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By Guang Ping Cui

In this paper the imminent relationship between rock burst and its phenomenon with normal rock pressure and its appearance, as well as the factors of one changing into another have been analyzed. Based on this, the necessary and sufficient appearing factors of rock bursts have been put forward, and the term ''burst pressure" has been defined. According to the statistics data of tremendous rock bursts which appear in collieries in Hunan Province, the features of high frequency, great strength and shallow depth of the beginning burst have been found. There are some special structures in the coal seams, which are closely related with the burst phenomenon. A hypothesis of "star structure" has been suggested for the appearing mechanism of bursts. Inside and around this star structure the distribution rule of burst pressure and rock strength has been researched depending upon the theory of the limited stress field. A new description of the appearing causes of bursts has been raised.

Jan 1, 1984

By C. E. Kemp, A. B. Dyes

Results of a field research project on the thermal recovery of oil by movement of a combustion front are presented. This field test was conducted in the South Belridge field, This The war paitern was a Southsing1e 2.5-acre five-spot pattern in the 700-ft deep Tulare sand. Results of this project indicate the technical feasibility of producing high viscosity, low-grallity crude oils by thermal means. It was demonstrated that heavy oils could be moved rapidly over considerable distances by thermal drive, and that high percentage recoveries of oil could be effected. The bulk of the oil recovery came after arrival of the burning front at a production well. However, rapid corrosion and high-temperature failure of conventional pipe and equipment both below and above surface occurred. Stainless steels gave more satisfectory performance under these conditions than did conventional steels. Oxygen was seldom observed in gas from wells ahead of the burning front, and it appears that the front was continuous throughout the life of the experiment. INTRODUCTION During late 1953 and early 1954, industry-wide attention was focused on the thermal recovery of oil by movement of a combustion front through an oil zone. Two separate Oklahoma field tests were described in publications by Kuhn and Koch, and Grant and Szasz. To obtain basic information needed for making engineering and economic appraisals of commercial recovery of heavy oil by this thermal recovery method, a new field research projecta3,4 was started May 31, 1955. Twelve oil companies contributed to this project with General Petroleum Corp. as operator. Since combustion recovery experiments* with heavy oils in other areas had been conducted in small patterns,"' an important purpose of this test was to determine whether the process could be operated in a pattern of near-commercial well spacing. The south Belridge field, located 30 miles north of Taft, Calif., was chosen because its oil sands are similar to many heavy oil sands which typically have low primary recovery and leave a large amount of oil in place. such fields are not particularly suited for common secondary recovery methods. DESCRIPTION OF TEST SITE The test interval was a Tulare sand at a depth of about 700 ft. Nine test wells were drilled, cored and completed from Oct., 1955, through Jan., 1956. The initial pattern shown on the map, Fig. 1, consisted of an injection well (II)', four producing wells (1P-4P), and four observation wells (IT-4T). An old well (81) was also recompleted for use as an observation well. The area enclosed by the original four production wells was 2.5 acres; the distance from the injection well to each production well was 233 ft. During the combustion period, Well 5P was drilled to replace Well 2P, and Well 6P was drilled to replace Well 3P. The new wells were 25 ft beyond the old production wells along a diagonal from the injection well, and resulted in an increase in pattern area to 2.75 acres. Isopachs are shown in Fig. 1. The average thickness of the oil sand in the test pattern was 30 ft. Fig. 2 presents two cross sections through the test pattern. Oil sand is represented by white and claystone by gray. The dashed lines indicate layers of conglomerate grading to claystone. The sand thickness was fairly uniform throughout the test pattern except in the 1P area. The sand body dips gently from the northwest to southeast, about 3 degrees from horizontal. The sand is unconsoli-dated, and grades from very fine material to pebbles as large as 2 in. in diameter. Table 1 presents the average initial properties of the formation. The in-place porosity of 37 per cent was estimated from the porosity of coke-consolidated cores taken after combustion. Original core analyses data were adjusted to 37 per cent, giving pore volume saturations of 60 per cent oil, 37 per cent water, and 3 per

By R. W. Shoenberger, J. A. Grina, R. J. VanPelt

The many alternatives open to coke plant operators for improving overall coke quality and strength are discussed in this paper. Programs undertaken by US Steel research and coal operations during the previous ten years to improve coke strength are described. New techniques in use, or being considered for future use, are also discussed.

Jan 1, 1982

By Robert Anderson

ROUGHLY, a crack in a casting may be considered, for the moment, to be due to fracture of the alloy resulting from the stress set up by the contraction in volume on passing from the liquid to the solid state. Cracks may be external or surface, internal or deep-seated, or incipient or so-called strain cracks. Draws may appear as depressions, unevenness, and "pinching in" of the surface of a casting. Roughly, draws are due to contraction in volume and are governed largely by the same factors as cracks. A casting may be cracked, however, without being drawn. Shrinkage is a foundry term; it connotes the contraction in volume of a metal or alloy on passing from the liquid to the solid state. Pattern-makers' shrinkage is the total contraction in volume (including liquid, solidification, and solid shrinkage) that occurs when an alloy is poured into a mold. The contraction in volume of aluminum is one of the principal factors affecting the occurrence of cracks, as will be shown later, and the question of shrinkage and its control requires careful study in any treatment of cracking in castings. In the case of, sand and die castings, cracks have been attributed to a number of causes, but in the case of most light aluminum alloys, they are due to the large contraction in volume on freezing and the lack of its regulation or control. The most important factors are: (1) Contraction in volume; (2) composition of alloy; (3) quality of melting charge; (4) design of casting; (5) method of molding; (6) hardness of ramming; (7) method of gating; (8) hardness and characteristics of cores; (9) chills; (10) risers; (11) melting temperatures; (12) furnace used for melting; (13) pouring tempera-tures; (14) inclusions in alloys; (15) hot shortness of alloys; and (16) physical properties of alloys at high temperatures. Of these, the first, second, third, and eleventh to sixteenth involve ascertainable metallurgical facts; the remainder are largely matters of opinion, judgment and technical knowledge of men experienced in the production of castings.

Jan 10, 1921

Jan 1, 1935

By F. V. Lenel

INTRODUCTION Two years ago in Chicago a seminar was held on the theory of sintering of pure metal powders As an introduction to this seminar Dr Rhines1 gave an excellent survey of the literature on this subject His method of presentation was to summarize the experimental observations on sintering and from them to develop a composite theory of sintering in which he combined all the important contributions to the theory into one organic whole In contrast to the mechanism of sintering of pure metal powders, which, of course, always takes place in the solid phase, sintering in the presence of a liquid phase, cannot be treated as one unified mechanism, such as the sintering mechanism of pure metals The reason is that there are really several mechanisms depending upon the type of alloy system which is sintered and the field of its constitutional diagram in which the sintering takes place Two mechanisms have been investigated and will be reviewed in this paper In the first mechanism the liquid is present during the entire time while the compacts are at the sintering temperature In other words they are sintered between the liquidus and the solidus of the alloy System and are heterogeneous during the entire sintering cycle The second mechanism applies to alloys in which the liquid phase is formed during the sintering process, but disappears before the sintering process is completed through diffusion and formation of a solid solution These alloys are therefore homogeneous at the end of the sintering cycle This second mechanism is more complicated because of the two stages of sintering, the liquid and the solid, as they may be called It is therefore not surprising that the few detailed investigations of sintering in the presence of a liquid phase have been concerned with heterogeneous sintered alloys, namely the tungsten-nickel-copper alloys, which is the so-called "heavy alloy," and the cemented carbides The mechanism of sintering of these systems is characterized by the fact that theoretical or near theoretical density is attained during sintering, while simultaneously a distinct grain growth takes place through solution of the smallest grains of the solid phase in the liquid phase and reprecipitation on the larger grains In the first part of the survey this sintering mechanism which is called for short the heavy alloy mechanism is treated in detail In the second part of the survey experimental observations for the sintering of homogeneous sintered alloys where the liquid phase disappears before the completion of sintering are discussed Much less systematic work has been done on these alloys to which the commercially important porous bronzes and the iron-nickel-aluminum permanent magnet alloys belong Emphasis will be laid throughout this survey upon the microstructural and density changes during sintering because the sintering mechanism can usually be described directly by these changes Other

Jan 1, 1948

THERE are two general types of scientific approach to a problem. One approach, which is the more widely known, involves an analysis of the situation at the beginning of the experiment; this is followed by an analysis of the situation at each instant of time during the experiment and leads to a-detailed description of the prevailing conditions at the end of the experiment. Suppose, for example, we wish to predict the final rest position on a billiard table of a ball moving initially in a certain known direction with a known speed. The obvious approach is to estimate or measure off its course by consideration of angles of rebound, taking account of the "English" or spin if necessary and finally estimating from experience (or calculating from coefficients of friction) the slowing down occasioned by friction, thus establishing the point of the course at which the ball may be expected to stop. Any interference with the calculated course occasioned by collision with an unanticipated object would obviously cause us to revise drastically our estimate of the rest position. This general method of approach characterized by detailed description of how one situation developed from another seems intuitively appealing and is the most widely known method. There is no doubt that it gives very satisfying results when it can be used. There is a second general method of approach. In this method, the final state of a system is predicted from knowledge of general broad principles and their application, considering only the restrictions imposed upon the system. It is unnecessary to follow the course in detail; intermediate steps are not even considered. For example, if the billiard table mentioned in the first paragraph were tilted to one corner, one could predict that the final resting place of the ball would be in that corner; this prediction can be made independent of any particular course the ball may follow. This second general method of attacking problems is the one used in thermodynamics. There its use is so outstand-

Jan 1, 1951

By M. W. Hayward

THE object of this paper is to record and tabulate the data and field observations obtained by the writers and their associates during 10 years of intensive study of lead-zinc deposits in the Cretaceous limestone areas in Northern Mexico, particularly in mines owned by the Cia. Minera de Peñoles, S. A. At the El Paso meeting of the Institute in October, 1930, J. G. Barry made the suggestion that a committee be appointed to correlate the ideas and theories which have been put forth by the numerous engineers and geologists who, during recent years, have made a study of the ore deposits in the area under consideration. The first step in a work of this nature would be to record all of the observed facts, and these facts would have to be accepted by those who attempted to formulate a theory of ore deposition. It is with this idea in mind that the writers have described as accurately as possible the actual, observed facts pertaining to the occurrence of the lead-zinc ores in dolomites or dolomitic horizons. By most writers the term "dolomite," is loosely used to designate magnesium-bearing limestones, regardless of the percentage of MgO present. Since no, true dolomites exist in the areas to be described, we shall also loosely use the terms dolomite or dolomitic limestone to designate those beds having a magnesia content of 5 per cent MgO or more. For a number of years the writers have been impressed with the fact that in areas where dolomite beds occur a large percentage of the lead ore is found in these beds, in spite of the fact that such beds may be overlain or underlain by pure limestone, which one would assume to be just as favorable for replacement as the dolomite, if not more 'so on account of its being more soluble in acid solutions than the dolomite. It is true that in some limestone areas, such as the Erupcion-Ahumada districts, Chihuahua, and Providencia, Zacatecas, where no dolomite beds have been found, large tonnages of lead ores have been mined. We venture to predict, however, that had there been dolomitic beds in these areas, the

Jan 1, 1931

By Ernest L. Ohle

The newly opened Hayden Creek lead mine represents a variation from the usual Southeast Missouri type. Galena mineralization occurs in sandy dolomite cementing a conglomerate of granite boulders and in cracks in the boulders. The conglomerate occurs at the base of the Bonneterre formation on the slopes of two buried pre-Cambrian knobs. IN 1943 diamond drilling from the surface in an area 2 miles southwest of Leadwood, Mo., discovered a lead deposit of a markedly different character from the usual southeast Missouri type. Subsequent drilling of about 500 holes indicated several million tons of ore, and in 1950 a 701-ft vertical shaft was sunk into the orebody. This paper describes the geology of this interesting occurrence insofar as it is known from the drilling and the small underground exposure at the bottom of the shaft. Geology The location of the Southeast Missouri Lead Belt and of the Hayden Creek property are shown in Fig. 1. As shown here, there are two separate producing areas, one from which the larger tonnage has come, located near Bonne Terre, Flat River, Desloge, and Leadwood, and the other to the south around Fred-ericktown and including famous old Mine LaMotte. The best published description of Lead Belt geology is by Tarr.* In pre-Cambrian time in this area, an assemblage of granites and rhyolitic flow rocks was eroded to a mature topography. Sedimentation, beginning in the Upper Cambrian, filled in the valleys and gradually covered even the highest hills. The first formation deposited was the La-motte sandstone; it is successively overlain by the Bonneterre dolomite, the principal lead-prodbcing formation, then the Davis shale. the Derby-Doerun limestone, and a succession of Cambro-Ordovician cherty dolomites. Several of these formations may be found in direct contact with the pre-Cambrian as their deposition progressively overlapped the older rocks on the flanks of the igneous knobs and ridges. Immediately overlying the pre-Cambrian there is, not uncommonly, a thin basal conglomerate of granite or porphyry boulders, which is incorporated into the overlying sediments. Deposition of the lower part of the rock section was fairly continuous, and the Lamotte sometimes grades almost imperceptibly into the lower sandy Bonneterre. Since the sediments were deposited on an uneven floor, they tend to reflect the irregularities in that floor. Most of the steep dips found in the district, that is, dips in excess of 10°, are original dips and not caused by deformation. Such domelike structures in the sedimentary rocks around the igneous knobs have localized a considerable number of the orebodies in the district and particularly those in the Frederick-town area. Many of the larger orebodies, however, have no close relation to the pre-Cambrian topography. Most of the lead production has come from the lower 150 ft of the Bonneterre formation, where disseminated ore spreads laterally parallel to the bedding for great distances. Average stoping height is about 20 ft, but in a few places there are stopes over 175 ft high.

Jan 1, 1953

By Ernest L. Ohle

The newly opened Hayden Creek lead mine represents a variation from the usual Southeast Missouri type. Galena mineralization occurs in sandy dolomite cementing a conglomerate of granite boulders and in cracks in the boulders. The conglomerate occurs at the base of the Bonneterre formation on the slopes of two buried pre-Cambrian knobs. IN 1943 diamond drilling from the surface in an area 2 miles southwest of Leadwood, Mo., discovered a lead deposit of a markedly different character from the usual southeast Missouri type. Subsequent drilling of about 500 holes indicated several million tons of ore, and in 1950 a 701-ft vertical shaft was sunk into the orebody. This paper describes the geology of this interesting occurrence insofar as it is known from the drilling and the small underground exposure at the bottom of the shaft. Geology The location of the Southeast Missouri Lead Belt and of the Hayden Creek property are shown in Fig. 1. As shown here, there are two separate producing areas, one from which the larger tonnage has come, located near Bonne Terre, Flat River, Desloge, and Leadwood, and the other to the south around Fred-ericktown and including famous old Mine LaMotte. The best published description of Lead Belt geology is by Tarr.* In pre-Cambrian time in this area, an assemblage of granites and rhyolitic flow rocks was eroded to a mature topography. Sedimentation, beginning in the Upper Cambrian, filled in the valleys and gradually covered even the highest hills. The first formation deposited was the La-motte sandstone; it is successively overlain by the Bonneterre dolomite, the principal lead-prodbcing formation, then the Davis shale. the Derby-Doerun limestone, and a succession of Cambro-Ordovician cherty dolomites. Several of these formations may be found in direct contact with the pre-Cambrian as their deposition progressively overlapped the older rocks on the flanks of the igneous knobs and ridges. Immediately overlying the pre-Cambrian there is, not uncommonly, a thin basal conglomerate of granite or porphyry boulders, which is incorporated into the overlying sediments. Deposition of the lower part of the rock section was fairly continuous, and the Lamotte sometimes grades almost imperceptibly into the lower sandy Bonneterre. Since the sediments were deposited on an uneven floor, they tend to reflect the irregularities in that floor. Most of the steep dips found in the district, that is, dips in excess of 10°, are original dips and not caused by deformation. Such domelike structures in the sedimentary rocks around the igneous knobs have localized a considerable number of the orebodies in the district and particularly those in the Frederick-town area. Many of the larger orebodies, however, have no close relation to the pre-Cambrian topography. Most of the lead production has come from the lower 150 ft of the Bonneterre formation, where disseminated ore spreads laterally parallel to the bedding for great distances. Average stoping height is about 20 ft, but in a few places there are stopes over 175 ft high.

Jan 1, 1953

By A. H. Shoemaker

THE shutdown of Homestake by Government order L-208, with its consequent disruption of a very stable and trained working force, coupled with postwar inflation and the coincidence that a mining depth had been reached that posed problems of ventilation, access to exploration areas, and choice of mining methods that would be applicable to zones of greater rock pressures made a very searching analysis of every phase of Homestake's operations a necessity. Any changes to be made had not only to meet the problems of deeper mining but also had to provide greater efficiency so that the mine might operate at a substantial profit until such time as a gold price adjustment might be forthcoming that would offset post-1945 inflation. Geology and Mining Situation The Homestake mine lies in the northern Black Hills in an area of Pre-Cambrian rocks exposed by the erosion of the paleozoic formations which covered the Black Hills. The Pre-Cambrian rocks in the vicinity of Lead comprise metamorphosed sediments with a total thickness of about 20,000 ft. The oldest formation, the Poorman, is ankeritic carbonate schist. The next oldest, the Homestake formation, host rock for all Homestake orebodies, is a siliceous iron-magnesium carbonate schist. The younger formations are dom-inantly argillaceous with some quartzites. Tertiary intrusive rocks cut all formations. The Pre-Cambrian rocks have undergone extreme isoclinal folding. Superimposed on this intricate folding are zones of shear folding which cross the isoclinal folds at small angles. The Homestake orebodies are pipelike replacements of the Pre-Cambrian Homestake formation where certain cross folds intersect some earlier isoclinal folds. These orebodies plunge flatly to the southeast at variable angles locally as steep as 45". The orebodies are replacement areas where numerous vein quartz of irregular shape have formed with surrounding zones of chlorite alterations containing disseminated sulfides and metallic gold. Where the numerous individual quartz veins with the sulfide and gold-bearing alteration zones are close together, large irregular orebodies with a roughly elliptical plan outline result. These ore zones may be more than 200 ft wide and 700 ft long in plan area. They have followed down the plunge of certain severely folded structures with great persistence. Two vertical operating shafts, the Ross and Yates, serve the mine, one with rope capacity to reach the 4850 level, the other to the 5000 level.

Jan 1, 1959

By B. Ladanyi, B. Hoyaux

A first requirement for assessing the safety of a rock slope, either artificial or natural, particularly if the rock behaves in an elastic-brittle manner, is a propw knowledge of the distribution of stresses within the slope and their development with time and advancement of workings. There are a uumber of different methods that can be used, in principle, for obtaining this information, such as (1) stress measurement in situ, (2) photoelasticity,1 (3) analytical methods, and (4) numerical methods. In cases where the stress distribution cannot be obtained by classical analytical methods, as in the one considered herein, either photoelasticity or numerical methods are norrnally used. However, actually, due to the rapid development of high-speed computers, increasing preference is given to the numerical methods. Among the latter, the most successful ones, to date, for determining the stress distribution in slopes have been (1) the finite difference method,2-4 (2) the lumped parameter method,5 and (3) the finite element rnethod.6 However, for determining gravity stresses in a natural rock slope, only the finite difference method has been used until now.7,8 A solution of the same problem by the finite element method will be shown here in which a particular reference is given to the development of tensile fracture zones within the slope. FINITE ELEMENT METHOD The stress analysis using the finite element method originates from an extension of the matrix analysis of structures.9 It consists in decomposing a continuous medium, assumed herein to be homogeneous and isotropic,

Jan 1, 1972

G. D. Kneip, Jr., and J. 0. Betterton, Jr. (Union Carbide & Carbon Corp., Oak Ridge, Tenn.)—The authors have contributed to the theory of zone melting by considering the effects of the solidification of the final zone on the distribution curves for the finite length bar. However, they do not consider in sufficient detail the restrictions imposed by the particular metals involved. Eq. 4 has the analytical solution which is equivalent to Pfann's' equation for normal solidification of the final zone. For distribution coefficients less than one, it is apparent from this form of the equation that, as the solidification approaches completion, the concentration attains extremely large values which are inconsistent with the density of physical materials. The necessary restrictions then are that the solute concentration cannot exceed the density of the alloy, or more frequently, the solubility limit in the solid phase. Secondly, the distribution coefficient cannot be constant from 0 to 100 pet solute unless the liquidus and solidus coincide over this whole region. It would thus be more correct to impose limits on the solubility such as would be indicated by a typical eutectic diagram. Furthermore, in this case the assumption that the distribution coefficient remains constant is more likely to be realized. Eq. 4 should then be replaced by the following C,,(x) =k/L-x [ ?11 3 C11 (x)Ddx - ?11 4 Cn(x)dx= k[Cn (L-l)/k] [ L-x/l]x-1 L-l = x = L-l [kCenterlie/Cn (L-l)]1/k-1 The typical shape for the distribution curve in the final zone is indicated schematically in Fig. 12 for the simple eutectic case. The solidification proceeds according to Pfann's' expression until the concentration reaches the maximum solubility in the solid phasc. At this point, the concentration changes abruptly to the eutectic composition and remains at this value for the duration of the solidification. The width of the flat region, and the back reflection of this effect into the concentration curve on subsequent passes, depends upon the ratio of the eutectic concentration to the original concentration, upon the distribution coefficient, and upon the number of passes. Similar effects on the concentration curves in the first zone length would be expected in many systems for which the distribution coefficient is greater than one, and where the maximum solubility is not too much larger than the original concentration. The discussers agree with the authors that the assumption that the liquid is uniform in concentration should be considered with caution. Kneip and Better-ton' have shown, however, that in floating zone refining of zirconium, using induction heating, the distribution of iron agrees with theory which assumes a uniform liquid composition. Hence, in this case, the experimentally realized distribution coefficient agrees with the present phase diagram within the experimental uncertainty. L. Burris, Jr., C. H. Stockman, and I. G. Dillon (authors' reply)—The authors are happy to have received the comments of G. D. Kneip, Jr., and J. 0. Betterton, Jr., which provide additional insight into the zone refining process. It is true that the equations developed are inapplicable if the solute solubility in the solid phase is exceeded. However, this restriction on the use of the equations was clearly stated in the paper. A closer approach to

Jan 1, 1957

By R. W. Raymond

Most of US, in this hurrying age, take little pains to preserve such records of our doings as will make the work of' our biographers easy. Now and then there is an exception, and Dr. Trippel was one. Methodical in all his habits, he kept diaries and journals comprising his own personal experiences, the details and results of his numerous scientific investigations, and his impressions concerning men and events; and also copies of all his technical essays, published by various societies or periodicals. It is a striking instance of " the irony of fate," that these carefully-preserved materials, which would now have a real historical, as well as biographical value, were totally destroyed by an accidental fire a few years ago. In addition to my own recollections of an acquaintance covering more than thirty years, I am indebted, for the fads upon which this sketch is based, chiefly to Mr. Engene J. Trippel, a son of the deceased, and now Register of the United States Land Office at Tucson, Arizona. Mr. Trippel, however, frankly confesses that his own knowledge of his father's work is, in the absence of written records, imperfect.

Jan 1, 1898

By F. S., Mc Nicholas

A practical discussion of the theory of A block caving is presented which applies particularly to the physical conditions of the Climax orebody although the conditions are sufficiently characteristic of caving ore-bodies to provide valuable information applicable elsewhere.

Jan 1, 1950

By Walter C. Lawson

THE primary objective in laying track in panel sections is to reduce the number of track laborers required. This is possible because the work is mechanized. Moreover, because the work is mechanized and each of the operations needs only a few men, and each is self-contained, the work can be carried on at night as well as in daylight; therefore, the method provides a means of preparing tracks on more than one shift. The laying of tracks in open pits and quarries in panel sections is not new but new methods have been made possible by the introduction of new types of equipment. The purpose of this paper is to describe the methods that are followed in' the Morenci open pit. GENERAL MINING OPERATIONS Full-scale ore production at Morenci is about 50,000 tons daily. The normal yearly output of ore and waste is 32,000,000 tons, of which 30,000,000 tons is handled by rail haulage. This requires the building of approximately 47 miles of loading and other temporary tracks during a 12 months' period (Fig I). Broken ore and waste, is loaded., into 90-ton capacity dump cars with 5-cu-yd full-revolving electric shovels. Shovel banks are uniformly 50 ft high:. They are blasted- with churn drill holes, and the broken material from a blast is loaded out with two shovel cuts, the first one being called (locally) the "splatter" cut and the second one the "clean-up" or "face-up" cut. When a shovel is making its clean-up cut, the loading track is about 70 ft from the toe of the bank and, under normal conditions, a bank is blasted against it without removing the track. It is thus evident that each track is used for two shovel cuts before relocation is necessary, inasmuch as a single position serves for both the clean-up cut prior to blasting and for the splatter cut following the blast. The normal advance of a solid bench by a single blast is 40 ft (Fig 2). PREPARATION OF PANEL GRADE In preparation of panel grades bulldozers and rooters are used for the bulk of the work and an auto-patrol road grader for the final stage. At Morenci, bulldozers have always been used for track-grade preparation, but before the introduction of the other two types of equipment grades were uneven and irregular at best, and always necessitated a big gang of track laborers to hand-block under the ties with rocks after a track was laid into place. High blocking also made poor track because of instability and caused frequent derailments. Under these conditions derailments were generally bad as re-railing became difficult. Much track was torn up and many ties broken in the process. The inadequacy of the hand-blocked track, together with the inefficiency of hand blocking, constantly pointed to the desirability of reducing the amount of labor required, so various means were tried to improve conditions, such as wood

Jan 1, 1947

By J. F. Martin, J. E. Friedline, L. M. Melnick, G. E. Pellissier

A method has been developed for determining gases in steel in which the gases are extracted by vacuum fusion and analyzed by mass spectrometry. This method is especially applicable for determining small amounts of oxygen and nitrogen. The lower limit of detection for both oxygen and nitrogen is 0.0001 pct with an average deviation of about 0.0001 pct for oxygen and 0.00008 pct for nitrogen. Hydrogen analyses by this method are in good agreement with analyses by vacuum tin-fusion. A complete analysis of all gases extracted from a steel sample can be accomplished in 40 min. It has long been known that certain of the gaseous elements exert particular effects on the physical and mechanical properties of steel. With the recent advent of new experimental steelmaking practices it is now possible to obtain steels with extremely low contents of such elements as oxygen and nitrogen. Present methods for determining these two gases are of insufficient sensitivity as applied to steels made by these newer practices, and therefore a new technique was considered necessary. A review of the literature showed that the conventional vacuum-fusion method1 was the procedure most suitable for modification to obtain a sensitive method for determining the gaseous elements present in steel simultaneously. However, for trace amounts of gases it is impractical to increase the sample size because of the physical limitations of the apparatus and the increased degassing time which would be necessary. Also, when only one of the desired gases is present in trace amounts, quantitative separation by conventional vacuum fusion is almost impossible. Since small analytical mass spectrometers are now commercially available, it was decided to use this instrument in conjunction with conventional vacuum fusion for both qualitative examination and quantitative determinations of the gaseous elements in steel. This technique has already been used with success for the analysis of copper and lanthanum.2"4 APPARATUS A vacuum-fusion unit was first designed and built, Fig. 1. This unit was designed especially for the determination of small amounts of nitrogen and/or oxygen in steel since an acceptable method (vacuum tin-fusion)5 was already in use for the determination of hydrogen in steel. The vacuum system was con- structed of Pyrex glass throughout. Mercury check valves were used in place of stopcocks in the high-vacuum section of the system. Ferromagnetic samples are normally introduced into the vacuum system through a mercury lift. In case of a break in the lift, the mercury is prevented from entering the furnace by a self-locking, mercury safety check valve, Fig. 2. This check valve, developed at our laboratory, is a modified T/S ball-and-socket joint placed in the sample inlet system between the mercury and the furnace. A sudden entry of mercury or air pushes this valve into the closed position, completely blocking the top of the mercury lift. The check valve is held in the closed position by the vacuum of the apparatus. A separate entrance tube also was placed in the system, so that samples which would amalgamate with mercury, or which are nonmagnetic, could be introduced into the furnace. A slightly modified Guldner-Beach furnace is used in this system.8 The optical flat was connected to the system by a ground-glass joint to facilitate cleaning, a quartz delivery tube was substituted for Pyrex, and the crucible was used uncovered. Fusion takes place in a high-purity graphite crucible insulated by — 200-mesh high-purity graphite powder. The crucible set (crucible and funnel) is suspended in a quartz crucible. The furnace envelope and the sample inlet system are exhausted by 2 single-stage, mercury-diffusion pumps in series. The first of these is a high-speed pump, which will work only with a very low backing pressure. This pump is used to exhaust the gases from the furnace as rapidly as possible. The second mercury-diffusion pump is used as a backing pump for the first; the capacity of this pump is much lower. However, it will work efficiently against a back pressure of 3 mm of mercury. To assure positive pumping, a modified Naughton and Uhlig condenser7 is used. With the use of proper valving the second pump is also used as a circulation pump in the catalyst system.

Jan 1, 1959

By E. P. Dahlberg, R. E. Reed-Hill

On the assumption that stress or strain relaxation occurs as the result of a thermally activated process, equations are derived relating to tensile experiments that give the strain as a function of the time under the condition of constant stress, and the stress as a function of the time for constant strain. It is demonstrated that if the strain-rate equation i = previously proPosed by Kuhlmann., is used as a starting point, then the relaxation of strain at constant stress may be expressed by the equation c = (-RT/(Y) 1tz tanh (t + is the strain capable of being relaxed at any given instant. Similarly, it is shown that the relaxation of stress at constant strain may be given by a = (-RT/B) In tanh (t + t0)/27, where a is the instantaneois value of the relaxable stress. The fact that these relationships reduce to well-known empirical equations at both large and small values of the stress Or strain is also shozcn. The present theory is shown to agree well with experimental data obtained from tensile elastic aftereffect experiments on a zirconium specimen prestrained at 77 k as to make it strongly anelastic. It is also demonstrated that elastic aftereffect data obtained using torsional specimens ?,Lay agree reasonably well with the equation derived for the case of tension. RELAXATION experiments are often employed as a means of studying metallic deformation mechanisms.' The simplest and most commonly employed techniques involve stress relaxation at constant strain and strain relaxation at constant stress. In general, however, investigations of this nature have been seriously handicapped in the past by a lack of suitable equations giving the time dependence of the relaxing variable over an interval that extends from small strains up into the region where internal-friction experiments become strain-amplitude dependent. This paper presents a derivation of such a set of equations for the case where the time-dependent part of the strain is anelastic or recoverable and the specimens are loaded in simple tension. The relaxation of strain under the condition of constant stress will be considered first. Let us assume that strain relaxation occurs as the result of a reversible thermally activated process that occurs at a number of relaxation centers lying in an elastic matrix. Then, following Kuhlmann,2 we may express the rate of strain relaxation as follows: where C is the strain rate, AFx the free energy of activation of the process controlling strain relaxation, a, the effective or average resolved stress at the relaxation centers, u an activation volume, R the universal gas constant, T the absolute temperature, > a factor with dimensions of a volume that accounts for the strain contribution of a successful operation of a unit process, N the number of relaxation centers per unit volume, and v the Debye frequency. The first term on the right of Eq. [I] represents a strain rate in the direction favored by the stress, while the second term represents the rate in the opposite direction. It is implied in Eq. [I.] that both F and v are symmetrical with respect to the two basic directions of operation of a relaxation process. Eq. [I] may also be written where and S and Q are the activation entropy and activation energy, respectively, of the relaxation process. In the following, A will be considered a constant. This is compatible with a set of experimental conditions where the relaxation rate is controlled by a single basic reversible process in which it may be assumed that the temperature dependence of the product ?Nv is negligible in comparison with the temperature variation of the exponential term. It is also implied that v, 7, and N do not depend strongly on a, . In deriving a relationship for the strain as a function of the time from her equation, equivalent to Eq. [2], Kuhlmann2 chose to consider only the limiting cases where the time was either very small or very large. It will now be shown that it is possible to integrate Eq. [2] to obtain a single equation valid over a wide range of strains if the concept of relaxable strain is introduced. The use of this quantity, which is the difference between the instantaneous value of the strain and the value of the strain at complete relaxation, represents the primary point of departure of the present theory from that of earlier workers. Let us express the effective stress at the relaxation centers in terms of strain. For this purpose we may use the following equation derived by zener3 for the case of strain relaxation at slip bands: where M? and M are the relaxed and unrelaxed moduli respectively, go the applied constant tensile stress, and m an average orientation factor that takes account of the fact that a,, the effective stress at the relaxation center, may not be a tensile stress (i.e., a

Jan 1, 1967

By J. F. Kemp

Introduction The Bulletin of the Institute for March, 1911, is chiefly devoted to papers upon the iron ores of northeastern Cuba. At that time information about the new developments in the peculiar brown hematites of the region was becoming widely circulated and interest was especially keen. For some years exploration had been conducted with pits and trenches and so great an area had been shown to contain ore in the Mayari, Moa, and Cubitas or San Felipe districts, that the reserves conveniently situated for the consumption of American furnaces were estimated as quite two billions of tons. In the subjoined footnote will be found a list of the principal papers of special interest which have already been published.1 The further remark may, however, be made that the

Jan 2, 1915

Jan 1, 1940