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By Charles Prasky, Robert K. Zahl, John C. Nigro

Bench scale and pilot plant research was conducted using dolomitic (CaO - MgO) lime as the basic additive in the preparation of self-fluxed pellets from a typical magnetic taconite concentrate (5.5% SiO2). The specific objective of this investigation was to ascertain the viability of the magnesia lime pellets in high temperature oxidizing and reducing atmospheres. Pellet basicity and induration temperature were major parameters affecting fired pellet quality; temperatures ranging from 1200° to 1250°C appeared to be the most favorable for production of self-fluxed pellets with basicities (B) above 1.0. Comparison of the mechanical and metallurgical properties of regular (acid) and self-fluxed pellets (B = 1.55) produced under similar conditions in a modified grate pelletizing machine showed that the selffluxed pellets were more resistant to abrasion and to high and low temperature reduction disintegration, an important consideration in commercial application. The +3 mesh Linder index increased from 68% (regular pellets) to over 90% (self-fluxed pellets). The reducibility and swelling indices of the self-fluxed pellets were found to be comparable to the regular pellets.

Jan 1, 1974

By O. A. E. Jackson

Pebble milling has been practiced in the reduction works of South Africa gold mines for well over 50 years. Originally flint pebbles were imported from Denmark to grind stamp-mill amalgamation- process tailing, which contained a good deal of extractable gold, but local operators soon found that large pieces of ore could be used for the same purpose. The ore is a hard, tough conglomerate in which quartz pebbles are cemented together by a matrix of redeposited silica interspersed with pyrite crystals. The gold, rarely visible, occurs as fine particles mostly segregated at the interface of the pebble and matrix, although a small fraction occurs within the pyrite crystals. There is seldom any gold in the pebbles themselves.

Jan 11, 1959

By Albert G. Zima

ACCORDING to recently published statistics, it is predicted that as much oil must be produced during the next 16 years as has been produced during the past 75, in order to satisfy the high rate of consumption of petroleum products. During 1934, over 17,000 oil wells were completed in the United States, and it is expected that over 20,000 additional wells will be drilled during the current year. Were it not for the remarkable progress made during recent years in the improvement of drilling technique and in the development of equipment used in the production phase of the oil industry, it is doubtful whether sufficient oil could be produced to meet present requirements. A few years ago, wells seldom were deeper than 3500 to 4000 ft., owing to the limitations of the drilling methods and equipment employed.. Today, 'however, through the application of scientific drilling methods and the adaptation of modern equipment and improved materials, many wells range from 6000 to 8000 ft. in depth, and a few recent completions exceed 10,000 feet. DRILL TOOLS Modern rotary drilling tools are the product of ingenious design and careful selection and adaptation of materials used in their construction. They must withstand terrific abrasion and, because of their compactness, must be designed to resist exceedingly high unit stresses. In bits, core drills and reamers, the bodies are made of either forged or cast alloy steels, heat-treated to develop a combination of high strength and toughness. To provide sufficient strength to the threaded portions and to protect the threads from distortion or damage, the box or pin sections of the tools are hardened to approximately 310 to 330 Brinell hardness

Jan 1, 1935

By William J. Priestley

In the manufacture of gun forgings and other steel parts that, in service, are subject to sudden high stresses and shocks, it is most desirable to use steel possessing the greatest toughness and ductility possible without sacrifice of strength. In order to obtain this condition, it is necessary to procure steel that shows the highest possible elongation and reduction of area without lowering the tensile strength and clastic limit. Proper heat treatment of the steel can control this condition within certain limits. When heat treatment has failed to produce the desired results, metallurgists have used steels containing molybdenum, zirconium, vanadium, chromium, tungston, etc. The purpose of this paper is to describe a method by which these desired physical properties may be procured—by the elimination of certain impurities that inherently exist in steel made by the open-hearth process, and without the use of expensive alloys. Design of Gun Forgings In the manufacture of gun forgings, a certain elastic limit is fixed by the designer, and the walls of the gun arc made of the proper thickness, allowing a suitable factor of safety for the high stresses and sudden shocks that occur during gun firing. The clastic strength of the gun is about 1.4 times the stress set up at any point along the bore of the gun during firing with the maximum powder charge. As the stresses set up in the walls of the gun during firing are mostly "tangential," all physical tests are taken in this direction. Due to the length of the forgings, these tangential test bars are always taken at right angles and transverse to the direction of flow of the metal in forging. Furthermore, test bars taken across the grain of the metal will more frequently expose defects and foreign inclusions in the steel than will bars

Jan 1, 1922

By William J. Priestley

In the manufacture of gun forgings and other steel parts that, in service, are subject to sudden high stresses and shocks, it is most desirable to use steel possessing the greatest toughness and ductility possible without sacrifice of strength. In order to obtain this condition, it is necessary to procure steel that shows the highest possible elongation and reduction of area without lowering the tensile strength and clastic limit. Proper heat treatment of the steel can control this condition within certain limits. When heat treatment has failed to produce the desired results, metallurgists have used steels containing molybdenum, zirconium, vanadium, chromium, tungston, etc. The purpose of this paper is to describe a method by which these desired physical properties may be procured—by the elimination of certain impurities that inherently exist in steel made by the open-hearth process, and without the use of expensive alloys. Design of Gun Forgings In the manufacture of gun forgings, a certain elastic limit is fixed by the designer, and the walls of the gun arc made of the proper thickness, allowing a suitable factor of safety for the high stresses and sudden shocks that occur during gun firing. The clastic strength of the gun is about 1.4 times the stress set up at any point along the bore of the gun during firing with the maximum powder charge. As the stresses set up in the walls of the gun during firing are mostly "tangential," all physical tests are taken in this direction. Due to the length of the forgings, these tangential test bars are always taken at right angles and transverse to the direction of flow of the metal in forging. Furthermore, test bars taken across the grain of the metal will more frequently expose defects and foreign inclusions in the steel than will bars

Jan 1, 1922

By C. E. Mills

Studies of ground movement and subsidence resulting from mining operations cover a broad field. It is also a very important consideration and one that eventually affects nearly every mining operation of any extent. The damage to surface buildings, removal of mine surface plants and replacements of main hoisting shafts must reach an astounding expenditure were these cost figures available over a period of years. Were the subject one of mathematical formula and dependent only on the angle of draw of the walls or country rocks, the problem would be relatively simple. Consideration must be given to depth and extent of workings; structural conditions of the orebodies and enclosing country rock; physical properties of these same rocks, including schistosity, bedding, jointing, slips, dikes, faults, and other structural weaknesses. The method of mining, extent of openings, supporting pillars, and amount of moisture or water underground are other pertinent factors. With such a large number of variable factors, it is apparent that the subject of subsidence is one that must be based largely on experience and results at other mines where conditions are somewhat comparable. In presenting this paper, it is the intent to describe the progressive results of past ground movements at the United Verde, to bring out physical conditions largely responsible for this movement, but to refrain from theorizing on the ultimate extent of subsidence resulting from future mining operations. Geology and Structure1 The ore deposits of the United Verde are of the massive sulfide, schist-replacement type. A structural anticline formed by the intrusion of diorite between bedding planes of steeply dipping and severely folded greenstones and porphyry localized the deposit of sulfide. The mineralized zone is of great horizontal extent varying from 200,000 to 400,-000 sq. ft., and extends from the surface to the lowest levels at a steep dip of from 50° to 75. The irregular interfingering of the sulfide with

Jan 1, 1934

By Peter K. Strangway

During 1973, a 20,000 net ton (18 100 metric ton) formcoke test was carried out at Inland's 26.5-foot (8.08-meter) hearth diameter on NO. 5 Blast Furnace. The formcoke briquettes were produced from Elko1 coal by FMC at their pilot plant in Kemmerer, Wyoming. The briquettes were shipped to Inland in open railroad cars and most of them were placed in an outside storage field until a sufficient amount was available for the actual blast furnace test. The test consisted of three phases: an initial four-week base period; the actual 33-day formcoke test period; and a final three-week post-test base period. During the formcoke test period, the regular coke skip loads were gradually replaced with skips of formcoke until, after a three-week period, the replacement ratio reached 80%. The furnace operated smoothly and quality hot metal was produced. The burden remained permeable and it was possible to maintain wind rates 9 of over 100,000 scfm (47 Nm3/s) without significant blast pressure increases. Dusting from the formcoke was not a problem either in the stockhouse or in the top gas. The formcoke briquettes maintained their original shape and density as they descended through the furnace. When the 80 percent replacement level had been reached, the inwall temperatures became higher than normal (about 2000 ºF (1090 ºC)) and followed an unusual steady pattern. In addition, the top gas temperature became higher than normal, and the hot metal analyses and temperatures began to fluctuate unacceptably. In general, it is felt that the high inwall temperatures were a result of channeling of the hot furnace gases along the stack walls. This channeling appears to have been promoted by a change in distribution of the burden in the top of the furnace which, undoubtedly, was caused by the increased increments of formcoke. Since it was felt to be unsafe to operate the furnace for an extended period of time with the inwall temperatures at the high level, a decision was made to remove the formcoke from the furnace. When this was done, the inwall temperatures returned to normal. Once the inwall temperatures had returned to normal, the remaining 3,800 net tons (3450 metric tons) of formcoke were used in the furnace at a nominal 40% replacement level for five continuous days. The furnace operated smoothly during this period, and the results were representative of satisfactory furnace operation with partial replacement of regular coke with formcoke. The test was successful in proving that formcoke can replace up to about 50% of the regular coke in a large furnace operating at high wind rates. However, additional work will be required to develop acceptable charging practices for using higher levels of formcoke replacement.

Jan 1, 1977

By Cyril Smith

SEVERAL investigators, mainly concerned with the mechanical proper-ties of the alloys, have studied the so-called aluminum bronzes after various quenching and reheating treatments. Of these works, perhaps the most complete is that of Bouldoires,1 who studied changes of length, electrical conductivity, thermoelectric force, hardness and micro-structure oh tempering quenched alloys containing 5 to 20 per cent of aluminum, although the work of Carpenter and Edwards,2 Curry,3 Greenwood,4 Braesco,5 Matsuda;6,7 Grard8 and others has added much to our knowledge of the changes occurring during tempering. The so-called acicular ß decomposes on tempering at temperatures between 350° C. and the eutectoid, giving rise to a Widmanstätten structure of a needles in a matrix of d or fine a + d, associated with an increase in hardness and almost complete loss of ductility. Matsuda, studied the' eutectoid transformation by means of dilatation and electrical "conductivity measurements during cooling at different rates. He found that on cooling at the rate of 10° C. per minute there was a decrease in electrical resistance and in length instead of the usual increase which occurred with slow rates of cooling. On tempering the rapidly cooled samples, the increase commenced at about 400° C. and at 520° C. the resistance and length had reached the equilibrium values. These peculiarities he accounted for as being due to a transitional phase ß' being formed, ß having an electrical resistance and volume less than either ß or a + d.

Jan 1, 1933

By Attilio Ligasacchi

The production of magnetite in copper smelting has been the subject of wide investigation in the past.1-9 It is accepted that most of the magnetite is produced in the converters and returned to the re-verberatory furnace with the converter slag. Part of this magnetite is circulated back to the converters in the matte. As a result, if proper fluxing practice is not followed, and temperatures in the converting process are not strictly controlled, an undesirable circulating load of magnetite may occur. This might ultimately lead to saturation in the reverberatory bath with consequent settling of the magnetite at the furnace bottom. This paper contains the cumulative results of a series of investigations on the formation and control of magnetite presently being conducted by the metallurgical department of the Chino Mines Division of Kennecott Copper Corp. THE METHOD USED FOR THE DETERMINATION OF MAGNETITE AND OTHER MAGNETIC MATERIALS Conventional wet chemical magnetite analyses are neither reproducible nor theoretically sound. These analyses are sensitive to time, temperature, and heating rate-all factors which tend to decrease their accuracy and reproducibility. To overcome the unreliability of the above method, H. W. Mossman1 developed an inductance bridge magnetite "meter" which completely replaces the wet chemical analysis with the advantage of quicker and reproducible results. Fig. 1 is a schematic diagram of the meter in use in the Chino metallurgical laboratory. When a pulverized specimen with magnetic properties is placed in coil A of the inductance bridge circuit, the permeability of the core is increased, causing a voltage drop across the coil. The unbalance is amplified to operate the balancing motor which adjusts the movable iron core in coils C and D to bring the bridge back to balance. An indicator arm connected to the movable iron core indicates directly the percent, or weight, of the magnetic material in the specimen. Coil B acts as a reference coil and a zero adjustment. The meter is standardized with a set of various amounts of -100 mesh pure magnetite crystals (99.8 pet Fe3O4) thoroughly mixed in a test tube with -100 mesh quartz sand. These mixtures are combined with inert transoptic powder and heated to 140° to 160°C (melting point of the powder) and subsequently cooled to room temperature, solidifying the whole mixture, in this manner eliminating any possible preferential orientation of the magnetite grains. In order to determine the effect of the particle size" of the magnetite and other magnetic materials on the meter determinations, five size fractions were obtained by wet screening of the 99.8 pet pure magnetite and several reverberatory matte and slag samples. The following size fractions were investigated: -80 + 100; -100 + 150; -150 + 180; -200 + 250; -250 + 300 and -100 mesh. The deviation of the meter readings for the various sizes of each sample never exceeded ±0.3 pet. This deviation is considered well within the accuracy needed for common smelter operation procedures. Further investigation proved also that grinding slag and matte samples in our laboratory disc grinder normally produced a powder constituted of 95 pet -200 + 300 mesh. For practical purposes a - 100 mesh size was used as standard for our studies. It was also found that for rapid determinations tamping of the sample in the test tube was sufficient and gave comparable results with those samples solidified with transoptic powder. For the purpose of this study we define the magnetite content in copper smelter slags and matte as the equilibrium amount of crystalline Fe3O4 existent in the specimen at a given reference temperature, excluding any secondary magnetite precipitated in the specimen during nonequilibrium conditions. MAGNETITE DETERMINATION IN SLAGS Since it is impossible to ascertain the status of equilibrium of a conventional slag sample, due to

Jan 1, 1965

By G. F. Comstock

THE subject of transverse fissures in steel rails has been discussed very thoroughly in recent years from various points of view and the final opinions expressed may be roughly classified into two groups: (1) That these fissures are the result merely of fatigue of the steel and are independent of the quality of the metal. (2) That the quality of the metal and the mill practice must have something to do with them. The first point of view was most-ably and logically presented by J. E. Howard,1 and in the discussion of this paper, as well as in several other preceding publications, Dr. P. H. Dudley, Consulting Engineer of the New York Central Lines, has strongly defended the other opinion.2 The steel makers of the country have naturally rallied under Mr. Howard's banner, hoping to place the entire blame for these. failures upon the railroads with their high wheel-loads, hard steel, heavy traffic, and sometimes inferior roach-bed; while the railroad men,, on the other hand, have been busy accumulating statistics and records in the effort to find an actual reason in the rails themselves that would account for the seemingly haphazard occurrence of transverse fissures under varying conditions and at widely separated points. The view that these fissures were due merely to normal fatigue under alternating stresses seemed most reasonable to the writer until quite recently, because from work clone in this laboratory, as well as the work of other investigators of the problem, no structural differences, in the vast majority of cases, were found between metal at the nuclei of transverse fissures and metal at similar positions in the same rails or in other rails that had not developed fissures. . Within the last year or two, however, since the method of etching polished sections for the microscope with a cupric chloride solution has been tried systematically. on lengthwise sections, passing through the nuclei of transverse fissures, evidence

Jan 11, 1918

By R. Hoffmann

THE Waelz process produces oxides of volatilizable metals from ores, metalliferous products and residues. The process was originally used for recovering zinc and lead, where tailings and residues containing those metals had accumulated at mines or smelters, but it is applicable for obtaining tin, arsenic or other volatilizable metals. It is useful when other methods of obtaining the metals from the ores or residues are too difficult or expensive or show too low a recovery. FIG. 1.-DAILY CAPACITY OF WAELZ PLANTS RUNNING OR BEING ERECTED. The Waelz process was developed in 1923 for the treatment of large calamine dumps in Upper-Silesia, which showed zinc contents of 8 to 10 per cent. and lead contents up to 3 per cent. The rapid development of the process, from the first trials up to the plants now working or in course of erection, is shown in Fig. 1. -The first industrial Waelz plant was started in 1925. Within two years the capacity of the working plants reached 700 tons material per day of 24 hr. During the year 1928 the daily capacity of the plants now at work or in course of erection will rise

Jan 1, 1928

By James Johnston

Synopsis.—A description of the working of the mills of this company and the metallurgical practice in vogue, by which a remarkably complex silver ore, averaging 54 oz. of silver per ton (run-of-mine ore), is treated to give a 95.66 per cent. extraction. The main features of the processes are: The cyanide amalgamation of the high-grade ore. The cyanide treatment of the low-grade ore, after extremely fine grinding and close classification, in a caustic soda solution. The use of a wet desulphurizing process to break up refractory silver minerals. The substitution of aluminum dust for zinc dust as a precipitant. The recovery and shipment of over 13,000,000 oz. of silver in bullion at 997 to 999 fine since this metallurgy was inaugurated, about 2.5 years ago. On the completion and successful operation of the mill to treat their high-grade ore,' the Nipissing Mining Co., under the general management of R. B. Watson, started a series of investigations of the possible treatment of the low-grade ore by the cyanide process, so that they would be in a position to market only silver bullion. These tests were run in July, 1911, on a large scale, by G. H. Clevenger, on an average mixture of Nipissing ore. The results obtained by a partiai amalgamation followed by cyanide treatment gave an extraction varying from 90 to 93 per cent. and were sufficiently encouraging to warrant Charles Butters, the company's Consulting Metallurgist, in recommending that the new low-grade ore mill under contemplation should be a cyanide mill, instead of a concentrator. The cost of such a mill, capable of treating 200 tons per day, to obtain a 90 per cent. extraction at a working cost of $3 per ton of ore treated, was estimated at $250,000. In coming to a decision as to which type of mill should be erected, the concentrator, with the subsequent shipping of concentrates to a smeltery,

Jan 1, 1915

By A. W. Dana, F. J. Shortsleeve, A. R. Troiano

The phenomenon of flake formation which may occur during cooling or room temperature aging of large steel sections is caused by a combination of hydrogen and stress. As such, the transformation characteristics of austenite in a particular section play a major role in the occurrence of flakes. Isothermal and continuous cooling studies demonstrated that flake formation is particularly sensitive to nature, distribution, and relative proportions of the microconstituents in the cooled sections. In the absence of transformation stresses, abnormally high hydrogen contents could be tolerated without flaking. Flakes were not found in the absence of transformation stresses. No correlation existed between average hydrogen content and flake formation where cooling stresses were low. Hydrogen in the steel was a necessary but not sufficient condition for flake formation. DESPITE a long history of laboratory and commercial investigations, the mechanics of hairline crack or flake formation in large steel sections remains unresolved. Recent publications1-5 emphasize that flaking is still a serious problem.* immediate cause of flaking is the pressure exerted by entrapped hydrogen gas that collects in small internal cavities or voids during cooling. When the temperature of steel is low enough to preclude extensive plastic flow, the cavity pressures cause local brittle fractures (flakes). 2—The microsegregation and transformation stress theory. According to this theory, flaking results from stresses arising from the volume changes accompanying the formation of martensite and/or low temperature bainite after a large portion of the section has transformed at elevated temperatures. The proponents of the hydrogen theory suggest that stresses from other sources may be additive to the stresses produced by hydrogen and may, in some cases, provide the increment of stress necessary to produce flakes. However, the critical aspect of this theory is that no stress, except that produced by hydrogen pressure, is believed to be sufficient in itself to produce flakes. For practical considerations, this means that the only safe thermal cycle is one that reduces the hydrogen content to some low critical level below which flaking will not occur regardless of the state of transformation. On the other hand, the transformation stress theory does not rule out the embrittling effect of hydrogen. This theory simply proposes that flaking does not occur in the absence of transformation stresses. With the transformation stress theory as a basis, commercial antiflaking cycles would be designed to complete the transformation of austenite prior to cooling to ambient temperatures. Both of these theories appear compatible with industrial experience. Antiflaking cycles, such as cooling at extremely conservative rates or soaking for periods of time in the upper subcritical temperature ranges prior to cooling to ambient temperatures, may allow the following: 1—diffusion of hydrogen out of the section and, as a consequence, reduction of the hydrogen content to some safe minimum value (hydrogen pressure theory) and 2—complete decomposition of the austenite at rela-

Jan 1, 1956

By D. R. Semmes

The possible oil territory of Alabama can be readily divided into two regions, the Paleozoic area of the north, and the Coastal Plain province of Cretaceous and younger formations lying to the south. This latter area has received much attention in the last few years and has been described by a number of writers.' Although the possibilities of the Cretaceous series have been much emphasized by recent writers, the fact remains that the two, or possibly three, localities where oil or gas have been found in anything like paying quantities are confined to the area of Carboniferous rocks. Moreover, almost all of the oil seeps and a good percentage of the gas seeps are confined to this area.2 Topographically, as well as structurally, the Paleozoic area can be divided into three rather well defined provinces: (1) The broad, open Coosa Valley lying adjacent to the crystalline oldland, with comparatively little relief, except for occasional longitudinal ridges and rather intense folding; (2) the plateau region of horizontal or gently warped Pennsylvanian strata broken by occasional anticlinal valleys aligned northeast and southwest, outliers of the Coosa Valley proper, in which the older Paleozoic formations are exposed—a region of much relief (200

Jan 1, 1921

By J. David Lowell

For his contributions to the field of mining geology, a striking example being his brilliant inte.rpretation of the complex geologic history of the San Manuel District (Pinal County, Arizona) which resulted in the discovery of the Kalamazoo orebody, and for his lecture, "Copper Resources in 1970." On a low desert ridge six miles south of Cairo lie the remains of the world's earliest known mining town, Maadi of predynastic Egypt. Copper artifacts, including ingots and an ax head which was spoiled in casting, indicate that copper ore was smelted in Maadi, and radiocarbon dating has placed the activity at least as early as 3300 B.C. This is the oldest documented date for the use of smelted copper, the first industrial metal used by man. Copper was mined and smelted almost as early in Asia Minor and on the island of Cyprus, but the greatest development of the budding copper industry was in Egypt, where specific historical records show that about 10,000 tons of copper metal were produced in the period from 1850-1580 B.C. Contrast this production of 35 tons per year with the present world production of about 7 million tpy. Evolution of the Copper Industry The copper ore mined by the ancients was high grade, and the copper produced was expensive. The copper industry began with narrow high-grade veins, but has evolved to the point where massive earth-moving equipment can be operated in huge, low-grade open pits. Indian pits dug before 3000 B.C. in the Lake Superior district were in ore which averaged 15% Cu. His- torical research done by Arthur Brant has shown that copper cost in the Middle East in 1840 B.C. in terms of 1970 labor dollars was about $25 per lb. The copper mined in northern Europe in 1540 in the time of Georgius Agricola averaged about 8% Cu, and the cost in 1970 labor dollars was about $10 per lb. Average ore grade had dropped to about 6% Cu in 1890, and the cost of copper in the U.S. in 1970 dollars was about 45¢ per lb. Butte, Mont., was a good example of the efficiently operated vein mines of this time. In 1906, Daniel Jackling made a dramatic entrance into the copper scene with the Bingham Canyon open-pit copper mine and proved that more profit was possible mining 2% porphyry copper ore on a

Jan 1, 1971

By J. L. Rodda, R. L. Wilcox, E. C. Truesdale

In recent years various problems in connection with research work on the preparation and properties of zinc-base alloys have required reliable information concerning the constitution of the zinc-rich portion of the iron-zinc equilibrium diagram. On numerous occasions rather positive indications were obtained that, for example, the solubility of iron in zinc was incorrectly represented on the current equilibrium diagrams. A careful study of all the available literature relating to the iron-zinc system led to the conclusion that much of the early work was unsatisfactory as measured by present standards of experimental accuracy, and as a result it was decided to redetermine the location of the liquidus curve and of adjacent portions of the diagram. Part I of this paper comprises a description of the experimental methods and a summary of the results by means of which the zinc-rich end of- the iron-zinc diagram has been revised in the following ways: 1. Measurements of the solubility of iron in liquid zinc by several different sampling methods, leading to a relocation of the liquidus curve. 2. Microscopic, conductivity, and X-ray studies of the solid solubility of iron in zinc, which, together with thermal analyses, have resulted in new values for the solid solubility and the eutectic temperature and composition. 3. Heating and cooling curves, obtained by a refined differential method, leading to new locations for the two peritectic horizontals. In Part I1 of the paper the attempt is made to review all of the published work having a bearing on the constitution of the iron-zinc system, and to correlate the present results, and some recently published data involving the use of X-ray technique, with the earlier work, much of which was done from 25 to 30 years ago.

Jan 1, 1936

By G. A. Vissac

In continental Europe the feldspar jig is used almost exclusively for cleaning the fine sizes of coal; it operates with an artificial bed, made up generally of pieces of feldspar or of any other hard and heavy rock with good cleavages. A primitive form of this machine requiring close supervision was used in this country years ago, but output was small. The modern machines are generally air-pulsated Baum-type jigs, with capacities up to 150 tph, and treat sizes from 3/s in. to 0, usually previously dedusted or deslimed. These jigs are equipped with very accurate and sensitive automatic controls insuring satisfactory operation even at low separating gravity and with feeds irregular in quality and quantity. This paper will deal more particularly with coal cleaning separation, but the technical studies apply equally to all minerals.

Jul 1, 1955

By A. H. Bromly

THE small agricultural village of Santa Barbara, in the State of Guanajuato, has been the center of spasmodic tin-mining operations during recent years. The deposits, so far as I know, are unique, and a few brief notes may be of interest. Santa Barbara, about 12 miles west of San Felipe station on the Mexican National Railway, and at an elevation of 2,400 m. above sea-level, is situated in a flat valley extending east and west, and bounded north and south by broken rugged bills rising about 330 m. above the general level of the valley. Tin-mining operations have been conducted-at the Queensland mine, near this village. A small concentrating-mill was erected and attempts were made to smelt the ore in reverberatory furnaces. The country-rock of the district for many miles is rhyolite of great thickness. There are some local variations due to differences in cooling, or subsequent alteration or impregnation; but throughout the whole district the principal constituents of the rocks remain the same, viz., free silica, orthoclase-feldspar and sanidine. The latter is especially marled. The crevice and joints of the rock are frequently filled with calcedonic and opalescent quartz. The ore-formation at the Queensland mine is of an unusual nature, consisting of cracks in the rhyolite which have been filled with clay. This phenomenon is largely developed over a width of from 80 to 100 m., in which the principal fissuring follows an approximate direction of north and south. The av¬erage clip ranges between 70 to 80 degrees. Some of the fissures bold sufficiently true for a time to afford the impression that they are clue to dynamic causes, or earth-movement. This may be true of some of the north by south fissures; but considering

Jul 1, 1905

Sailing westward from the Society Islands in the fall of 1774, England's noted explorer Captain James Cook discovered New Caledonia-that long, linear island that has played such an important and varied role in the history of nickel. Upon his return to England the following year, Cook's announcement of this uncharted island generated governmental interest, but its distance from the Island Empire, the troubles in the colonies, and the difficulties with France combined to keep English interest indirect and in the background of the then-current events.

Jan 10, 1968

By C.A. Zapffe

Both the foundryman and the theoretical metallurgist are now generally agreed that the anomalous "rising" or "bleeding" of certain ferrous castings of killed metal is primarily attributable to hydrogen. How and why the phenomenon occurs, however, have not been made clear. The following discussion is intended to harmonize foundry experience with metallurgical theory so that the foundryman may possibly improve his ability to prognosticate whether a certain casting may bleed or not. Bleeding, Rising, and Piping The "rising" to be discussed here is not to be confused with the action in rimming ingots as a result of the carbon-oxygen reaction, although a conclusion will be drawn that may apply to the art of controlling the rimming action. Only killed metal is considered, which includes both steels and irons. In Fig. I, three killed, chill-cast ingots are shown: a porous ingot whose evolution of gas during late stages of solidification has ejected metal through the top; an ingot in which moderate gas evolution during solidification has lifted the mushy central metal, i.e., it has "risen"; and, third, a sound ingot with good piping characteristics. The first type is referred to as "bleeding," and generally infers that a solid skin had first formed through which the liquid metal later erupted. There is no fundamental distinc- tion between bleeding and rising in reference to killed metal.* Porosity Hydrogen appears as a cause of bleeding because the gas evolution simultaneously leaves a porosity of a type traceable to hydrogen. Twenty years ago, Melmoth' noted that killed steel that rose unexpectedly in the mold, if returned while liquid to the furnace and heated further under a reducing lime slag, would again rise in the mold; but that if the ingot were allowed to solidify and was then remelted no rising occurred. A critical quantity of the responsible gas is therefore removed by the rising action. Melmoth associated rising with high silicon (0.7 to 0.9 per cent) and concluded that silicon increased gas absorption. Because silicon is a strong deoxidizer, oxygen must, therefore, be eliminated from consideration of the three common gases in steel—oxygen, nitrogen, and hydrogen. Butterworth2 later decided that pinhole porosity was caused by gases dissolved in the metal and that hydrogen was obtained from steam in the mold. Allen's classical work on copper castings,3 soon followed by

Jan 1, 1943