Search Documents

By Louis E. Toth, Alan W. Searcy

A modification of Le Claire's microscopic model for self-diffusion is developed in a form suitable for prediction of activation energies for diffusion in disordered substitutional solutions as well as in pure metals Bonding is considered as a localized interaction, and the energy of bonding between atoms of different types is taken as the arithmetic mean of the energies in the pure elements. The activation energies for vacancy formation and migration in substitutional alloys are shown to depend on the empirical constants developed for self-diffusion when the equations are adjusted for the mole fractions of the two elements. The differences in activation energies between alloys and pure metals are calculated and compared with the experimental differences. MaNY different correlations have been proposed for use in predicting activation energies for self-diffusion or diffusion in dilute alloys. Usually theories for self-diffusion cannot be applied to alloys nor can theories for dilute alloys be satisfactorily adapted to self-diffusion. We present here a correlation scheme which can approximate activation energies for diffusion, vacancy formation, and atom migration in substitutional-alloy systems of any concentration. The activation energy for self-diffusion QD has been correlated to the melting temperature Tm,1, 2 the sublimation energy L,,l the heat of fusion Lf,3 crystal structure, and valence.4 Working with mechanical parameters Le claire5 proposed that the activation energy for vacancy migration Qm could be related to appropriate shear moduli. He also proposed that the activation energy for vacancy formation 62, is proportional to Ls. THEORY We consider that Le Claire's expression for 4, is satisfactory. But an alternate expression for Qm in terms of the bulk modulus is just as satisfactory from a theoretical point of view for the prediction of the energy of vacancy migration in pure metals and can more easily be used for alloys. In order for Qm to be a minimum, not only the moving atom but also adjacent and nearby atoms must undergo distortions. These distortions are neither isotropic as is implied by a correlation with the bulk modulus nor unidirectional as implied by a correlation with a shear modulus, but are complex and multidirectional. A complete analysis in terms of the bulk modulus and all the shear moduli is not yet available. In a first approximation in which only one parameter is used, there is no obvious theoretical reason to prefer the shear modulus over the bulk modulus. The bulk modulus is a much more convenient parameter for use in predicting Qm. Shear moduli are known for less than half of the metallic elements while bulk moduli are usually available. Furthermore, because of the directional dependence of shear moduli, their estimation for alloys appears inherently more difficult than is the estimation of bulk moduli. We assume that the bulk modulus Bs reflects an average value of the shear moduli such that the strain energy at the point of maximum distortion of the lattice during vacancy migration can be expressed as

Jan 1, 1964

By Grant E. Casley

Since 1970 Mount Isa fines Limited has made a significant increase in blister copper production from approximately 100,000 to 155,000 mt per annum and in fact 161,040 mt were produced in the calendar year 1974. Flowsheet developments including fluidised bed roasting and converter slag flotation are discussed, particularly their contributions to minimising major equipment changes in smelting and converting. The use of model- ling and simulation techniques for such an exercise is mentioned. The paper reports the alterations made to both equipment and operating techniques in the reverberatory furnace and converter sections to achieve the regular production of 250 mt of blister per converter day from a 41% Cu matte grade. The effects of flux composition on converting performance are highlighted. The air quality control programme is discussed in relation to its restriction of blister copper production.

Jan 1, 1976

By R Burgess-Limerick, D Lynas

A number of standards and guidance materials currently exist to assist equipment designers. The ISO process, however, is a formal process and change often lags behind technology development. In some cases, this may result in weak or ineffective standards that need to be written in general terms to accommodate future technology developments, meaning some standards may only establish minimum requirements and not be overly helpful to equipment designers, in particular when designing for workforce diversity and inclusivity. By contrast, advisory information as issued by various mining regulatory bodies is able to respond more quickly to changes in technology. Standards do however have a safety and productivity focus providing design consistency between equipment manufacturers, a basis for auditing purposes, assistance in mining regulation and compliance, and in the development and application of safety management systems. As an example of challenges facing equipment designers, ISO3411 (2020) provides data approximating the 5th, 50th and 95th percentile of the ‘earth-moving machinery operator population’ for numerous static dimensions relevant to the design of earth-moving equipment. These data are then utilised in ISO6682 (2020) to provide recommendations regarding the location of controls. Attempting to utilise the data provided in ISO3411 (or other sources of static anthropometric data) creates further challenges for equipment designers, in that reference percentiles is problematic for design purposes. There is no ‘5th or 95th percentile operator’ as individuals vary along each dimension (Robinette and Hudson, 2006). Although dimensions have some degrees of correlation, when multiple dimensions are considered, the range of individuals which fall within a given range on all dimensions reduces substantially. For example, only about 82 per cent of individuals in a population will fall within the 5th to 95th percentile ranges for both height and weight. The more dimensions are considered, the smaller the range of people who actually ‘fit’ the description.

Apr 16, 2024

By J. Gunaselvam

This article deals with an investigation into the specification and use of appropriate seating systems to reduce whole-body vibration (WBV) exposure in typical vehicles used in the SA mining industry. The EU Directive EU/44/2002 to be legislated in 2005 in European countries, provides legal and economic motivation for this project. The criteria for seat selection can be condensed to the requirements in the directive, which mandates an action level of 0.5 m/s2and a vibration exposure limit of 1.15 m/s2 for an equivalent 8-hour daily exposure period. As part of this study six suspension seats, which the manufacturers claim satisfy the requirements in ISO 70966, were tested to determine the most suitable seat for an articulated dump truck. Six test subjects, three ?light? and three ?heavy? as specified in ISO 70966, were used to estimate the seat transmissibility functions in the vertical direction of the six different suspension seats. Transmissibility functions were measured in the laboratory with two excitation levels of 1 m/s2 and 2 m/s2 r.m.s. in the 0.5?30 Hz frequency range, as well as one spectrum approximating the EM5 spectral class. SEAT values were calculated for road vibration data measured on a typical articulated dump truck. A set of seat selection guidelines that can be followed by vehicle manufacturers and suppliers, procurement officers and and the technical staff on a mine is proposed in this article. It is recommended that additional studies of the use and operating conditions of seating systems in the SA industry, as well as an epidemiological survey be commissioned to gather additional information on this subject. Nomenclature ADT Articulated dump truck DSTF Dynamic seat testing facility EM1 Frequency spectra associated with earth moving equipment (?articulated or rigid frame dumper?) according to ISO 7096 EU European Union ISO International Standards Organisation PSD Power spectral density r.m.s .Root mean square SEAT Seat effective amplitude transmissibility WBV Whole-body vibration

Jan 1, 2005

By Thomas H. Dubaniewicz

The National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, conducted a study of past mine explosions to identify the ignition locations and ignition sources responsible for the most severe explosion events resulting in death. Since the Scotia disaster of 1976, many fatalities from underground coal mine explosions have been linked to nonpermissible electrical equipment ignition sources located in intake air courses. With few exceptions, explosion protected equipment is generally not required in intake air courses of gassy underground coal mines in the US. Cigarette lighters were another prevalent ignition source for fatal explosions ignited in intake air courses. Several mine rescue/ recovery teams have encountered electrical ignition hazards. The study provides evidence that intake air courses of gassy underground coal mines fit the description of certain Hazardous (classified) locations described in the US National Electrical Code®. Class I Division 2 or Zone 2 explosion protection tech¬niques may be used to design intake air equipment so that it does not present an ignition source under normal operation, before mine power is shut down in emergency situations. Nonpermissible circuits in intake air courses that are likely to remain energized during emergencies, e.g. battery powered equipment, should be protected by more stringent Class I Division 1, Zone 1, or Zone 0 techniques, to protect rescue/recovery personnel.

Jan 1, 2009

By A K. Raina, P B. Chourdhury

Flyrock is the unwanted throw of rock fragments to excessive distances in opencast blasting. The incidence is relative in nature incorporating the distance of objects of concern like structures within and outside the mine, equipment within the mine & near the blast and persons within and off the mine. Several attempts to predict and defi ne fl yrock made worldwide could not address the problem since the phenomenon is not a regular feature in blasting. This probabilistic nature of fl yrock allows for risk calculation. CIMFR, India developed a Factor of Safety based risk criterion (10, 14) for evaluation of throw/ fl yrock in opencast mines that incorporates all the above in terms of distance and allowable limit of throw – which in turn determines the risk. The criterion provides the blaster a tool for mathematical evaluation of fl yrock risk in terms of a Factor of Safety and threat ratio (defi ned for the 1st time), thereby enhancing confidence when blasting. The method is easy to use and has been applied to several mines in India and the results are signifi cant. This paper details the evolution of the concept and its application in three limestone mines of India and the results obtained. The application of the method for defi ning a fl exible danger zone is also discussed.

Jan 1, 2008

This paper details successful implementation of a revolutionary pit access system involving excavation of an 'in-the-wall' ramp at Three Mile Hill open pit operated by Gold Mines of Coolgardie, formerly Goldfan Limited, at Coolgardie, Western Australia. Three Mile Hill is a medium-size, open pit, gold operation typified by hard, competent, fresh rock conditions from near surface. The project involved construction of a haulage tunnel or decline access located in the wall of an open pit in place of a conventional pit access ramp. Works undertaken as discussed herein included excavation, support, ventilation, dewatering, services installation, commissioning and monitoring. Prior to implementation, the conventional hardrock pit slopes and designs were constrained by the presence of infrastructure and a main road to the North and by adjoining leases to the Southeast. The combination of these factors and economic considerations resulted in a decision to proceed with an innovative in-the-wall ramp access system that is believed to be the first of its type in Australia. Back-analysis indicates that implementation resulted in a cost saving of as much as A$3.6 million and increased mineable pit reserves. The paper deals with the successful implementation and operation of the in-the-wall ramp haulage as well as an economic evaluation that is aimed at drawing some general conclusions on favourable conditions for implementation in other mining scenarios.

Jan 1, 1996

By Peter Cain

The Phalen Colliery in the Sydney Coalfield is extracting the 2.6 m thick Phalen Seam by the panel and pillar longwall retreat method. Abandoned workings occur in the Harbour Seam 140 m above and overlie the Phalen Colliery. Parts of these workings are flooded, and pose a number of questions relating to the safety of operations in the Phalen Colliery. In order to answer some of these questions, the Cape Breton Development Corporation re-entered an abandoned non-flooded roadway in the Harbour Seam directly above a retreat panel in the Phalen Seam to allow the deployment of instrumentation to monitor interaction effects. Fifteen monitoring sites, each 4.5 m apart, were installed in the 5 East Top Level after it had been re-entered and made safe. Each monitoring station included a vibrating wire strain gauge piezometer and a potentiometric extensometer. The piezometers were attached to rock bolts anchored into the floor and were connected by a flexible standpipe to a constant head apparatus. Variations in hydraulic head due to subsidence were monitored to determine subsidence. The extensometer units were mounted on rock bolts anchored into the floor of the roadway beneath the ribside and monitored ground strains. The instrumentation was capable of remote reading in the event that access to the site was restricted after installation. This paper describes the instrumentation, the installation programme, and some preliminary results.

Jan 1, 1993

The paper describes developments since 1959 in major excavators to meet the demand for higher outputs of overburden and coal under less favourable batter conditions than used hitherto in the coal deposits of the Latrobe Valley. Particular reference is made to investigations of designs of bucket wheel head configurations for the digging of these flat batters on high faces, and examples are given of the wide use of models inthese studies. An explanation is given of how solution of these problems and surface conditions unfavourable for wheeled transport confirmed selection of the long boom rather than the compact type of bucket wheel excavator for the Latrobe Valley applications.The past decade has seen advances in the manufacture in Australia of components for excavators and similar machines. The history of Australian manufacture of components for major brown coal excavators is traced;and reference is made to study and application of Australian and overseas (mainly German) codes and practices in the design and construction of machines made partly here and partly in Germany.A section of the paper deals with advances in electrical engineering for large excavators in Australia and its interdependence with mechanical design and construction.Finally, as an example of the versatility of the bucket wheel excavator, a description is given of a recent application for the mining of mineral sands in northern N.S.W.

Jan 1, 1971

MOWRY BATES, ? Tulsa, Okla.-In the first part of this paper the author says: "In an unpublished paper on Water Problem in the Augusta Field, S. K. Clark reaches the following conclusions: (1) That the great amount of water present is bottom water, occurring in the Varner sand, the main producing or the 2500-ft. horizon. (2) That the only striking connection between structure and water is in the area of the marked

Jan 4, 1919

By Paul J. Fopiano

SOME relationships between the flow characteristics of iron single crystals of 99.9 pct purity and the behavior of imperfections have been investigated. X-ray rocking-curve measurements and etch-pit counts were made as a function of plastic strain, and compared to the stress-strain curve obtained on a modified Polyani tensile machine. Crystals grown from rolled strips of vacuum-melted iron by the strain-anneal method1 had a high preference for a (110) longitudinal direction and a (211) face normal. The tensile specimens were prepared from 2 by i by 0.040 in. single crystals having a gage area of 3 by \ in. Rocking-curve measurements were carried out with a highly perfect germanium monochromating crystal in which the dazz spacing was matched to that of the dZl1 in the ir0n.l Well-collimated CuKal radiation was used throughout. These procedures practically eliminated errors due to geometrical and wavelength resolution. Inasmuch as the rocking-curve half breadth may vary markedly from point to point in the specimen being irradiated, the crystals were strained in place by mounting a hydraulic loading device on the double-crystal spectrometer. The rocking curves were taken after each increment of strain in the unloaded condition, since no observable difference was found in the rocking-curves between the loaded and unloaded states. The rocking-curve half breadths of the as-grown specimens were in the range 90 to 120 sec of arc when the beam irradiated an area of about -£ by -& in. on the specimen. DeMarco and weiss3 have shown that, for a well-colli- mated X-ray beam, irradiating about 10"! sq in. of the very same material, half breadths within 10 pct of the Darwin natural half breadth were observed. Since the rocking-curve specimens were stressed by the load-unload technique, the strain achieved at any given stress depended on the time of holding because of low-temperature creep. Fig. 1 shows the rocking-curve half breadth (also area/peak height) as a function of plastic strain for a relatively short holding time (2 to 5 min) at each stress level. For strains less than 0.1 pct the rocking-curve breadth is essentially constant; it is only for larger strains that there occurs a significant increase in this breadth. Where the holding times at each stress level were longer (by well over an order of magnitude) there occurs a significant increase in the rocking-curve breadth only after plastic strains of the order of 0.6 pct had been introduced into the specimen. This observation is related to the time dependence of creep phenomena and emphasizes the difficulty in comparing data obtained by two such different straining methods. Etch-pit results were obtained using a 2 pct nital etch on specimens strained in the range of 0 to 1 pct. Prior to etching, all specimens were annealed for 3 hr at 150°C, the carbon content being sufficient to decorate the dislocations for strains of at least 1 p~t.~ The data points were all taken from parts of the same single crystal which had been strained with short holding times at stress in increments of strain of the order of tenths of 1 pct. The (211) plane is particularly difficult to etch-pit in vacuum-melted iron and therefore it is felt that these values are as much as an order of magnitude low. Fig. 2 shows the etch-pit density as a function of plastic strain. The smooth curve passing through the data points is not meant to infer a quantitative correlation with the rocking-curve data. What is of interest, however, is the change in etch-pit density in the region of 0.2 pct plastic strain. The first three increments in strain (points 2,3, and 4) did not produce a measurable change in the etch-pit density while subsequent increments did produce a measurable change. While the absolute values of these results do not appear to be cor-

Jan 1, 1967

By M. Bevis, E. O. Fearon, P. C. Rowlands

Fe-Ni and Fe-Ni-C martensite specimens have been deformed in compression at room temperature and the habit planes of operative deformation twins determined by two-surface optical trace analysis. The full orientations of the martensite crystals were determined from divergent X-ray beam diffraction patterns. The experimental results are in excelled agreement with predicted twinning modes. In particular, the habit planes of some deformation twins in bcc martensites are consistent with a "Type XI compound'' twinning mode with Kl, Kz, 71, 77~ elements given by {5, 8, 11) {ioi}, (33) (ill) Tetragonal derivatives of this mode are operative in bct martensites. UnUSUAL deformation twinning modes have been reported by Richman' to occur in Fe-Ni-C martensites with bcc and bct structures. The twin habit planes were determined by single-surface trace analysis (pole locus method) and the remaining twinning elements were determined from the geometry of twin-twin intersections. The indices assigned to the observed habit planes are (3 101, "(089)" and "{0, 1,13)" or "{1,2,7} ", and only in the first case do the twinning elements correspond to a predicted twinning mode. This is mode 1.4 in the paper by Bevis et al. The results presented in Ref. 2 indicate that previously unpublished bcc and bct modes should be operative in preference to the (130) mode and anomalous modes reported by Richman. In view of these results and the uncertainties involved in determining habit planes from single-surface trace analysis and twinning elements from twin-twin intersections5 a two-surface trace analysis of deformation twins in Fe-Ni and Fe-Ni-C martensites has been carried out. EXPERIMENTAL PROCEDURES Two alloys with compositions Fe-23 pct Ni-0.6 pct C and Fe-30.4 pct Ni were prepared from 4N pure materials by induction melting under a vacuum of 10"5 mm Hg. The alloys were homogenized at 1350'~ for 5 days. Both of these alloys are austenitic at room temperature with M, temperature - — 50"C. The aus-tenite grain size of the Fe-Ni-C alloy was approximately 300 to 400 p. The Fe-Ni alloy was remelted in a vertical tube furnace and the melt lowered slowly from the hot zone of the furnace to produce s ingle -crystal austenite specimens. Specimens approximately 10 by 5 by 5 mm were cut from the ingots and quenched to various temperatures below the Ms temperature. The specimens were elec-tropolished in a 10 pct perchloric acetic electrolyte before being deformed in compression at room temperature. Martensite plates which exhibited profuse deformation twinning were selected for analysis and the specimen polished on a second surface such that the two surfaces which contained the martensite plate enclosed an obtuse angle of approximately 145 deg. The specimens were then electropolished to reveal the traces of the deformation twins on both surfaces. The full orientations of the martensite crystals were determined using a divergent X-ray beam technique (Kossel line technique) employing an AEI SEM2 electron probe microanalyzer. Details of this technique which include a detailed description of the Kossel camera attachment to the microanalyzer used in the present experiments have been discussed elsewhere.3 Only additional details relevant to this investigation are discussed here. The specimens were mounted with one surface normal to the incident electron beam as illustrated schematically in Fig. 1. The martensite plates to be analyzed were located using the normal scanning equipment of the microanalyzer. The position of the electron beam and hence the position of the source of divergent X-rays generated within the crystal could be located to within 1 p. Exposure times of approximately 8 to 10 min were required for back-reflection Kossel patterns and it was found that useful diffraction patterns could be obtained consistently from heavily deformed martensite plates. A reference line (carbon contamination mark) produced on the two surfaces of the specimen by scanning the electron beam in a direction having a known relationship with the reference !ine in the X-ray camera enabled the full orientation of the crystals to be determined. Martensite plates with widths as small as 8 p could be oriented using this procedure. The Kossel line patterns were interpreted using the charts developed by Rowlands and ~evis~ as generally

Jan 1, 1969

By Paul G. Shewmon

The migration of slightly solzrhle spherical particles through a solid under the infllrence of a temperature gradient is analylzed for the cases of various transport mechanisms. It is shown that the variation of the velocity of the particles with radius, r, depends on the dominant mechanism of matter transport around or through the inclusion. Thus the velocity varies as r-1 jor surface-dijf1~sion controlled migratzon. is independent of r for volume diffusion in either phase, and varies as if the rate is determined by an interfacial reaction (n is the order of the interfacia1 reaction). These same results hold tor the migration of a cvlinder of length much greater than its radius. and .for other types of potential gradients, e.g., an electrical field. These equations are combined with recent electron-microscopic ohservations to show that the rate of migratzolz of small helium-silled bubbles through copper is determined by surface diffusion of the metal atoms. With these equations and the temperature gradients attainahle in an electron-microscope joil, the dominant transpar/ mechanism (or any migrating pnrtzclos can he determined. AS a result of fission, rare-gas atoms are created in the hot fuel element of a nuclear reactor. These insoluble atoms precipitate to form bubbles of the gas in the fuel. The subsequent migration and coalescence of these bubbles is thought to play a dominant role in the swelling of fuel elements which in turn can limit the fuel-element life. As a result of this practical problem and because of the relative simplicity of the system, workers in several laboratories have imbedded rare-gas atoms in metals with the aid of an accelerator and studied the formation and behavior of the bubbles that form on annealing. Recently Barnes and Mazey have studied the migration of such helium-filled bubbles in copper foils using the electron microscope and the temperature gradient that can be induced in the foil by the electron beam. They found that the smaller bubbles moved faster than the larger ones. It is shown below that, if this is true, the rate-controlling step in their migration is surface diffusion of metal atoms instead of volume diffusion, vapor transport, or an interfacial reaction. The analysis given is in no way limited to gaseous inclusions so the variation of velocity with particle size for any relatively insoluble precipitate particles could be used to obtain information about the relative importance of surface diffusion, volume diffusion, and interfacial reaction in such two-phase systems. VOID MIGRATION IN A TEMPERATURE-GRADIENT ANALYSIS Barnes' studies indicate that helium does not dissolve or diffuse in metals to a measurable extent, so that when the voids move they must do so through the movement of metal atoms from the leading to the trailing sides of the void.' Thus voids might move by surface diffusion, diffusion of vacancies in the surrounding lattice, or vapor transport. We consider first the case of flow by surface diffusion alone. We assume that there is a force, in the sense of irreversible thermodynamics, tending to move the atoms around the bubble in a given direction. We designate this direction as the x axis and the force per atom as Fa. The net rate of flow of atoms from one side of the bubble to the other, under the influence of this force, is the surface flux, Js, times the cross-sectional area available for flow, A,. A, is taken as the circumference times the thickness of the high-diffusivity surface layer 6. Thus where 51 is the atomic volume. For bubbles to advance a distance dx, a volume equal to nr : dx must flow around the void so that The minus sign enters because the bubble moves in the direction opposite to that of the force on the atoms. Equations for volume diffusion and diffusion through the vapor can be obtained in the same manner. For vapor transport we have Ag = and the ratio of the densities of metal atoms in the gas and the solid (pg/pl) enters so that

Jan 1, 1964

By Thirumalai, K.

Although the term "spalling" has long been known, Norton l first referred to its usage for the fracture or disintegration of materials subjected to rapid temperature changes. Spalling of ceramic materials at high temperatures has received attention in the past. Removal of the char formed during ablation in re-entry of space vehicles has been referred to as mechanical spalling. The first experiments to evaluate the process of rock fragmentation by thermal spalling were conducted by Stoces using a series of gasoline burners on the quartz veins of the Zinnwald deep mines in Germany. After the development of rocket-jet burners, the principles of 'thermal spalling combined with high fluid momentum found wide practical application in rocks. The well-known jet piercing process for drilling blastholes in taconite and for jet channeling in the quarrying of granite are among the more notable of these application^.

Jan 1, 1970

By R. E. Cech, J. H. Hollomon

KURDJUMOV and Maksimova reported experiments with manganese steels and high carbon steels' and with an Fe-Ni-Mn alloy' in which mar-tensite was formed isothermally over a range of temperatures. They found in some cases that mar-tensite formation could be suppressed by rapid quenching to liquid nitrogen temperature. From their microstructural observations of martensite formed isothermally, they concluded that the rate controlling step is nucleation rather than growth. Kulin and Cohen,3 in an attempt to reproduce these experiments, found that with a steel having the same composition as that reported by Kurd-jumov and Maksimova, the transformation to martensite was essentially complete above the temperature range of Kurdjumov and Maksimova's isotherms. The possible reasons for this disagreement were not considered. Recent papers by Das Gupta and Lement4 and Kulin and Speich5 report the formation of isothermal martensite in a high chromium steel and in an Fe-Cr-Ni alloy, but neither paper can be considered a verification of the original Kurdjumov and Maksimova results. Further, in neither case were the authors able to suppress the formation of martensite entirely. Because of the important bearing the Kurdjumov and Maksimova results have to an understanding of the mechanism of martensite reactions it was felt that an experimental investigation directly concerned with checking the validity of their results was in order. This paper describes the results obtained on the isothermal transformation over the temperature range from —79" to —196°C of an alloy of iron, nickel, and manganese. Experimental Apparatus A 15 lb heat of an alloy containing 73.3 pct Fe, 23.0 pct Ni, and 3.7 pct Mn was melted by induction and cast under argon. The ingot was forged to 1-in. bar and a portion rolled to 1/16x1 1/2-in. strip. This strip was pack-homogenized 300 hr at 1100" in a helium-filled sealed iron tube. The composition after homogenization was 73.2 pct Fe, 22.94 pct Ni, 3.73 pct Mn, 0.05 pct C, and 0.015 pct N. The strips were cut to 1/2-in. width for dilatometer and metal-lographic specimens. Only the center portion of the 11/2-in. strip was used in the present investigation. The dilatometer employed was similar in design to one described by Flinn, Cook, and Fellows." A concentric fused auartz rod and tube assembly with hooks for holding the specimen was mounted so as to transmit the specimen dilation to a 1/10,000 in., 1/10 in. travel dial gage. The dilatometer proper was mounted by means of extension arms to a counterweighted sliding member on a vertical standard. This method of mounting permitted rapid transfer of the dilatometer from the austenitizing furnace to the quenching bath and low temperature chamber. A small electrical vibrator on the dilatometer kept frictional effects of the quartz members at a minimum. The austenitizing unit was a vertical, molybdenum-wound, hydrogen atmosphere furnace maintained at a constant temperature ±3°C by means of constant power input. A 12-in. stainless steel jacketed copper liner having 1/2-in wall thickness acted to equalize the temperature in the hot zone of the furnace. This liner, closed at the bottom end and open at the top to permit entrance of the dilatometer and specimen, was kept filled with dry nitrogen gas. A chromel-alumel thermocouple was placed inside the tube to determine the temperature. The 4-in. dilatometer specimens in the chamber varied less than 1/2° across the specimen length except for a 1 1/20 drop at the end nearest the open end of the furnace. The low temperature isothermal holding bath was a double Dewar arrangement similar to one described by Turnbull7. The outer bath was filled with a refrigerant at a temperature lower than the desired holding temperature. The inner bath was filled with Freon "11" or "12" or a mixture of both, depending upon the holding temperature. This inner bath which tended to be cooled by the outer bath was kept at a constant temperature by introducing a small amount of heat with a manually controlled electric heater. Stirring was accomplished by bubbling dry air through the bath. A Leeds and North-rup type K potentiometer was used to measure the inner bath temperature as indicated by a five element copper-constantan thermopile. The bath temperature was maintained within ±0.2°C of the desired temperature by occasionally adjusting the heater current so as to keep the Leeds and Northrup galvanometer at zero deflection with a constant setting of the potentiometer. Isothermal tests were usually continued for 300 to 400 min and another reading made at approximately 1000 min if the bath, unattended overnight, had not deviated in temperature more than 5°C. Transformation curves are drawn dashed (Fig. 1) through the time region where temperature was not controlled precisely. Experimental Procedure Dilatometer specimens of 1/2x1/16-in. strip were cut to 41/2-in. length and holes were drilled for the quartz hooks with proper spacing to give a 4-in. measured length. A thermocouple consisting of 0.012-in. diameter chrome1 and alumel wires was spot welded to the specimen and threaded between the dilatometer rods to binding posts near the dial

Jan 1, 1954

By R. F. Tenney

No detailed information has been published heretofore on the performance of small industrial-type anthracite stokers in building-heating service, apparently because of the difficulty of comparing the performance of one unit with that of another over an entire season's operation. Studies of competitive heating fuels have been similarly handicapped, and attempts to compare fuels are seldom technically sound in this investigation, the performance of a 60-in. Losch4 stoker burning rice-size anthracite in a standard commercial boiler was observed during a 4-month winter-spring season. It was used to heat two buildings at the Bureau of Mines' Anthracite Research Center at Schuylkill Haven, Pa., with the customary type of automatic pressure-range control. Attendance was limited to inspecting, fuel weighing, data recording, and ash removal. Results were computed daily and grouped by weekly periods to minimize daily irregularities. The same stoker-boiler unit had already been tested in a series of American Society of Mechanical Engineers (ASME) test code runs, with the stoker running continuously and with other conditions well stabilized A comparison of results from the code test and the building-heating tests provided information not available in the past for a single stoker unit, assisted in analyzing heat losses not computable in a cyclic operation, and established a basis for evaluating stoker performance in heating service.

Jan 1, 1963

By Chee Theng

"What would you do if you are an industry leader and disruptive technology threatens to overturn your business model? Although bearings and seals are in little danger of being displaced in the near future, one company is taking no chances in an age of digital disruption.“For SKF, digital transformation and the Industrial Internet of Things (IIoT) make this time right now arguably the most exciting time in our 100-plus years of history,” John Schmidt, president of SKF USA Inc., said during the SKF Technical Press Day in Philadelphia, PA.The company is not merely integrating digital technologies into its products and services but is taking a forward-looking, strategic approach. “To be successful, legacy companies have to undertake a process called digital transformation. It’s not just an IT initiative but is really about upgrading the strategic thinking,” explained Michael D’Argenio, vice president of digital transformation and customer experience at SKF Americas.Learning from those who went beforeD’Argenio cited the examples of two companies that saw entirely different outcomes in the face of digital disruption. The well-known case is that of Kodak, one of the storied brands in history, whose business was disrupted by the advent of digital photography. Although it invented digital photography, Kodak decided to box it up and put it on the shelf because it was scared of disrupting its business in photographic fim. Instead, it was disastrously disrupted from the outside.Less well known is the case of Encyclopedia Brittanica Inc., publisher of the longest-running English-language, general-knowledge encyclopedia in the world. Sales peaked at 120,000 sets in 1990, plunging to 8,000 sets in 2012. In 20 short years, it saw not one but two massive digital disruptions. The first was in 1993, when Microsoft published the first digital interactive encyclopedia on a CD-ROM, called Encarta, priced at just $99. The second was in 2001, when a communitycurated, free website called Wikipedia launched. Taking the opposite approach from Kodak, Encyclopedia Brittanica looked at its industry, its company and its customers through the lens of the new technologies, made a prediction about the future and, based on that prediction, took a bold move. Having identified its core value proposition as the delivery of reliable, high-value, verifiable knowledge, Encyclopedia Brittanica replanned, restructured and rebuilt its company from the ground up to deliver that same value proposition, only in a different way. It stopped producing the only product that it had known for 244 years and began producing digital products that it sold to educational institutions.“There is a lot to learn from the Encyclopedia Brittanica case,” said D’Argenio. “The company embraced its market change, it embraced its customer change, and it rethought what it needed to do to be successful. Because it owned that disruption internally, it was never disrupted from the outside. It continues to operate today and is as profitable as it has ever been.”"

Aug 1, 2019

By Robert Bakish

VARIOUS aspects of structure-sensitive corrosion of single crystals and polycrystalline aggregates of Cu,Au have been presented in papers by the author, in association with W. D. Robertson. Prompted by some observations in the course of these studies, a new approach to the problem was undertaken. Results of these new experiments are reported here. Thin slices, less than 2 mm thick, were prepared from single crystals 3.5 mm in diam grown by the Bridgman technique. The crystals were homogen- ized for 300 hr at 850°C. Crystals with no deformation, crystals deformed in tension to the yield point, and crystals deformed 20 pct in excess of the yield point were used. Crystals of several different orientations were studied. Slices were immersed for one month in 2 pct aqueous solution of FeCl3 and, subsequent to this immersion, were subjected to bending. Immersion and bending were carried out at room temperature. The size and geometry of the crystals did not permit accurate data on the loads involved. A most unexpected result was obtained in the process of bending these slices of Cu3Au crystals normal to the (110) plane. Completely brittle be-

Jan 1, 1958

By Fulian He, Jianhang Chen, Dongdong Chen, Shoubao Zhang

"The Wangjialing Coal Mine is the main colliery of the China Coal Huajin Energy Limited Liability Company. The average thickness of the coal seam in District 201 is 6.21 m. Fully mechanized longwall mining was used in this district. The ventilation roadway of panel 20102 was influenced by the retreat mining of the adjacent panel 20104. Therefore, large deformation and severe roof falls occurred in this roadway, seriously influencing the safety production of this coal mine. To support the roadway, cable truss was proposed to strengthen the reinforcement of this ventilation roadway. First, numerical simulation was used to optimize the reinforcement parameters, including the cable installation angle, cable length, and eccentric distance. Based on numerical simulation results, in-situ tests were conducted in the ventilation roadway of panel 20102 with the cable truss technology. In-situ monitoring results showed that the roof-to-floor convergence and the convergence of roadway on two sides were within the safety range. Furthermore, no apparent separations occurred in the roof. These indicate that based on the designed parameters, the cable truss system can effectively maintain the roadway stability under the severe influence of the adjacent longwall mining.INTRODUCTIONCable bolts are flexible tendons composed of multi steel wires, which are wound into a strand (Chen, Hagan, and Saydam, 2018). They were initially introduced in the hard rock mining industry in the 1960s. Later, they found rapid application in coal mines to maintain the stability of excavations (Wang et al., 2015).The standard cable bolt is composed of seven steel wires with a diameter of 15.2 mm. Laboratory and in-situ tests showed that there is a low bonding capacity between the standard cable bolt and the grout (Craig and Holden, 2014; Chen, Hagan, and Saydam, 2018). Then, modified cable bolts are developed based on the standard cable bolts. They are improved by changing the surface geometry of standard cable bolts, such as birdcaged cable bolts (Hutchins et al., 1990) or nutcaged cable bolts (Hyett et al., 1993). Further tests proved that modified cable bolts have better mechanical interlock and friction between the cable bolt and grout, leading to larger load transfer capacity of cable bolts.Although cable bolts have been used for many years, failure of the cable bolting system still occurs. A common failure mode is the damage of surrounding confining medium while the cable bolt is still hanging in the roof, which is caused by the bond failure of the cable/grout interface (Hutchinson and Diederichs, 1996). To prevent the cable bolting system from failing, the cable truss system is more widely used in mining engineering."

Jan 1, 2019

By F. D. Rosi, F. C. Perkins, L. L. Seigle

An investigation was made of the mechanism of plastic flow in coarse grained specimens of both sponge and iodide titanium at low (-196°C) and high (500° and 800°C) temperatures. Deformation by slip occurs predominantly on a {1011} plane and in a <1120> direction over this entire temperature range, and secondary slip on {101-1} planes becomes more prevalent with overthisentireincreasing temperature.range, The crystallographic habit of the predominant twin planes becomes more prevalent with type is temperature-dependent, and deformation by twinning increases as the temperature of testing is lowered. Kink bands were not observed at -196OC and rarely at the high temperatures. A LTHOUGH the deform a tional mechanisms in . -titanium at atmospheric temperature have been extensively investigated," there is little information regarding the influence of testing temperature on these mechanisms. The only available data come from the recent work by McHargue and Hammond, who extended single crystals of iodide titanium at a temperature of 815°C. No significant changes in the types of slip and twinning planes were observed, but increased activity on the type I, order 1 pyramidal slip planes and on the type 11, order 2 twinning planes was reported. These planes contribute very little to the deformation process at room temperature.&apos;&apos; &apos; Since there is interest in titanium as a material for use at both low and high temperatures, the present investigation was undertaken to examine the slip and twinning behavior in coarse grained specimens of titanium at -—196", 500°, and 800°C in order to determine the general effect of temperature on the mechanism of plastic deformation. Experimental Material Used and Specimen Preparation—Both sponge and iodide titanium were used in the present investigation; chemical analyses appear in Table I. These materials were arc-melted under argon into 25 g slugs, which were then cold-rolled approximately 90 pct to a sheet thickness of 0.05 in. Since the strain-anneal technique was used for obtaining coarse grains, the cold-rolled sheets were made into tensile specimens which were then annealed to produce a relatively coarse uniform grain structure prior to critical straining. The details of the strain-anneal treatment. size of grains, and the method for preparing the specimen surface for optical microscopy have been described in a previous report.&apos; In order to obtain a wider spread in crystal orientation for the present work, it was necessary to vary the rolling schedule to reduce the degree of preferred orientation in the annealed sheets prior to critical straining. Methods for Tensile Testing—The apparatus for experiments at the temperature of liquid nitrogen (—196°C) consisted of two concentric stainless steel

Jan 1, 1957