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By Joseph W. Mills

"The Mic Mac property comprises 994 acres held under mining concession and approximately 2,000 acres held under development licenses in Bousquet township, Abitibi county, western Quebec.Gold was first discovered in this locality by Tom Duval in June, 1936. In February, 1937, Cassels Duval Mines, Limited, was incorporated under Quebec charter to take over the property. In September, 1937, the property was examined by Agaura Explorations, Limited, and an option agreement was signed on October 6th, 1937. In June, 1938, an option for complete ownership was taken on adjoining claims belonging to Norgold Mines, Limited, and in September, 1938, a mining plant was installed and the sinking of a 3-compartment shaft begun. In June, 1939, an option was taken by Mic Mac Explorations, Limited, on seven claims of Mooshla Gold Mines Company, Limited, that adjoined the Norgold block to the east. In December, 1939, a new company, Mic Mac Mines, Limited, was formed, amalgamating the Cassels Duval, Norgold, and Mooshla claims, as well as two claim groups to the west of the mine known as the Vaughan and West Cassels groups."

Jan 1, 1954

By P. E. Auger, J. E. Gill

"The zinc deposits to be described are in Lemieux township a few miles south of the Tabletop mountains, in the central part of Gaspe peninsula, Quebec. Although they have not been worked, they constitute a potential source of zinc and lead and structurally are of considerable interest.GENERAL CHARACTER OF THE OCCURRENCEThe deposits are in sharp-walled quartz-carbonate veins and breccia zones carrying locally, and in varying amounts, sphalerite, galena, pyrite, marcasite, chalcopyrite, and specularite. Those so far investigated strike generally north-south, have steep dips, and cut through sediments of Lower Devonian age, mostly calcareous argillites or siltstones. Wall-rock alteration is negligible.BROADER STRUCTURAL FEATURESThe principal known occurrences are in the south-central part of a dome structure measuring 6 by 5 miles. The argillaceous sediments are overlain, on the flanks of the dome, by sandstones and lavas. These have been stripped from the central part of the dome, revealing the veins in the argillites beneath. The veins formed after the volcanics, but the fractures and breccia zones in which the deposits formed are confined mainly to the argillite series, presumably because of the greater strength of the lavas.The argillite series is cut by dykes, sills, and small stocks of diorite and acidic 'porphyries' that are older than the veins.THE FEDERAL HILL AREAThe distribution of known veins is shown in Fig. 1. The characteristic features of the veins are well illustrated by the Federal Hill area shown in Figs. 2, 3, and 4, and described below."

Jan 1, 1954

By L. C. IlsLey

The theory and practice followed by the Bureau of Mines in investigating electrical equipment4/ made for service in gassy mines are of particular interest not only to manufacturers but also to those organizations that deal with safety anal inspection at the mines. This publication purposes to discuss the theory upon which tests of equipment in explosive atmospheres are based and to consider inspection and other matters pertaining to investigations made by the Bureau in ascertaining whether a machine merits approval. The material in this report is taken from an earlier bulletin,5/ which is row out of print, and has been revised and brought up to date to make the information again available to manufacturers, inspectors, and others interested in the development of safe equipment.

Jan 1, 1954

By J. J. Gilman

The data presented indicate that the critical shear stress and strain-hardening Thedatapresentedrate of a zinc monocrystal depend on the orientation of its slip direction with respect to its external boundaries. The tendency of a crystal to form deformation bands also depends on its shape. THE plastic behavior of pairs of zinc monocrystals in which both members of the respective pairs had the same orientation with respect to the longitudinal axis, but each had different orientations with respect to their rectangular external shapes, were compared in this investigation. The purpose of the investigation was to see what influence the shape or surface of a zinc crystal has on its mechanical properties. In a previous investigation of triangular zinc monocrystals,1 anomalous axial twisting was observed which seemed to be related to the triangular shape of the crystals. Wolff,' in 400°C tensile tests of rectangular rock-salt crystals bounded by cubic cleavage planes, found that, of the four equivalent slip systems, the two with the "shorter" slip directions yielded and produced slip lines at lower stresses than the other two. This observation and the work of Dommerich³ as formulated by Smekal4 as a "new slip condition" for rock-salt: "among two or more slip systems permitted by the shear stress law, with reference to the formation of visible slip lines by large individual glides, that slip system is preferred which has the shortest effective slip direction." More recently, Wu and Smoluchowski5 reported essentially the same effect for ribbon-like (20x2x0.2 mm) aluminum crystals at room temperature. Experimental Chemically pure zinc (99.999 pct Zn), purchased from the New Jersey Zinc Co., was the raw material. Glass envelopes, containing graphite molds and zinc, were evacuated while hot enough to outgas the graphite but not melt the zinc. At a vacuum of about 0.2 micron the envelopes were sealed off and then lowered through a furnace at 1 in. per hr so as to melt and resolidify the zinc and produce mono-crystals. One-half of one of the molds is shown in Fig. la. Each mold consisted of four pieces from a cylindrical graphite rod that was split longitudinally and transversely at its midpoints. Rectangular milled grooves 0.050 in. deep and % in. wide formed the mold cavity when the split halves were assembled with twisted wires. Fig. lb shows the specimen shape obtained when the top and bottom mold-halves were rotated 90" with respect to each other. Good fits prevented leakage and excess zinc was necessary to provide enough liquid head to fill the mold completely. In removing soft crystals from the molds it was impossible to avoid small amounts of bending. However, manipulations were carried out whenever possible with the crystals protected by grooved brass blocks. All specimens were annealed prior to testing. From the top and bottom sections of each crystal, X-ray specimens and tensile specimens 7 to 8 cm long were sawed. The tensile specimens were annealed inside evacuated tubes for 1 hr at 375°C. Next the crystals were cleaned and polished by 2-min dips in a solution of 22 pct chromic acid, 74 pct water, 2.5 pct sulphuric acid, and 1.5 pct glacial acetic acid.' Cleaning was followed by a 10-sec dip in a 10 pct caustic solution, then washed in water and alcohol, and dried. This treatment results in a bright surface covered by an invisible oxide film. The testing grips were a slotted type with set screws and were supported in a V-block during the mounting operations in order to avoid bending the crystals. A schematic diagram of the recording tensile-testing machine is shown in Fig. 2. The machine has been described elsewhere.' The head speed was 0.3 mm per sec for all tests. The crystal orientations were determined by the Greninger X-ray back-reflection method with an estimated accuracy of 1. Description of Crystal Geometry A schematic picture of a rectangular zinc mono-crystal is shown in Fig. 3. ABD designates the front edge of a basal plane (0001) of the crystal, the only active slip plane for zinc at room temperature. Of the three possible (2110) slip directions, the active one is indicated by an arrow. Cartesian coordinates are taken parallel to the specimen edges. The normal, n, to the basal plane (n is parallel to the hexagonal axis) has the direction cosines a, ß and ?. X0 = 90 — y is the angle between the longitudinal axis and

Jan 1, 1954

By J. E. Gill

"The name 'Canadian Shield' is used for a vast area; largely in northeastern; Canada; underlain by Precambrian rocks. The part in Canada has an area; of about 1; 790; 000 square miles. Extensions in Greenland; Labrador; Newfoundland; and the United States bring the total area to around 2; 800; 000; square miles. The boundaries of the Canadian part are shown in Fig. 1.; At its margins; the Precambrian rocks can be seen at many places to; extend beneath a cover of flat-lying Palxozoic or later sediments. Information; from borings in the Plains and natural exposures in mountain-built belts; show that similar rocks form a large part of the continental platform. The; Shield; therefore; is a large exposure of what may be regarded as the foundation; of the continent."

Jan 1, 1954

By P. C. Benedict

"The Island Mountain mine is at the southeast end of Island mountain; across Jack of Clubs lake from the Cariboo Gold Quartz mine.; The orebodies consist of quartz veins and pyritic replacement deposits in limestone. To December 31; 1944; there has been mined 296; 273 tons of quartz-vein ore averaging about 0.34 oz. gold a ton; and 101; 002 tons of sulphide ore averaging about 0.83 oz. gold a ton; a total of 397; 275 tons averaging 0.46 oz. From this; 175; 985 fine oz. of gold and about 26; 450 fine oz. of silver were recovered; having a value of $6; 510; 521.More than 95 per cent of the production has come from a band 500 feet wide along the contact of the Rainbow and overlying Baker members and extending about 100 feet into the latter. Evidence that the Rainbow belongs stratigraphically above the Baker is presented later in this paper. Both members are most variable lithologically, and individual beds and whole series of beds pinch out in short distances. In part, at least, this is due to squeezing out incidentally to intense folding. No section can be claimed with assurance to be really representative. However, both memb.ers are composed predominantly of quartzitic rocks. Both contain argillaceous quartzite, argillite, limy quartzite, limy argillite, limestone (marble), and minor amounts of highly ankeritized rocks believed to be igneous sills possibly originally approaching diorite in composition."

Jan 1, 1954

By Robert H. Merrill

This report contains a summary of the various studies made to determine the structural design of the production mine area of the Oil-Shale mine, Rifle, Colo. Prior to this investigation, it had been determined from a study of the geology, the structure of the deposit, and mining costs that the deposit should be mined by open stoping. The problem remained to determine the maximum safe roof span, the optimum extraction ratio, and the size of the pillars. These factors were determined from a study of the geologic structure of the deposit, the physical properties of the oil shale, and the magnitude and distribution of the stress around proposed underground openings. The latter was determined from both theoretical calculations and model studies. Safe roof spans, pillar sizes, pillar contours, and optimum extraction ratios were calculated from elastic theory and the physical properties of the mine rock. Safe roof spans, pillar sizes; and time effects were determined by Wright and Bucky by testing mine models in a centrifuge. The models were made from rock specimens taken from the proposed mine roof and pillars. The results from both studies agreed.

Jan 1, 1954

By E. D. Kindle

"The Duthie mine is on the southwest slope of Hudson Bay mountain 7 1/2 miles west of Smithers, British Columbia. A good motor road about 15 miles long connects the mine with the Canadian National railway at Smithers. The principal workings are on the Henderson group of claims between elevations of 3,200 and 4,000 feet above sea-level. Silver, lead, and zinc were produced from this mine between 1924 and 1930.Three adit drifts known as the Compressor, McPherson, and Thompson levels were driven along the Henderson vein-lode in 1922, and the following year the operating company, known as Duthie Mines, Limited, shipped some high-grade silver-lead-zinc ore. Further shipments of high-grade, handsorted ore were made in 1926, and in 1927 a modern flotation-type mill was built, having a capacity of 50 tons of ore a day. Mining operations were suspended in March 1930."

Jan 1, 1954

By F. Y. Grepe

"THE MOST common type of mine hoist is, as is very well known, that in which the a.c. wound rotor motor is the driving medium. The reasons for the use of the wound rotor motor are, of course, economic. This type of equipment has, during the years, proved to be very reliable and reasonably satisfactory. It is, in fact, still being installed and in some places where a very hard and exacting duty cycle is demanded. As an example, a 600 h.p. 2,300-volt job was recently installed at the Caledonia mine (1) at Glace Bay. This is a vertical. hoist in a shaft only 175 feet deep but it is, nevertheless, working hard bringing coal to the surface and in making a trip at a speed somewhat better than every 20 seconds.The control equipment for such installations usually consists of a pair of primary reversing contactors which are interlocked both mechanically and electrically, together with some form of secondary controller. This, in the case of small hoists, can be a drum controller and metallic resistors or, in the case of larger hoists, a magnetic contactor panel and metallic resistors or, alternatively, can be one of the various forms of liquid rheostats which are available. The liquid rheostats, if of the dipper type, may be manually operated or it may be operated by some form of servo motor mechanism. In the weir type of liquid controller, the electrolite is, of course, pumped in and out of the rheostat."

Jan 1, 1954

By H. C. Cooke

"This paper has reference in a general way to the region extending from the north shore of lake Buron to the northern limit of the elliptical-shaped area generally known as the Sudbury Basin, and more especially to the district lying south of the Basin (Fig. 3). Attention is concentrated mainly on the structure of the district and, as space does not permit of much geological description, it is assumed that the reader has some knowledge of the general geology. The accompanying table outlines the sequence of the rock formations according to the most recent available information; for further details the interested reader may consult the publications of the various authors mentioned in the paper.STRUCTURE OF THE SEDIMENTARY ROCKS SOUTH OF THE SUDBURY IRRUPTIVEThe rocks south of the Sudbury irruptive, excluding certain intrusives, are, in order from north to south:(1) A band of basic lavas.(2) A band of well-bedded greywackes and quartzites, long termed the McKim greywacke.(3) The Copper Cliff formation, with McKim greywacke' both to the north and south.(4) The Ramsay Lake conglomerate.(5) A thick quartzite formation.All these rocks strike approximately east-northeast, dip steeply south, and generally face south, though there are local exceptions."

Jan 1, 1954

By N. E. Hanna

[Testing explosives for safe use in coal miner ran boon an important factor in preventing mine explosions. In the United States, explosives that have been approved by the Bureau of Mines are called permissible explosives. A purvey of the history of coal mining since permissibility testing welt, instituted some 4 years ago shown that there is no record of a coal-mime explosion caused by permissible explosives when used in a manner prescribed by the Bureau. To maintain the appropriate standards of quality, the Bureau of Mines conducts a series of examinations and tenth on samples of explosives collected in the field. In what is considered the most crucial test, teat 1, the explosives An fired from a steel cannon into a gallery atmosphere containing a mixture of natural gas and air, In another important test, test 4, the explosives charge to fired into a mixture of natural gas, air, and coal diet. To satisfy the permissibility requirements, the explosive must undergo throe gallery teats without igniting gas or coal duet. Other tests also are required for permissibility, but they do not come within the scope of the present paper, which studies the factors affecting the incendivity of explosives when fired into methane, air, and/or coal-dust mixtures. It in believed that a better understanding of the factors will contribute to the development of safer explosives.]

Jan 1, 1954

By C. H. Riggs

This report of a petroleum-engineering study of the Flat Rock oil field, Osage County, Okla., describes the geology, reviews the production history, and estimates remaining oil reserves. The Flat Rock field in the southeastern corner of Osage County approximately 6 miles northwest of Tulsa. Okla., was discovered in November 1904. The field was one of the first of many Bartlesville-sand fields developed in eastern Osage County during the early part of the 20th century. Although substantial oil reserves remain in the pressure depleted sands in some parts of the field, their economic recovery by water flooding will require careful consideration of the many factors involved.

Jan 1, 1954

By Samuel H. Dolbear

THE value of a mine is basically dependent on its capacity to yield profits. Since the ore must be mined, treated, and sold, some of it in various future years. there is a risk involved as to future costs, selling price, and working conditions. It cannot be expected that the economic condition existing at the time of valuation will continue unchanged for long periods in the future. During the past 20 years, mineral production in the United States has been conducted under a changing economy in many respects more exacting than that applied to other businesses. There have been increased production incentives, technical aid, exploration of privately owned mineral deposits by government at federal expense, and liberal loans for development and equipment, with risk partially assumed by government.. Some of these benefits have been counterbalanced by price ceilings, consumption controls, and stimulation of competition from foreign producers who have been offered the same advantages extended to American operators. For the present, mines will operate under a government policy directed toward reducing federal aid and control. The tenure of this change will depend upon future elections and the status of foreign relations. War and threat of war are now of the most vital significance to the mineral industries. Other factors which influence cost of production, markets, and price of mine output might be classified as Acts of God or Acts of Government. In some countries expropriation and the difficulty of exporting earnings or investment returns are risks that must be considered by foreign capital. Recognizing that this retards American investment in foreign countries, the Mutual Security Agency offers insurance against such expropriation and guarantees the convertibility of capital and profits. Since it is impossible to predict with certainty either cost of production or selling prices of metals for long periods, some assumptions must be made as to profits in the future. The basic assumption must be that the price of the company's product will vary in proportion to changes in operating cost. There is often a lag in this reaction, however, for prices of minerals are generally more sensitive to declines and less sensitive to increases than are costs. This reflects in part the resistance of labor to downward wage revision and a corresponding alertness in realizing its share of price advances. Some labor contracts include automatic adjustments to metal prices. Notwithstanding the complexity of the, problems involved and the difficulty of weighing their effect on value, such risks may be appraised with reasonable accuracy and a rate of earnings adopted that is compatible with the risk. It is, of course, possible to revert to a yardstick of value such as the commodity dollar, which has been advocated from time to time, but while revaluation in 1933 disturbed public confidence, the theoretical gold dollar continues to be the standard of greatest stability. Its gain or loss in purchasing power is reflected ultimately in cost of production and selling price of the mine product. At present 35 dollars are allocated to one ounce of gold. Measurement of Risk In the application of the Hoskold and most other formulae, a yearly dividend rate commensurate with the risk involved is set aside out of annual earnings. If the risk is great, this rate may be 15 to 25 pct of the amount invested. The remainder is placed in a sinking fund invested in safe securities such as high grade bonds or conservative equities, and the interest or dividends from these securities are added to the sinking fund. The sum of these sinking fund payments and the compounded interest at the end of the mine life is taken as the value of the mine. Admittedly the decision as to the size of the risk rate is the most difficult element in valuation and one requiring the most exacting consideration. It is necessary to look years ahead in an effort to determine future costs, market prices, demand, competition which may develop, including that of substitutes, and other influences common to the mine and to the region in which it is situated. Another phase of risk is the enactment of unfavorable legislation, taxes, and what appears to be an alarming spread of nationalization and expropriation. Capital is sometimes borrowed from the government to finance strategic production. Such loans may be collectable only out of production and involve no liability otherwise. Valuation in these cases must recognize the effect of such a reduction in liability. Offsetting some of these risks are the possibilities of mechanization and other cost-reducing discoveries, improvements in mining and treatment methods, new uses for minerals and metals, and normal growth of markets. In this paper, the terms risk rate, dividend rate, and speculative rate are synonymous. Safe rate and redemption rate are also used interchangeably. These alternatives are used here because they are commonly found in the literature on mine valuation. In Michigan, the State Tax Commission has long employed a risk rate of 6 pct in its valuation of iron mines. There the outline of reserves is well established and operating costs and conditions are based on adequate experience. The following comment on rates appears in the report of the Minnesota Interior commission on Iron Ore Taxation submitted to the Minnesota Legislature of 1941.1 Most engineers agree that 7 percent for the specu-lative rate is "an absolute minimum". C. K. Leith in

Jan 1, 1954

By W. A. Jones

"The Hollinger gold mine is in the Porcupine area, Cochrane district, in northern Ontario. The adjacent town of Timmins, which has a population of 25,856, lies 490 miles by railway north of the city of Toronto.The property was staked in the late summer of 1909. The original four claims were staked by Benjamin Hollinger, after whom the mine was named. Development commenced in the autumn of 1909 and mill construction in the winter of 1910. A catastrophic forest fire swept the district in 19ll, destroying the surface plant, so that the original 300-ton mill was not completed until June 1912. From that date up to December 31, 1945, 44,280,750 tons of ore have yielded 13,636,796 oz. gold and 2,613,354 oz. silver. The total value of the production has been $363,638,315.0REBODIES AND MINERALIZATIONThe orebodies consist of quartz veins, stringer lodes, and scockworks, with associated pyritized wall-rocks. The width of individual orebodies, as exposed by mining operations, ranges from 1 to 70 feet and averaged approximately 10 feet in 1942. The vein system forms a complex pattern in a favourable zone, which in places is 6,000 feet long and 4,000 feet wide. The deepest level being developed is 5,150 feet below the surface. Few veins are persistent for long distances, although some are continuous for more than 1,000 feet longitudinally and vertically.The host rocks consist of a closely folded series of Precambrian lava flows of Keewatin age. These are schistose and hydrothermally altered, but are believed to have originally been of intermediate to basic composition. The schistosity strikes N.70°E. and dips to the south at 75° to 80°. The structure of the formations is complex, but in the principal ore-bearing zone the general dip of the flows is to the south at a slightly flatter attitude than the schistosity."

Jan 1, 1954

By D. Harrington

This paper is a revision of Information Circular 7380, by D. Harrington and J. H. East, Jr., published in 1946, entitled ?Safe Storage, Handling, and Use of Commercial Explosives in Metal Mines, Nonmetallic Mines, and Quarries.? Issued soon after the close of World War II, this earlier circular described the unprecedented increase in the production and use of commercial explosives during the war as a result of expanded industry and the tremendous demand f or metals and minerals. In the years following World War II, the production and use of commercial explosives in the United States have continued to rise. Hence, the Bureau of Mines presents these revised figures through 1952. In rewriting this Wormation circular, most of the text prepared by Harrington and East has been retained, with newer statistical information compiled by Seth T. Reese, Accident Analysis Branch, and V. E. Wrenn, of the same branch.

Jan 1, 1954

By A. Todd Davis

"Introduction“CAN YQUR Company afford not to train?"" This question was asked by Jack Taylor in the Factory Management Magazine for June, 1950. Mr. Taylor went on to say, ""No, it can't; no Company can"". It's true that many training programmes have not done the job they were designed to do because of a number of factors such as parts of management resenting training, management failing to understand the abstract values of training, and management giving impossible assignments or picking the wrong trainers. However, Mr. Taylor summarizes his article by saying that a properly-designed and •conducted training programme brings a company or a corporation to the point where the question is: ""Can my Company afford not to train?""About two years ago, in July, 1952, Nevada Mines Division of the Kennecott Copper Corporation embarked on a training programme, the same type of programme that had been inaugurated earlier at the •Utah Copper Division at Bingham, Magna, and Garfield, Utah. President Charles Cox of Kennecott, in •a speech made •before the Utah Bankers Association in June of 1951, stated that, ""I think that our programme of employee training is one of the most important phases of our entire operation"". That statement might be said to be one of the guiding principles of training at Nevada Mines Division. Training is supported by top managements and down the line to Division managements. As the years go by, the Company expects to receive many benefits from training."

Jan 1, 1954

By Jas. E. Thomson

"The Omega mine is in McVittie township in the Larder Lake area, Ontario. Production at the mine commenced in 1936, and, until the end of 1946, ore milled amounted to 1,558,604 tons, from which 207,074 oz. gold and 28,205 oz. silver, valued at $7,585,470, were recovered. The mine workings extend to a depth of 1,975 feet.GEOLOGYThe geology of the mine has been described in detail by C. P. Jenney (l) and the writer (2). The general geology and structure in the vicinity of the mine is discussed on an earlier page in this volume. The rock formations found in the mine workings are indicated on the accompanying plan and section (Figs. 1and2). They consist of an intermingled, south dipping complex of volcanics, sediments, and secondary talc-chlorite schists and carbonates. The carbonatized rocks, which are often referred to as 'dolomite' in the Larder Lake camp, are siliceous-carbonate replacements in the talc-chlorite schist zones. In places they contain green mica, probably fuchsite, and are cut by a stockwork of quartz veinlets and stringers. A stock of syenitic intrusives lies south of the mine workings.STRUCTUREThe main structural features are indicated in Figs. 1 and 2. The formations and orebodies have a pronounced southerly dip, which flattens with depth. The talc-chlorite schist and 'dolomite' zones are part of the Larder Lake fault or 'break' on which there appears to be very large displacement. Evidence throughout the district would indicate that the south side moved up and, in the case of the Omega mine, the thrust may have been distributed throughout the several intensely sheared zones. This slice faulting could account for the repetition of sediments and volcanics. An alternative possibility would be original interbedding of volcanics and sediments."

Jan 1, 1954

By Alexander Smith

"The three principal known mineral deposits of the Taku River area lie in the Tulsequah synclinorium. The axis of this north-south trending structure is along Tulsequah River valley; about 6 miles east of the eastern contact of the Coast Range batholith.The one proven mine of the area, the Polaris-Taku, is on the west side of the valley. It is a gold property, the gold occurring in fine needles of arsenopyrite disseminated in carbonatized volcanics. The mine was originally called the Whitewater, and the adjacent area the Whitewater gold belt. During the years 1937 to 1942 gold having a value of $3,284,000 was produced from 313,500 tons of ore milled."

Jan 1, 1954

By Roberto Antoniolli

"IntroductionSINCE ancient times, the precious metals have played an important role in influencing the course of history. Silver and gold happened to occur, although in small amounts, in those countries where the early civilizations developed. Their persistent brightness certainly amazed the primitive people, who also found it easy to shape them into ornaments •and implements. Ever since then their properties have made them seem desirable possessions.Use of precious metals as money was the natural consequence of man's desire for them. The possibility of changing an ornament into a tool or food at any time, and the ease with which such medium of exchange could be carried and hidden, further increased the demand for the two metals.Silver was probably discovered after gold and copper, and was undoubtedly found by prehistoric man as native silver. The oldest silver articles have been discovered in Chaldean tombs and date back to 5000 B.C. The earliest ascertained producers of silver were Asia Minor and the Iberian Peninsula. The Romans worked deposits in Spain, Britain, and France. In the Middle Ages, some silver was extracted from German deposits, and near the end of the Middle Ages systematic workings were carried on at Freiberg, Schneeberg, and Joachimsthal (1).Before the discovery of the New Continent, the Aztecs and Toltecs in Mexico, and the Incas in Peru, had made extensive use of silver. In the 16th century the Mexican deposits became the largest source of the world silver."

Jan 1, 1954

By K. R. Van Horn

RESIDUAL stresses in metals operate under a cloak of mystery, as they have neither been seen in the laboratory nor detected by means of the microscope. In spite of their phantom-like nature, they frequently exert metallurgical effects that cannot be ignored. In some cases the results have been detrimental, causing rejections or premature failures, but frequently the effects have been highly beneficial to the producer or consumer of metal products. First, however, what is a residual stress? When a metal is plastically deformed by bending, rolling, pressing, or by a phase transformation or precipitation from solid solution, or by a sharp temperature gradient resulting from nonuniform cooling, quenching, or welding, it remains in a state of strain. The strains or strain gradients produced by such operations and retained after all external forces are released are known as residual strains, and the accompanying stresses as internal or residual stresses. Many defects or failures in metal products have been ascribed to residual stresses, sometimes erroneously, because there was no other apparent explanation after the usual metallurgical tools of diagnosis had been applied. For example, during World War 11, the forged aluminum alloy aircraft cylinder head in the reciprocating engine began to replace the cast head with the familiar cooling fins. The fins were machined in the solid forged head by an ingenious milling operation. One plant reported an epidemic of excessive distortion during the delicate high-speed milling. A thorough examination revealed that the composition, heat treatment, mechanical properties, and metallurgical quality of these heads were comparable to those of forgings that machined satisfactorily. It was then claimed that the cause of the machining difficulties was connected with residual stresses resulting from the quenching during the solution heat treatment. An elaborate stress analysis actually demonstrated, however, that the magnitude of residual cooling stresses was lower in the cylinder heads which machined poorly than in those which were satisfactory in this respect. Subsequent tests proved that the machining problems in this case originated from variations in the tools and tool design. Sources of Residual Stresses in Metals Residual stresses are of two origins—mechanical and thermal. Thus, stresses may be produced in a metal by any cold-working process. The distribution and magnitude of these mechanically produced stresses can be calculated in a satisfactory, although approximate, manner for such simple cases as bending, torsion, and expanding of tubes. However, most manufacturing processes are too complex, and the original stress-strain relations in the products are not sufficiently known to permit calculation of the resulting residual stresses. Also, a specific process, such as wire drawing, may vary in complexity or uniformity of working, and large or small residual stresses may result, depending on the conformation of the dies and other features of the working process. Neither substantially unidirectional deformation, such as can be imparted by stretching a metal product having essentially the same mechanical properties throughout the cross section, nor deformation

Jan 1, 1954