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By William C. Buell

As used in connection with open-hearth or other high-temperature operations, "insulation" refers to a multitude of substances, natural or manufactured, that have the one principal property of preventing the flow of heat by conduction to a greater degree than refractories can prevent it, the principal properties of the latter being resistance to temperature and/or chemical action. The term "control" as commonly applied to the mechanization of management functions is inappropriate without qualification, for without some degree of control of every operation we could produce no steel worthy of the name. Although grouped together in this paper, insulation and control in open-hearth furnaces have little, if any, interrelationship, therefore the paper is made up of two distinct parts. INSULATION OF OPEN-HEARTH FURNACES More than ten years ago the writer proposed the insulation of an acid open-hearth furnace system below the charging floor, and it was accomplished, with gratifying results. Possibly that was the first time the insulation of regenerators and slag pockets of any open-hearth furnace was undertaken, but shortly thereafter such insulation became general, and when the six groups of 150-ton furnaces1 were built in 1929-1930, they were completely insulated below the charging floor. While the practice was accepted at least five years ago, it was not well understood, however, as indicated by the following incident which occurred in connection with an installation made in 1929. After the

Jan 1, 1935

By M. B. Truehaft

Expectations for coal in the early to mid-1970s prompted the government and industry to pursue research and development programs to increase underground and surface mining coal Productivity and net coal recovery. Several programs concerned advanced surface mining methods for thin seam coal recovery. Three such programs, along with related areas of interest, presented in this paper are: extended depth augering for trench-strip applications; high recovery auger heads for enhanced recovery; and variable wall mining in low cover longwalls. Conceptual development is examined, prototype testing is discussed, and potential operations are considered.

Jan 1, 1985

By A. M. Lovelace

Introduction One area of engineering utilization of materials in which the requirements are especially rigorous and demanding is that of aerospace systems, including aircraft, helicopters, missiles, and space satellites. Materials used in these systems must reliably perform many critical functions in a broad range of adverse environments. Some of the most critical functions are performed by polymeric nonmetallic materials such as elastomers (rubber), coatings, fibrous materials, and reinforced plastics. These types of polymeric materials have some common characteristics that make them attractive to aerospace system designers: light weight, corrosion resistance, and relative ease and low cost of processing and fabrication. Each type also has its own special characteristics that enable it to perform certain required functions better than other competing materials can (Table 1). The desirable properties of polymeric materials, which in some applications make them the only practical candidates, are partly offset by their principal limitation, which is degradation by exposure to high temperature. [ ]

Jan 1, 1971

By H. D. Hoskold

DuRing the last few years, various persons have been put forward as originators of some mechanical device for the purpose of finding distances without the use of a chain or other linear measuring-instrument, and among these, the Englishman, Gascoigne, 1639, is prominent as the first in England; while James Watt, 1771, and William Green, 1778, are also included in the list of inventors. It is possible that this useful and important problem occupied the attention of others prior to the date cited, and, consequently, it is difficult to decide what nation first gave birth to the inventor of an instrument for the object under consideration. A very important work appeared, not long since, in Paris, devoted to a history and discussion of some of the older and newest forms of surveying-instruments,* and at page 79 of that work a curious old instrument is exhibited, called Bigonometre, i. e., an instrument for finding distances and solving trigonometrical problems. in surveying. A copy of the diagram of the instrument exhibited in the book referred to is represented in Fig. 1. Having had an occasion to read the French work referred to, I communicated with the author of it, and he was good enough to reply that he found a diagram of this old instrument in a book published in 1597, by Danfrie, existing in the library of the Academy of Sciences, in Paris. Col. Laus-

Jan 1, 1904

FEW whose good fortune it has been to gaze on the Utah Copper mine but will agree that it is one of the two or three most magnificent man-made spectacles in the world. Skyscrapered Manhattan Island perhaps is more inspiring; but there the effect is obtained by aggregating a thousand separate units. The Utah mine is a single thing- the biggest thing that men have made. By the end of 1931 there had been moved at Utah 222,000,000 cu. yd. of material, including ore and the waste rock that overlay it. This figure will be increased at an average rate of nearly 20,000,000 yd. per year. Excavations for the Panama Canal are estimated at 232,300,000 cu. yd., but the Canal is 50 miles long, and it is impossible to obtain a comprehensive view of the whole project at one time. The spectator, on the other hand, need only walk part way up the east slope of Bingham Canyon to see unfolded before him the whole panorama of the great copper mine. In the foreground is a huge pit bottomed for the time being 100 ft. below the normal floor of the canyon, which also is the elevation of the main railroad yard. Here from 500 to 800 standard steel railway cars, each of 80-ton capacity, are assembled daily to carry the ore to the concentrators. But the main part of the mine and that from which ore is now coming lies above this level. As can be seen in the accompanying photograph, a series of terraces or benches reaches to the top of the mountain that projects between the main branch of Bingham Canyon and Carr Fork. From bench A (the yard level) to bench W is a vertical distance of 1500 ft. In height the benches vary from 40 to 70 ft. and in width from 30 to 450 ft. The lower benches, as they skirt the mountain,

Jan 1, 1933

By Zhengbo Pan, Fujun Gou, Jifei Chen

This paper discusses the various alternatives that are technically feasible for "over-the-raise" continuous advancing in gently inclined coal seams and the computer-aided selection of the optimal mining option. Examples in Wangshiao Coal Mine and Chaohua Coal Mine are cited to illustrate the interval between raises, face length, single or double raise layout and single or double face layout.

Jan 1, 1983

By Martti E. Maliniemi

The Svappavaara mine is located 47 km southeast of Kiruna C. The ore deposit now being worked, Leveäniemi, belongs to Luossavaara- Kiirunavaara AB (LKAB) and is the company's, and also Sweden's, third biggest mine after Kiirunavaara and Malmberget. The distance by rail to the Norwegian port of Narvik is 214 km and to Lulei on the Gulf of Bothnia 340 km (Fig. 1). The village of Svappavaara has about 800 inhabitants. The climate is arctic in character. The temperature during the months of December to February is about -20º to -35ºC, and the ground is covered by a blanket of snow for about eight months of the year. The brief, intensive summer often arrives with startling speed, bringing both sunshine and warmth. HISTORICAL BACKGROUND Mining operations took place in Svappavaara as far back as 300 years ago. During the period 1655-1684, copper ore was taken from the deposit called Gruvberget in the vicinity of the village. The total production of raw copper was probably about 1,045 tons. During the 18th and 19th centuries, several attempts were made to extract iron ore from the numerous deposits found within the district. These brave attempts, however, were foiled by the high phosphorus contents and the enormous transport difficulties. The present-day mine fields in Leveäniemi were discovered in 1897. At that time, it was difficult to determine the size and value of the deposit because of the thickness of the soil cover (3 to 15 m) and the

Jan 1, 1969

DURING the past year the Committee on Coal and Coke has been collecting data concerning various points in the bituminous industry about which a large amount of misinformation circulates through the press and, in some cases, through the coal trade papers. The data presented have been compiled by various members, from the most authentic sources available, and where possible cover the period 1913-1924. They will enable comparisons to be made within the industry, and of this and other industries, and will explain some of the differences between conditions existing now and in the prewar period. CAPACITY AND OVER-DEVELOPMENT The capacity of bituminous mines is frequently stated at figures ranging between 800,000,000 to 1,400,000,000 tons per year. Table 1 shows statistics for the industry, mainly from U. S. Geological Survey sources but partly from U. S. Coal Commission reports. Column 3 gives the mine capacity with equipment and labor as of given date, as estimated from the data published by the U. S. Geological Survey. This is calculated for each State by obtaining the total man days worked as. reported by the operators (multiplying average men employed by total days worked at each mine) and dividing this figure into the total production, getting the production per man day; this figure times number of men employed times 308 (a theoretical full working year) equals estimated- full-time capacity. Two major objections are made to this method-one that the total number of men employed is used, instead of the number actually working, and the other that the number of days used only deducts Sundays and five holidays. The first objection is answered by the fact that the same number of men is used in estimating capacity as is used in actual production, and while this number is always from 12 to 20 per cent. more than are actually working, this condition exists at all times, although it is worse at times of maximum output. Few coal men will agree with the conclusion that the use of 308 days is correct, as it is practically impossible to keep any mine working full time at the same

Jan 2, 1926

By R. G. Webber, F. C. Langenberg

During the course of some magnetic investigations which the authors have under way, six bars of 0.43-carbon steel were tested, a permeameter designed after the Hopkinson yoke type being used. The results obtained were of some interest and although far from complete serve at least to show the necessity for a careful investigation of the previous history of the samples under study as well as the chemical composition. A steel of given chemical composition may assume a great variety of structures, depending on its treatment. Professor Sauveur has devised a very clear and effective means of illustrating this point. The accompanying microphotographs show some of the possible structures assumed by a 0.30 carbon steel (Fig. 1). It is now a well-established fact that a structural change is accompanied by changes in the tensile strength, elastic limit, hardness, etc., and it seems reasonable to assume also, a change in the magnetic properties. Six bars of a 0.43-carbon steel were used, all the bars being taken from the same rod and treated as follows: Bar 1. Heated to 1,100° and cooled in the furnace. Bar 2. Heated to 1,000° and cooled in the furnace. Bar 3. Heated to 900° and cooled in the furnace. Bar 4. Heated to 1,000° and cooled in air. Bar 5. Heated to 900° and cooled in air. Bar 6. Untreated. The bars were then turned to 13 mm. diameter and tested by the Hopkinson yoke method. After testing, three specimens were taken from each bar, one from each end and one from the middle. The homogeneity of the bars was tested in this manner and in no instance could any difference in structure in the three specimens1 be detected. Bars 1 to 3 inclusive are pearlitic in structure. The white areas are ferrite (iron with certain impurities in solution) and the dark areas pearl-

Jan 1, 1915

By Arthur H. Wilson

INTRODUCTION The stratified deposits of the coal measures are strongly laminated and exhibit a high degree of anisotropy. The stronger rocks in the sequence possess joints and shear planes, the coal itself has a closely spaced cleat pattern, and the softer rocks are capable of flowage. To calculate the general distribution of stress in such a medium by analytical means based on the theories of elasticity is difficult, and has not yet been satisfactorily achieved. Nevertheless, some estimate is required to aid the design of supporting pillars and permit the correct siting of main roadways. This is important when laying out districts for longwall extraction, particularly if the results of previous experience are not available in the area to be exploited. Although elastic stress analyses, including finite element analysis, may not be very appropriate, the basic equilibrium conditions will apply. These, combined with logical deductions based on observed fact, can be used to give appropriate solutions which experience has shown to be capable of giving acceptable results in the design of pillars associated with longwall workings. Constancy of cover load is one of the fundamental equilibrium conditions. When mining below ground, the cover is not removed, therefore the average vertical load after mining must equal the initial cover load. If mining produces a local decrease in load in any particular area, it must be balanced by an equivalent increase in load nearby. Bending moments in the strata above are capable of compensating for the turning moments which this redistribution of load may produce, and the existence of a "rear abutment", much discussed between 1950 and 1960, is not an essential equilibrium requirement. If the distribution of vertical stress is plotted three-dimensionally, then the load on any small element of area 6S will be o.6S, where o is the average stress. This also represents the volume of the "stress envelope" which lies above 6s. By making the individual areas very small and summing together, it is possible to show that the total load on any particular area can be found by calculating the volume of the stress distribution envelope which lies above it. A similar consideration applies to the stress distribution in a two-dimensional situation. If the stress distribution curve is drawn, then the area below any portion will represent the load per unit depth of section. For example, Figure 1 represents the possible stress distribution across a caved waste and associated ribside. If AW is the load deficiency [ ] These loads must balance, therefore area AW = AS, and if one can be deduced, the other will then be known. Attempts have been made to measure stress distributions in the ribside and in the waste. Stress meters in soft rocks such as the coal measures have not proved very effective. Those based on the measurement of strain have experienced difficulty in strata capable of flowage, high modulus stress meters suffer from cross sensitivity, and overcoming to obtain absolute stress is almost impossible. Load measuring instruments left in the waste have also proved largely ineffective, mainly as a result of the difficulties of protecting the leads in a caving environment. Certain logical deductions, however, can be made about the conditions in the waste. CONDITIONS IN THE WASTE Over the area of the waste the surface trough which develops is remarkably consistent, despite the geological variations which occur from coalfield to coalfield. In Britain, an accuracy of 210% is claimed for subsidence prediction based on width of extraction and depth of cover (National Coal Board, 1975). The subsidence in the USA is more variable (Adamek and Jeran, 1981), particularly with respect to the point of inflexion, but the same general pattern occurs. At the shallower depths the somewhat harder roof strata involved in the caving in the USA may suffer less compaction, giving reduced values of subsidence. Subsidence at intermediate horizons below the surface

Jan 1, 1982

By William Victor Vietti

A METHOD of determining the average density of the fluid column in a flowing oil well is presented. Actual field data from several wells are used to illustrate the application of the method in the Yates Field, Pecos County, Texas. The depth of the wells in the Yates Field varies from 900 to 1700 ft. depending on surface elevation and the location of the wells on structure. Production rates over 8000 bbl. hourly have been determined and many

Jan 1, 1930

By Martin Mayers

IT has long been recognized that it would be highly desirable to be able to predict the temperatures at various points in a burning fuel bed and their variations with changes of the properties of the fuel and the rate of air supply. Experimental investigations of fuel-bed tempera-tures1-4 have not been lacking, but the absence of any theoretical back-ground has made it impossible to use the results of these tests as a basis for prediction, except in a very general way. A mathematical analysis5, based on a somewhat simplified theory of the distribution of heat in a, fuel bed, has recently been completed by the author. Even though numerical values of some of the coefficients are not. known, the calcula-tions result in some conclusions of general significance. Thus, for example, it appears that when the temperatures throughout the fuel bed can be calculated, the rate at which ignition of the fuel by underfeed action can be maintained can also be calculated. The uncertainty concerning the values of the coefficients referred to above is a serious limitation on the use of that method. The following paper presents a discussion of these coefficients and includes estimates of their values based on the data now available. A brief description of the theory on which the analysis is based, and some results of the calculations showing their degree of agreement with experimental results, are presented by way of introduction to the discussion of, the coefficients. For a more extended discussion of the theory, see the A.S.M.E. paper5.

Jan 1, 1937

By James E. Reynolds, Duane N. Goens, Charles W. Kenney

A process for recovery of lead and silver from high-grade lead sulfide concentrates by dry chlorination and fused salt electrolysis was developed by Hazen Research, Inc., for Cyprus Metallurgical Processes Corporation (Cymet). A pilot plant was designed to handle mixed sulfide concentrates and to produce high purity lead in a 2,000- ampere capacity fused salt cell. Design of the dry chlorinator and fused salt cell is discussed. Integration of modern chlorine caustic cells for reagent generation was evaluated in the pilot plant program. Also included in the paper will be process chemistry; pilot plant flowsheet, equipment and data: by-product and impurity removal: and scaleup and economic considerations for the process.

Jan 1, 1977

By R. T. Mishler

I WISH to express my keen appreciation of the article on the above subject by Coe and Clevenger.1 It has been doubly interesting to me, for the reason that the experience recorded and the principles evolved practically parallel the results of similar investigations made by myself and others at The Lucky Tiger Mine, El Tigre, Sonora, Mex. An outline of the work at El Tigre may aid in confirming the principles expressed by Coe and Clevenger. El Tigre has the unenviable distinction of possessing a slime with a much lower settling rate than any recorded in the article discussed. Under most favorable conditions the settling rate is about one-third that reported for the Liberty Bell mill, and one-tenth that reported for the Nipissing, Golden Cycle, and Presidio mills. This slow settling characteristic of Tigre ore has necessitated careful investigation of settling phenomena throughout the various evolutions of the plant. PREVIOUS SETTLING INVESTIGATION AT TIGRE During construction work at the mill, the Metallurgical Engineer in charge, D. L. H. Forbes, ran a series of experiments on settling. His tests proved that deep settling tanks were not ordinarily necessary. The use of tanks 2 or 3 ft. in depth was suggested.2 Later experiments demonstrated that the following principles of settling applied to Tigre pulp.3 1. In settling dilute pulp, settling rates are independent of pulp depth. 2. In settling thick pulp, settling rates are approximately proportional to pulp depth.4

Jan 3, 1917

By G. C. Gould

The nature of freckle segregation is determined by chemical analyses, microradiograplzy, and electron microprobe. In addition, the influence of chemistry variation on freckle formation is studied in laboratory experiments. It is demonstrated that controlled laboratory solidification can produce freckle segregation. "FRECKLE" segregation is a discontinuous, rod-like segregation observed in vacuum consumable -electrode ingots. Figs. 1 and 2 show this segregation as pencil-like, dark etching areas of segregation found in longitudinally and transversely sectioned consumable-electrode ingots. In most cases the segregation is perpendicular with respect to gravity and parallel to the longitudinal axis of the ingot. The segregation is most often encountered at or around midradius in large vacuum consumable-electrode ingots. The austenitic alloys, A-286* and 718, † have shown particular susceptibility to this mode of segregation. The origin of these rodlike pockets of segregation is not well-understood. It has been suggested that the segregation is a result of a portion of the electrode dropping off and passing through the arc un-melted. On the other hand, smeltzer1 has demonstrated the freckle segregation in A-286 to be comprised of low-melting constituents relative to the matrix melting point. The discontinuous nature of the segregation is the most perplexing facet of the freckle-segregation problem. It was to gain some insight into this part of the problem that this work was undertaken. I) PROCEDURE At the outset of the work identification of the phases present and the elements concentrated in the freckle areas was undertaken. The electron micro-probe was used to determine general enrichment as well as -specific phase chemistry. Microradiography using cobalt and chromium radiation was also used on the freckle areas again to determine the elements involved in the segregation. X-ray diffraction patterns were made from portions of these same foil specimens. Optical microscopy and Knoop hardness measurements were also used

Jan 1, 1965

By Richard D. Hagni

Mississippi Valley-type ore deposits contain significant quantities of minor elements, which are present partly in the form of separate mineral phases and partly in solid solution in the major sulfide phases for which these deposits are exploited. These elements, as separate phases, are: copper, mainly in chalcopyrite and enargite; cobalt and nickel, chiefly in thiospinels and bravoite; rare earth elements associated with certain fluorites; and native gold. Many economically important minor elements occur in solid solution in sphalerite, including silver, cadmium, iron, germanium, gallium, indium, thallium, cobalt, nickel, and mercury. Significant amounts of silver and antimony, and perhaps very small amounts of gold, are present in solid solution in galena. Chalcopyrite may contain small amounts of silver, molybdenum, bismuth, cadmium, cobalt, and nickel. Marcasite and pyrite may contain silver, thallium, cobalt, and nickel. Although some of the minor elements contained in the Mississippi Valley-type deposits are currently recovered at the smelters and refineries, many are lost in tailings, sludges, and slags; consequently, important quantities of these elements are potentially recoverable as non-conventional resources.

Jan 1, 1983

By Charles M. Rolker

THIS remarkable and well-known district lies about 320 miles south of Salt Lake City, in Washington County, near the Arizona border of the territory. It is now reached by the Utah Southern Railroad and its extension, and the last 100 miles are run by stages. These vehicles are called "jerkies" in the West, which name conveys a good idea of the comfort they afford, and the relief experienced when you alight. Arriving at Silver Reef, the main amp of the district, one sees at once that he stands where once a surging sen had its domain, marked now by heavy sandstone deposits of a red and white color. The town itself, a neat, clean, and orderly mining town, is encircled on the north by trachyte and granite mountains, skirting to the west. They are cut through in places by deep gorges, left US as the only brace of the force of former currents, which drained the adjoining territory to the north; and which when swelled and infuriated by tempests and cloud-bursts, took in their grasp the huge blocks of

Jan 1, 1881

By M. P. Tixier, M. Gondouin, G. L. Simard

In the quantitative interpretation of the SP logs, the electrochemical component is generally taken equal to — K log Rm /Rw where K has the theoretical value corresponding to solutions of pure sodium chloride. This method may be misleading when relatively large quantities of salts other than NaCl are present in form-rrtion waters—as is generally the case for low salinities —or in gyp-base muds. In such cases recourse is made in the field to changing the K value or to adding a correction term to the equation on the basis of local experience. An investigation has been made in the laboratory of the influence of HCO3, SO4=, Ca++, and Mg++ on the amplitude of the SP deflection, which included in par-ricular determinations of the activity coefficients of Ca++ and Mg++. The theory, the experimental techniques and a tentative method for applying the results are described. So far, applications to actual field cases where chemical analyses of waters were available have provided an excellent confirmation of the proposed method. The case of the SP in very salty brines is also considered and it is shown that the use of activity data for sodium gives satisfactory results. HISTORICAL In early times of electrical logging, the SP curve was used exclusively as a tool for the location of permeable beds and the definition of their boundaries. Later, with the introduction of methods of quantitative analysis, attention was called to the possibility of deriving from the SP log some information on the formation water resistivity, which constitutes one essential element for the computation of water saturation from log data. The first laboratory experiments' in 1932 had shown that, as a result of electrochemical phenomena arising at the contact of the niud and the formation, the amplitude of the deflection of the SP curve was, at least partly, a function of the salt concentration of interstitial water and accordingly of its resistivity. It was indicated that the amplitude of the electrochemical component of the SP should be equal to K log R1/R2, R1 and R2 being the resistivities of the mud and of the formation water respectively. However, the exact value of the K coefficient was not determined at that time because the surface clay used for a laboratory model was far from an ideal shale membrane. Consequently, the way was not yet open towards quantitative interpretation. In the early forties, Tixier reported2, on the basis of field log observations, the following equation for the case of NaCl solutions, SP = -71 log f1c1/f2c2, c1 and c2 being the concentrations and f1, f2 the mean activity coefficients. The local variations observed in the empirical values of K, chiefly in the Rocky Mountains, led him to advance the opinion that, besides the relative amounts, the nature of the salts present in the solutions had a bearing on the magnitude of the SP. At about the same time Mounce and Rust- ad published laboratory results which emphasized the part played by the shale in the generation of the SP. On the basis of laboratory tests and theoretical considerations, Wyllie in 1948' published the following equation of the electrochemical SP for the case of NaCl solutions, SP= - 71 log (a1)m/(a2)m

Jan 1, 1958

By E. C. Carris

THE loading of bituminous coal mechan¬ically was recognized about the year 1900, but during the following 28 years less than 5 per cent of the bituminous pro¬duction in the United States was loaded by mechanical means. During the past i6 years, however, the usage of some form of mechanical loader has had a very rapid and accelerated growth, until at present production of bituminous coal by mechanical means has reached an all¬time high of approximately 46 per cent, and is still increasing. This rapid growth in the use of the mechanical loader has been supplemented by an increase in mechanical cleaning. The importance of mechanical cleaning of coal was recognized many years before the mechanical loader was introduced, because of the impossibility of cleaning manually the sizes below 2 in., and the increasing competition from other fuels. Utilization of mechanical loaders without mechanical cleaning on the surface for at least one or more sizes is the exception, rather than the rule. One exception is a mine that employs caterpillar-mounted mobile loaders exclusively, and mines the entire seam without any selectivity, and yet loads and ships six grades of coal of the very highest quality without mechanical cleaning. Such a fortunate situation can exist only where mining conditions are ideal, where top and bottom are exceptional and there are no impurity partings, and where there is loader height. The conversion from hand loading to mechanical loading has definitely intro¬duced many problems in the preparation plant of yesterday and in the modern streamline plant as well. Many of these problems have been solved by good, sound, conscientious initiative on the part of the plant personnel, with minor expendi¬tures; the solution taking the pattern of rearranging and improving the equipment at hand. Other problems have caused, and are causing, considerable concern and difficulty. LARGE IMPURITIES The removal of large quantities of large impurities from the lump coal, and their handling and disposal, is definitely a troublesome and costly problem. The cost of manually removing the impurities from the picking table alone, based on the actual recovered lump coal, can reach a cost of 42 cents per ton or more. In the design of future plants it would be wise to give this phase of preparation considerably more time and thought, particularly if the seam of coal contains one or more heavy partings and the mining procedure is all seam. This same caution applies to seams that may not contain heavy partings but have poor and heavy draw-slate top, which falls with the coal during the mining cycle. One of the more recent of the modern preparation plants has answered this problem by installing a rock crusher under the picking table in such a manner that the impurities can be diverted by gravity directly to the crusher. This reduces the

Jan 1, 1946

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 fen 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 clearly 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 closer 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 presscre 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