Search Documents

By Bunting S. Crocker

Pebble grinding was used at Lake Shore Mines in 1949. A full description of experimental evidence and test plant results was published in 1952 1 and further operating details in 1954.2 In more recent years the term autogenous grinding has been coined and is now frequently seen in the technical literature. Autogenous crushing and/or grinding covers any grinding mill in which the larger of ore are made to grind the fine pieces; the crushing and grinding may be either dry or wet. This discussion deals only with wet autogenous grinding, and only in the fine grinding part of the circuit, i.e., from 6 mesh to 92 pct -325 mesh. The term pebble milling could apply to fine autogenous grinding in which the pebbles are made from the ore itself, or it could also refer to grinding with pebbles, such as flint pebbles, from a source outside the mine.

Jan 5, 1959

By F. R. Hensel

The present paper describes a number of experiments with fine silver, coin silver, silver-cadmium oxide and silver-nickei-copper compacts, prepared by powder metallurgical methods. The test data are of a preliminary nature, since most of the work was exploratory. Fine Silver Eject of Compacting Pressure on Hardness and Density during Cold and Hot Pressing The cold-welding properties of silver have received considerable attention and the welding characteristics are functions of such variables as: cleanliness of metal particles (impurities and adsorbed gases), chemical nobility of particles, plasticity and hardness, particle assortment, particle shape, particle porosity, apparent density, temperature, pressure, time, recrystalliza-tion characteristics. Chemical nobility, plasticity and low temperature of recrystallization after work-hardening are responsible for the excellent low-temperature bonding properties of silver. Several series of compacts were pressed at pressures of 5, 10, 20, 30, 40, 50, 60 70 and 80 tons per square inch, at temperatures of 32°C. (room temperature), l00°, 2000, 300°, 400°, and 450°C. Silver powder of minus 325-mesh, produced by displacing silver from a nitrate solution by means of copper, was used. The density was calcuiated from accurately measured and weighed compacts. The hardness was measured on the Rockwell F scale. The investigation shows that an increase in pressure promotes a higher density and hardness regardless of pressing temperature, up to a temperature of 400° C. The pressure-density curves at various pressing temperatures are shown in Fig. I, the pressure-hardness curves at various pressing temperatures, in Fig. z. The greatest increase in both hardness and density was obtained in the pressure range of 5 to 20 tons per square inch. A compact from each series was annealed at 300°C. in air, for various lengths of time. The hardness values after annealing are shown in Table I. A minimum hardness was obtained after one hour of annealing. No change in density occurred during annealing. The maximum density was obtained at 80 tons per sq. in., and at this pressure the hardness is equal to that of hard-drawn wrought

Jan 1, 1945

By Eugene A. Stephenson

THE year 1935 is noteworthy for the superior legislative measures passed by several states. Sincere efforts have been made to establish equity between the various producing tracts in oil and gas fields. Outstanding legislative measures include the New Mexico law, known as Senate Bill No. 79, approved on Feb. 23; the Oklahoma law on April 22; the Texas law on April 30; and the Kansas law, which became effective July 1. Primarily designed to prevent waste, but more or less the direct out- growth of the current excess of potential oil and gas production, these statutes fall in the class of "Proration Laws."

Jan 1, 1935

By J. J. Gilman

The dependence of ortho kink-band formation on crystal orientation, on temperature, and on the conditions at the ends of a specimen is described. Load-compression curves for crystals that kink are presented. The reversibility of ortho kinking is demonstrated, and motion of kink planes through crystals is shown. Finally, a phenomenological explanation of ortho kink-band formation is given. ORTHO compressive kink bands (Fig. la) were discovered for the case of metals by Orowan,1 and they have been discussed by Jillson2 and in some detail by Hess and Barrett." However, their history in nonmetallic crystals is considerably older. It is not known when they were first observed in mineral crystals, but descriptions of them may be found as early as 1885.* They were sometimes mistaken for twins.6 Mügge seems to have been first to realize their true nature and importance. He reviewed the knowledge of them for a wide variety of crystals: anhydrite, antimonite, kyanite, vivianite, gypsum, mica, graphite, molybdenite, barium bromide, cal-cite, sodium nitrate, and barite. Also, the "twins" observed by Bridgman7 in sapphire crystals resemble kink bands more than twins. The terms ortho and para kink bands have been coined in order to distinguish between two types of kink bands which seem to represent the same geometrical configurations, but which have different origins and sizes. Ortho kink bands are the usual type that form at low loads when zinc crystals are compressed parallel to the basal plane. Para kink bands form at much higher loads in highly deformed crystals. These terms refer to compression phenomena and are not to be confused with analogous tension phenomena such as tensile kink bands and deformation bands. Mügge described the geometry of ortho kink bands quite completely for kyanite crystals, Fig. lc. The geometry observed for cadmium by Orowan1 and for zinc by Hess and Barrett3 is very similar to that described by Mügge. (See Hess and Barrett for a complete discussion.) Mügge associated kinking with bending combined with basal slip. He pointed out that the kink angles

Jan 1, 1955

By James P. Sloss

A PERMANENT assay office is commonly established as part of the general plant equipment of operating gold and silver properties, but during the development stage of a mine, the cost of such an office is usually so assay work must be done elsewhere. In most instances only a few samples will be taken each day, but if the mine is to be developed scientifically, the analyses of those samples will guide further development. Under such circumstances, the time element in assay returns is important, since the lapse between the taking of the samples and the receipt of results may determine the success or failure of a small-mine operator. The following description of fur-

Jan 1, 1935

By Robert Leach

THIS paper gives a brief summary of the process of manufacture of sterling silver, and some of its more important physical properties, as observed in commercial production of rolled sheet and wire. Although papers have been published by Turner and Smith,1 Rose,2 Sperry3 and Jordan,4 there are few technical data available, and unfortunately the time allowed for the preparation of this paper has not been sufficient to make it as comprehensive as the title might indicate. ANALYSIS OF STERLING SILVER Fine or pure silver is too soft for coinage and the manufacture of articles in which strength and resistance to wear are desired. From the earliest times of which we have record, copper has been the metal generally used to harden silver. Analyses of coins and silver articles from ancient tombs show varying amounts of copper, and old Roman silver objects in the British Museum have approximately the same analysis as our sterling. The first authentic record of the establishment of a standard alloy is during the reign of Henry II in England. During the twelfth and thirteenth centuries, the people in the Eastern Provinces of Germany had a reputation for the standard and purity of their silver coinage, and it is said that Henry II employed some of these Easterlings, as they were called, to improve and standardize the English coinage, which had become debased. The peculiar standard adopted is probably accounted for by the system of weights used. A troy pound contains

Jan 1, 1928

By Jacques B. Wertz

Both the San Andreas fault complex and the Murray fracture zone are apparently found to be contemporaneous with the Laramide mineralization period. Their compounding effects certainly have disturbed the Texas lineament belt and its components with serious lateral offsets and most probably have been instrumental in allowing intrusives to be emplaced as well as mineralization to accompany these intrusions at some of the fracture intersections. While the main fracture centers can be almost accepted as being structurally linked together, the Texas lineament trend definitely predominates, exerting a prevailing direction to graben (Silver Bell) and to elongated depressions (Bisbee). That this lineament belt also influenced the concomitant mineralization seems a logical inference. The orebodies are generally found at intersections near the most centrally-located intrusive with a distance varying from contiguity to one or two miles. The Southeast Arizona copper province owes its existence primarily to a particularly favorable structural setting of broad semi-continental scope. Thus, various regional structural elements are to be considered as possibly direct or remote cause for the widespread mineralization, although the one or the ones really responsible may never be singled out. There arc three basic regional elements: (1) The north-northwest-trending anticlinorium that diagonally crosses Arizona is quite obvious because many mountain ranges follow this direction. This anti- clinorium, which merges northward into the Wasatch-Jerome Belt, marks a broad zone of weakness where tension seems to prevail. Mineralized trends such as Jerome-San Manuel-Bisbee may give some weight to the economic value of this structural element. (2) Northeast-trending fractures, parallel to the Colorado Mineral Belt (Landwehr, 1967), appear troincident with mineralization as evidenced by the Questa-Grants-Morenci and the Lordsburg- Tyrone-Santa Rita alignments. This structural direction is accepted as one of the most economically significant in the Southwestern United States. (3) The Texas Lineament.

Jan 1, 1970

By I. R. Kramer

I. R. Kramer (Martin Co.)—In a recent paper Nakada and Chalmers24 reported some observations of effects of surface conditions on the stress-strain curves of aluminum and gold single crystals. It is of interest to compare these observations with the results published previously in this journal and to comment on their general conclusions. In brief, Nakada and Chalmers concluded that the removal of the surface layer of a prestrained specimen lowered the stress-strain curve for aluminum but not that for gold. Further, they concluded that the surface work hardening of aluminum is confined to a depth not more than l0-3 cm. In our results25 published previously, it was pointed out that when prestrained specimens of aluminum and gold were polished to reduce the thickness upon reloading the initial flow stress decreased markedly. Further if a sufficient amount of metal was removed, the yield point failed to appear. With continued application of the load the stress-strain curve became coincident with that of the virgin crystal. We have found this behavior in some 100 determinations to hold consistently for gold, aluminum, and copper in both single and poly-crystalline specimens. The amount of strain required before the curves coincided depends upon the amount of metal removed but it is usually less than 0.01. This type of behavior is the same as that reported for metarecovery by other investigators.29 For aluminum specimens which have been prestrained and then heated to temperatures above 50°C we have consistently found that the stress-strain curve was typical of the orthorecovery28 type. In this case the stress-strain curve always lies below that of the virgin specimen. With respect to Ref. 24 the curves for aluminum are always below that of the virgin curves, while those for gold become coincident. This observation indicates at least for aluminum that the specimens must have been heated to a temperature high enough to cause recovery by an alteration of the internal dislocations. In addition, a recovery would be expected because of the removal of the surface work-hardened layer. Nakada27 had reported that, with his particular apparatus in which a perchloric acid polishing solution was used, the temperature of the specimen increased 65°C. The curves presented in Ref. 24 for gold do not permit one to detect the initial flow stress upon reloading after the surface-removal treatment. In fact, contrary to the method used by Nakada and Chalmers, the change in the stress-strain curve produced by a surface-removal treatment cannot be described in terms of a decrease in stress at strains much higher than that at the initial flow stress because of the coincidence of the curves at the higher strain values. With regard to the depth of the work-hardened surface layer, our data show for aluminum single crystals (7.5 by 0.3 by 0.3 cm) that the initial flow stress remained constant after 12 x 10-3 cm had been removed from the thickness. This depth was independent of the prior strain. For gold crystals this depth is somewhere between 10 x 10-3 and 20 x 10-3 cm. Y. Nakada (author's reply)— Kramer states,28 "for aluminum specimens which have been prestrained and then heated to temperatures above 50°C, we have consistently found that the stress-strain curve was typical of the orthorecovery28 type. In this case the stress-strain curve always lies below that of the virgin specimen." However, Cherian et a1.26 discovered that aluminum polycrystals annealed at 32" and 100°C showed the metarecovery behavior. They showed that the orthorecovery behavior did not appear until the crystals were annealed at 150°C. Kramer suggests28 that the drop in the flow stress of aluminum crystals after the surface removal by electropolishing24 may be due to the recovery caused by the temperature rise which may occur during the electropolishing.27 However, as indirectly stated in Ref. 24, the current density used in these electro -polishing experiments was 0.15 amp per sq cm. According to ref. 27, this current density should cause a temperature rise of only 40°C. This may cause the metarecovery but not the orthorecovery. Furthermore, as stated explicitly in Ref. 24, the surface removal was accomplished by chemical etching as well as by electropolishing. The results were the same for both electropolishing and etching. During the etching, the specimen temperature did not rise above 35°C. Some aluminum crystals were placed in water at 35° C for 30 min. These crystals did not show the decrease in flow stress. Therefore, it is quite clear that the flow-stress drop after the surface removal is not caused by a high-temperature recovery. However, as Kramer points out,28 it is quite possible that the internal dislocation structure may have been altered because of the removal of the highly work-hardened surface layer. However, how much this rearrangement contributes toward the flow-stress decrease is not known at present.

Jan 1, 1965

By Charles Hardy, George D. Cremer

POWDER metallurgy has been established for some time as a novel method for manufacturing a great variety of articles generally specialties that could not be made conveniently by any other method. In this category are such parts as porous hearings cutting tools of sintered carbides, and electrical contacts in which the metallic constituents do not tend to alloy in the proportions employed. The industry, however, is now at a stage where it has begun to manufacture articles that can and have been made by other methods. Thus, powder metallurgy is now preferred technique for the production of numerous machine parts characterized by high strength, accuracy of configuration, and substantial lack of porosity. Manufacture of such machine parts from metal powders has no doubt been stimulated by the war, although the trend in this direction has been apparent for several years. In any case, quantity production of high-density precision pieces by ponder metallurgy is now in full suing in the United States, and such production can and should continue to expand during and after the war.

Jan 1, 1942

By Freeman Bishop

More than a few discussions are taking place these days among management economists seeking a way out of the dilemma of lower productivity vs. higher labor costs. Most suggestions would be illegal under present antitrust laws. Otherwise interindustry cooperation could be used to divide up some of management's tasks. Or price structures might be tuned to the special machinery and skills of some plants. Both remedies would be under attack almost immediately. There is one other remedy that is getting lots of attention: some form of compromise between management and labor to phase out no longer needed work practices that unions insist shall be retained. Railroads are the national industry suffering the most from this disease, still known as "featherbedding," an epithet coined by the railroaders themselves.

Jan 1, 1971

By AIME AIME

WITH the recent increase in the price of gold, its economic recovery at depths formerly considered impractical has become a present possibility. Two important difficulties must be met: pressure bursts of the rock, and the reduced efficiency of human labor subjected to the higher temperatures and the increased humidity at the greater depths. In the following abstract of a paper by J. H. Dobson, presented before the South African Institution of Engineers on

Jan 1, 1935

By David H. Browne

(Pittsburg Meeting, March, 1910.) NICKEL has always been a fruitful mother of problems. Previous to the year 1906 nickel was regarded as an element replacing iron in copper-mattes, and it was believed that the same laws which governed the elimination of iron could be applied-to nickel. This conception has lately undergone a complete change, and nickel in all its stages is now regarded as an element replacing copper; in other words, copper-nickel is considered now as two elements, but as one metal. When we commenced our investigations on Monel metal we made a great many experiments on the conversion of mattes, both high copper and high nickel. We studied closely the composition of the mattes and the changes produced by the blow. We found in all cases certain agreements which we believe are due to some law. Briefly stated, our conclusions are as follows 1. Nickel is not an element replacing iron in matte. 2. Nickel-copper alloys act in the matte-blow like one metal. 3. Nickel-copper alloys follow, during the matte-blow, exactly the same laws as govern. the behavior of copper alone. This brings up the question : What are the laws governing the production of metallic copper, and what are the relations copper to sulphur and iron during the Bessemer blow ?

Apr 1, 1910

By Claus G. Goetzel

POWDER metallurgy is known as the art of producing metal powders and fabricating them in a nonfusion process by a simultaneous or consecutive application of pressure and heat under controlled operating conditions. Before the advent of powder metallurgy, the high melting points of the refractory metals and nonmetals made their manufacture and use practically impossible. Today, however, the uses of refractory materials in high-speed cutting tools, surgical instruments, brake linings, electrical contact switches, and filaments in incandescent lamps are commonplace in industry. Lately designers have even been turning to powder metallurgists to develop new techniques of fabricating refractory materials for extreme-service use in high-temperature zones of such modern products as gas turbines and jet engines. The new techniques being born will undoubtedly provide industry with a great number of new alloys and materials for future designing.

Jan 1, 1948

By Scott Turner

GOLD AND SILVER, the monetary metals, have presented in the last year a striking contrast; gold has experienced unusual prosperity, while silver has been depressed more severely than ever before. Gold mining has been hailed as the only basic industry that is able to thrive on depression; the new gold produced is thought by many to be the most important material for the reconstruction of prosperity. Silver production, meanwhile, has been sinking to its level of 40 years ago, and its price to a level never before recorded. These factors have reduced the value of silver produced in 1932 to about the value of the average annual production more than a century ago, that of the decade 1801-1810. No other major commodity in world trade appears to have suffered a greater decline during the present depression.

Jan 1, 1933

MR. Woo's succinct description of the mining and smelting of silver-lead in Mongolia, with the roasting-and-reduction process and cupellation, has much interest as a picture of methods that not only may have been in use, as he suggests, a thousand years ago, long before the existence of mining schools or chemical laboratories, but probably vary little, if at all, from the practice of prehistoric times, when King Priam's handsome silver vases, cups and bowls were formed. For it is highly improbable that such large objects were made from comparatively rare native silver, and the metal must have been smelted from ore, and most likely in great part from galena,, with cupellation of the lead. Dr. W. A. P. Martin, in his excellent book on the Lore of Cathay, points out that Chinese alchemy is over 2000 years old, antedating the European by at least six centuries; and he infers that the Chinese skill in metallurgy and many branches of practical chemistry owes its origin to " those early devotees of the experimental philosophy who passed their lives among the fumes of the alembic." Those alchemists, however, may have more likely derived some of their leading ideas from the mys terious, and at that time wholly unexplainable results observed in already very ancient metallurgical processes; in which, for example, certain stones were transmuted, as it were, into metals widely divergent in character from their ores, and even silver and gold were obtained from the most unlikely-looking mate rials. It is therefore, in any case, not improbable that the Chinese may have preceded western nations in the discovery of metallurgical methods. At all events, it is now evident that the Japanese acquired these arts from China, the former source of all their higher civilization. My own observation of old-fashioned silver-smelt ing at Hosokura, on the main island of Japan, and about 220

Jan 1, 1903

By Robert Linton

THE PURCHASE of silver by the United States Government under the provisions of the Pittman Act is practically completed. Producers of silver in this country will now have to market their silver in competition with the rest of the world. It therefore becomes of interest to study such data as are available and endeavor to obtain such suggestions as may be afforded therefrom as to the probable future market position of the metal. Conditions influencing the marketing of silver are numerous and complex. It is a commodity entering. into the arts and manufactures, and therefore influenced by the condition of various lines of business which make use of it; it is currency-being used by all countries for subsidiary coins and even as the founda-tion of the system by a very few; and it serves as a frequent basis for speculation. The various factors involved can easily set up so many cross-currents in the flow of the metal that predictions in regard to the market position of silver can never be safely made, although it may be possible to form some idea of prob-able trends over a sufficiently long period. Of course price is determined, as is the case with all commodities, by the inexorable workings of the law of supply and demand.

Jan 6, 1923

By Theodore Marvin

FOLLOWING the receipt of questionnaires from many parts of the world, the Aviation Committee is completing a review of the use of aviation in mining and petroleum operations. The summary of this study should be available at the 1937 Annual Meeting in New York City, at which time several papers will be presented on specific application of aerial geologizing. From the reports received, there is little question that this air branch of mining is here to stay. Of course, the transportation of personnel arid material continues to merit attention but it is in the division of aerial geologizing that flying is finding its widest, most technical application.

Jan 1, 1937

By C. R. Austin

THE investigation described in this paper deals with the development of high-temperature alloys of the Konel series over a considerable period of time at the Research Laboratories of the Westinghouse Electric and Manufacturing Co. The word "Konel" has been coined to designate a class of alloys which are essentially nickel-cobalt-iron with other elements added, usually in small quantities. Most of these alloys contain titanium, usually about 2.5 percent. The main consideration related to strength at high temperatures but the thermionic characteristics of the alloys was also of considerable importance. It is, however, with the mechanical properties at elevated temperatures that we are herein concerned. Much attention has also been devoted to their age-hardening characteristics. There is little need to stress the utilitarian aspect of this subject, as it has been discussed frequently. Alloys exhibiting superior properties at normal or elevated temperatures rapidly find many suitable applications. There may be some question, however, as to what constitutes a "superior alloy, " or an alloy that may have good service possibilities at high temperatures. The problem is complex and various means have been employed to predict the useful life that may be expected of a material. In recent years the "creep limit" has been used as the best means of evaluation. Such tests necessarily are prolonged and hence collection of data is very slow. In a general survey of many alloys therefore the creep test is not desirable and recourse must be had to much shorter time tests in order more rapidly to select alloys which appear to show promise. For this reason the present survey has been made using the high-temperature tensile test and a bend' test developed by Howard Scott.1 In the tensile test the conditions have been standardized for all tests, so that values obtained are at least comparable, one alloy with another, although the absolute values recorded merely indicate the mechanical properties at the given temperature under a definite rate of loading.

Jan 1, 1931

By Stuart St. Clair

EARLY in 1936, when the American Petroleum Institute issued -J "American Petroleum Industry," which was a survey of the current position of the petroleum industry, and its future outlook, and the figures for petroleum requirements .for 1950 and 1960 were widely publicized by the several oil journals, the impression was given that the petroleum- industry must be nearing maturity and would by 1950 have passed the high' point of its obligations to business progress in the United States.`' Let -us look at the figures which might conduce, this thought. Referring to p. 32 of the report, the total indicated crude-oil requirements in 1940 are 1,099,000,000 bbl-; for 1950, the peak, 1,109,800,000 bbl.; for 1960 a decline to 1,071,020,000 bbl. This downward trend, then established, is probably expected to continue. And this in the face of a crude production in 1935 of 993,942,000 bbl., 38,858,000 bbl.

Jan 1, 1936

By G. W. Josephson

JUDGING by the progressive atmosphere prevailing in the nonmetallic mineral industries during the past year, postwar conditions were healthful though inflationary. Demand for most industrial mineral products has been exceptionally high and many new production records were attained. Severe shortages of some commodities existed, especially building materials and fertilizers. Production costs and prices increased and profitable operation was general. Under these conditions expansion programs were the order of the day. Ample funds were available to finance the purchase of good equipment; and, as wages and other operating costs were increasing, primary emphasis was placed on attaining maximum efficiency in new installations. These efforts were hampered by shortages and slow delivery of desirable equipment, so compromises in design were often necessary. However, on the whole, production practice improved.

Jan 1, 1948