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By W. L. Phillips

The recovery properties of compression-deformed lithium fluoride single crystals were investigated as a function of prior strain, annealing time, and annealing temperature. The recovery process was studied by observation of etch pits and birefringence stress patterns. The recovery process involved first a redistribution of the dislocations and then a decrease in their number. Only by annealing at high temperatures after small strains (<0.02 in. per in.) was it possible to obtain complete recovery of mechanical properties. LITHIUM fluoride affords unusual opportunities to extend the knowledge of deformation mechanisms of nonmetallic crystalline compounds. Single crystals of high purity are readily available. These crystals deform by slip on the (110) <110> system.&apos; Unlike those of several other ionic crystals, the stress-strain curves of annealed lithium fluoride are reproducible.2 Dislocations generated in the crystals during deformation can be revealed by etch pits.3 This fact makes possible more detailed studies of mechanisms than is usually the case with metals. Also, because lithium fluoride is transparent, it is possible to follow the recovery process with birefringence stress patterns. It has been shown that with metals an increase in temperature increases the amount of recovery for a given time, and the amount of recovery increases with increasing time at the same temperature.4-6 The yield stress has also been shown to be dependent on the rate of cooling after annealing.&apos; Annealing germanium, a covalent-bond material, at high temperatures after deformation redistributes the dislocations and reduces their number. The purpose of the present paper is to extend the knowledge of recovery properties to an ionic crystal, lithium fluoride. The effect of strain, time, and temperature of recovery on the stress-strain curve was investigated. The recovery process was followed by observations of etch pits and birefringence stress patterns. EXPERIMENTAL PROCEDURE Specimens measuring approximately 0.10 by 0,10 by 0.30 in. long were cleaved from a single bulk

Jan 1, 1961

By Y. C. Liu

The orientation relationship between the dejormation and recrystallization textztres of binary Cu-P alloys of high phosphorus content was observed to he a ± 14-deg (110) rotation. According to the ori-ented-gvowth hypothesis, the same relationship should exist between a successfully flowing pain and the strained single-crystal matrix of alloys of corresponding composition. The orientations of thirty successfully growing grains were obtained in a Cu-1.0 at. pct P alloy. Both a conventional analysis and the more detailed analysis advanced in the present study demonstrate that the observed orientation relationship is not comparahle to that predicted by the oriented growth hypothesis. IT has been shown experimentally that the formation of recrystallization textures in metals may be explained on the basis of the oriented-growth hypothesis. This conclusion is based primarily on the results of cooperative experiments carried out by various investigators in aluminum. Beck and HU&apos; suggested that the orientation relationship between the recrystallization and deformation textures of aluminum is a 38-deg(111) rotation. A similar relationship, i.e., a 40-deg(111) rotation, was observed between the primary and secondary recrys-tallization textures.&apos; Since the secondary grains result from a process of selective growth, this naturally implies that the same mechanism is also responsible for the formation of the primary re-crystallization texture from the deformed matrix. Further evidence was provided by the experiments of Liebmann, Liicke, and Massing3 and Yoshida, Liebmann, and Lucke.4 They observed that grains which could successfully grow into strained aluminum single crystals invariably exhibited the same orientation relationships with their matrix. Thus, regardless of other opinions,5&apos;9 these results offered good evidence in favor of the oriented-growth hypothesis. In order to examine broader applications of this oriented-growth hypothesis, experiments should be carried out in metals other than aluminum. In a recent investigation on the recrystallization textures of binary copper alloys with phosphorus, arsenic, and antimony,7 it was found that the predominant recrystallization components were related to the deformation textures by a (110) rotation. The (110) rotational relationship is different from the (111) relationship generally proposed between the recrystallization and deformation components of other binary copper alloys. 1,8,9 Applying the observations made for aluminum, the oriented-growth hypothesis predicts that the orientation relationship of grains successfully growing into the strained single crystals of either one of these copper alloys should correspond to that observed in the textural study. Verification of this prediction would provide a critical test of general applicability of the oriented-growth hypothesis to the formation of recrystallization textures in fcc metals other than aluminum. The Cu-1.0 at. pct P alloy was selected in the

Jan 1, 1964

Gold mineralisation at the Macraes Gold Project is hosted in the Hyde-Macraes shear zone and can be traced for ~30km along strike, although economic resources are confined to a 7 km section in the vicinity of the Macraes township. The shear zone, which typically dips at a low angle (~20 o ) to the NE, is bounded by an upper hanging wall shear and a lower footwall fault. Mineralisation occurs along the hangingwall of the shear zone as well as in low angle concordant shears and stockworks. Ore types include graphitic cataclasites with variable amounts of quartz veining, ælode schistsÆ and quartz-vein stockworks. Rehabilitation at the mine has focused on creating an environmentally benign site dominated by pasture to allow continuation of the traditional pre-mine farming economy. Changing regional economics, continued urbanisation and a reduction in traditional employment opportunities has seen a rethink in the long-term rehabilitation outcomes. The community has recognised that the rehabilitated site will provide the basis of a viable tourism venture and the creation of a Heritage and Art Park (working title æGolden Point ParkÆ) is the culmination of that process.

Jan 1, 2002

Design and selection of support systems for longwall faces call for in-depth knowledge of strata mechanics and in particular of strata-support interactions. The paper presents the results of field investigations and analysis of a difficult-to-cave roof using powered supports under a massive dolerite sill in Central India using a state-of-the-art datalogger system. The mechanised longwall face was equipped with 4/680 tons chockshields operated on the IFS mode using a 300 K W DERD shearer. The datalogger system was capable of storing data simultaneously in 32 channels. The paper describes the monitoring system and the monitoring programme. The system provided useful information on support behaviour, build-up of leg pressures and face convergence during an intense dynamic periodic weighting phenomenon which destroyed the integrity of almost half of the face supports. At this point, the face had advanced by about 197 metres from the barrier. The paper outlines a post-mortem analysis of this dynamic event and provides a critical evaluation of the data collected for understanding strata support interaction and the behaviour of the massive sill in the overburden.

Jan 1, 1992

By Ghose AK

Design and selection of support systems for longwall faces call for in-depth know- ledge of strata mechanics and in particular of strata-support interactions. The paper presents the results of field investigations and analysis of a difficult-to-cave roof using powered supports under a massive dolerite sill in Central India using a state- of-the-art datalogger system. The mechanised long wall face was equipped with 4/680 tons chockshields operated on the IFS mode using a 300 KW DERD shearer. The datalogger system was capable of storing data simulta- neously in 32 channels. The paper describes the monitoring system and the monitoring programme. The system provided useful information on support behaviour, build- up of leg pressures and face convergence during an intense dynamic periodic weighting phenomenon which destroyed the integrity of almost half of the face supports. At this point, the face had advanced by about 197 metres from the barrier. The paper outlines a post-mortem analysis of this dynamic event and provides a critical evaluation of the data collected for understanding strata support interaction and the behaviour of the massive sill in the overburden.

Jan 1, 1992

By W. A. Walker, G. W. Ostroot

An increase in the number of deep wells being drilled where extreme bottom-hole temperatures are encountered, and the anticipated drilling of wells where temperatures in the range of 500°F or higher may occur, has brought about a comprehensive investigation of cementing materials and of the techniques involved in their proper usage at these elevated temperatures. Included are developments in cements, retarders, weighting materials and other cement additives which make it possible to formulate a variety of compositions to help resolve the cementing problems of these extreme well conditions. The problems associated with the selection and testing of cements are discussed, and a resume of field results is included. Previous studies on strength retrogression indicate that caution should be exercised in the selection of a cementing composition for use in high-temperature wells. It now appears that, by the addition of silica flour as a stabilizing additive to certain cements, compositions covering a wide range of slurry densities can be designed to meet extreme well conditions without strength retrogression. Improvements in cement retarders make it possible to produce a four-hour thickening time at static temperatures up to 500°F. This temperature is considerably higher than conditions presently being encountered in drilling and completion work. Inert weighting materials, used to produce 20-lb/gal or heavier cement slurries, are reviewed. INTRODUCTION As the search for oil continues, the number of wells being drilled to depths of 10,000 ft or below has continued to increase over the past decade. During 1959, there were 50,893 wells drilled in the United States for a total of 209 million ft of hole. Of this total, approximately 4.45 per cent were drilled below 10,000 ft and 0.30 per cent below 15,000 ft, with a record depth of 25,340 ft recorded (Table 1). With the drilling of this record-shattering hole comes the question, "How deep can wells be drilled?".&apos; Limitations with respect to equipment (surface and subsurface), cementing materials and techniques would cause some concern; however, a panel of experts have agreed that the U. S. oil industry has the equipment and know-how to drill a 50,000-ft hole. The greatest deterrent would be the 700°F temperature they would anticipate encountering at this depth. Although the number of wells drilled under what is generally considered hot-hole conditions (230°F and higher) has been relatively high, each well often presents distinctly individual problems and requires separate consideration and selection of special materials, techniques and equipment. At the present time there are over 30 additives and special cements available for use in "tailoring" a cementing composition for a specific well. It is not uncommon to use three or four different additives with the basic cement to produce the desired slurry characteristics. A generally accepted procedure is to make laboratory tests on selected cementing compositions prior to pumping them into wells deeper than 12,000 ft, or where static temperatures are in the range of 260°F or higher. In some instances, it is recommended that laboratory tests be made where less severe well conditions are encountered. Prior to selecting a cementing composition for a particular well, key personnel representing the operator, drilling contractor and service company should meet to determine that each individual is acquainted with every detail which might influence cementing results and to discuss the execution of the job. For cementing hot-holes, a number of factors must be evaluated before proceeding with the operation. Consideration must be given to the following. 1. Thickening time—The slurry must remain fluid for a sufficient length of time to allow displacement down the casing and up the annular space in a primary cementing job or, in squeeze-cementing, adequate thickening time for both the build-up of a satisfactory squeeze pressure and the reversing out of excess cement. The thickening time of standard retarded cements will often be too short under extreme temperature conditions, thus involving special formulations and requiring laboratory tests to determine the proper amount of additional retarder to obtain the desired pumpability.

By Brian Wingfield, Greg Williams, Richard W. Givens

Application of required energies into the rig design can have a dramatic impact upon productivity. Computer modeling of these production variables has led to changes in design with values closely approaching actual field data. Knowledge of these required energies can also specify the proper drilling technique to the application. With this knowledge, productivity-to-cost ratios can be determined with the most efficient option chosen.

Jan 1, 1995

By B. Yarar

Samples of coal from an adit in the Fording River District of British Columbia showed hydrophilic properties between depths of 0-24.5 meters and was naturally hydrphobic at higher depths. Laboratory experiments indicated that weathered samples (i.e., those mined at 0-24.5m) could be upgraded by froth flotation at pH<2 following slimes removal. The i.e.p. of samples varied regularly between pH=1.6-4.1, the weathered fractions being at the lower end of the pH scale. These values followed a pattern comparable with the flotation behavior of samples. A patchwise structure for coal surfaces determining the resultant disjoining pressure, which in turn determines flotation-non flotation relationships is postulated.

Jan 1, 1982

By Luis Bernardo Varela Jiménez

Amostras de aço inoxidável UNSS31803 duplex foram nitretadas sob plasma em atmosfera gasosa de 75% de nitrogênio e 25% de hidrogênio em temperatura de 400°C durante 20 horas. A microestrutura do material como recebido apresentava cordões de ferrita e austenita, alinhados no sentido da laminação, com aproximadamente 50% de cada uma das fases. A caracterização microestrutural foi feita por microscopia óptica, difração de raios X, MEV e EBSD. As propriedades mecânicas e tribológicas das superfícies tratadas foram avaliadas utilizando ensaios de microdureza e esclerometria linear instrumentada. As camadas obtidas na nitretação a plasma em baixa temperatura (LTPN) eram constituídas por ferrita expandida (aN) e austenita expandida (?N), com durezas de 1509 HV e de 1362 HV, respectivamente. Os ensaios de esclerometria linear mostraram que, num primeiro estágio, o indentador se movimenta sobre a camada nitretada, promovendo deformação plástica nas bordas do sulco, denotando a possibilidade de movimentação de discordância nas fases expandidas da camada nitretada. O coeficiente de atrito medido durante esse estágio ficou estável em torno de 0,05. Ao final do primeiro estágio houve início de formação de microtrincas, aumentando o coeficiente de atrito aparente. A transição para o 2º estágio ocorre com formação de microtrincas cuja densidade aumenta com o aumento da profundidade de risco. Nesse estágio o coeficiente de atrito cresce linearmente com o tempo e profundidade de risco, o número de microtrincas cresce e as microtrincas observadas são predominantemente transgranulares, típicas de falha coesiva da camada. Foram observadas, também, microtrincas intergranulares que causam o destacamento individual de pequenos grãos de ferrita e/ou austenita expandida. No terceiro estágio de riscamento o coeficiente de atrito aparente tende a se estabilizar em torno de 0,16. O ensaio de esclerometria linear realizado no aço como recebido apresenta coeficiente de atrito sempre crescente até atingir um valor em torno de 0,21.

Aug 8, 2018

By Stopford Brunton

For many years it has been accepted as axiomatic that the greater number of &apos;veins&apos; or &apos;leads&apos; in the gold districts of Nova Scotia are of the &apos;interbedded&apos; type. The corollary to this hypothesis is that the vein or lead will have a continuous hanging-wall of one kind of rock, and a continuous footwall of the same or another kind of rock; but the essential point is that the foot and hanging walls are, according to this theory, both continuous and of uniform composition throughout; and that the vein or lead conforms to the bedding of the adjacent strata. With regard to the deposition of the gold in the rocks, the probability is that the key of the problem is contained in a statement by E. R. Faribault, of the Geological Survey of Canada: "The combined effect of cleavage, jointing, and stratification is to cause the rocks, especially the quartzites, to break into rhombohedral blocks". It is essential to comprehend that the rocks of the Province are no doubt folded into anticlines and synclines; but also it must be fully realized that the gold deposits and pay-shoots do not depend so much upon these as upon the fractures resulting from the disturbance caused by the intrusion of granite masses, and controlled by the combined effect of cleavage, jointing, and stratification. These fractures would form the channels through which the ore-bearing vapours and solutions would rise, and at the junctions of these fractures, where the fracturing was greatest, the easiest passages would be afforded to the ore carriers, with the result that the ore-shoots would be found at or near the intersections of fractures. It is a significant fact that in at least thirteen different districts throughout the Province, operators have at various times remarked upon the occurrence of rich ore at the intersection of &apos;leads,&apos; &apos;veins,&apos; &apos;beds,&apos; etc.

Jan 1, 1928

By S. M. Moos, R. E. Dugger

In reviewing available vacuum filtration equipment in this paper, several types of filters have been included which are probably not familiar to operators in the mining industry. However, it was felt that these units might be of interest in the event that an application should arise for the filtration of a product in the future that does not exist today. In addition, exposure of our industry to equipment used in other industries might have a tendency to be thought provoking and perhaps lead to the development of equipment and/or applications in our industry which do not necessarily exist at this time. Most innovations in filtration equipment have been confined to the improvement or design change of components and accessories, particularly reflecting the availability of materials of construction that have been developed. Recent developments in the application of horizontal belt filters have been innovative. The application of this unit as a substitute for or an adjunct to thickeners in a CCD circuit can certainly be innovative and perhaps provide a basis for reduction in capital and operating costs in this area. For example, mill tails are generally pumped at the highest possible density that will adequately flow. Tailings ponds and dams with their attendant design requirements are based upon this estimated water volume. Availability of a much dryer, non-flowing filter cake opens up several new options for disposal. Considerable cost savings could result in the design and planning of disposal areas for containing dryer material. No attempt has been made in this paper to provide a manual for the operation of all of the many types of equipment that are available. Rather, the paper tries to present an overview. Fundamentals of Vacuum Filtration Filtration may be defined as the separation of solids from a liquid effected by passing the liquids through a porous medium. If the filtrate is induced to flow through the medium by hydrostatic head, we refer to it as gravity filtration. If we utilize super-atmospheric pressure upstream of the medium we call it pressure filtration and if sub-atmospheric pressure is applied downstream of the medium we call it vacuum filtration. Centrifugal filtration occurs when a centrifugal force is applied across the medium. Centrifuges will not be discussed in this paper. The process goal of filtration may be the production of dry solids where the cake is the valuable product, clarified liquid

Jan 1, 1980

By K. Adham, T. Buchholz

"Significant capacity increases to meet new production demands can often be fulfilled through debottlenecking of an existing production facility, rather than the more expensive option of building new plants and facing new environmental and infrastructure challenges. To achieve that goal, it is important to model and calculate the existing ultimate capacity of each processing plant area, and that of each key equipment sector within the plant areas. This paper describes a methodology of how process modeling tools can be used to simulate the processing steps, how to estimate their existing and ultimate capacities, and how to determine the sweet-spots (minimum cost points) for a plant expansion – leading to a road map of the subsequent debottlenecking project implementation.The debottlenecking technique is presented through a generic work-flow narrative which can be applied to different mineral processing studies, starting with establishment of heat-and-mass balances, drawing a bottleneck diagram, brainstorming capacity increase options, and preparing a cost-capacity curve. Hatch has successfully applied this technique to a number of plant capacity studies, with great benefits to our industrial clients.INTRODUCTIONWith the softening of the metals and minerals prices, and the escalated costs of building new processing plants, it is now economically more viable to improve and debottleneck the existing facilities, rather than build new ones. However, spending new money on old plants requires careful considerations, in order to identify the most economically advantageous incremental steps of improvement and the best potential returns on investment. Process modeling, hand in hand with plant measurements, can identify the best scenarios to balance the three aspects of plant capacity (nameplate, utilization and yield), both at the global and the individual system and subsystem levels."

Jan 1, 2016

The stability of surfactant-free foam films was studied using the thin film pressure balance (TFPB) technique. In pure water, it was not possible to produce foam films due to weak film elasticity and strong hydrophobic force. In the presence of NaCl, however, the hydrophobic force was sufficiently dampened to allow metastable films to form. At 10-5 M NaCl, the equilibrium film thickness reached a maximum of approximately 130 nm at pH 6.0-7.3. The thinner films obtained on either side of this pH range was due to the increased ionic strengths associated with the HCl and NaOH additions for pH control.

Jan 1, 2009

By T. Newton, G. A. Bezuidenhout, P. J. Tauetsile, F. Trask

The technology to selectively leach gold, silver and base metals from ores, concentrates, and wastes, using an alkaline glycine solution, has initiated significant interest in using the new technology in various environments such as in-situ, in-place, dump, heap, and vat and agitated tank leaching. It has been shown that glycine acts synergistically with a number of other lixiviants to lower the net consumption of the other lixiviants while allowing low cost glycine solution recovery. Glycine is a non-toxic, stable, environmentally benign reagent that is available in bulk industrial quantities. It has the ability to dissolve most copper oxide and sulfide minerals, as well as native copper, whilst not interacting with acid consuming gangue nor dissolving iron and various or ubiquitous gangue elements. It acts synergistically with small amounts of cyanide to leach gold-copper ores at leach rates higher than either glycine or cyanide on their own, while significantly reducing cyanide consumption and eliminating detoxification requirements. The leaching behaviour of various glycine based systems will be reviewed, followed by the evaluation of the adsorption of gold onto activated carbon. Where the economics merit it, copper can be easily recovered using solvent extraction or sulfide precipitation.

Jan 1, 2017

By R. S. Scheetz

The search for a more effective means of coping with methane liberation has resulted in the expanded use of seam degasification. Its advantages are measured not only in reducing the hazards due to methane, but also in producing a marketable commodity: .the gas, itself. However, the success of a methane drainage system is the culmination of many complex factors, the most important being the coal seam permeability. The two most popular drainage techniques used mining today are the vertically simulated borehole method and the in-seam horizontal borehole method. The objective of this paper is to determine the permeability range in which the selection of the degasification technique is based primarily on equipment and economic analysis. A discussion of the equipment involved will be incorporated into examples evaluated by the Penn State coal methane simulation model.

Jan 1, 1989

By C. Z. Serpan, L. J. Wittenberg

The density of liquid plutonium was determined, by a pycnometm&apos;c technique, from 664 to 788°C and exhibited a temperature dependence, which could be expressed as:. P= C17.63 - 1.52 x 10-"t] +0.04 g per cc where t = OC. These density values compare favorably with the values previously obtained by a technique utilizing Archimedes&apos; principle. The apparatus and method were evaluated when the densities 0.f molten tin and bismuth were measured and found to be in agreement with accepted literature values. PLUTONIUM or an alloy of plutonium in the liquid state has been proposed as a fuel for a fast-breeder type nuclear power plant.&apos; Since knowledge of the liquid density of plutonium is required for the proper design of such a system, this study was undertaken. In addition, the density and volume expansion coefficient of liquid plutonium are of interest for comparison with these same properties of the six allotropic modifications of the solid metal. Comstock and GibneyZ were first to report a value for the density of liquid plutonium. The value for only one temperature, 665"C, was calculated from data obtained by the radiography of the meniscus, Fig. 3. Recently, the density at a series of temperatures has been reported by Knight,3 who obtained his values by using a differential volumeter, and by 01-sen, Sandenaw, and Herrik, who obtained their values from measurements of the loss in weight of a tungsten bob immersed in the liquid. The density of liquid plutonium reported here was determined by a vacuum pycnometer method. In an evacuated system, the tips of calibrated tantalum pycnometers were lowered beneath the liquid sur-

Jan 1, 1962

By Morrison R. S, Doennilan N

Recent mapping (1989-1992) by the Northern Territory Geological Survey in the Tennant Creek 1:250 000 map sheet area has resulted in substantial revision of the lithostratigraphy of the Tennant Creek Block (Donnellan, Hussey, and Morrison, in press). Briefly, the former Warramunga Group (Dunnet and Harding, 1967; Dodson and Gardener, 1978) is divided into the Warramunga Formation, and an overlying less deformed volcano-sedimentary succession, the Flynn Subgroup. The latter is conformably overlain by the Tomkinson Creek Subgroup of the Tomkinson Creek province in the north of the Tennant Creek Inlier. These two Subgroups constitute the Churchills Head Group which is essentially equivalent to the Hatches Creek Group of the Davenport province to the south of the Inlier.

Jan 1, 1994

By J. L. Huitt, J. L. Pekarek, D. K. Lowe

In a theoretical study of hydraulic jetting, the velocity of the abrasive material relative to the velocity of the fluid in the jet stream is analyzed as the jet stream moves through the convergent and straight sections of the nozzle and the region between the nozzle exit and target. The results revealed that the abrasive material exits from the jet nozzle at a lower velocity than the fluid. The exit pmticle velocity can be increased by increasing either the density of the fluid or the length of the nozzle, and/ or decreasing either the particle density or particle diameter. In the divergent jet stream, there exists a point after which the particle velocity exceeds that of the fluid. The relative velocities were considered in the derivation of an equation to predict cutting rate of a circumferential notch and maximum notch depth. Data of a general nature and data which substantiate the theoretical results were obtained experimentally. INTRODUCTION The use of a fluid containing an abrasive material has been an established technique for cleaning and cutting for many years. In the petroleum industry, the early effort to use this technique1 to perforate and/or to overcome wellbore damage met with only limited acceptance because of the short life of the jet nozzle. With the introduction of improved perforating techniques, and later, hydraulic fracturing, the use of hydraulic jetting as a well completion technique became even less appreciated. It was only in recent years that interest in hydraulic jetting was revived. Once this interest was revived, the results of surface tests stimulated the interest of the industry even more than the state of the technology probably warranted because many of the tests were not appropriate for down-hole conditions. However, because of the stimulated interest, the development of the jet nozzle progressed very rapidly to the point where the nozzle life was no longer a prob- lem. With this accomplished, the use of hydraulic jetting in well completion became an accepted practice in a short time. The purpose of this paper is to present a theoretical analysis of the hydraulic jet stream as it passes through the nozzle and travels to its target. With a better understanding of the jet stream and the effects of various parameters, the performance of the process can be predicted more accurately. Equations are presented for cutting rate as applied to circumferential wellbore notching that relate the jet stream make-up, notch configuration and formation material. Also, experimental data are presented on some factors pertinent to hydraulic notching that are not theoretically analyzed. RELATED STUDIES Most of the studiesl-5 reported in the recent literature have pertained to the more practical aspects of hydraulic jetting; i.e., the effects of certain parameters as interpreted from experimental results, and the application of hydraulic jetting in well completion. In reviewing the effects of various parameters, it is interesting to note the reported depths of penetration obtained under various imposed conditions. In general, the depths vary from a few inches to several feet; however, a depth of penetration of less than 6 in., as reported by Thompson,4 seems more realistic for the usual field practice of hydraulic jetting with sand in water for a period of 20 to 30 minutes. In addition to the practical aspects, the study of Brown and Loper5 included a theoretical approach to hydraulic jetting. Their study resulted in the development of a theoretical expression for the maximum depth of penetration if jetting were continued for an infinite time. An analysis of the equations presented reveals that the initial cutting rate is infinite. The equation expressing centerline velocity is that of Forstall and Gaylord,6 which is applicable for a jet stream exiting in a large stationary medium. Since practically all of the fluid pumped into a perforation (or cut) must flow back through the perforation prior to re-entering the wellbore, a description of the medium as finite and non-stationary seems more reasonable. Thus, in this

By John C. Shyne, Eric R. Morgan

WHEN temper rolled low carbon sheet is stored at room temperature before use, changes take place in its mechanical properties. This phenomenon is known as strain aging. Normally these changes are observed by means of Olsen ductility and Rockwell B hardness tests but&apos; unfortunately such tests are relatively insensitive. Strain aging can be readily observed in the laboratory by means of tensile tests. The tensile test method is even more sensitive if the aging is allowed to take place in specimens which have been prestrained in tension rather than by cold rolling. In fact one of the great benefits of commercial temper rolling is that it introduces a residual stress pattern which tends to mask the effects of strain aging when the sheet is finally used in a pressing operation. Curves B, C, and D of Fig. 1 illustrate the changes that take place during the aging of commercial rimmed steel at room temperature following straining in tension, curve A, Fig. 1. The first important change that can be observed is an increase in the stress required to produce plastic flow. This increase is, in this paper, called the aging index. As aging proceeds and the aging index increases, there is also an observable return of the yield point, an increase in the ultimate tensile strength, and a decrease in elongation to fracture. The results of strain aging in deep drawing steel manifest themselves as stretcher strains (L?ders bands) buckling, 2nd tearing. In deep drawn parts such effects are undesirable and strain aging is a serious problem. The rate of strain aging of a steel depends upon its composition and prior mechanical and thermal history? but for most temper rolled ope

Jan 1, 1958

By R. Dawson Hall

R. DAWSON HALL (The Coal Age, New York City) : Mr. Chairman and gentlemen: I do not feel that I have anything in particular to say. I have not prepared anything for an occasion such as this. I just came from New York City, and as one man said to me today, "That is not any recommendation in particular." (Laughter.) In answer to your request for a few remarks of a timely character I would say: One of the possibilities in the Rocky Mountain Region coal mines is the use of steel arches, posts and straps. The timber of the region seems unusually subject to dry rot and does not last long, especially in those places as in southern Wyoming, where the mine atmosphere is likely to contain a large quantity of carbon dioxide. It is true that, in many mines, much care is taken to drive out this gas and to arrange that the timber will have the fresh air that will prolong its life, but despite such provision much timber is subjected to speedy rot. Steel has made rapid progress in England, Germany and France and is recognized as an economy, not an extravagance. Frequent replacement of rotting wood and removal of broken rock are a source of great waste, risk and inconvenience in operation that together spell great cost. The very dryness of the mines and the lack&apos; of acid water are favorable to the use of steel where support of roof or sides is necessary.

Jan 1, 1932