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By Robert W. Hunt

Having had some twenty years' experience in trying to make good Bessemer steel rails, and now devoting my thoughts and energies to seeing that other people seek the same end, I venture to lay before the Institute some of the conclusions deduced from my practice and observation.

Jan 1, 1889

By Raymond Mancha

A TEST of any fan requires the determination of such data as fan pressure, air volume handled by the fan, and power input to the fan shaft. When testing operating mine fans of the centrifugal type, test methods have been employed, for the sake of convenience, that permit great latitude in detail of procedure resulting in wide variance in results by different investigators. Some controversial aspects of field fan testing are the result of past failure to define dearly the various forms of fan pressure and to a lack of understanding of the accurate procedure for the measurement thereof. Also, the anemometer for air-volume measurement, although convenient, if carelessly used and maintained is subject to a wide error range with variation in method of application and in instrument accuracy. The appearance of the axial-flow type of mine fan offers the possibility of refinements in field testing that were impractical with the centrifugal fan. First of all, the fan inlet and outlet are more sharply defined, giving loser agreement as to just where the fan begins and ends; thus there is less disagreement as to the proper location for measurements of fan pressure. The area of passage into the inlet of an axial-flow mine fan usually constricts, causing high air velocities with accompanying steadiness of flow. Thus the fan inlet offers an ideal location for accurate air-volume measurements with the Pitot tube, the proper use of which is well established by code. Thereby the controversial aspects of such measurements are eliminated. Use of the Pitot tube also facilitates a more accurate measure of fan pressure, since the individual pressures measured can be properly weighted, as will be explained later. Determination of power input to the axial-flow mine fan operating in the field is subject to the same inaccuracies as with the centrifugal fan if the axial-flow fan is also belt driven. However, because of the higher rates of rotation usual with axial-flow fans, direct-driven units are more numerous and it is unnecessary to assume a drive efficiency, thus eliminating one possible source of error. It is the purpose of this paper to define and explain the various types of pressure measurements involved in a field test of an axial-flow mine fan, and to further explain the proper use of the Pitot tube when measuring pressures and volumes. DEFINITION OF FAN PRESSURES The two fan pressures most commonly discussed are fan total and fan static pressure, each of which has the same meaning regardless of whether the fan is blowing, exhausting, or blowing and exhausting, as in the case of a fan with ducts connected to both outlet and inlet. Fan total pressure is the amount by which the total pressure of the air delivered by the fan exceeds the total pressure of the air received by the fan. This pressure is a measure of the maximum amount of the work done on the air by the fan that is available for external use.

Jan 1, 1942

By H. S. Strouth

JAMAICA-bauxite and gypsum-but what else? J Does the Caribbean island have anything more to offer in the form of mineral wealth? One answer may be iron ore deposits which show enough promise to warrant exploitation in the near future by a company associated with Standard Ore & Alloys Corp. In addition, Jamaica is reported to have gold, silver, platinum, copper, lead, zinc, manganese, cobalt, and a great many nonmetallic minerals. Of these, only platinum has not been produced commercially in the past. Right now, Jamaican bauxite is getting most of the publicity, but not too long ago other mining operations were in progress. Lack of proper interest, insufficient roads, and scarcity of venture capital forced those mining properties to suspend production.

Jan 7, 1954

By Ta M. Li

A record 340 senior students with majors in mining and mineral engineering from 21 shcools in the US may be expected to enter a manpower-hungry mineral industry in 1975. While starting salaries may have been the deciding factor in job selection in the past, 1975 graduates will find salaries almost the same in most mining sectors. Meanwhile, the survival prospects of various mineral engineering schools had the usual ups and downs in 1974, but tightening state budgets could still take a toll in reducing the number of schools offering mineral engineering degrees. Two such schools on the endangered list include Montana College of Mineral Science in Butte, Mont., and the College of Mines, University of Idaho, in Moscow, Idaho.

Jan 3, 1975

By P. Schwarzkopf, J. H. Brophy

A modification of the Mendenhall wedge blackbody1 has been used to determine solidus temperatures and to anneal alloys in the tantalum-rhenium binary system. The technique has proven to be simple and accurate with modest power requirements. For temperatures up to 2800° C a piece of 10-mil tantalum sheet was folded double and formed as shown in Fig. 1. The middle of the resulting ribbon filament was a cylindrical-shaped crucible with less than a 1/8-in. opening. After inserting a specimen in the cavity, the filament was clamped between molybdenum electrodes in a high vacuum chamber. A representative filament 2 in. long and % in. deep was heated to 2800°C with a current of 700 amp at 4 v. The specimen temperature was determined by sighting into the cavity with a Leeds and Northrup optical pyrometer. The twisted filament shape was necessary to avoid serious geometric changes during thermal expansion. For temperatures between 2800" and 3000°C a 4-mil tungsten filament was employed. To facilitate fabrication it was warm-folded, and a twisted segment of 10-mil tantalum was used to support one end to absorb thermal expansion. This element assembly required about 700 amp at 10 v to reach 3000°C. Two geometric modifications of the filament were helpful for solidus temperature determinations. A shallow chamber, with depth to opening ratio of 3 to 1, permitted direct observation of the specimen through the optical pyrometer. The fact that the specimen was visible permitted the melting point to be determined when sharp features on the specimen surface became rounded; it also indicated that blackbody conditions did not prevail. By standardizing against the melting point of molybdenum, the observed melting temperature was corrected by the following form of Wien's Law: in which T is the true temperature, To is the observed temperature, and K is a constant characteristic of the filament geometry and determined experimentally for the molybdenum standard. The resulting corrected melting point for each alloy served as a reference temperature for the second more precise filament geometry. With a 6 to 1 depth to opening ratio, the specimen was indistinguishable from the filament interior, indicating good blackbody conditions. Using this technique, a series of specimens was isothermally treated at temperatures above and below the corrected direct reading. Incipient melting was detected by visual or micrographic examination of the specimen after cooling. This procedure was checked with specimens of pure chromium, molybdenum, and tantalum. Table I represents the values obtained, together with the solidus temperatures in the tantalum-rhenium binary system determined by the same technique. The alloy specimens were approximately 1/8 in. in diam. They were pieces of 10-g buttons melted four times in a nonconsumable tungsten electrode arc furnace on a water cooled copper hearth in 2/3 atmos of titanium gettered helium. Several sources of error are possible in such temperature measurements. Within the accuracy of the pyrometer no gradients were detectable near the specimen, and element distortion was virtually eliminated by twisting the tantalum. Compensation was made for the 1/8-in. sight glass by inserting several identical thicknesses and extrapolating to zero thickness. As a result an additional 10°C correction was added to all observations in the temperature range of 2500" to 3000°C. The principal source of error was then in the operation of the

Jan 1, 1961

By F. N. Kissell, W. E. Schroeder, N. I. Jayaraman

This article discusses methods of improving airborne capture by conventional dust suppression systems. The work was performed in a full-scale plywood model of a mine entry with a wooden mockup of a Joy 12 CM continuous miner. Dust was introduced at the front of the entry, and water sprays knocked down part of the dust cloud. Sampling in the return air determined the percentage dust reduction. Based on the results, guidelines are offered for continuous miner spray systems to control dust. Empirical relations have been developed to determine the effect of changes in water spray pressure on air movement, dust knockdown, and pollutant concentrations in the face return. Nozzle selection and arrangement are discussed for high dust knockdown efficiencies.

Jan 1, 1986

By G. Sandoz, D. A. Meyn

The fracture surfaces of specimens of titanium a1loys which exhibited susceptibility to subcritical crack growth in a wide variety of environments, including aqueous solutions, alcohols, hydrocarbon gases, carbm tetrachloride, and dry air, were examined. The dominant and characteristic fracture mode was cleavage. which became mixed with an increasing porportion of ductile fracture modes (dimples. and so forth) as the applied KI was increased. The cleavage plane in all the alloys was oriented at 15 deg from (0001) of the a phase. No indices could be assigned to the 15 deg cleavage Plane because of uncertainty as to which zone it belonged to. SLOW crack growth and delayed fracture take place in certain titanium alloys at stress intensity (KI) lower than the critical values for complete fracture (KIc) found in short-time tests for plane strain fracture toughness.' Such crack growth may take place in very dry air on sustained loading if the alloy contains a sufficient amount of hydrogen and if the stress intensity factor is higher than a threshold value designated KIH.2 Similarly, a number of environments such as water, alcohols, and hydrocarbons may cause slow crack growth provided the stress intensity factor exceeds the threshold value KISCC. In this paper it is intended to examine some fracto-graphic and crystallographic details of this subcritical crack propagation process as related to alloy composition, environment, and stress intensity. It has been previously reported that subcritical crack growth takes place in titanium alloys in aqueous environments by cleavage.2"6 The observations to be described here indicate that in the alloys investigated the mode of subcritical crack propagation is more dependent on the stress intensity during cracking than on the environment. The fracture mode is illustrated with photographs of the fracture surfaces at a wide range of magnifications. The crystallographic character of the cleavage mode is also presented and the results discussed. EXPERIMENTAL APPROACH The studies were made on four titanium alloys— Ti-8A1-1Mo-lV, Ti-5A1-2.5Sn, Ti-7Al-1Mo-lV, and Ti-0.350. Of these four alloys the first two were mill annealed and fine grained. The latter two were noncommercial and coarse grained, having been prepared for other experimental purposes. The crystallographic studies required a large-grain size. Consequently the fine-grained alloys were an- nealed in a vacuum at 1950°F and furnace cooled to produce samples for these studies. This treatment did not alter the microstructure significantly except for grain size. All the aluminum-containing alloys showed primary a with a network of ß-phase particles within the a grains; Figs. 1 and 2 show this microstructure for the specific case of fine-grained Ti-8A1-1Mo-1V. The cracks in the figures will be discussed later. Fractographic studies were made on all the alloys, but the electron fractographs displayed herein are from the Ti-8A1-1Mo-1V alloy in the fine-grained condition. Emphasis was placed on this commercial alloy because considerable information was available on the stress-corrosion cracking characteristics in a variety of environments. Sufficient supplementary studies of the alloy after the anneal to produce large grains were conducted to establish that the stress-corrosion cracking susceptibility and fractographic characteristics were not changed significantly. Thus it could be inferred that the crystallographic data obtained exclusively on large-grained specimens would apply also to fine-grained specimens. Fracture surfaces for study were obtained using precracked cantilever beam specimens loaded as described by Brown. The precracked section of a specimen was immersed in the environment of interest. Values of initial stress intensity factor Kli were chosen slightly higher than KISCC in order to obtain a fairly extensive region of slow crack growth. Fracture surfaces representative of a variety of stress intensity levels could then be examined because in the cantilever beam test KI increases as the crack propagates.

Jan 1, 1970

By G. H. Kennedy, H. E. Criner

CYCLONE thickeners are "hydraulic centrifuges" designed either to produce a maximum practical separation between the water and solids of a feed slurry or to classify the slurry solids according to particle settling rate. The possibilities of utilizing the thickener to "close" plant water circuits have been investigated. Since the thickener becomes an integral part of the plant water circuit when installed, the basic means by which the solids content of all circulating water systems must be controlled is reviewed. All coal not separated from the circulating water by means of dewatering screens or settling devices must be bled from the plant at the same rate as they are being fed or created by degradation. If this were not true, the circulated volume would finally be completely filled with solids. If the rate of bleed is low, the solids concentration in the bleed and circulating water generally will be high. To keep a reasonable circulating water concentration, large amounts of fresh water must be supplied and the bleed rate must be high. These conditions are usually undesirable because of the difficulty in securing fresh water, the loss of large quantities of coal, and the pollution of nearby streams. Thickeners are the primary stage in the separation of the water contained in the bleed from the coal. Since a thickener, when operating with reasonable efficiency, usually cannot be expected to deliver an underflow containing less than 50 pct water, secondary dewatering devices such as a slurry screen or vacuum filter must be used to separate additional water from the bleed. The surface area required by the filter or screen will be nearly proportional to the total water which must be handled, and therefore the thickener becomes necessary to hold down the original cost. The water separated from the coal is then returned to the plant circuit to maintain the water balance and thus becomes the source of fresh water. It is not necessary to return clear water to the plant to maintain control of the circulating water concentration. It is only necessary that the bleed dewatering devices remove coal in all sizes at a rate equal to that at which these sizes are entering the circulating water. However, practically speaking, in order to maintain low solids concentration, it is usually necessary that the thickener have good recovery characteristics on bituminous coals in those sizes down to 400-mesh. The thickener can remove the smaller sizes from the closed-circuit system at the "solids in" rate and prevent their "build up" in the circulating water as shown in Fig. 1. With the portion of the feed water going directly to the underflow, comes the very fine solids not concentrated by the cyclone. All the larger solids are removed from the feed and delivered in a concentrated condition at the underflow. To apply thickeners with some reasonable assurance that operating requirements will be met, it is necessary to know the rate at which solids of all sizes must be removed from the circulating water and to know the thickener characteristics. The required removal rate of fine solids not recovered by other dewatering devices may be estimated from the size distribution and tonnage of the plant feed with a reasonable allowance for degradation in the circulating water system. A more reliable estimate may be secured by sampling the plant bleed water during a constant load period.

Jan 1, 1952

By Winthrop P. Haynes

The symposium on production for the year 1943 contains few papers on the foreign situation. It has always been the policy of officers in charge of the symposium to refrain from publishing information that might possibly injure national or private interests. At the close of the war we hope again to publish full and accurate records of production abroad. A noteworthy feature of the reports on Texas this year is the map on page 469, which shows the districts covered by the statistics. Excerpts from Circular to Authors In order to facilitate interpretation of the data in this chapter, we print the following excerpts from the Circular to Authors. The field is the unit in this tabulation. In cases of fields extending across State boundaries, such as Rodessa, it is suggested that each State author treat the section of the field in his State as a unit, and by a footnote indicate that the field extends into an adjacent State. Each place in the table may represent one of three possibilities; either the proper entry is determinable and can be supplied by the author, or an approximate figure can be supplied which is the author's best guess and should be entered followed by an x, or it does not apply to the particular field and the space is left blank. Contributions of great value may be made by the author in many cases where entries are not subject to precise determina-tion. In such cases the author should use his good judgment and make the best entry possible under the circumstances. The entry of a zero is a positive declaration, and it is an important declaration where it is in order. It is thought that the nearest whole numbers are suficiently accurate for our purposes except as to percentage of sulphur in oil. If an author desires to report any other figures to tenths, he may do so. The quantity of gas produced should include, where possible, gas sold or otherwise marketed, and gas blown into the air, burned as flares or otherwise wasted. Segregation of these figures would be interesting if the authors can make such segregation. In any event, the figures should represent as nearly as possible the total quantity of gas removed from the reservoir. Under the columns on ''Depth," the average depth to the top of the productive zones and to the bottom of the productive wells, when subtracted, should give the approximate thickness of the productive zone. For fields where this is not true because of unusually high dip or for some other reasons, it is suggested that the authors indicate in their text the approximate average thickness of the productive zone. The net thickness of the producing formation should be the thickness of the producing zone, less the estimated amount to cover the portions of the zone that do not yield oil, such as dense shales, etc. It is recognized that for some fields the authors can only make rough guesses; in such cases, they should enter their best estimate followed by an x. Average production per acre-foot need not be reported as it can be calculated by those interested from the figures given. In classifying wells as to producing methods, enter all wells that are not "flowing" in the column headed "Artificial Lift." If possible, add footnotes to indicate whether the lift is "pumping," "gas lift" or "air lift."

Jan 1, 1944

By Leo Behr

RECENT years have seen important practical advances in the construction of recording instruments for use with thermocouples. The difficulties of the problem will be appreciated when it is remembered that a 10° F. change in temperature of a base-metal couple at 1500° means a change in the electromotive force of about 0.00035 volt. In a circuit having a resistance of 350 ohms, this means a change in the current of 0.00000,1 amp.; and despite this requirement of great sensitivity the instruments must be sufficiently robust to withstand the rough usage which is so often their lot. Two methods are in common use for the measurement of the electromotive force produced by a thermocouple: 1. The milliammeter method, in which the current produced by the thermocouple in a circuit of known resistance is measured and from. this the electromotive force is deduced by Ohm's law. 2. The potentiometer method in which a known potential difference is opposed to the thermocouple electromotive force. The use of thermocouple and milliammeter for measuring temperature introduces some possible sources of error, for the reading depends on a number of factors, including the following: (1) Electromotive force set up at the hot junction, (2) electromotive force set up at the cold junction, (3) resistance of the circuit including thermocouple, lead wires, and meter, (4) field strength of magnets, (5) strength of controlling springs in meter, (6) friction at pivots, of pointer on paper, etc. It is obviously necessary to so design and maintain the installation that the reading is independent of all the factors except the first. The electromotive force set up at the cold junction can easily be taken care of provided it is constant. This has been approximately accomplished by burying the cold junction in the ground or actually secured by locating it in a container, the temperature of which is kept constant by means of a thermostat.

Jan 9, 1919

By R. I. Jaffee, H. R. Ogden, D. J. Maykuth, W. L. Finlay

Titanium with up to 7.5 pct Al forms single-phase a alloys that are work hardening, not heat treatable, and ductile as welded. The high aluminum Y phase alloys are not usefully ductile, despite their low hardness, but they have excellent oxidation resistance and hot hardness. LITTLE has been published on the effect of aluminum on the mechanical properties of titanium, despite the fact that two of the first four commercial alloys released by titanium alloy producers contained aluminum as an important alloying ingredient. These were both a-ß type alloys, one containing 4 pct A1 and 4 pct Mn and the other containing 3 pct A1 and 5 pct Cr. However, neither of these alloys reflects the true alloying nature of aluminum, since each contains important amounts of the ß-stabilizing addition, manganese or chromium. In a previous publication on the constitution of Ti-A1 alloys,' the authors showed that aluminum had a high solubility in a titanium and was strongly a stabilizing in nature. About 25 wt pct A1 is soluble in a titanium at room temperature. With as little as 5 pct added aluminum, the a transus temperature is increased from 882" to 970°C, and the correspond- ing ß transus to 995°C. The first intermediate phase in the Ti-A1 system is the ordered face-centered tetragonal TiAl phase, which extends from 34 to 46 wt pct Al. The present paper presents hardness data over the entire titanium-rich region of the system, through the TiAl phase, and mechanical property data on the alloy range capable of being fabricated. Methods of Investigation The materials used and general preparation of alloys, as well as experimental techniques used in the investigation of Ti-A1 alloys, have been adequately described.' Briefly, the preparation consisted of arc-melting the desired amount of high purity aluminum (99.99 pct purity) and iodide titanium (maximum hardness 100 Vickers, as deposited) together on a water-cooled copper hearth under a partial pressure of argon. The resulting button ingot was of such form that it could be fabricated without further treatment. All work was done using ingots weighing 10 to 15 g, which were hot-rolled to strip form whenever possible. Tensile samples were 3.25 in. long, 0.5 in. wide, and 0.040 in. thick, with a reduced section 1.25 in. long by 0.250 in. wide. The gage length used was 1 in. Electrical strain gages mounted on the

Jan 1, 1954

By H. M. Kraner, R. C. Devries, K. H. Gee, E. F. Osborn

On the basis of liquidus measurements in the system COO-Mg0-Al2O3-Sio, and previously published data, diagrams have been constructed at 5 pct Al2O3, intervals from 5 to 35 pct Al2O3,. Liquidus temperatures and primary phase fields are shown. The optimum composition of a blast furnace slag for a given alumina content is indicated. At the optimum point, ordinary slags will be entirely liquid and will have maximum desulphurization potential and minimum viscosity. The relation of optimum composition of slags to the "plateau region" of the liquidus surface, and the application of these data on synthetic quaternary slags to actual slag compositions are discussed. Index of refraction of glasses is given as well as composition, temperature, and phase data for each mixture. THE usual blast furnace slag, as a first approximation, can be considered a mixture of the four oxides, CaO, MgO, Also,, and SiO,. Systematic, extensive data for the quaternary system, CaO-MgO-A1,0,-SiO, is therefore required for the understanding of the properties of such a slag as a function of composition and temperature. With sufficient data, it should be possible to fix unequivocably the relative amounts of lime, magnesia, and silica required for a given alumina content to result in a slag composition having optimum properties. Other constituents, such as FeO, MnO, Ti02, and S, have an effect on the properties of a slag, but as long as they are present in small and approximately constant amounts they produce only a second-order effect superimposed upon the major changes in properties of slags determined by the relative amounts of the four major components. Viscosity and desulphurization data have been reported for mixtures approaching blast furnace slags in composition, but systematic liquidus data have not been obtained. Inasmuch as a slag must be all liquid in order to be most effective as well as practicable, clearly the temperature above which a mixture is all liquid (liquidus temperature) is a type of data needed. Such data have been obtained through the study of 446 compositions and are pre- sented in this paper along with a discussion of their bearing on the optimum composition of blast furnace slags. For an orderly presentation of the data, the quaternary system is viewed as a tetrahedron with one component at each apex. Fig. 1 shows a tetrahedron representing the system Ca0-Mg0-A1,0,-Si0,. The base is the ternary system Ca0-Mg0-SiO,, A1,0, is the top apex, and the front face, the system CaO-

Jan 1, 1955

By H. L. Hopkins, OHIO, L. W. Kemph, CLEVEL AND, E. V. Ivanso

A balanced system of internal stress is set up in any metallic structure by plastic deformation below the annealing temperature. The internaI stress induced by cold rolling or other fabricating processes is generally recognized and its magnitude is known to be, within certain limits, a function of the degree of cold deformation. The plastic deformation that may accompany rapid cooling from elevated temperatures may not materially change the form of the product. The internal stresses so induced are not, therefore, so evident and nonrecognition of their presence has at times led to engineering failures. The heat treatment of aluminum alloys is a relatively new art and little information is available regarding the magnitude of stresses induced during the commercial heat treatment of aluminum alloy products. As the industrial use of aluminum increases, it is inevitable that products of increasingly large volume will be required. It has become necessary in the present commercial utilization of aluminum to heat-treat castings and forgings weighing hundreds of pounds. One of the factors governing the magnitude of internal stresses arising from rapid cooling from elevated temperatures is that of the size of the structure being treated. Some of the other factors are: cooling rate, elastic properties of the alloy, thermal expansivity, thermal conductivity, and the presence or absence of phase changes. Practically all aluminum alloys have a high coefficient of thermal expansion and some are capable of developing relatively high elastic limits. On the other hand, all commercial aluminum alloys have relatively high thermal conductivities, no invariant phase changes, and the quenching temperatures are comparatively low. In the absence of invariant phase changes involving change in the type of crystallographic lattice, the fundamental basis for the development of internal stress

Jan 1, 1934

By G. J. Ballmer

Drilling and blasting 12-in. blastholes started about the middle of 1946 and has worked out so well that about one half of the blasting, formerly done with 9-in. holes, is now done with 12-in. holes. In most of this work the harder benches were chosen for the 12-in. size because these were the areas where the greatest difficulty was encountered in thorough fragmentation. At the start of this experimental work a 42-T Bucyrus- Erie churn drill was available whereas all other blasthole drilling was being done with 29-T rigs. The large drill was first equipped with a standard 9-in. string of tools but it could not drill quite as fast as the 29-T drills. How- ever, when the weight of the string was increased about 700 lb, or to a total weight of about 3500 lb, it was found that the 42-T exceeded the drilling speed of the 29-T by about 25 per cent. When a 12-in. bit was substituted for the 9-in. bit the 42-T rig again dropped behind the drill- ing rate of the 29-T rigs. At this stage of the experiment the 42-T was using a 12-in. bit with detachable points and the total weight of the string of tools was about 3800 lb. It took longer to change the drill points than it did the regulation bit and this accounted for some of the slower drilling rate. When a heavier stem and standard construction 12-in. bits were used it was found that the 42-T could drill a 12-in. hole slightly faster than a 29-T could drill a 9-in. hole even in the hardest rock in the pit.

Jan 1, 1949

By L. R. Plitt, E. O. Lilge

Tests carried out with both kaolin and silica slurries show that flocculants of the polyacrylamide type can be used to improve the thickening performance of hydrocyclones. This thickening improvement demonstrates that contrary to previously held theories, flocs can be formed which are capable of resisting the shear forces in a hydrocyclone. For the 1.25-in.-diam cyclone used, optimum thickening occurs when the flocculant solution is injected into the slurry stream at or near the feed inlet. Hydrocyclones offer many distinct advantages over gravity thickeners. These advantages include simplicity, low initial and operating costs, small space requirements, and flexibility of operation. In spite of these advantages hydrocyclones have not been widely used as thickeners. The main reason for their lack of application is that hydrocyclones are unable to efficiently remove semicolloidal particles (less than 5 microns) from the suspending solution. In gravity thickeners, the fine particles can be induced to form particle aggregates, or flocs, which have the settling characteristics of large particles. In the hydrocyclone, however, it was always assumed that the existence of shear would prevent the formation of flocs.1-3 Thus, if no floc structure is retained, the thickening hydrocyclone must be designed so that its separation size is below the size of the smallest particle to be recovered. To obtain a very small separation size requires the formation of very high centrifugal forces, which necessitates the use of small-diameter cyclones. Small hydrocyclones have, in turn, very low throughput capacities which render them impractical for many industrial thickening applications. Thus, if the effects of flocculation cannot be utilized, the usefulness of hydrocyclones as thickeners remains limited to pulps which contain no very fine particles. It is well established that most substances acquire a surface electric charge when brought into contact with an aqueous medium. The repulsive interactions between similarly charged particles act to prevent flocculation. One method of flocculating a dispersion is to neutralize the repulsive surface charges by the addition of an electrolyte. The reduction of the electrostatic surface charge (Zeta potential) then permits the universal van der Waals attractive forces to operate between the atoms of the various particles and form particle aggregates. The lime additions used by thickener operators promotes flocculation by this mechanism. A second method of flocculating a dispersion is by the addition of long-chain macromolecules. In this case flocculation is brought about by a bridging mechanism in which the molecules are adsorbed with part of their length on two or more particles, thus forming a molecular bridge between the particles.4,5 The molecules also form bridges between themselves when a single particle is bonded to several polymer molecules. The type of bonding between the flocculant molecule and the particle may be hydrogen bonding, chemical bonding, or electrolytic attraction.6 The flour and glue which are used as thickener additives are believed to promote flocculation in this manner. In the past decade synthetic long-chain polymers with extremely high flocculating capabilities have been developed. The flocs formed by these new polymeric flocculants are larger and more shear-resistant than those formed by the presence of electrolytes.7 The advent of these flocculants raises the question: Are the flocs formed by these synthetic polymers stable enough to resist the liquid shearing forces in a hydrocyclone? The investigations reported in this paper were carried out in order to provide some answers to this question. EXPERIMENTAL WORK For the bulk of the test work a 5% slurry of commercially available kaolin with an average particle size of 5 microns was used. An initial evaluation of the available flocculants was carried out to determine which flocculant formed the most shear-resistant flocs. A combination of the techniques used by Healy7 and Booth8 was used for this purpose. This initial study revealed that the neutral high-molecular weight polyacrylamides produced the most shear-resistant flocs. One of these flocculants, Separan MGL*, was selected and then used for all the hydrocyclone tests. The flocculant was dissolved in water and added to the hydrocyclone as a dilute solution.

Jan 1, 1968

By LOWELL LAWRENCE

MAGNETITE minim and milling in the Eastern States continued at a low rate of production during 1934. The year's output was 50 per cent greater than in 1933, but when one considers that the 1934 output was only 1.5 per cent of the combined plant capacities of the eastern iron ore producers, the far-reaching effect of unrestricted importation of foreign ores and pig iron is apparent. The Chateaugay Ore and Iron Co., at Lyon Mountain, N. Y., produced 1.00,136 gross tons of concentrated and sintered ore up to Nov.1, when operations were closed clown. At Mineville, the Witherbee, Sherman Corp. confined its productivity to part-time operation of its Old Bed and Harmony mines front May 1 Lo Oct. 27. This period of activity was brought about by the use of Mineville ores in the recent blast made by the Green Island furnace at Troy, N. Y. The Forest of Dean property at Fort Montgomery, N, Y., has continued closed down during the year.

Jan 1, 1935

By C. Allen Born

INTRODUCTION As the title of this paper suggests, the author does not believe that risk can be managed. Rather, the objective is to identify the risk which will be present in a given venture and assess the level of that risk which is acceptable. More often than not, the risk which is present is subject to little or no modification. After identifying and measuring the risk a corporation will decide to accept it and proceed in such a way that it will be less exposed, or it will decide not to proceed at all. The exercise for a corporation is different only in degree from everyday judgements made by average people in average situations. However, that word "degree" means that it is considerably more complex on the corporate level. There is good reason for the additional complexity of corporate risk evaluation. The variables influencing a company's decision can be more numerous and the penalties for miscalculation much greater than those normally encountered by an individual. It should be understood that no analysis of risk, certainly not one as brief as the following, can do more than touch on some of the high points. Before examining the sorts of risk which affect the development and operation of specific mines, let us consider the broader aspect of the term with which mining companies, and all other business corporations, must deal. Companies must determine their long-term objectives and strategies within the context of a constantly changing world. To plot their direction they must attempt to read the future by seeking answers to questions such as: How will society evolve? Which businesses will thrive? In which of these should we place our emphasis? If a company hopes to be around five or ten years from now it must make the attempt to answer such questions in order to judge the impact of changing patterns in the evolving business environment. Information is available to allow the lessons of the past to be projected on the future. We have data on birth rates, economic booms and busts, patterns of conflict within and between nations, drought and other forces of nature as well as individual events which cannot be predicted, but which over time, do seem to occur in regular cycles. Ultimately the question "where will we be and what will we be doing a decade from now?" must be answered by one or more senior people with responsibility for the company's future. The compilation and interpretation of hard data by competent support staff, can only be used up to a certain point in determining future corporate strategy since there will be alternative possible futures and a high degree of risk will always remain. At this point those elusive qualities of experience, instinct, and - "gut feeling" - become important factors in choosing a long-term corporate direction. The goals of a company have a significant bearing on its attitude towards risk. This in turn dictates the "hurdle rate of return on investment" which a project decision-maker will require. The hurdle rate is the minimum-discount-percentage-rate applied to forecast cash flows to give a present value of zero to the All-Equity-Funded Investor. The feasibility study for a project is a fundamental tool in the management of risk. An experienced team has an established and well-understood set of ground rules for the preparation and assembly of a feasibility study. The necessary degree of conservation is built in at all levels of study data and, if the project is technically feasible, the hurdle rate becomes a catch-all measure of risk in a base-case project cash flow.

Jan 1, 1985

By Phillip A. Stoll, Young Ku Yoon

ThE deterioration of the magnetic properties of silicon-steel core materials during service (magnetic aging) is quite undesirable. Although some information about the effects of impurity elements on magnetic properties is available, 1,2 magnetic aging that occurs at low temperatures has not been extensively studied. Moreover, the microscopic techniques used by earlier workers were not suitable for study of fine metastable phases that are precipitated at relatively low temperatures. Recently, several investigators3,4 successfully used transmission electron microscopy in the study of low-temperature precipitation in Fe-C, Fe-N, and Fe-Mn-C alloys. To investigate metallurgical factors that affect magnetic properties after aging, the microstruc-tures of steels having different magnetic-aging

Jan 1, 1964

By W. M. Myers

Certain minerals possess inherent color and other properties that make them suitable for the pigmentation of paints, mortar, plaster, concrete, face brick, and other materials. Their production is one of the most ancient of mineral industries and their use by primitive man is well known. These natural pigments have some economic factors in their favor, particularly wide geographic distribution, low cost of production, ease of preparation, chemical stability, and permanence in use so that they continue to form the basis of a small but useful industry. When used in paints such pigments act as a filler and supply body and opacity in addition to color. Natural mineral pigments are prepared for the market by the comparatively simple operations of washing, grinding, blending, and calcining. Any one, or all of these processes may be applied to a single pigment. The development of synthetic pigments and the use of byproduct materials have introduced competition with the products of nature and are having a growing influence on the economic position of the mined minerals. Development of the Industry The industry developed to commercial stature in Pennsylvania largely because of the presence of beds of ocher extending from Easton in a southwesterly direction toward Reading, and a variety of small iron mines in the region. The mining of paint ores in the Lehigh Valley was active as early as 1850 and shortly after the Civil War the establishment of mills expanded production and led to the development of new products and eventually the manufacture of synthetic pigments. Pennsylvania continues to maintain it.s leadership as a producer of mineral colors. Production is recorded also in New Jersey, Illinois, Virginia, Ohio, and Georgia. Iron as a Pigment Iron in various compounds is the most important pigment in nature. The iron pigments are characterized by stability, light fastness, good covering power, high index of refraction, and economy in production. Ferrous compounds display a typical green coloration. This has not been employed as a commercial pigment to any great extent except incidentally in such greenstones as have been used in construction, or crushed and sized for application as a granule to roofing. Ferric oxides are characteristically red and form an important group of industrial pignents. Hydrated ferric oxides exhibit various shades of yellow and are present in such familiar pigments as ocher and sienna. The addition of small amounts of manganese oxide or carbon as organic matter to the yellows produces the brown umbers. Magnetite is one of the few black minerals that grinds to a black powder. The mineral pigments vary from earth colors of low intensity and great dilution of iron content to almost pure iron compounds with high tinting strength and correspondingly greater value. There has been some relationship between the mining of iron ores and the production of mineral pigments; although the production of colors is not carried on appreciably as a byproduct of iron mining. A number of mineral pigment producers, particularly in the eastern states, have operated mines which in the past were small producers of hematite, bog ore, or carbonate ore. The knowledge of the location of the deposit and its possibilities as a producer of pigment are due to its past history as a producer of metallic ore. Many iron compounds may be changed in color by calcination, the end product being Fe2O3, a stable red oxide. The yellow hydrated oxides may be changed to red. The gray carbonate, found in Carbon County, Pa., calcines to a fine red product. Ferrous sulphate (copperas) often available in tonnage as a byproduct of the steel industry, breaks down under heat or chemical action leaving a residual red oxide. Pigments produced by calcination or dissassociation of compounds possess the advantage of fine particle size and ease of grinding. Mineral Pigments MINERAL BLACKS Many black minerals grind to a light colored powder. This characteristic is familiar to the mineralogist as the white streak produced by a black

Jan 1, 1950

By M. A. Grossman

The harden ability of most steels can be predicted within 10 to I5 per cent provided the complete chemical composition is known, including "incidental" elements; and provided the as-quenched grain size is known; and provided, finally, that the composition and heating temperatures for hardening are such as to result in austenite free from carbide particles. In the method proposed herein, the steel is considered as having a base hardenability due to its carbon content alone (the hardenability of a "pure steel" of the given carbon content, without any other elements), and this base hardenability is multiplied by a multiplying factor for each chemical element present. After multiplying all these together, the final product is the hardenability. Grain size may be taken into account either in the base hardenability or after the multiplication. Hardenability is stated in terms of "ideal critical diameter", namely, the diameter of bar, in inches, that will just harden all the way through (absence of un-hardened core) in an "ideal" quench, and the calculation may also be related to the Jominy test The data bring out certain features rather clearly. For example: i. It is quite useless to attempt to predict hardenability unless all elements, including "incidentals,,) are known; thus an "incidental,, chromium content of 0.20 per cent increases the hardenability by about 50 per cent. 2. The relative effectiveness of different alloys is sometimes unexpected; thus molybdenum when calculated in this way appears to be of the same order of effectiveness as manganese, rather than much more powerful, as would appear to be common experience; observe that an increase from no manaanese to 0.20 per cent Mn provides a multiplying factor of 1.67, and an increase from no molybdenum to 0.20 per cent Mo provides a factor of 1.63, an increase of over 60 per cent in each case. However, if to a steel containing 0.50 per cent Mn there is added "20 points of manganese," the factor is raised from 2.65 (for 0.50 per cent Mn) to 3.35 (for 0.70 per cent Mn), or an increase of only 26 per cent. Thus the fist small addition of an element has a much more powerful percentage effect than an equal further addition when some is already present, and in most cases the effect of molybdenum is considered in relation to a steel in which molybdenum is absent. 3. If two elements are equally effective, a greater hardenability will be obtained by using, for example, 0.5 per cent of each than by using I.o per cent of either of them alone. 4. A knowledge of the as-quenched grain size is essential for precise work, since a difference of only one grain size number (say No. 7 instead of No. 6) makes a difference of almost 10 per cent in hardenability (in these units); this, however, does not apply to certain It should be emphasized that in chromium steels (over 0.30 per cent Cr) and chrome-molybdenum and chrome-vanadium steels, un-dissolved carbides are likely to be present in the steel as quenched, and that in such cases the charts can indicate only a maximum Passible hardenability, whereas the extent of hardening actually obtained may be much less. Thus tests on a number of chrome-molybdenum steels have indicated a degree of hardening amounting to only 50 to 65 per cent of the maximum possible, and in chromium steels from full hardening (100 per cent) down to as low as 70 per cent. On the other hand, when the amount of such elements is small (Cr under 0.30 per cent, Mo up to 0.25 per cent in the

Jan 1, 1942