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By G. L. Oldright

THE development of the reverberatory furnace for smelting copper ores up to 1912 was described by E. P. Mathewson1 with details concerning the great changes in dimensions of the furnace. Hayward2 tabulated similar data, giving developments up to about 1924, in his revision of Hofman's Metallurgy of Copper. DEVELOPMENT OF PRESENT SMELTING PRACTICE Dimensions of Furnace Very great changes were made in the dimensions of the smelting hearths of the furnaces in the period from about 1800 to 1906, the length increasing from about 11 to 116 ft., and the width from 8 to 19 ft. During this time the tonnage smelted increased from about 9 to 250 tons per 24 hr., and the tons of charge smelted per ton of coal increased from 0.77 to 4.3. Dr. Mathewson3 noted no great difference in the "fuel ratio" (i. e., the amount of charge smelted per ton of coal) as the furnace at Anaconda was increased in length by stages from 85 to 116 ft. (The percentage of copper in the slag, however, was lowered from 0.42 to 0.36 per cent. The other components of the slag were not given.) Lump coal fired on grates was the fuel used during this period. The practice in operating the furnaces over such a length of time naturally varied considerably, and there were differences in composition and nature of the charge, yet it may be considered that the improvements made were due largely to increases in the size of the furnace used. Doubt-less some credit should be given to improvements in operating technique, like changes in the methods of firing the lump coal. However, the greater part of the advance was probably due to factors influencing the

Jan 1, 1928

By Samuel M. Cassidy, John A. Garcia

IN some districts of the bituminous coal field the problem of constructing bulkheads to seal off water under pressure is becoming increasingly important. Recently this matter has been brought very much to the front by the loss of a large Illinois mine due to failure of a bulkhead that separated it from several old, flooded mines. As this great misfortune has provoked much inquiry about proper bulkhead design, it is felt that a description of the successful and extensive water-sealing practice at three mines that have different natural conditions will be of considerable interest to those connected with properties having a present or future water problem and to engineers that may have to design safe bulkheads of economical construction. These three mines are the Saxton and Dresser, near Terre Haute, Ind., and the Hegeler, near Danville, Ill. All three have water conditions that make it necessary to regularly seal off all worked-out sections of the mine, and there are considerably over a hundred bulkheads in each. As far as the writers know, these three mines are the only ones in the bituminous coal fields of the United States with anything like so large a number of water seals and experience, although a number of other mines are known to have a few bulkheads. More detail will be included herein on the Saxton mine than on the others, as the writers are more familiar with it. General Mining System All three of the mines use the same general panel room-and-pillar system, which consists of rooms turned both ways off room entries and a solid block of coal left on all sides of the completed panel except on the cross-entry side, where a heavier pillar is pierced by two entries for haul- age and air. On completion of the panel the two entries are sealed and the panel is then isolated from the rest of the mine. Owing to water conditions, no pillars are pulled; recovery inside the panel barrier pillars is approximately 65 per cent.

Jan 1, 1937

By Robert H. Richards

If one holds up a prism, or wedge of glass, with narrow angle, say l° to 2O, and compares the transmitted image with the image seen above or below the prism, the former will be found to be thrown to one side by an amount varying with the angle of the wedge. Speaking of the two rays as the direct ray and the bent ray, we may say, that when the bisecting plane of the prism is at right angles to the line of sight, the angle between the direct ray and the bent ray will be constant for any given prism. If now we place a prism or wedge of glass in such a position that it half-covers the objective of a telescope, we shall obtain on looking through it two images of every object seen—one image by the direct ray, which comes through the unaovered half of the objective, the other which comes through the prism, and is the image by the bent ray. The angle of divergence of these two raps will be constant and unalterable, whether the telescope is directed to a near object, with its eye-piece at increased distance from its objective, or upon a ' distant object, with eye-piece nearer to the objective. That is to say, if the " throw " or apparent dislocation of the image is one foot in one hundred feet it will be two feet in two hundred, ten feet in a thousand, and so on. The usual form of stadia-telescope has at the focal point of the objective two spider-lines, placed at a definite distance apart and intended, let us say, to represent a throw of one foot in one hundred feet. But as the distance between lines remains the same, while the distance from the objective to the webs diflers with every variation in the distance of observed objects, it follows that the angle between the lines of sight which these two spider-lines define cannot be con stant, but must vary with every increase or decrease of distance be tween the instrument and the object viewed. If in Fig. 1 we represent three positions of the spider-lines by W1, W2, W3, and three objects corresponding to those positions by 01, O2, 0, at near, medium and distant positions, we see at

Jan 1, 1892

By Kenneth Schellinger

THE terms surface tension and surface energy are well known when applied to liquids and are generally described by referring to the excess energy of the air: liquid interface as a result of unsaturated molecular forces surrounding the surface molecules of the liquid due to the presence of the air phase on one side. Such unbalanced forces produce the familiar water droplet of spherical form and are generally summed up as a surface tension measured in dynes per centimeter which can be shown mathematically to be equal numerically to a corresponding surface energy expressed in ergs per square centimeter. A specific surface energy, however, is best thought of as the energy necessary to produce one unit, of new surface on a substance. Hence, in producing a bubble in a flotation cell the impeller must supply surface energy corresponding to the air: liquid interfacial area on the interior of the bubble. Inasmuch as it is relatively easy to extend or contract the surface of a liquid, there are a number of successful methods for liquid surface tension, or energy, measurement based upon surface deformation. This happy state of affairs does not, however, extend to solids, which are considered to possess surface energies for the same reasons as do liquids, i.e. because of unsaturated ionic bonds at the solid: gas interface. As in the case of the flotation cell producing surface on liquids as new bubbles, it takes energy to produce new surface on solids as new particles. As every mill man knows, this surface is produced on mineral solids in a grinding mill by the action of a tumbling mass of iron balls. But here so much energy usually is wasted by the inefficient action of these balls that a large amount of heat is generated, and the surface energy production may be easily confused with the energy necessary to produce this ineffective heat. The tumbling balls and fracturing minerals ultimately take their energy from a rather large electric motor. It has been variously estimated that from 10 to 20 pct'" only of this energy from the motor does not appear as heat and may be presumed to appear as surface energy on the min- erals present. Such a production of new surface on the mineral phases is accompanied, of course, by a size reduction that is inevitable as more and more mineral interior molecules become surface molecules by the fracture exposure. This size reduction of mineral particles, although the most obvious feature and perhaps the sole object of the milling operation, is from this energy viewpoint the outward manifestation of the production of surface energy only. Measurement of the characteristic surface energies of pure minerals and their various mixtures in ores would be a step towards understanding of the energetics of the commercial grinding operation. In addition, the characteristic surface energy of a mineral is probably a physical property specific for that mineral, and therefore, from a scientific standpoint, should be measured. It is interesting to note that, in contrast to the large body of work on the surface tensions of liquid systems and biological systems, the field of solid surface energies has been neglected. Prior to 1920 it is difficult to find more than one or two references to work on solid surface energies in Chemical Abstracts. Since 1920 such references number somewhat less than 100, while those on liquid systems are numbered in the thousands. Much of this apparent neglect of the field of solid surface energies (the term is intended to be somewhat inclusive at this point and refers both to the solid: gas, and the solid:liquid interface) is because of the lack of a reliable method of measurement rather than any lack of scientific curiosity. It was, and still is, difficult to produce new surface on a solid without the simultaneous production of interior changes in the same solid which may consume part of the energy used. The extension in the surface area can be measured, but the interior crystal-

Jan 1, 1953

By Kenneth Schellinger

THE terms surface tension and surface energy are well known when applied to liquids and are generally described by referring to the excess energy of the air: liquid interface as a result of unsaturated molecular forces surrounding the surface molecules of the liquid due to the presence of the air phase on one side. Such unbalanced forces produce the familiar water droplet of spherical form and are generally summed up as a surface tension measured in dynes per centimeter which can be shown mathematically to be equal numerically to a corresponding surface energy expressed in ergs per square centimeter. A specific surface energy, however, is best thought of as the energy necessary to produce one unit, of new surface on a substance. Hence, in producing a bubble in a flotation cell the impeller must supply surface energy corresponding to the air: liquid interfacial area on the interior of the bubble. Inasmuch as it is relatively easy to extend or contract the surface of a liquid, there are a number of successful methods for liquid surface tension, or energy, measurement based upon surface deformation. This happy state of affairs does not, however, extend to solids, which are considered to possess surface energies for the same reasons as do liquids, i.e. because of unsaturated ionic bonds at the solid: gas interface. As in the case of the flotation cell producing surface on liquids as new bubbles, it takes energy to produce new surface on solids as new particles. As every mill man knows, this surface is produced on mineral solids in a grinding mill by the action of a tumbling mass of iron balls. But here so much energy usually is wasted by the inefficient action of these balls that a large amount of heat is generated, and the surface energy production may be easily confused with the energy necessary to produce this ineffective heat. The tumbling balls and fracturing minerals ultimately take their energy from a rather large electric motor. It has been variously estimated that from 10 to 20 pct'" only of this energy from the motor does not appear as heat and may be presumed to appear as surface energy on the min- erals present. Such a production of new surface on the mineral phases is accompanied, of course, by a size reduction that is inevitable as more and more mineral interior molecules become surface molecules by the fracture exposure. This size reduction of mineral particles, although the most obvious feature and perhaps the sole object of the milling operation, is from this energy viewpoint the outward manifestation of the production of surface energy only. Measurement of the characteristic surface energies of pure minerals and their various mixtures in ores would be a step towards understanding of the energetics of the commercial grinding operation. In addition, the characteristic surface energy of a mineral is probably a physical property specific for that mineral, and therefore, from a scientific standpoint, should be measured. It is interesting to note that, in contrast to the large body of work on the surface tensions of liquid systems and biological systems, the field of solid surface energies has been neglected. Prior to 1920 it is difficult to find more than one or two references to work on solid surface energies in Chemical Abstracts. Since 1920 such references number somewhat less than 100, while those on liquid systems are numbered in the thousands. Much of this apparent neglect of the field of solid surface energies (the term is intended to be somewhat inclusive at this point and refers both to the solid: gas, and the solid:liquid interface) is because of the lack of a reliable method of measurement rather than any lack of scientific curiosity. It was, and still is, difficult to produce new surface on a solid without the simultaneous production of interior changes in the same solid which may consume part of the energy used. The extension in the surface area can be measured, but the interior crystal-

Jan 1, 1953

By William Romanoff

As you are no doubt aware, virgin copper, tin and zinc are strategic metals today and little, if any, is available in the manufacture of brass and bronze ingots. The source of alloys used in the manufacture of implements of war are, therefore, from ingots made almost exclusively from the refining of available scrap. It is amusing to hear of the unusual physical properties of various alloys because they mean nothing unless the foundryman is able to produce good sound castings. A discussion therefore means little unless something is said about the relative foundry practice of the various brass and bronze alloys. Among the factors that influence the quality of castings produced are: (I) improper gating, (2) wrong pouring temperatures, (3) poor sand conditions, (4) bad melting practice, (5) faulty pattern equipment, (6) metal. It seems to be the consensus of opinion that about 95 per cent of defective castings can be attributed to the first three causes. Metal while a source of trouble at times, is probably the least responsible for foundry difficulties. As you all know, a molder never makes a bad mold. His first thought is to blame the "damn" metal as this is the path of least resistance. Let's consider the "damn" metal and how it is made. In the manufacture of ingot, scrap is collected at various sources and is shipped to the refiner either directly or through the scrap dealer or broker. It is usually sorted, although not always. In working toward a specified chemical analysis, weighed amounts of various grades of scrap metals are melted, and then oxidized by blowing air through the molten bath to rid the metal of detrimental impurities or reduce them to within specification limits after which they are skimmed off with the aid of some added fluxes. The bath of metal is then poled with wood, chemically tested before and after additions are made to bring it up to required specifications, and finally poured into ingots, after which a final chemical and physical examination is made. As mentioned above, the impurities have either been eliminated or reduced to the point where they meet the specifications of all Government Agencies or Technical Societies. Therefore, why worry as to whether castings are to be made from strategic virgin metals or secondary ingots from available scrap. Tests have continuously been made and it is a proven fact that physical properties are no better from virgin metals than from secondary ingots of the same composition. It is definitely more fool-proof to make castings from secondary ingot than from virgin metals because if an error is made in weighing the copper, tin, lead or zinc of the latter, the analysis is off balance. If an error is made in weighing secondary ingots, you merely have more or less metal but the analysis remains constant. Furthermore, when pure copper is melted. it is susceptible to reducing gases as well as oxides. Secondary ingot is already alloyed with natural deoxidizers such as zinc, etc., and the volatilization of the latter also tends to eliminate reducing gases mechanically.

Jan 1, 1943

By Donald P. Richards, John F. Abel

Geotechnical site investigation for new mine shafts can reduce the level of design uncertainty for shaft linings. The parameters which determine the lining strength required include rock strength and hydrologic properties, the in situ stress conditions, and the concrete strength. These parameters are applied to analytical methods of shaft lining design using the plastic and clastic assumptions of rock response to determine the required lining thickness to maintain the stability of the shaft excavation.

Jan 1, 1982

The difficulty of finding new ore bodies, the complexities of patenting them when they are found, and the absence of incentive legislation for exploration have limited mining exploration in the United States mostly to the big companies. This situation, coupled with ECA spending abroad, has caused American capital to look outside our national boundaries for investment opportunities which are further made attractive by some relaxing of restrictions to gain American dollars and patronage.

Jan 1, 1950

By L. G. Austin

INTRODUCTION Autogenous (including semi-autogenous) grinding has probably been the most important single innovation in milling practice for the last twenty years. However, the design of these units has been largely a matter of trial-and-error, since the normal empirical laws for the design of ball mill circuits do not apply with exactitude to autogenous grinding circuits. There have been examples of autogenous mills failing to achieve output or product specifications. It is worthwhile, therefore, to attempt to develop a more detailed and precise set of design laws, using the concepts of specific rates of breakages and daughter fragment distributions (1), and performing mill simulations by computer. This type of approach has been applied to ball and rod milling (2, 3,4,5), but even for these mills it is by no means complete as yet (6), because of the amount of experimental work involved. There has not been a strong incentive for industry to develop new design procedures in ball and rod milling because the prior back-log of experience with these mills makes for easy design by empirical comparsion with existing systems. The new approach has been followed mainly by University groups (7,8,9,10), although experience in Australia (9,11) has shown the advantages of the approach. Stanley (12) has applied the approach to results from a large autogenous mill, and we will use many similar concepts to his work, but extend the concepts to a more

Jan 1, 1977

By H. A. Schlesinger

Various studies have estimated that for the next few decades, about half of all new power plants will be nuclear. The other half will be fueled with coal. Pending legislation on air pollution control would require all new coal-fueled power plants to install stack gas scrubbers or other technology to reduce sulfur oxide (SO,) emissions. These regulations would require flue gas desulfurization (FGD) or other technology for SO, reduction even on lower sulfur western coals. Among the options for FGD are single or dual alkali throw away processes using lime or limestone as the major reagent. These processes are currently more economically attractive than recovery processes, such as magnesium oxide and Wellman- Lord, that produce a salable product such as sulfur or sulfuric acid. One of the major problem areas with the throw away processes is disposal of the thrown away solid wastes, primarily calcium sulfite (CaSO3) and calcium sulfate (CaS04). Coal ash also must be disposed of, even if SOx reduction is not required. This paper addresses the alternatives for handling and disposal of throw away lime, limestone, and dual alkali process solid wastes. Advantages, disadvantages, and the economics of various methods are discussed. Both large central station power plants (500-1000 MW capacity) and smaller industrial power plants (up to 100 MW capacity) are considered. High sulfur eastern coals (53% S) and lower sulfur (3 1% S) western coals are considered.

Jan 1, 1981

By T. T. Field, M. Gell

MUCH has been learned about plastic deformation behavior in crystals through the use of dislocation and slip band etchants. Slip in nickel and nickel-base alloys has previously been revealed by various etching techniques.l-5 The techniques for nickel-base super-alloys4,5 were successful only in the Udimet 700 composition in specific heat-treated conditions. The objective of this work was to develop a more generally applicable slip-band etching procedure. The nominal compositions of the alloys used in this study are listed in Table I. The low carbon Mar-M2OO alloy referred to in the text is the same as listed in Table I with the exception that the carbon content is less than 100 ppm. Mar-M200 and Udimet 700 were solutionized at 2250" and 2150°F, respectively. The aging treatment for both cast alloys was 32 hr at 1600°F and for wrought Udimet 700 was 4 hr at 1975"F, 24 hr at 1550°F, and 16 hr at 1400°F. The new slip-band etching technique consists of a chemical etch followed by a short electropolish, Table 11. Fig. l(a) shows the best result obtained on an internal section of a plastically deformed single crystal of Mar-M2OO when using a conventional slip-band etching procedure which consists of electropolishing followed by etching. Ghostlike traces corresponding to planar slip bands are observed, but the contrast between the bands and the background is weak. Fig. l(b) shows the same field using the new slip-band etching technique. After the etching step of this technique, the same ghostlike traces of Fig. l(a) are observed, but the subsequent electropolishing accentuates the slip bands and the subgrain boundaries while the rest of the matrix is being polished. Longer electropolishing obliterates the slip bands. The new slip-band etching technique makes use of the etchants and electrolytes that are normally used for a given material. Because of this, it should be possible to slip-band etch other nickel-base superal-loys by using existing etchants and electrolytes for a material and following the procedures outlined in the "Comments" section of Table 11. All the illustrative examples given below show internal plastic deformation in single crystals of regular and low carbon Mar-M200 in the solutionized and

Jan 1, 1970

By AIME AIME

ONE test is worth a thousand expert opinions, say the engineers of the John A. Roebling's Sons Co. of Trenton, N. J. Confronted with the job of building the cables for the new Hudson River Bridge between Fort Lee and upper Manhattan, the Roebling organization, in spite of its long and varied experience in building cables for suspension bridges of various sizes, recognized that old yardsticks would be of little value in estimating safety factors for the immense span across the Hudson.

Jan 1, 1929

Jan 1, 1929

Jan 1, 1931

Jan 1, 1930

[PRESIDEST ASD DIRECTOR ................................................... HARVEY S. MUDD 3. .Los Angeles, Calif.]

Jan 1, 1946

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Jan 1, 1938

By Gregg A. Scott

Upper Stillwater Dam is to be a roller-compacted concrete gravity structure, founded on nearly horizontally bedded sandstone and argillite rock. An overview of the testing and analyses used to evaluate the adequacy of the foundation relative to deformation, seepage, and stability is presented.

Jan 1, 1984

By Gerald Laswell

Jan 1, 1976

By C. M. Marquardt

Tramp iron and steel moving on a conveyor belt cause small currents to be generated in a coil situated in a strong magnetic field, which are converted to an alternating current and are amplified. The output voltage from the amplifier fires a thyratron with a relay in its anode circuit, which actuates a howler and simultaneously drops a spot of marker material on the belt.

Jan 6, 1950