Search Documents

By W. C. McClain

In the design of underground excavations, rock mechanics considerations are nearly always based on an elastic behavior of rock. Most rocks do exhibit a certain amount of elasticity, and the application of principles and concepts of elasticity to rock mechanics problems has been largely responsible for progress in the field over the past 10 or 15 years. NO doubt the theory of elasticity will remain the most useful analytical tool available for both the design of underground openings and the interpretation of phenomenological data. Dr. Cook's analysis of rock behavior based on energy considerations represents a significant new approach to mining rock mechanics problems. Although the foundations of this analysis are somewhat broader and more general than elastic analysis, the development and applications are grounded almost entirely in the theory of elasticity. It has long been known1,2 that all rocks, even granites and dense limestones, exhibit nonlinear time-dependent strain properties to a greater or lesser degree. Creep strain (that is, deformation under constant stress) in salt, potash, and trona can be several orders of magnitude greater than instantaneous elastic strain. Design of underground workings in these materials must incorporate provisions for these strains and must therefore go considerably beyond elastic analysis. Some of the principles of underground design in highly plastic materials will be discussed in this paper. Since all rocks, especially when highly fractured, exhibit a certain amount of creep-type strain, these concepts should be at least recognized in any rock mechanics problem. The discussion will be illustrated largely, but not entirely, by examples drawn from

Jan 1, 1967

By A. D. S. Gillies

The effectiveness of coal mine face ventilation and the ability of airflow to maintain satisfactory methane and respirable dust levels in the working face area has been studied through the use of scale modeling techniques and underground testing procedures. In particular, consideration has been given to examination of the effects of operation of a high airflow, machine mounted dust scrubber unit on face air patterns. Results obtained through a cooperative study with the Peabody Coal Co. demonstrate that new mining cycles can be considered that increase production efficiency while maintaining satisfactory ventilation conditions.

Jan 1, 1986

By P. J. van der Walt, P. J. F. Fourie, L. M. Falcon

Various methods for the beneficiation of minus 0,5 mm coal are examined briefly, and tests are described on a cyclone of 150 mm diameter operating with magnetite as the medium. It was found that, for sharp separations, at least 50 per cent of the magnetite should be finer than 1Oµm. At that size, the ash content of the product was about 7 per cent at yields of 59 to 64 per cent, and the loss of medium was reasonable (about I kg per ton of fines treated).

Jan 1, 1980

By S. L. Couling, D. J-P. Adenis

i2) twinning in poly crystalline magnesium does not usually occur homogeneously but is concentrated in localized regions or bands inclined at about 45 deg to the stress axis. These bands of twinning are in many ways similar to the Luders bands seen in mild steel alzd Al-Mg alloys. Within a hand the percentage of the volume twinned may approach 100 with no twinning outside the band. Bands are not produced in specimens of grain size a3 x 10-= in. or in samples deformed at temperatures 300°F. Annealing of heavily twinned regions leads to re crystallization textures markedly different from those found in the starting material. The exact preferred orientation appears to depend on the starting grain size, the amount of compres-sive strain and the manner in which it is introduced. MAGNESIUM, with its hexagonal crystal structure, deforms plastically at room temperature by a variety of deformation mechanisms, one of the most important of which is (1012) twinning. In single crystals such twinning occurs on compression parallel to the basal plane or tension perpendicular to it. In wrought polycrystalline magnesium, such as rolled sheet, the preferred orientation is such that almost all the grains have their basal planes nearly parallel to the sheet surface. Therefore, if sheet material is deformed by cold rolling or by tension in the plane of the sheet, deformation of the grains by (1012) twinning is not favored. On the other hand, twins form readily on compression parallel to the plane of the sheet as in a compression test, on the compression side of a bent sample, or at the outer rim of a drawn cup. The first part of this paper deals with the morphology of (1012) twinning in polycrystalline magnesium. Some aspects of this subject were covered by Barrett and ~aller.' Of direct bearing on the work to be reported here are the comments of Jetter' in discussion to Ref. 1. He shows that Mg + 1.5 pct Mn alloy sheet when bent about a transverse axis develops a pattern of transverse bands on the surface of compression. A longitudinal section through the sheet shows that the bands are wedge-shaped and inclined to the rolling direction. The bands were identified as "outcrops of regions in which deformation is localized as the result of the reorientation brought about by (1012) twinning". The second part of the paper treats the recrys-tallization texture of the specimens twinned by compression. Magnesium deformed and then annealed generally recrystallizes with no change in orientation.1'3'4 This statement is true provided that the amount of (1012) twinning occurring during deformation is small. In an isolated observation, Anse15 has shown that, when deformation produces much (1072) twinning, annealing causes new maxima to appear in the pole figure. The second part of the paper elaborates on this point. I) MATERIALS AND PROCEDURES All of the experimental work to be reported was done using the commercial sheet and plate alloy AZ31B (nominal composition: 3 pct Al, 1 pct Zn, 0.4 pct Mn, balance magnesium). This alloy is available commercially in two tempers, -0 (fully annealed) and -H24 (partially annealed), and specimens of both tempers were used in various experiments. The average grain. diameter (AGD) for -0 temper 0.125-in. sheet is about 0.5 x 10- in.; where material of larger grain size was desired, anneals at elevated temperature were used to grow the grains. compression tests were made on a screw-driven "hard" machine. The specimens were clamped in a

Jan 1, 1964

By J. D. Miller

Physical separation of bitumen from low-grade Utah tar sand deposits containing a relatively high viscosity bitumen phase (Sunnyside and Tar Sand Triangle deposits) has been accomplished by traditional size reduction and froth flotation techniques. At appropriate experimental conditions more than 90 percent of the bitumen can be recovered in a concentrate, containing more than 20 weight percent bitumen, which should be a suitable feed material for subsequent hot water or thermal processing. The efficiency of bitumen recovery depends on the extent of size reduction, promoter and dispersant addition. Rejection of greater than 60 percent of the sand at ambient temperature and ease of water removal from the concentrate make such a process strategy both energy and cost effective. The energy required to achieve effective separation by the ambient temperature process is significantly less than the energy required for the recently developed hot water process. The flotation behavior of the tar sand has been analysed with respect to flotation pH, contact angle measurements and the apparent iso- electric point of the bitumen. The best flotation response at pH 7.8 to 9.0 can be correlated with the maximum in contact angle developed between the air bubble and bitumen surface and with the apparent iso-electric point of the bitumen (-pH 8.0).

Jan 1, 1981

By René Dufour

Jusqu?à son acquisition par MM René Dufour et Alain Robin en 1994, les claims miniers et les droits de surface de la propriété étaient détenus depuis 1953 par la société Québec Columbium, une filiale de la socité américaine Kennecott Copper qui y a réalisé d?importants travaux miniers. En 1995 la compagnie NIOCAN inc. fut incorporée; ses actions furent inscrites à la bourse de Montréal en 1997, et à la bourse de Toronto en décembre 1999. Jusqu?à maintenant, NIOCAN a investi plus de 7 millions de dollars dans le développement de sa propriété minière de niobium située à quelques 40 kilomètres au nord-ouest de Montréal. Le haut rendement économique des deux gisements principaux que compte exploiter la compagnie, le S-60 et le HWM-2, a été établie par des études de faisabilité effectuées par le consortium Met-Chem/SNC-Lavalin. La mission que s?est donnée NIOCAN inc. consiste à mettre en production ses deux gisements et à devenir ainsi productrice de ferroniobium dans les plus brefs délais. Figure 2 Le projet est présentement à un stade avancé d?obtention du certificat d?autorisation du ministère de l?Environnement. À plus long terme, la compagnie compte aussi exploiter les sous-produits de ses gisements (apatite, forsterite, magnétite, calcaire et terres rares).

May 1, 2003

By K. S. Gritton

The Bureau of Mines investigated the feasibility of numerlcally modeling the sorption of cobalt, a vulnerable strategic and critical metal, from spent copper leach solutions in a multiple-compartment ion-exchange (MCIX) column. Equilibrium resin loadings, cobalt-sorption kinetics, and resin-fluidization characteristics were determined in simple laboratory tests, and a numerical model was developed to predict cobalt extraction and the MCIX-column resin inventory based upon the test results. The model was implemented on a microcomputer to approximate the solution to the set of differential equations that govern model performance. Results compared very well with data from 12 pilot-scale MCIX-column experiments. The average difference between predicted and actual cobalt extractions was 3.2 pct; the maximum difference was 9.3 pet. The actual and predicted resin inventories differed by an average of 5.8 pet, and the maximum difference was 12.0 pct.

Jan 1, 1987

By John Hollow

The Fort Knox Mine is an open-pit operation, located in Alaska, which started commercial production in March 1997. A conventional Mill processes 38,000 tpd of a low grade (1.0 g/t Au) free milling gold ore with a low sulphide component (below 1%). Gold production (11% from gravity and 89% from cyanidation) exceeds 400,000 ounces per year. Short retention time (20h), low temperature (7oC) and low grade make high leaching kinetics critical for the performance of the process. In April 2001, the treatment of True North ore, which represented 14.4% of the mill throughput and contained more sulphide in the form of pyrite, arsenopyrite and stibnite, resulted in a substantial drop in the average gold extraction from 87% to 72.6%. Laboratory investigations indicated that the addition of lead nitrate increased gold extraction to 91.7%. Further investigations were initiated to determine the leaching parameters and the nature of the problem. Subsequently, a lead nitrate addition scheme was implemented at the Fort Knox Mill that resulted in 2002 gold production being in excess of 31,000 ounces higher than that estimated for the non-lead nitrate reagent scheme. This paper presents the results of laboratory investigations and modifications in plant operating practices.

Jan 1, 2003

By K. O. Bennington

The thermodynamic properties of aegirine, of composition [(Na0.869Fe30+7362 Fe20+16Mn0.03Ca0.1121)(A10.141Sil 9738)(06)], were experimentally determined at the Bureau of Mines as part of its efforts to advance minerals technology. The standard enthalpy of formation determined by hydrofluoric acid solution calorimetry is AHf298 = -641.12±0.73 kcal/mol. The standard enthalpy of formation from the oxides is AH298 = -37.136±0.509 kcal/mol. Low-temperature heat capacities were determined by adiabatic calorimetry from 19.1 to 304.6 K. The derived standard entropy is S298 = 38.03±0.14 cal/mol?K. The heat capacity was measured over the range 348 to 1,198 K by differential scanning calorimetry. These experimentally determined data were combined with data from the litera¬ture to calculate the Gibbs energies of formation and equilibrium constants of form¬ation over the temperature range of the measurements. Standard enthalpies of forma¬tion are given as functions of temperature. The standard Gibbs energy of formation at 298.15 K is AGf298 = -600.36 kcal/mol.

Jan 1, 1984

By Lynce AJ

A method has been developed for the prediction 'of 'the- . performance of a multi-stage grinding=cyclone classification circuit of any degree of complexity on any ore for a wide range `of operating conditions, The-.method involves ;the. s` inu ation b'f the circuit on a digital computer by means of. matheinatical' models ":bf the"' individual units:, the. development of which is- also discussed'., At present, in order to establish 'the!'" charac'teristtics of they ¦ore- and the machines. in mathematical terms;. it is necessary to know'the performance of a , simpl,.e. ; system on tri.e ore - for! one known ,,feed rate and.fe.ed s,l-zing, analysis. ' ,Fiiither work on :the- separate identification 'of the terms defining the characteristics of the ore and the machines may permit the method to be, applied directly to the cj.4ta,derived from small scale tests on ores,

Jan 1, 1964

By P. E. Palmer, A. H. Daane, C. E. Habermann

Jan 1, 1965

By F. J. Meringer, C. W. MacGregor

Various investigations have been carried out to determine the effects of cold-rolling on the common physical properties as represented by the yield strength, tensile strength, percentage of elongation and ordinary reduction of area. Very little information is available in the literature with reference to the effects of cold-rolling on the true stress-strain properties. Since the ordinary physical properties base both the stresses and the strains on the original dimensions of the test piece, which are greatly changed during the test, they are essentially empirical values and do not represent physically either true stresses or true strains. Consequently, they do not give an accurate picture of the effects of different conditions, both mechanical and metallurgical, on the strength and ductility of the material. It is not, however, the purpose of this paper to review the various advantages accruing from the use of true stress and true strain values, since these have been shown elsewhere,1-l2 but to utilize them in representing the various effects considered. The true stress S and true strain (e = q') values mentioned above for the tension test are defined by1 S =1/A and where P, A, Ao are the axial load, the instantaneous area and the original area of cross section, respectively. From simultaneous readings of the axial load and the dimension or dimensions determining the instantaneous area of cross section, the true stress-strain curve is constructed by using the relations given in Eq. I. It is then the object of this paper to discuss the general effects of cold-rolling on the true stress and strain values for a low-carbon steel together with the effects of age-hardening and directionality on these properties. Preliminary Investigations The material considered throughout the paper is a low-carbon steel of the following chemical analysis: C, 0.19 per cent; S, 0.118; P, 0.092; Mn, 0.85; Si, 0.01. The stock was received in bars, 7 by 3/4 in., and was first annealed for one hour at 1650°F. followed by a furnace cool. Photomicrographs of this material showed considerable directionality even in the annealed condition. In view of the possible effects of the nonhomogeneity and directionality in this material, it was considered important to investigate their influence on the true stress-strain diagrams. In addition, the effect of strain-aging in this steel was also made the subject of a preliminary study. Effect of Aging on True Stress-strain Properties Since a certain time element would elapse between the cold-rolling operation and the final tension tests, it was determined to investigate the aging character-

Jan 1, 1945

By H. E. Wilborg

This chapter deals with those sands employed by the foundries for the manufacture of cores and molds used in the casting of such common metals as steel, gray iron, ductile iron, aluminum-based alloys, and copper-based alloys. Most metal is cast in "green sand" molds in which the sand mixture, consisting primarily of silica, clay, and water, forms a plastic material. This plastic material is rammed around a pattern in a split box called a flask, then the box is separated, the pattern is withdrawn, and the metal poured. These green sand molds are broken apart when the metal has solidified. The sand is then remixed and a new mold made for the next casting. To a lesser extent silica sand is mixed with resins or oils and, after forming, the mixture is hardened either by heat or chemical reaction. In any case, the foundry mold or core is used just once before being broken up and remixed for manufacturing another core or mold. By far the greatest consumption in the foundry is of those types of sand high in silica, low in clay (under 0.5%) and occurring in numerous locations thoughout the United States.

Jan 1, 1975

By S. Banisi, S. M. Mousavi, S. D. Tafvizi, Gh. A. Parsapour, M. Mahmoudi

Generally, regrind circuits are used to increase the degree of liberation of value minerals which are fed to flotation circuits. At the regrind circuit of the Sarcheshmeh copper complex, four ball mills are in closed circuit with their hydrocyclone clusters. In the initial design of the plant, feed and underflow percent solids, and pressure drop of the hydrocyclones were 39% and 65%, and 15psi, respectively. Over the years, due to a reduction in the feed grade from 1.17% to 0.67% and changes in the operational conditions, the feed rate to each hydrocyclone cluster has decreased from 401 to 70t/h and consequently the pressure drop, feed and underflow percent solids have reduced to 4psi, 17% and 25%, respectively. The main objective of this research was to audit the feed solids concentration and pressure drop of the hydrocyclones and make the necessary modifications based on the Plitt’s model. The results of sampling showed that water recovery to underflow was 59% which was higher than normal values. By reducing the number of operating regrind mills from 4 to 2, the feed rate to each mill increased. After this modification and taking necessary measures in the plant to implement the new operating approach, the pressure drop, feed and underflow percent solids increased to 18psi, 28% and 58%, respectively. The water recovery of the hydrocyclones underflow decreased from 59% to 12%. These changes in addition to increasing the circuit efficiency saved 1000 kWh energy and decreased ball consumption by 925 ton/year because of reduction in the number of operating ball mills. Keywords: Regrind mills, flotation, audit, troubleshooting

Jan 1, 2020

By A Mackay

As a result of the explosion in the 512 panel at the Moura No 2 mine in 1994 the role of the ventilation officer (VO) to submit sealing plans (on behalf of the operator/underground mine manager) has become one of the key duties of the VO of an underground coal mine in Australia. The intent of a sealing plan is to document the controls used to manage the build up of flammable concentrations of gases, and for these controls to be reviewed by the industry regulators. These sealing plans have brought a large amount of focus onto the sealing process and served the industry well. The legislation does not define sealing, or when it begins, but throughout the industry typically sealing plans are submitted 30 days prior to the last seal being constructed. This practice appears to have originated from the Moura 512 panel being a standing bord and pillar panel and where the explosive gas mixture could only occur after it was sealed. However, since the Moura disaster the industry has become dominated by goafing style longwall mining. Goafing panels differ from standing bord and pillar panels in that they typically have an unventilated goaf that can potentially contain an explosive mixture from start-up. This was recently highlighted by the explosion and fire on Longwall No 1 Tailgate at the Blakefield South Mine in 2011. The author ponders whether the industry should revisit sealing plans to focus on the core hazard and define that sealing begins when flammable concentrations of gases are created. Although defining when mine sealing begins is the key outcome of this paper, the main point is that VOs and industry regulators need to clearly understand what can occur in the atmosphere of underground coal mines. CITATION:Mackay, A, 2013. A case for change - Defining mine sealing and understanding flammable mixtures during sealing, in Proceedings The Australian Mine Ventilation Conference , pp 307-310 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 1, 2013

By T. A. Rickard

Flaubert, as we know, laid stress on the selection of the right word, le mot juste, the precise epithet, the word that belongs to the thing. A sentence, or even a paragraph, may be spoiled by the use of a word that is not proper, that does not fit or is foreign to the meaning intended. An Australian mining expert is reported to have said: You have a property of considerable value, and what I saw warrants a good development of very rich cubicular galena, with gossan intermixed. 'Cubicular' means `belonging to a small bedroom', a `cubicle' being a sleeping compartment. He meant `cubic', of course. This is a malapropism, and reminds me of the lady from Chicago that, on her return from Europe, said how much she had enjoyed the rural parts of France, because, among other things, it was "so delightful to hear the French pheasants singing the mayonnaise to the tune of the Los Angelus". It is impossible to amalgamate coal-tar thoroughly with the pulp in the agitating-tank. In metallurgy, `amalgamate' refers to the combination of mercury with one or both of the precious metals, forming an amalgam, which is an alloy of mercury with another metal. It differs from other alloys, such as brass or bronze, in being made without the aid of heat, inasmuch as mercury is molten at the ordinary temperature. The word comes to us from the Greek. through Old French and means `something soft'. It is a mistake to use technical terms, having a specific meaning, for purposes that are foreign to that meaning. The writer of the quotation is not discussing any combination of metals; he is dealing with the physical process of mixing and is using 'amal-

Jan 1, 1931

By R. W. Armstrong, D. H. Feisel

Self-diffusion in pure crystalline solids has been described through extension of the Cohen and Tum-hull volume -fluctuation model originally proposed for diffusion in simple liquids. It is shown, for a number of crystalline solids, that the self-diffusion coefficient, D, obeys the relationship where a is the lattice spacing, v the Debye frequency, Z' the lattice-volume fluctuation per atom required for a diffusion jump, and (?V/Vo) the relative increase in the lattice volume resulting from thermal expansion between O°K and the temperature under consideration. The calculated value of Z' is dependent upon the difiusion mechanism and the lattice geometry. ThE need for an increased understanding of mass-transport processes in crystalline solids has resulted in much research to determine rates of self-diffusion.' For several metals (e.g., copper, silver, and iron), the experimental values of the self-diffusion coefficient, D, have been determined over a large interval of temperature and the accuracy of D has been investigated through repeated experiments. Also, a number of empirical and theoretical diffusion studies have established a rational basis for understanding the D values for the different elements.2"6 The empirical diffusion analysis by Sherby and simnad6 supplied the main stimulus for the present study. Sherby and Simnad, reviewing the self-diffusion data for a substantial number of pure crystalline solids, suggested that sufficient data were available to establish with some certainty the apparent intrinsic material properties which influence D. Without explicit regard for any mechanism of diffusion, these investigators obtained an empirical relationship for D which correlated the self- diffusion coefficient for each element with the melting temperature, crystal structure, and valence of the particular element. Their analysis is only unsatisfactory in that the effect on D of crystal structure is not very clear and the valence to be assigned to an element is not always straightforward. The present study is an attempt, from a very different viewpoint from that of Sherby and Simnad, to establish a basis for understanding the self-diffusion coefficients for crystalline solids. This analysis was undertaken for the purpose of developing a general expression for D which would explicitly depend on the mechanism of diffusion. The main result of the study is that diffusion in crystalline solids may be described in terms of a volume-fluctuation model which was originally proposed by Cohen and Turnbull7 to describe diffusion in simple liquids. The model appears to be useful for predicting self-diffusion coefficients in crystals. The following sections describe the volume-fluctuation model for diffusion, the application of this model to crystals, and the resultant agreement with experimental data. 1) THE VOLUME-FLUCTUATION MODEL FOR DIFFUSION Cohen and Turnbull7'8 developed their model for liquid self-diffusivity for the purpose of describing certain properties of liquids, glasses, and the liquid-glass transition. A hard-sphere model for the liquid structure is used. In this model, the size of a spherical molecule or atom is fixed for all temperatures by the interatomic spacing at the absolute zero of temperature. At any temperature above O°K, the atom is viewed as being contained within a larger spherical cage defined by the interatomic spacing of the atoms at that temperature. A random distribution of varying cage sizes is assumed to exist in the liquid. An individual diffusion jump occurs when the free volume of an atom (the volume of the cage containing the atom minus the volume of the atom) is large enough for the atom to jump out of its cage. With this physical picture of diffusion in liquids, Cohen and Turnbull derive the following equation for self-diffusivity: D=Doe-yv*/vf [1] where Do is the product of three factors which are the diffusion-path geometry, the diffusion-jump distance, and the velocity of the diffusing atom, v*

Jan 1, 1964

By J. B. Cheatham, C. E. Murphey

Presently, computer control of Borobolic direction cannot be obtained during drilling, and most straight-holc drilling methods attempt to resist hole deviation rather than control direction. Many of the theories advanced as possible explanations of the cause of hole deviation are Summarized berein. A new correlation of physical partables is introduced to indicate bow factors such iis drill collar stiffness clearance and hit weight influence borehole deviation, .A methord is proposed for predicting the rate of change of hole angle when drilling conditions are changed. INTRODUCTION Control of borehole direction during drilling can be difficult and costly. Unintentional crooked holes are often lrilleti in dipping formations and many times directional drilling is required when the surface location is not directly above the target area —- for example, at offshore and mountainous locations. Prilllng progress can be greatly hindered in either air or liquid drilling when it be comes necessary to use low bit weight to prevent excessive hole angle build-up. If hole inclination becomes too great, drill pipe drag becomes excessive and fishing risks are increased, logging is more difficult and problems of differential sticking, key seating and fatigue failures may be encountered. Dog-legs and key seats are more serious problems than steep inclination angles: therefore, reducing rate of direction change is preferred to attempting to maintain absolutely vertical holes. Consequently, a straight inclineti hole is preferable to a nearly vertical crooked hole containing numerous dog-legs. In this paper, theories of the cause of hole deviation and analyses of drill string behavior under down-hole conclitions are summarized. Methods for computing hole deviation are presented und systems for resisting deviation as well as neans for provic!ing control of holt- direction are iliscusseI. A new correlation of physical variables is introduced tu indicate how factors such as drill collar stiffness, clearance and bit weight influence borehole deviation. A method is oroposeti for predicting the rate of change of hole anFrle when drilling conditions are clianged. IIEVIEU' OF PREVIOUS WORK ON HOIaE DEVIATION Significant progress in the theoretical analysis of hole deviation problems has been made in the past 1 5 years. The pioneering work has been primarily a result of the efforts of Lubinski and Woods.l-5 In 1950, Lubinski 1 considered the buckling of a drill string in a straig:rt vertical hole, a problem also considered by Willers6 in 1941. It wns concluded that very low bit weights must be used to prevent hole deviation resulting from drill collar buckling. The use of conventional stabilizers was proposed2 in 1951 by Mac Donald and Lubinski as a method for permitting greater Sit weights to he carried without drill collar buckling. These authors pointed out that a 2° nearly vertical spiral hole can cause severe key seatinp, and drill pine near, wilereas n 3 straight inclined hole with deviation all in one direction, while not vertical, will not result in serious drillirig or producing problems. Studies were continued with an investigation of straight inclined holes by Lubinski and Woods3 in 1953. In this paper they concluded that perfectlv vertical holes cannot be drilled even in isotropic forriations unless extremely low bit P-eights are used. .l'l~ey postulated that constant drilling conditions produce holes of constant inclination angle and varying conditions cause the hole to drill at a neiv equilibrium angle. This analysis was not concerned with drill string buckling since it was based on an equilibrium solution in which the ~irill string Was presumed to lie along the lower side of the hole abcrve the point of tangency. Weight of the drill collars below the point of tangency tends to force the hole toyard the vertical, whereas the weight on hit tends to force the hole aurav from the vertica l. The concept of an anisotropic formation Lvas introduced as an empirical method for explaining actual drilling data and as a means for extrapolating known deviation data to otiier conditions of hit

Jan 1, 1967

By A. J. Shaler

The subject of the mechanism of sintering has received much attention in the past few years, particularly since the beginning of the series of AIME seminars in powder metallurgy of which this paper introduces the fourth. In the first of these, F. N. Rhines1 brought together and discussed the available experimental data on the sintering of pure metallic powder, and succeeded in bringing to a sharp focus the attention of workers in this field on the established observations which a satisfactory theory must explain. Several other authors3,5,6 have, in the last few years, studied the phenomena that occur when cold metallic powders, loose or in the form of compacts, are first brought to elevated temperatures. Some workers' in the field of friction have recently studied the adhesion of solid metal surfaces when they are brought into close contact. These researches have indicated that several separate mechanisms operate simultaneously, at least during the first part of the sintering process. Some of them have been called transient mechanisms4 because they are in general not absolutely necessary to sintering. Powders may be so prepared and so treated that these transient phenomena do not take place during subsequent sintering. This does not mean, of course, that their industrial and scientific importance is any less than that of the steady-state phenomena. The latter are changes that go on during sintering no matter how the powders are made or treated; they cannot be divorced from sintering. One way to analyze the process of sintering into its component parts is perhaps to distinguish between these transient and steady-state phenomena. Some of the transient phenomena have been studied in the past few years. Huttig3 has shown that, when the temperature of metallic powder is slowly raised, the following events generally occur in order: (1) physically adsorbed gases are desorbed; (2) there is an atomic rearrangement of the surface, a sort of two-dimensional "surface-reciystallization"; (3) there is a breakdown of chemically adsorbed surface compounds; (4) there is a recrystalliza-tion in the volume of the metal. All these changes are shown by Huttig and his coworkers to be completed fairly rapidly at lower temperatures than those generally used in sintering and are therefore not a part of the mechanism whereby the density of a mass of powder continues to change after long heating at an elevated temperature. But the first and third of these changes release gases in quantities which may or may not help to control the steady-state mechanisms, depending on when the voids become isolated from the outside of the compact. Among the phenomena studied by Steinberg and Wulff,8 there is the effect on sintering of residual stresses arising from the pressing operation. They found that the lateral surfaces of a green compact of iron are under a longitudinal residual tension-stress of the order of magnitude of half the yield-point for solid iron. If the outside surface is in tension, the core must be under longitudinal compression. When the compact is heated, the surface residual stress is thermally relieved first, and the compact therefore initially expands in the direction of its axis. This is a transient phenomenon, if for no other reason than the possibility of sintering unpressed powders, as demonstrated by Delisle,9 Libsch, Volterra and Wulff10 and others.1 The subject of recrystallization is dealt with further in a separate section, in view of its prominent place in sintering literature. It, too. is one of these transient phenomena. Among the steady-state parts there may be distinguished the attraction between particles and its consequences, the spheroidization of voids in the compacts, and the densification or swelling of the compact. There is considerable evidence4,7 showing that cold metallic surfaces, when brought to within a few interatomic distances of one another, are attracted to each other by forces of the order of many thousands of pounds per square inch. A calculation, discussed in greater detail in another section, shows that this force changes but slightly when the temperature of the surfaces approaches the melting point. Actual measurements of forces of adhesion of this magnitude have been made by Bradley12 on some nonmetals, but none has yet been made on cold or hot metals. This force is of sufficient magnitude to cause some plastic deformation in powder compacts, as will be shown below. A second force of steady-state nature is due to the surface tension, which probably has the same origin as the force of attraction between surfaces.164 A paper by Udin, Shaler, and Wulff1,3 gives the results of precise direct measurements of its value for solid copper. The demonstration of the tendency for the surface tension to shrink a pore was long ago given by Gibbs.17 He showed that its effect on a curved surface between two phases is equivalent to a pressure perpendicular to that

Jan 1, 1950

By W. M. Rust, W. D, D. W. Mounce

The almost universal acceptance of electrical logging by the petroleum industry calls for a critical examination of the physical bases of the common methods. This is particularly needed for the natural potential log. The conventional explanations are based on the phenomena of electrofiltration and electro-osmosis. However, experimental data show that they fail to give a basis that is quantitatively sound. Moreover, they lead to interpretations of details of electrical logs that are erroneous. It was found experimentally that when a plug of shale is placed in a chain of dissimilar electrolytes, a current flow results. Experiments on oil-well cores and fluids similar to those existing in wells show that potentials are set up which are in reasonable agreement with those encountered in electrical logging. Doubtless other sources of potential are important but this explanation not only accounts for much of the potential but also clarifies some fairly familiar examples of misinterpretations. Introduction The extraordinary value of electrical well logging as a tool for petroleum engineers and geologists is now so uni- versally recognized that it is not necessary to point out the ways in which it can be useful. It is sufficient to mention only the saving that has resulted from the elimination of much coring that would have been necessary under former practices and the considerable additions to reserves resulting from the discovery of sands missed in coring. Paradoxically, the very remarkable success that has resulted from the application of electrical logging to correlation and completion problems has cost some of its most consistent users dearly.' The fact that some operators have placed unwarranted faith in erroneous interpretations of electrical logs does not reduce the value of the logs. It should, however, make one pause long enough to ask why experienced users should be misled. The answer to this question is not hard to find. In nearly every case, the fault has been oversimplification. This is illustrated very aptly by the familiar interpretation and theory of the natural potential log. Recording and Interpreting Logs The natural potential log is extremely simple to record precisely enough for all present-day uses. One needs only an electrode, a cable to lower the electrode through the drilling mud, a recording meter and a surface ground connection. The electrode can be elaborate but need not be. A simple brass rod 2 in, in diameter and 2 or 3 in. long is quite satisfactory. The cable need not be particularly well insulated, nor need it have a very low resistance. The recorder can be a vacuum-tube 1 References are at the end of the paper.

Jan 1, 1944