—Variations in the physical characteristics of fume and dust, which are inherent in this blast furnace operation, should not substantially affect the operating efficiency of a baghouse. 3—For the same capital cost, metal losses (stack and water losses) would be appreciably less in a baghouse. 4—A baghouse would be easier to operate, and would not require the use of highly skilled labor. 5—Operating and maintenance costs of a bag-house would be lower. 6—The only available space for reconstruction was relatively small, and not suited to a Cottrell installation. Once the baghouse system was decided upon, detailed design of the installation was begun. Baghouse Design Gas Cooling: Before the required capacity of the baghouse could be determined, the method of cooling the gas to the temperature necessary for bag-house operation had to be chosen. The problem confronting the design engineers was how best to cool 153,000 cfm of gas from a temperature ranging from 350°F to brief peaks of 1100°F, down to 210°F, the maximum safe baghouse inlet temperature. A survey of existing blast furnace gas temperatures in the outlet flue showed that the normal range was as given in Table I. The obvious choices of cooling method were: 1— cool completely by the addition of tempering air; 2—utilize a heat exchanger; 3—cool by radiation; and 4—cool with water spray in conjunction with the admission of tempering air. The advantages and disadvantages of the various cooling methods were: Air Addition: To cool completely by the admission of tempering air involved tremendous volumes, Fig. 1. For example, to cool 1 lb of blast furnace gas at 450°F requires 1.84 lb of air at 80°F or 1.60 lb at 60°F. As it is necessary to design for peak conditions, it can readily be seen that volumes of tempering air in the order of 1,500,000 cfm would have to be handled. Using the normal design figure of 2.5 cu ft per sq ft of bag area, a baghouse installation comprising some 600,000 sq ft of filter cloth would be necessary. Such design requirements would be prohibitive, not only from a standpoint of capital expenditure, but also because of space limitations. Heat Exchanger: The utilization of a heat exchanger was given serious consideration. A horizontal tube unit using air as the medium to cool the required volume of blast furnace gas from 400" to 250°F was investigated. Cooling above 400°F would be done by water spray, and below 250°F by admission of tempering air. The estimated capital cost of such a unit was found to be prohibitive. From an operating standpoint, there was considerable doubt as to whether the soot blowing equipment provided would effectively keep the dust from building up on the tube surface. The performance of heat exchangers operating on dusty gas in other company operations had not been too favorable. Radiation Cooling: Although somewhat cumbersome, gas cooling by radiation from 'trombone' tubes or other similar equipment (cyclones) is employed in many metallurgical operations. Such an installation was also considered. However, calculations showed that an installation much larger than the space available would be required to handle the gas volume involved. For example, to cool 153,000 cfm of blast furnace gas from, say, 600' to 250°F (i.e., remove in the order of 58,500,000 Btu per hr with heat transfer rates varying from 1.1 Btu per sq ft per hr per OF for the higher temperature ranges to 0.88 Btu per sq ft per hr per OF for the lower ranges) would need a cooling area of some 175,000 sq ft.

Jan 1, 1953

By M. Yokoi, K. Yoshida, T. Ishihara

The solubility of aluminum in cryolite melts has been determined by measuring the weight loss of aluminum submerged in melts contained in closed silicon nitride crucibles. The solubility in pure cryolite has also been checked with radioactive isotopes. The solubility decreases with increasing A1203 concentration, decreasing temperature, and decreasing cryolite ratio. The change of aluminum solubility in pure cryolite with the activity controlled by using Al-Ag and A2-Cu alloys supported the assumption that aluminum would dissolve in the form of monovalent ions according to the reaction 2AI + A1' —3 A1'. DURING the electrolytic production of aluminum, the electrodeposited metal redissolves in the bath in some form and is subsequently oxidized back to the former ionic state. This dissolution is believed to cause a decrease in current efficiency. Reported data on the solubility of aluminum in cryolite melts are scattered. The mechanism of the dissolution has not yet been determined, although certain tentative interpretations have been proposed. Many previous studies were performed under different test conditions. Studies were performed in open Systems and closed systems,'o and some were apparently not given sufficient time to Saturate." The solubility can be determined either analytically or gravimetrically. The analytical determination involves measurement of hydrogen gas evolved when frozen cryolite bath saturated with aluminum is treated with sodium hydroxide or hydrochloric acid. The gravimetric determination, adopted by many investigators,'-37'3>14 involves measurement of weight loss of the metal after equilibration with a known amount of salt. It appears that the former technique yields much smaller values of solubility than the latter technique. This large difference in results strongly suggests that the dissolved metal in the cryolite melt is no longer in the metallic state. In the present study, the solubility was determined by the gravimetric technique at various activities of aluminum using A1-Ag and Al-Cu alloys. An attempt was also made to determine the ionic (or atomic) state of the dissolved metal from the solubility data. 1) EXPERIMENTAL Apparatus. Preliminary tests demonstrated that silicon nitride was suitable as a container material since it is compatible to both the fluoride melts and molten aluminum. Crucibles were made from silicon powder nitrided with Nz gas at 1600°C. The good compatibility between crucible and melts is due to the near perfect nitrogenation of silicon. Only small amounts of silicon were found in the aluminum metal after the experiments. The crucible dimensions were 90 mm inside height, 38 mm ID, 105 mm outside height, and 50 mm OD. Close-fitting lids made of silicon nitride were also prepared. The crucible was placed in a close-fitting graphite crucible heated by a vertical Kanthal furnace, Fig. l. The lid and crucible are fastened tightly together by the condensation of vaporized bath in the narrow gap between them. The temperature was measured in the wall of the graphite crucible and controlled within * 5°C. The temperature difference between the measuring point and the interior of the melts was initially determined. Materials. The materials used were: Greenland cryolite (impurities CaF,, 0.5 pct; AlzO3, 0.2 pct; high-purity aluminum metal (purity 99.99 pct); A1203 and AlF, (provided by Nippon Light Metal Co., Ltd); reagent-grade NaF and CaF2; and 99.9+ pct Ag and Cu. Powdered reagents were carefully dried before use. A1-Ag and A1-Cu alloys were prepared before the experiments; their composition was checked by analysis

Jan 1, 1969

By T. E. Tietz, J. E. Dorn

Activation energies for creep of copper at intermediate temperatures, where crystal recovery was negligible, were determined by the simple technique of rapidly alternating the test temperature between and T2 (T2 = TI + about 10°K) throughout a constant stress creep test. The activation energy for creep H was found to be 37,000± 3,000 cal per mol, independent of stress and strain. The same creep laws as have been previously established for high temperature creep were found to be valid for creep at intermediate temperatures. But the AH was found to be lower than that for self-diffusion in the intermediate temperature range whereas it is known to be equal to that for self-diffusion at high temperatures. IT is now well established that creep at high temperatures can be correlated by the functional relationship'-" e = f(?) s = constant [I] where E is the total plastic strain, f is the function that depends on the stress, ? = f e -- dt, t is the duration of test, e is the base of natural logarithms, AH is the activation energy for creep, R is the gas constant,T is the absolute temperature, and s is the stress. Thus, identical values of are achieved during creep under a given stress at two alternate temperatures at the same total strain. At the same strain therefore where subscripts refer to the two alternate temperature conditions of test. Consequently, the activation energy for high temperature creep is readily obtained with the aid of Eq. 2. Activation energies so obtained have been observed to be insensitive to the creep strain at which they are evaluated, the applied stress, grain size, minor alloying additions,'-' cold worked state, and the presence of thermally stable dispersions of intermetallic compounds in an a solid solution matrix Furthermore, the activation energy for high temperature creep is very nearly equal to that for self-diffusion in all cases where adequate data are available for comparison." " The apparent identity of the activation energies for high temperature creep and self-diffusion strongly suggest that high temperature creep arises from a dislocation climb process. This hypothesis is further strengthened by the fact that the energy of activation for high temperature creep is insensitive to the applied stress," and by the observations that the correlation suggested by Eq. 1 cannot be ex- tended to temperatures below those for rapid crystal recovery. When using the activation energy for self-diffusion, Eq. 1 fails to give the required correlations between creep curves at various intermediate temperatures.' This suggests that the dislocation climb mechanism for creep might be superseded by some alternate mechanism in the intermediate range of temperatures. This investigation was initiated in a preliminary attempt to ascertain the type of creep law that might be valid in the intermediate range of temperatures. Special consideration, however, was given to the determination of the activation energy for creep in this range because the Becker-Orowan', " and the Mott-Nabarro10 theories for transient creep suggest that the activation energy should increase

Jan 1, 1957

By D. R. Mitchell

MEETING for the thirteenth time in New York as part of the five-ring circus known as the Annual Meeting A.I.M.E., the Coal Division experienced a wartime boom in attendance. Technical sessions were crowded and whereas 65 seats were set up for the annual luncheon meeting of the Division over 100 members showed up, many of whom had to be fed elsewhere. Possibly the Coal Division should adopt "13" as its lucky number. Discussions at technical sessions, formal and informal, were lively. Those papers containing material directly concerned with the war, or containing information that might be usable for war industries, were enthusiastically received. Some criticism was made in regard to the present method of handling discussions and it was suggested that better success would be had in getting discussions in the record by the use of hired reporters. This is being considered by the executive committee of the Coal Division.

Jan 1, 1943

By Eugene A. Alexandrov

The Minister of Geology of the Soviet Union P.Ya. Antropov, recently visited China and claims that this country occupies one of the foremost places in the world in reserves of tin, tungsten, molybdenum, antimony, iron ore, coal, and phosphates. Occurrences of economic value of chromite, nickel, gold, beryllium, tantalum, niobium, rare earths, and asbestos have also been reported. MINERAL RESOURCES Coal: The inferred reserves of coal are estimated at at 1,500 billion tons. A considerable part of the coal reserves is represented by coking coal, 80% of which is bituminous. Thicknesses of coal seams range up to 150 ft in the principal deposits located in northern and northeastern China. The total output of coal in 1958, 270 million tons, was produced by an army of 20 million people mainly in small mines operated by the agricultural communes. Modern hydraulic mining is applied besides primitive, obsolete methods and equipment

Jan 3, 1960

By E. W. Enqelmann

INCREASED metal consumption throughout the world in the past three years has brought greater activity in the concentrators and mills that treat the ores.' Comparatively low prices have made greater economies necessary, with a continuing search for more efficient flow sheets, equipment, processes, and reagents. Comminution GRINDING has long been too ex- pensive and even any small increment of saving has been eagerly sought. Although not recently new the use of rod mills to cover the gap between intermediate crushing and coarse grinding has made further headway. They eliminate dusting and the closed- circuit operation of fine crushers, either roll or Symons cone, and the rod-mill product is suitable for secondary mills which can be operated with smaller balls and iron liners instead of coarse balls and steel liners. The newer practice is radically different from the older application of rod mills where they at- tempted to use them instead of ball mills for fine grinders. For that purpose they were not well adapted, as they do not have sufficient grinding surface available per cubic foot of mill volume.

Jan 1, 1940