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By R. H. Frazier, F. W. Boulger

THE performance of welded structures is closely associated with the ductile-to-brittle transition temperature of the steel from which they are made. A low transition temperature is desirable because it indicates that the steel is less likely to fail suddenly at low ambient temperatures. Structures such as bridges, ships, storage tanks, and pipelines are usually made from hot rolled semikilled steel. Changes in rolling practice or chemical composition appear to be the most practical methods for improving the toughness of such materials. This results from the fact that production is likely to be seriously curtailed if improvements were obtained by recourse to heat treatment or complete deoxidation. This paper discusses the effect of variations in carbon and manganese contents on the properties of semikilled steels. The transition temperature, a property to which considerable importance is attached, varies with specimen configuration, testing method, and criterion of performance. Both the Navy tear test' and the keyhole Charpy test were used in the investigation. According to the terms used by Vanderbeck and Gensamer,V he tear test was used to measure a fracture transition and the Charpy test to measure a ductility transition. In either case the specimens absorb considerably less breaking energy in tests below the transition temperature than in tests above the transition temperature. Decreasing the testing temperature of notched-bar specimens seems to be equivalent in its effect to increasing the severity of loading on fabricated structures. Therefore, structures built from steels exhibiting lower transition temperatures in laboratory tests are expected to be less susceptible to sudden brittle fractures in service. Consequently, changes in composition which lowered the transition temperature of the experimental steels were judged desirable. Materials and Methods The steels for this study were made in a laboratory induction furnace and rolled to 3/4 in. plate, using a finishing temperature of 1850°F. Precautions taken to insure reproducible melting and testing practices are discussed in detail elsewhere.' All tests were made on hot rolled steels. The analyses of the experimental steels are given in Table I. The list includes steels with manganese contents ranging from 0.21 to 1.46 pct, at each of five carbon levels. The phosphorus, silicon, sulphur, and nitrogen contents of the steels are reasonably constant. The tensile and notched-bar properties of the experimental steels are presented in Table 11. Both upper and lower yield points are listed, and all values are averages for duplicate specimens. Transition temperatures based on three criteria are given. The keyhole Charpy transition temperatures are the temperatures at which the energy-temperature curves based on averages of four specimens cross the 20 and 12 ft-lb levels. Both definitions of Charpy transition temperatures have been used by other investigators. Charpy tests were made at intervals of 10°F, using a pendulum with an available striking energy of 220 ft-lb and a velocity of 18.1 ft per sec. The specimens were oriented parallel to the rolling direction and notched normal to the surface of the plates. The tear test transition temperatures are based on the usual' criterion of the highest temperature at which at least one of four specimens exhibits brittle behavior. The dimensions of the tear test specimens are shown in Fig. 1. The specimen is loaded eccentrically in tension, with pin and shackle fixtures, through the large holes while submerged in a liquid bath at the proper temperature. A specimen developing a fracture area with less than 50 pct shear or ductile texture is classed as brittle. Tear tests were made at intervals of 10°F.

Jan 1, 1955

D. HARRINGTON: Owing to lack of funds, the United States Bureau of Mines have made no experiments in the Bruceton mines in the use of mudite. MR. McAULIFFE: I doubt that mudite cam be delivered at fifty cents a ton and that a mile of heading can be treated with mudite for ten dollars. You could not dig a ton of sand out of a sand hank for that money. L. C. CLARE: The tram road leading to Wattis mine crosses a shale bed and it is easy to screen the shale through a %-inch sieve and load it into a mine car. W. J. REID: A slow trip passing through a mudited entry will dislodge practically no dust, a rapid trip will make air disturbance enough to coat the cars with fine dust. MR. PRYDE: We have used mudite on stoppings around a fire in Reliance and for two months thought they were getting good results, but the fire was found to be drawing air and to be spreading. This mudite was smeared over the stoppings with a trowel. After this apparently failed we used dry adobe.

Jan 1, 1925

? The economic health and national security of the U.S. depends on the continued availability of, and access to, reliable and affordable energy and mineral resources. However, America is hindered by a costly, inefficient and often redundant regulatory structure that thwarts domestic investment, expansion and job creation. The annual cost of federal regulations in the U.S. increased to more than $1.75 trillion in 2008; averaging $8000 per employee.(The Impact of Regulatory Costs on Small Finns, SBA, 2010) ? The complexity, uncertainty and delays within the current permitting system places the U.S. at a competitive disadvantage with many other countries that have both abundant mineral resources and a more welcoming business and regulatory climate. As a result, American and international mining companies often move overseas or across borders to invest capital, create local employment, and produce the critical minerals America must then import at higher cost, while sacrificing employment and economic stimulus. ? According to Behre Dolbear, the U.S. is ranked lowest globally due to the lengthy permitting period required before mine development can commence. (Where not to Invest, 2010).

Jan 1, 2011

By Qingchun Yu, Bin Yang, Yong Deng, Heng Xiong, Fei Wang, Minxiu Chen

"Metal aluminum produced by non-electrolysis process received much attention due to its lower energy consumption. In this paper, carbothermic reduction and carbothermic-chlorination of alumina in normal pressure and vacuum were studied. The products were examined by means of XRD, EDS and SEM. During the carbothermic reduction process using carbon reductant in normal pressure, no metal aluminum was found. However, when coal was used as reductant, a mixture containing metallic aluminum, A14C3, and silicon was obtained, but metallic aluminum couldn't be separated from the mixture. During the carbothermic-chlorination process in vacuum, Al404C and Al4C3 were produced by the reaction between alumina and carbon, and Al Ch gas reacted with Al404C and Al4C3 to produce Al Cl gas. Metallic aluminum was produced due to the disproportionation of A!Cl gas and condensed on the collecting plate. Meanwhile, the initial temperature of carbothermic reduction of alumina reduced in vacuum compared with that in normal pressure.IntroductionIndustrial production of primary aluminum is carried out in alumina cell by the so-called Hall- Heroult process, necessitating the use of very high currents of low voltage. The alumina from which metallic aluminum is gained must be chemically pure, otherwise impure metal results. The main drawbacks of the electrolytic production are its very high energy consumption, the release ofperfluorocarbons, and the high specific C02 emissions [1]. During the past years, there were a lot of attempts to produce metallic aluminum by carbothermic reduction of A1203 [2, 3]. Cox [4] determined the vapor pressure over the A1203-C system and performed X-ray diffraction analysis of condensed products. It was demonstrated that an increase in the carbon content in the system leaded to the sequence of transitions: A1203~Al404C~A1zoc~A14C3 ~AI [5]. In any carbothermic reduction process for aluminum, extremely high temperatures (2000 °C ) were required [6]. In spite of considerable effort, the carbothermic reduction of alumina to aluminum remains a formidable technical challenge, due to the high temperatures required, and to the formation of aluminum carbide and oxycarbide byproducts [7]."

Jan 1, 2013

By G. W. Rhodes, B. P. Cavan, F. K. Mussger

The New Austrian Tunneling Method (NATM) has been successfully applied to two very different tunneling projects in the U.S.. In the case of Pittsburgh's Mt. Lebanon Tunnels, two original design alternatives were prepared. The NATM alternative incorporating a reinforced shotcrete final lining was successfully bid and constructed. At Washington Metro's (WMATA) Section B-10 Glenmont Route, Wheaton Station and tunnels, a NATM value engineering redesign was prepared for the low bidder. The design incorporating a waterproofing system based on a PVC membrane between the initial and final linings was accepted by WMATA. In both cases, European experience and standards were meshed with U.S. standard practice. Examples of NATM flexibility as an original design and as a value engineering proposal are presented.

Jan 1, 1985

The use of QemSCAN in providing mineralogical input to detailed ore and product characterization has proved of immense value in recent years. In this paper, a brief review of selected Cu-case studies is presented to demonstrate the versatility of automated, quantitative mineralogy by QemSCAN. This versatility ranges from measurement and analysis strategies through to data processing and presentation. As a rapid diagnostic service, it is common to find that only grain size, the degrees of liberation and/or ore mineral modal mineralogy are of interest. By contrast, the detail afforded by the simultaneous determination of both gangue and ore minerals can alert mineral engineers to fatal flaws and attributes deleterious to processing that are directly a function of silicate and other gangue mineralogy. Examples of the latter effects include the influence of micaceous minerals and acid consuming species, while the former include fluorine minerals, which can provide both processing and environmental challenges.

Jan 1, 2007

By R. A. Beall

Homogeneous zirconium-alloy ingots have been cast on a production basis by the consumable-electrode arc-melting process at the Northwest Electrodevelopment Experiment Station, Bureau of Mines, Albany, Oreg. This paper describes the various methods used to introduce alloying materials into the ingot and evaluates 1 each method by the degree of homogeneity of resulting ingots, as determined in tests on sections cut from the ingots. As many as 30 or more ingots, each 6 to 10 inches in diameter and weighing 300 to 500 pounds, were melted, using each method; and, as most of them subsequently were fabricated to strip 0.1 inch thick, the test results are considered to be representative of production practice. Ingot homogeneity has been considered more difficult to achieve in arc-melting practice than by methods where the molten metal is poured into molds and the addition can be stirred into the total mass of metal before casting. Owing to the unique requirements of consumable-electrode arc melting the addition can be made only to that part of the total mass of the ingot that is molten at one time. Observation of the flowlines in 500-pound ingots produced at Albany indicates that the molten pool has a maximum depth about equal to the ingot diameter. The weight of metal molten at one time is, therefore, not over 100 pounds. Characteristically, the arc-melting process is conducive to segregation, which can be overcome, at least partly, by adding the alloy constituents almost continuously during casting.

Jan 1, 1956

By A. Mboma

Keywords: Furnace, decommissioning, care and maintenance, re-start, funding, nickel Bindura Nickel Corporation (BNC) operates two nickel mines, and treats concentrates from these mines as well as toll concentrates from the region around its Bindura Smelter and Refinery (BSR) complex. At the smelter, concentrates of at least 5% nickel content are blended and dried to 4% moisture in a coal-fired rotary kiln. Matte smelting of concentrate is carried out in a six-in-line electric arc furnace, where the furnace slag is granulated and discarded. Furnace matte is transferred via ladles into Peirce-Smith converters, where, after granulation, a leach alloy containing 68%Ni, 20%Cu, and 6%S is produced. Converter slag is recycled via the matte-smelting furnace. The onset of the global economic recession towards the end of 2008 resulted in a collapse of metal prices, worsening the local situation that was already marred by unfavourable macro-economic conditions in Zimbabwe. As a result, BNC mines were put on care and maintenance in November 2008, followed by Bindura Smelter and Refinery in February and March 2009 respectively. The business environment has since changed, and BNC is getting ready to re-start the plant. This paper describes the decommissioning of the Bindura furnace, asset preservation during the care and maintenance programme in the past two years, and preparation for starting up of the Bindura smelter in the near future.

Jan 1, 2011

By Yubo Tu, Lianqi Wei, Tianyi Zhao, Peiwei Han, Zhengchen Li, Shufeng Ye

The effect of oxygen partial pressure on the volatilization percentages of valuable metals from iron-rich pyrite cinder by chlorination-volatilization method using CaCl2 as chlorinating agent was investigated in this study. The volatile products were collected directly and analyzed by X-ray diffraction. It was found that there were CuCl2, CuCl, PbCl2, and ZnCl2 existed in the volatile products. Au and Pb volatilization percentages were almost not affected by oxygen partial pressure. Both Cu and Zn volatilization percentages were negatively correlated with oxygen partial pressure when CaCl2 dosage was no more than 4 wt%, and almost uncorrelated with oxygen partial pressure with a CaCl2 dosage of 6 wt%.

Dec 19, 2023

By A. Oleynik

The paper presents the modeling and simulation experience in field of research into the mineral row material separation. Features of the subject domain generate a need of different approaches using for modeling and simulation. The general scheme of separation modeling process and some examples of developed simulators are presented. Due to different features and standards of knowledge, different formal models should be used to describe and analyze separation processes in the frame of general scheme. The main types of simulators are modeling tools based on statistical, analytical or expert (logical) methods. Advantages and disadvantages of each method above are mentioned in the paper. Based on the studies in the field considered, an aggregated mathematical model of a separation process has been generated. The aggregated model is presented by two combined equations. The actual apparatus model is formed by substitution of the particular functional expressions of the forces acting in the apparatus into the aggregated model. The developed simulation tools are based on integration of limited experimental data and on ex-pert knowledge available on separation processes. Simulation does not allow producing an optimal, in terms of mathematics, solution. But it gives an opportunity to produce and compare quite adequate solution variants in real time. The results obtained are the theoretical and methodological base for integrated information technologies to support studies in the field of mineral processing.

Jan 1, 2014

By Don Morris

The Building Products Company is Phoenix based and owned by Mission Clay products of California. Building Products is the only manufacturer of vitrified clay pipe in Arizona. The marketing area includes Arizona, Nevada, Utah, New Mexico, and California. Building Products, promoted by Arizona Public Service, was formed in 1970. Raw-materials prospecting was undertaken for 2 years, after which a $5-million plant was built. Initially, a satisfactory vitrified product could not be made with the raw materials then in hand. Subsequent prospecting and testing led to an acceptable raw-materials mix. Testing to upgrade the final product is a continuing process. The basic raw-materials supply must be adequate, secure, and capable of sustaining close tolerances in the final product. These needs are met by mining four geologic materials at three different localities: (1) refractory aluminous shales (two horizons-one pit) Colorado Plateau Province (Mogollon Rim); (2) less refractory aluminous materials from late Cenozoic lacustrine materials near Dewey in the Transition Zone (TZ); and (3) Precam¬brian "slate" from near New River along the southern edge of the TZ. Other additives include grog (ground-up, broken pipe) and barium carbonate that ties up what gypsum there is. Calcium magnesium carbonates are deleterious components that are minimized by careful selection of the mined products. The raw materials are blended and mixed, ground to 12 mesh, mixed in a pug mill, depleted of air, extruded into pipe ranging from 6 inches to 42 inches in diameter, transported to a hot-air drying room, fork-lifted to an appropriate kiln, and fired at a 1900-2000° F range. The "Rim" kaolinitic shales, being the most refractory ingredient, stabilize the pipe during the firing process. They are very plastic, and therefore facilitate extrusion. The Dewey clay fuses at a low temperature and forms an impervious glasslike binder. It also is plastic. The "slate" forms platy particles that tend to orient themselves during laminar flow. This provides strength for both the green and dried product. It doesn't absorb water, which helps the drying process. Grog remains stable during firing, and therefore helps to control shrinkage. The development of appropriate raw materials and proper mixtures has been done empirically.

Jan 1, 1987

By G. B. Hudson

Previous papers (1, 2) pertaining to the treatment of uranium-bearing ores were concerned with the flotation of the radioactive minerals. In this investigation, the application of flotation to the removal of acid-consuming minerals from uranium ores was considered. Two pitchblende-bearing ores, which, because of the presence if dolomite were abnormally high acid consumers, were studied. In both in-stances commercial reagents of widely varying fatty acid composition proved satisfactory as flotation col-lectors, particularly at a pH of 10.5, for the carbonate minerals. From an economic viewpoint, however, Neo-Fat 42-12 was favoured. A mixture of sodium tripolyphosphate and citric acid was an effective depressant for the pitchblende in the ores. The tailings remaining after the removal of the dolomite by flotation contained, in one case, 88.5 per cent of the uranium in the original sample, and, in the other, 93.8 per cent. Analyses conducted on these tailings and on the original ores showed that

Jan 1, 1963

By Peter Zhang

The immediate roof at the test site consisted of laminated clay shale that is likely to be susceptible to weathering. With seasonal dry-wet cycles in the mine ventilation air, the roof in the intake air would deteriorate and lose integrity over time. In many instances, the weathering-prone roof would gradually scale off piece by piece between bolts and over the entry corners. In some long-term entries, roof weathering could develop up to 2-3 ft deep with columns of bolted roof hanging under the upper intact roof. If wire mesh is used, the roof bags down and reduces the entry height, and the weight of the bagged roof tends to pull the bolts out and poses a safety hazard. An effective measure is always sought to support this type of weak roof that is sensitive to moisture degradation. One solution is to seal the roof shortly after entry development to prevent moisture penetration so that roof integrity can be maintained for the long term. In this application, a polymer-based sealing material was tested in the Rockspring mine for weathering protection and reinforcement. The material is a one-component polymer powder for spray application onto the roof and rib. The sealant material is mixed with water in the spraying nozzle to apply to the roof and rib as a paste. The product sets within 5-10 minutes and forms a membrane as thin as about 1/8-in. The membrane will quickly develop tensile and bonding strength within minutes and completely cure within a few days. Through sealing, bonding and lateral reinforcement, the integrity of the weak roof can be maintained. The material has been tried in a long-term evaluation over several months in a set of main entries in the Rockspring mine owned and operated by Rockspring Development, Inc., affiliate of Foundation Coal. Preliminary evaluation has shown that the material is an effective and economical solution to ensuring the long-term stability of weathering-prone roof.

Jan 1, 2009

By L. Lü, M. O. Lai

"Mechanical alloying is a dry, high energy ball milling process which has been used to synthesize metallic powders in the solid state. The present study use this technique to synthesize Cu-base shape memory alloy powder from commercial Cu70Zn30, Cu86Zn14 and element AI powders. The evolution and formation of shape memory alloy powder were monitored using X-ray diffraction and microscopy. It was observed that shape memory alloy powder started to form after 1.8 ks of mechanical alloying. ? phase was clearly detected after 3.6 ks of mechanical alloying. The intensity of X-ray diffraction of the y phase increased when mechanical alloying duration was prolonged indicating an increase in the amount of y phase. Microstructure observation showed different stages of formation of alloyed powders: welding between powders and formation of layered structure, deformation and fracturing of layered structure, and finally the formation of alloyed powders.IntroductionMechanical alloying (MA) is a process used for producing powders with controlled and extremely fine microstructure. It was original developed in 1966 (1) to produce aNi-based superalloy combining oxide dispersion strengthening with gamma prime precipitation hardening. In recent years this technique has been used in producing a wide range of materials including intermetallic compounds (2, 3), amorphous materials (4-6) and other materials (7-9). In MA, a blend of powders is subjected to highly energetic compressive collision. The powder panicles are welded and fractured during ball milling. Therefore, it is essential that at least one of powders should be ductile to act as combiner. It has however been found that brittle components without soft element can also be mechanically alloyed (10), even ceramic powders (11).The present work aims to study the mechanism of formation of shape memory alloy powder during MA."

Jan 1, 1994

By Erwin L. Zodrow

THE AUTHORS welcome this timely opportunity to comment o n a paper by MacLean and Merner (" Room-and- Pillar Mining at the Prince Mine of the Cape Breton Development Corporation " , ClM Bulletin , June 1978, pp. 59-62) concerning the rock falls and their relation to "a change in the strata". First, however, it is proper to express our gratitude to the Cape Breton Development Corporation, and in particular to A. R. MacLean, for making it possible for us at the College of Cape Breton to start two new collections. The first of these is a fossil plant reference collection from the Sydney Coalfield, Cape Breton (Upper Carboniferous period) , and the second is a documentation of the role o f pyrite in the formation of hydrated sulphates (samples from No. 26 Colliery, 1-B Mine, and the Prince Mine at Point Aconi). Conditions of sedimentation in the deltaic-type basin of the Upper Carboniferous time in the Point Aconi area were such that on the (coal) swamp, now represented by the Stubbart (or Hub) seam , (a) clays of varying thickness and extent were deposited , (b) biogenetic sulphur was introduced and (c) flora were buried. These are essentially the culprit s that make rock falls possible and at the same time predictable over large areas (in the present mine). The clays lithified to become shale, and biogenetic sulphur combined with iron to become pyrite (marcasite?), which exists as nodules and in fine-grained layers.

Jan 1, 1978

By Soumitry J. Ray

Poor visibility of powered industrial vehicles, such as forklifts, used in industry is often the cause of accidents that include pedestrians. Current standards allow up to 20 % non-visible regions for forklifts where measurement of these regions is performed by using lamps. A collaboration of research organizations, including National Institute of Standards and Technology, Georgia Institute of Technology (NIST), and Direct Dimensions, has been evaluating advanced methods for measuring a forklift operator?s visibility. These methods can potentially improve visibility standards. They can also help forklift and sensor manufacturers to determine (1) how visibility-assist sensors and algorithms can be designed and (2) where sensors can be mounted on forklifts. This paper includes explanation of visibility measurement experiments performed and results, associated language suggested to standards organizations, and a prototype design for measuring the visibility of forklifts automatically.

Aug 1, 2013

By R. V. Ramani, C. B. Manula, A. Owili-Eger

MINE PROTOTYPE The prototype chosen for application demonstration is from Kingery (1960). The mine and the ventilation plan is presented in Figure 11. A new coal mine is projected with entrance by slope 1,500 feet long. Nine train entries will be standard for development, five as intake and four as return. One return shaft is planned near the slope bottom. The slope will have an area of 150 square feet and a perimeter of 55 feet. The return shaft will be circular with a diameter of 18 feet and will be 500 feet deep. Two hundred feet of the shaft and 500 feet of the slope will be concrete lined. Will it be possible to operate five units per shift with amount of air at each unit not less than 25,000 cfm? Additionally, a shop at the slope bottom will require 10,000 cfm. The problem is completely worked out using standard ventilation formulas and simple manual calculations in the above reference and is reproduced here in Appendix II for ready reference. APPLICATION In this manual, four different applications of the PSU/MVS are outlined. An article by Stefanko et al (1972), outlines how one can move from a mine map to a network for the generation of computer input. Attention is drawn to Figure 12, which is the network line diagram of the mine ventilation system in Figure 11. Note that every roadway junction has been numbered. The dotted lines represent leakage paths and the letter 'R' on a branch denotes that the split is regulated for the quantity shown. For example, there is a leakage

Jan 1, 1975

By Graham W. Marks

This report is the fourth of a series concerning the development of spectrochemical methods for the analysis of ore samples and related Metallurgical materials by the total-energy method. In this report, the application of this method to the determination of thallium is discussed. This element lies in group III of the periodic tale; one other Clement of this group; indium, has already been investigated.

Jan 1, 1949

By E. C. Dominguez

INTRODUCTION The first commercial plant in the world to successfully produce pellets from manganese ore fines is the ICOMI pelletizing facility in northern Brazil. The main purpose of this paper is to describe the manganese pelletizing process that was developed through a cooperative R & D program by the Bethlehem Steel Corporation and ICOMI, i.e., Industria e Commercio de Minerios, S. A. The process combines heavy- media and gravity separation, reduction roasting, magnetic separation, and pelletizing on a straight-grate indurating machine. It produces high-grade manganese pellets from reviously unsalable low-grade ore fines at a rate of 20,000 tonnes (1) per month. The physical properties of the manganese pellets are comparable to those of iron ore pellets. The pelletizing plant, built at a cost of about 18 million dollars, is part of an ICOMI complex that includes manganese ore mining, an ore-washing plant, and railroad and port facilities, as well as two town sites. These two towns, one at the mine and the other at the port, each with complete community services, were built by ICOMI to serve the needs of over 1500 employees that operate the industrial complex. To give an idea of the magnitude of the investment represented by this complex, the cost up to 1957 to develop the mine and supporting services and social infrastructure was over 100 million dollars. It should be borne in mind that the above capital cost figures are in dollars of the years during which the respective projects were initiated and completed.

Jan 1, 1977

By Leslie F. Tedsen, Alan E. Flanigan, John E. Dorn

IT is necessary occasionally to use aluminum-alloy sheet where moderately elevated temperatures are encountered. Considerable attention has been directed toward determining the influence of "artificial aging" on the room-temperature properties of the precipitation-hardenable alloys, as testified by numerous company reports and by references 1 to 4. Investigations on the properties at elevated temperatures are few, however,5-7 and have not always covered the range of times and temperatures of greatest interest. The present investigation was instituted to overcome this deficiency. The work was done for the Office of Production Research and Development of the War Production Board, under the supervision of the War Metallurgy Committee, as a part of the "restricted" Project NRC-548. It has been released for publication by the Office of Production Research and Development. As is well known, the high-strength aluminum alloys achieve their remarkable properties as a result of precipitation-hardening. In production they are subjected to a solution heat-treatment followed by quenching, to retain the supersaturated solid solution. The solution treatment is followed by "aging" (precipitation-hardening) either at room temperature or at a suitable elevated temperature. A considerable increase in tensile and compressive yield stresses results from precipitation at room temperature ("natural aging"). Through the elevated-temperature process ("artificial aging") it is possible to obtain values of yield stress considerably higher than those attainable by natural aging. The increase in yield stress is accompanied by a smaller gain in ultimate tensile stress and by a decrease in elongation. During [TABLE I.-Sources of Materials Used in the Testing Program MATERIAL ORIGIN AND TREATMENT 24S-T Alclad.... From Lockheed stock. 24S-RT Alclad... Direct from mill. 24S-T80 Alclad.. 24S-O Alclad from Lockheed stock, solution-heat-treated (925°F., water quench) and aged at 375°F. for t0 t % hour. 24S-T8I Alclad.. 24S-T Alclad from Lockheed stock, plant stretched up t0 I per cent and aged t0 ± % hr. at 375°F. 24S-T86 Alclad.. 24S-RT Alclad from Lockheed stock aged 534 ± 34 hr. at 375°F. 6IS-W (bare).... From Lockheed stock. 6IS-T (bare) 6IS-W (bare) from Lockheed stock aged 8 hr. at 350°F. XB7SS-T Alclad. From Lockheed stock.] the first stages of artificial aging the yield stress increases steadily until it reaches a maximum value. In this condition the material is said to be "fully aged." Further exposure results in "overaging," attended by a steady decrease in yield stress. In the production of the artificially aged materials, temperatures and times are selected to achieve full aging. The following important characteristics are associated with the process: I. The higher the temperature, the more rapidly is the fully aged condition attained.

Jan 1, 1945