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By H. R. Hanley

IT is a well-known fact that the solubility of zinc compounds decreases when these compounds are roasted in contact with iron compounds, but descriptions of tests to quantitatively express the fact have not appeared in the literature. Possibly such an expression cannot be uniformly and exactly duplicated by different operators because of the variation in the personal equation. In a general way, however, the reactions between zinc compounds and iron compounds under roasting conditions will show a certain trend with changing conditions and the approximate quantitative expression of this trend appears reasonably well established by experimental work conducted for this purpose. Ferrites and Marmatites The name "ferrite" has been given to the compound of zinc and iron which has the formula Zn0.Fe203. Among the questions pertinent to this subject are those involving inherent or natural ferrite, and also the synthetic or artificial variety. The inherent or natural product is formed when the mineral containing iron and zinc sulfides isomorphously crystallized is subjected to oxidation at roasting temperature. These isomorphously crystallized minerals are known, mineralogically, as marmatites, and contain ZnS and FeS in ratios of 2 to 1 up to 5 to 1 respectively. The zinc and iron sulfides form a definite mineral. They are firmly attached to each other and form common contact planes through which diffusion of the entities occurs during the roasting process. This diffusion of the molecularly intimate entities produces, during roasting, the compound referred to as ferrite, in proportion to the amount of iron originally present in the marmatite. For example, a marmatite from British Columbia containing 9.739 per cent. Fe and 56.87 per cent. Zn corresponds with the mineral having the formula 5ZnS.FeS. The ferrite produced in roasting, which has the formula ZnO.Fe203, contains 27.07 per cent. Zn and 46.40

Jan 1, 1929

By Thomas Adair

Moderator-Thomas Adair is now a tunnel consultant with Perini Corp., Spring Lake, N.J. He has had 40 years experience in tunnel and shaft-sinking work in both soft and hard rock, as well as subaqueous rock. He has used moles in various locations and has traveled around the world studying the problems. SOME BRIEF COMMENTS ON "MOLES" by Thomas Adair We of the Perini Corp. have been, over the past 15 years, in the forefront of the battle to develop the mechanized miner. We have contributed much to pioneer, develop, and promote the use of the mining machine. Our money and talent have not been spared in this effort. However, we are sorry to say that as of the present time (1968), at least from the economic stand- point, this effort has not been very rewarding. But, I must say to those who are presently involved in the work of building mining machines, do not be discouraged. There is money in it. We of Perini Corp. know because we put it in there. It has been estimated that during the next 15 years, some $20 billion will be spent on underground excavation; more than 13 thousand miles of sub- surface tunnels will be excavated throughout the nation. An aggressive, properly structured research and development effort would produce, within the next five or ten years, a better excavation technology and improved boring system capable of reducing present costs drastically, with a resultant great saving. The time for this effort is now, but where the enabling money for this effort will come from, I have no idea. Machine builders should be encouraged to design and develop a shield- type boring machine capable of continuous mining through varying types of ground or rock by incorporating the possibility of making minor modifications such as change of bit type, power package, etc. Such a machine could

Jan 1, 1970

By C. O. Lee, Z. W. Bartlett, R. H. Feierabend

The Grand Isle sulfur mine is located in the Gulf of Mexico, approximately seven miles off the coast of Grand Isle, Jefferson Parish, La. The deposit is on acreage covered by oil, gas, and mineral leases originally issued in favor of Humble Oil & Refining Co. by the State of Louisiana which were continued, maintained, and redesignated by the U.S. Department of the Interior after passage of the Outer continental Shelf Lands Act. The sulfur deposit was discovered in 1949 when Humble Oil & Refining Co. penetrated more than 200 ft of sulfur-bearing limestone in a zone between 1813 and 2075 ft below sea level. In 1954, Humble drilled ten more sulfur prospect holes, eight of which encountered sulfur ore.

Jan 6, 1960

By Avnulf Muan, P. V. Riboud

The effect of Cr2O3 on melting relations of iron oxide at oxygen pressures slightly above those prevailing in contact with metallic iron has been determined. Liquidus and solidus temperatures of wüstite are raised by the addition of Cr2O3, from 1385°C for pure iron oxide to 1420°C at the peri-ledie point where wüstite, iron chromite, liquid, and gas coexist in equilibrium under the atmospheric conditions used in the present investigation (CO2/H2 = 1). It has been shown in a previous investigation1 that the liquidus and solidus temperatures of iron oxide are drastically increased by the addition of Cr2O3 under the relatively oxidizing conditions prevailing in air. This is to be expected in view of the easy substitution of cr3+ for Fe3+ in crystalline oxide structures which are stable at high oxygen pressures, as demonstrated for instance by the completeness of the solid solution series Fe2O3-Cr2O3 at high temperatures (>1000°C). The stable phase of iron oxide at oxygen pressures approximating those prevailing when metallic iron is present is wüstite. This phase, although commonly represented by the simplified formula FeO for sake of convenience, in reality has a defect structure in which a part of the iron ions are present as Fe3+. It is to be expected that at least a limited amount of cr3 ions will substitute for Fe in this structure when Cr2O3 is added to wüstite. Depending on the ease of this substitution in comparison with that of cr3 substitution for Fe in iron oxide-Cr2O3 liquids under the same atmos- pheric conditions, the liquidus and solidus temperatures of wüstite may increase or decrease upon addition of Cr2O3. The methods of establishing these melting relations and the results obtained are presented in the following. I) EXPERIMENTAL METHOD 1) General Procedure. The quenching technique was used in this study. Oxide mixtures were heated at chosen constant temperatures in an atmosphere consisting of equal parts of CO2 and H2 until equilibrium was established among gas and condensed phases. The samples were then quenched in mercury to room temperature, and the phases present were determined by microscopic and X-ray investigation. 2) Preparation of the Mixtures. Starting mixtures were prepared by weighing and thoroughly mixing Fe2O3 and Cr2O3, or wüstite and Cr2O3. The Fe2O3 and Cr2O3 used were "Baker Analyzed" reagent grades, whereas wüstite of composition was synthesized by reducing Fe203 at 1325°C in an atmosphere consisting of equal parts of CG andHz. In order to avoid contact with crucibles, the equilibration runs were made with small pellets suspended from thin (-0.004-in.) platinum wires. Mixtures made from FOs and Cr203 were readily pelletized at a pressure of 500 atm in a 9.5-mm die, whereas mixtures made from wüstite and Cr203 when treated identically were too weak for handling. In order to obtain a stronger product, these pellets were sintered by heating for 2 min at -1200°C in the same atmosphere as was subsequently used for the equilibration runs (CG/H2 = 1:1). During the sintering, these pellets were wrapped in thin (0.0004-in.) platinum foil, which was stripped off before the equilibration runs. In order to reduce the time needed for equilibrium to be attained, preliminary equilibration of relatively large pellets of each mixture was carried out at -1200°C for 4 to 12 hr. Smaller pellets

Jan 1, 1964

Plans have been completed with only details to be arranged for the first Metals Branch Conference in the Northwest. The two day meeting will be held jointly with the Industrial Minerals Div. on Friday and Saturday, May 9 and 10, 1952, at the Davenport Hotel in Spokane, Wash. For, some time the metals activities in this area have been neglected. Expansion of metal producing and fabricating industries in Washington and neighboring states has brought sufficient interest to insure the success of such a meeting. A committee has been hard at work for several months. Nonferrous extractive metallurgy men will find an extensive program in the April issue of JOURNAL OF METALS. Sessions for iron and steel producers, physical metallurgists, and educators will make the Metals Branch picture complete. Metals Branch members residing in Washington, British Columbia, Oregon, Idaho, Montana, Wyoming, Nevada, and Utah, or who can be in the Northwest at this time should make plans now to attend. A Metals Branch luncheon is planned for Friday and a dinner jointly with the Industrial Minerals Div. is planned for Saturday according to F. R. Morral, metallurgist with the metallurgical research div. of Kaiser Aluminum & Chemical Corp., P. O. Box 1451, Spokane, Wash.

Jan 1, 1952

By I. R. Kramer, L. J. Demer

Aluminum single crystals were pulled in an electrolytic cell allowing surface removal during the deformation. The extent of Stages I and 11 of the stress-st-aitz curve was increased and the slope decreased as the rate of metal removed from the surface was increased. An increase of the strain rate caused a decrease in the effectiveness of the metal removal. The data indicate that the work-hardening coefficient in Stage I is determined primarily by the conditions which exist on the surface of the crystal. In Stages 11 and 111, both surface effects and internal barriers are important. ALTHOUGH numerous investigations have been conducted on the plastic flow characteristics of metals in an attempt to explain the mechanism of work-hardening, relatively few studies have taken into account the influence of the surface. In all current theories of work-hardening it is assumed that the impediments to the movement of dislocations are within the crystal. The barriers due to the surface and the existence of solid and liquid films have been neglected even though it has been demonstrated that the surface exerts a large effect. A number of investigators1-l8 have shown that solid films on the surface of single crystals markedly affect their mechanical behavior. In general, the presence of a solid film tends to increase the yield stress and increase the work-hardening rate. Often, on single crystals, Stage I and, at times, Stage II regions are completely suppressed. Various mechanisms have been offered for the effects of oxide and metal films as well as the influence of electrolytes. Of these, concepts concerned with the locking of surface dislocation sources and the blocking of dislocations at the surface resulting in pileups appear to be actively considered at present. Barrett,11 Takamura,6 Gilman,19 Lipsett and King,20 Shapiro and Read,10 and Weiner and Gensamer21 are among those who have interpreted their results in terms of piled-up dislocations at the surface, while Adams.22 and Chalmers and Davis23 have explained their experimental observations in terms of locking of surface dislocation sources. In general, the change in plastic flow properties due to electrolytes has been explained in terms of the unblocking or unlocking of dislocations by the removal of the oxide films. In considering the two proposed mechanisms, it appears that the locking of sources of surface dislocations by a solid film should exert a primary influence only on the critical resolved shear stress for flow and not on the slopes of Stages I and 11. However, the blocking at the surface of dislocations from internal sources may also affect the critical resolved stress and furthermore exert an influence throughout the whole plastic range. In certain cases it does not seem feasible to explain the results of experimental observations in terms of locking of surface dislocation sources. The abnormal aftereffects found by Barrettll,12 by removing the oxide by an acid treatment are excellent evidence of the blocking of dislocations at the surface. Additional evidence in favor of a blocking due to a pileup of dislocations at the surface may be found from the observations that the critical resolved shear strength continues to increase with the thickness of the oxide layer until very heavy oxide layers are formed. If the locking of surface dislocations sources were the dominant factor, the critical resolved shear stress would not be expected to increase after all of the surface sources were locked by the formation of the oxide. This may be expected to happen after a few atomic layers of the oxide are formed. In spite of the above evidence on the strong influence of the surface on the plastic flow characteristic, this has been ignored in current theories of work-hardening. Seeger24,25 suggested that most of the dislocations may slip out of the crystal only when the specimen axis is within certain areas of the orientation triangle. In other areas the resolved shear stress in other glide systems is large enough to generate dislocations which can form Lomer-Cottrell locks, thereby decreasing the average slip distance in some directions and causing a larger hardening rate. Friede126 assumed that at the beginning of Stage 11, a large number of Lomer-Cottrell dislocations are formed by a catastrophic process which used up all the Frank-Read sources on the secondary slip-planes. In this manner a fixed number of Lomer-Cottrell locks is formed which act as barriers against which the dislocations can pile up. In Stage 111, Seeger24 and Diehl, Mader, and Seeger25 proposed that Lomer-Cottrell barriers are circumvented by the cross slip of extended screw dislocations. Cottrell and Stokes,27 Friedel,26 Cottrell,26 and stroh29 suggest that the Lomer-Cottrell dislocations collapse under the stress field of the dislocation pileup. It is the purpose of this paper to report the changes in Stages I, II,and III of the deformation process in

Jan 1, 1962

By W. R. Shimer

(New York Meeting, October, 1913.) THE investigation herein described was carried out for the purpose of studying, both by chemical and metal-lographical means, the extent of over-oxidation of steel that can be accomplished by excessive over-blowing in a Bessemer converter. In addition there are appended some results of basic. open hearth and crucible steels. Remarks on Chemical Methods. The test block used was hemispherical in shape, 4.5 in, in diameter and 2 in. thick. Drillings for analysis were obtained by drilling through the entire solid part of the. block, carefully avoiding all cracks anti blow-holes and mixing these drillings thoroughly. Drillings were carefully examined for scale and the finest were gone over with a microscope to be sure all scale from whatever source had been. removed. Oxygen was determined by the well-known method of Ledebur, modified according to Cushman,1 with, however, the removal of the preheating tube, which was found unnecessary. This method has been found to give concordant results. Blanks run from 0.0003 to 0.0006 g. Duplicate determinations varied not more than 0.001 to 0.003 per cent. It seems to be generally supposed that the hydrogen method gives only that oxygen which is combined with iron. Whether this be true or not, the content of oxygen existing as iron oxide no doubt predominates sufficiently, so that the result obtained is sufficient to indicate whether the steel is over-oxidized or not.

Jan 9, 1913

By William L. Fink, Dana W. Smith

In parts I1 and II2 of this series, there were presented results of investigations on the age-hardening of an aluminum-copper and an aluminum-magnesium alloy. It was shown that the simple precipitation theory of hardening3 adequately explained the aging phenomena, including certain so-called "anomalous" behaviors which had caused other investigators to reject or modify the precipitation theory. However, these papers did not discuss the double aging peaks, which have been stressed in recent articles by Dr. M. Cohen4 and Dr. M. L. V. Gayler.6 The present paper is devoted to an explanation of this "anomaly." Fig. 1 is a generalized schematic representation of aging curves at different temperatures. Curve A corresponds to the aging at the lowest temperature, and D at the highest temperature. Certain previous investigators have explained curve A and the initial peaks

Jan 1, 1938

By William L. Fink, Dana W. Smith

In parts I1 and II2 of this series, there were presented results of investigations on the age-hardening of an aluminum-copper and an aluminum-magnesium alloy. It was shown that the simple precipitation theory of hardening3 adequately explained the aging phenomena, including certain so-called "anomalous" behaviors which had caused other investigators to reject or modify the precipitation theory. However, these papers did not discuss the double aging peaks, which have been stressed in recent articles by Dr. M. Cohen4 and Dr. M. L. V. Gayler.6 The present paper is devoted to an explanation of this "anomaly." Fig. 1 is a generalized schematic representation of aging curves at different temperatures. Curve A corresponds to the aging at the lowest temperature, and D at the highest temperature. Certain previous investigators have explained curve A and the initial peaks

Jan 1, 1938

By Evangelo Agelopas

Steelmaking operators are familiar with the costs involved when ingot molds must be scrapped prematurely because of the failure of a stripping or turning lug. Some mold sizes can be expected to produce one hundred or more ingots per mold before normal wear causes the mold to become unserviceable. Therefore, the failure of lugs at less than the average life for that mold size represents a sharp increase in terms of mold cost per ingot ton produced. To combat these wasteful and costly occurrences, it was determined that an efficient method of replacing lugs should be developed to extend the life of molds which are otherwise in good condition. The purpose of this paper is to describe a lug welding method which has proved effective and economical. This method is known as the Oxygen and Mapp Process.

Jan 1, 1972

By L. Moussoulos

Pyrite concentrates produced at the Olympias mines, Northern Greece, show an unusually high gold and silver content (16-20 and 25-40 ppm respectively), associated with the presence of arsenopyrite; their high As content (5-8%) has hindered their utilization so far. In the present paper a simple and environmentally safe method that permits their complete utilization for the production of SO2 gas, As203, and the recovery of Au and Ag is described. According to this method, the pyrites are subjected to a single-stage oxidizing roasting in a fluid bed reactor. The precious metals, and approximately 45% of the contained As, remain with the cinders, while the rest of the As is removed with the SO2 - bearing gases and can be recovered by suitable treatment. The gases, after further cleaning, can be utilized for the production of sulfuric acid.

Jan 1, 1984

By Frank S. Shuri

INTRODUCTION The Calumet Pumping Station, located on the south side of the Greater Chicago area, is part of the Tunnel and Reservoir Plan to accomodate the city's wastewater. The Station consists of two parallel rock caverns, each 18 m high, 20 m wide, and 62 m long, located in Silurian dolomite approximately 91 m below the ground surface. The caverns are oriented N-S with a 24-m-wide pillar between them. Prior to construction, rock mechanics studies were conducted in an L-shaped test adit at the location of the west cavern. The purpo3e of the rock mechanic studies was to characterize the site, particularly the in situ stress field and deformation characteristics of the rock. This information, together with other physical properties of the rock and geologic data, was used to evaluate the stability of the preliminary cavern design, with particular emphasis on cavern orientation, rock reinforcement, and pillar stability. GEOLOGY OF THE SITE Stratigraphy The Chicago area is located on the Kankakee Arch, a broad, gently sloping arch of Paleozoic sediments. Rocks in the project area consist of Silurian dolomites unconformably overlain by Pleistocene glacial deposits. The formations of interest to this study are: - Racine Formation, inter-reef facies. This dolomite is gray- brown, silty, and compact. It contains occasional prominent bedding surfaces. The Racine Formation in the project area varies from 73 to 74 m in thickness.

Jan 1, 1984

By Reno H. Sales

EVERY mine manager, mine geologist, and every prospector in the field who appraises the future of mining properties does so on the basis of a theory of ore deposition whether he recognizes this fact or not. Wherever the ultimate value of a mine or prospect is dependent upon undeveloped ore, any estimate by an engineer or geologist necessarily involves a theory of origin of the deposit. In view of these facts the importance of a thorough understanding of the genesis of ore deposits cannot be overestimated. It well may be that the greatness of our country will depend upon finding reserves of natural resources as yet undiscovered. The genesis of ore deposits offers a fascinating field for study and investigation. This is attested by the large number of geologists who have written at length on the subject. For progress made toward a better understanding of ore genesis we owe much to Kemp, Lindgren, Ransome, Vogt, Emmons, Spurr, Graton, and a host of others. Within my own experience, I have attempted to apply in practice the various concepts and theories that have been advanced by these men.

Jan 5, 1954

L. E. WEMPLE, St. Louis, Mo. (written discussion *).-Mr. Stone refers to cadmium as one of the worst impurities in ores used for the production of zinc oxide for pigment purposes, because it is very volatile and its dark brown oxide and bright yellow sulphide both have strong coloring powers so that small fractions of 1 percent. injure the whiteness of the oxide. Numerous tests have recently been made by the American Zinc, Lead and Smelting Co. to determine what effect the percentage of cadmium, as ordinarily present in zinc ores, has upon the color of oxide made from such ores by the usual grate-furnace process. It has been found that while the cadmium is readily volatile and may be detected in the oxide product by chemical analysis, the oxide product is not discolored, but is of a clear white color. Analysis of the 12 leading brands of zinc oxide, French process, lead-free, and leaded grades now on the market for pigment purposes, show them to contain from 0.02 to 0.35 per cent. cadmium, figured as metal. If these proportions of cadmium were present as oxide or sulphide, the percentages would run from approximately 0.022 to 0.40 per cent. in the first case and 0.025 to 0.45 per cent in the latter case. All these grades of oxide are widely used for pigment purposes and are of a clear white color, except the leaded grades, the whiteness of which may be diminished by the lead sulphate. Tests made with admixtures of as low as 0.02 per cent. of cadmium oxide or sulphide to zinc oxide of the greatest hiding power (lead-free

Jan 1, 1918

By C. B. E. Douglas

In an interesting article on evaluation of the water problem at Eureka, Nev., W. T. Stuart describes how a difficult water problem, or one phase of it, may be evaluated by means of a small scale test. Test data are plotted by a method rendering, under certain conditions, a straight-line graph that can be projected to show how much the water table will be lowered by pumping at any specified rate for a given time. A formula is then used to determine the size of opening, or extent of workings, necessary to provide sufficient inflow to enable pumping to be maintained at that rate. At first glance this might seem the answer to a miner's prayer, but a word of caution is in order. It may not be the whole answer. Moreover, results obtained by the method described are reliable only for conditions approximating those assumed. Even where conditions do not meet this requirement, however, it may be possible to draw helpful inferences from the results, perhaps enough to facilitate another approach to evaluation of a problem.

Nov 1, 1955

By Donald L. Katz, Michael J. Rzasa

With greater effort being devoted to the discovery of new oil and gas reserves and a consequent increase in bottom hole pressures due to greater drilling depths, the phase relationships of hydrocarbon fluids at pressures above 10,000 lb psi are becoming increasingly important. The present paper discusses the results of research with a windowed cell on a methane-Kensol 16 system to pressures of 25,000 Ib psi and temperatures to 260°F. Kensol 16 is a commercial high narrow-boiling-range oil. It is shown that for the temperature range of 60 °F to 260 °F, this particular system exists in two phases to pressures of approximately 14,000 lb psi, and data are presented giving the relative amounts of liquid and vapor phase? coexisting under these conditions. Partial phase diagrams are shown for six different mixtures of methane and Kensol 16, three of which include the critical region. In contrast to mixtures composed of substances of fairly close volatility. critical opalescence was noted for as much as 200°F of the critical temperature. The critical locus of the methane-Kensol 16 system was estimated and the conventional pressure-composition and temperature-composition diagrams were prepared. From these, the equilibrium vaporization factors for methane and Kensol 16 were estimated for temperatures from 60 °F to 700 °F and to pressures above 12,000 lb psi. The relations of this study to petroleum production problems and other phase equilibria research are discussed. INTRODUCTION A knowledge of the physical behavior of naturally-occurring hydrocarbon mixtures is fundamental to a thorough treatment of nearly all operations involved in the recovery, refining, and transportation of petroleum. The operations may involve the applications of phase relationships, and the relative

Jan 1, 1950

By Harold Linke

THE following article presents notes and data compiled and computed by the writer for use in the determination of: size and slope of mill launders, details of junction boxes and downspouts, and distribution of pulp. It also includes pulp formulas, volume of discharge through bushings, paths of discharging streams, banking of turns and curves. In the design of a concentrating mill, the draftsman usually considers launders to the extent of providing ample "head" for transmission of pulp from one department of the mill to another. The superintendent of construction aims to build his launders wide and deep, and on a slope steep enough to ensure positive flow. So launders are laid generally on too steep a slope, with the result that the repair gang works to maintain launder bottoms and sides against the erosive action of the conveyed pulp. To this end many kinds of liners have been devised: concrete, mastic, white iron, glass, rubber. True, the reduction of slope to the point where a pulp will flow with minimum wear, will minimize labor and expense; but when the desired slope is not predetermined, the millman hesitates to readjust his launder slopes by cut-and-try methods. To the end that the desired size and slope may be found readily, the writer has: (1) conducted experiments with pulps of different specific gravity, screen analysis and dilution; (2) gathered a few graphic data from standard reference works (such as Peele's Mining Engineer's Hand-book and Taggart's Handbook of Ore Dressing); (3) computed several tables; and compiled results that have proved dependable for Utah Copper ore. It is quite possible that the following tables and graphs may not be applicable to all ores, but it is hoped that they may prove helpful, even in slight degree, in alleviating a portion of the trouble and migraine of some other millman.

Jan 1, 1939

By Giovanni B. Barla, Stefan H. Boshkov

The block caving method is examined in this paper on the basis of experimental results and observations in the field, and through the use of numerical modeling by the Finite Element Method. The Grace Mine, developed by a panel caving method, served as a reference case. However, the results obtained and the simulation techniques which have been developed may find useful application in more general conditions as encountered in other mining operations by block caving. Following a brief description of the Grace Mine and of the mining method, the problems associated with the behavior of underground drifts at the production levels, during undercutting and caving, are addressed. The most important results obtained through monitoring of strains and loads in the supports of a runway are discussed, while giving relevance to the sequence of mining operations in the immediate vicinity. The most important geomechanical data, as provided for subsequent modeling, are described with reference to: (a) rock mass characterization and (b) in situ state of stress. Then, the numerical modeling procedures, developed by the Finite Element Method in order to predict the caving phenomena and the behavior of underground openings during undercutting, are discussed. Finally, an attempt is made to compare the pre- dictions of the numerical analyses with, the measurements carried out at the instrumented site. Suggestions as to how to improve the results both qualitatively and quantitatively are also given.

Jan 1, 1984

By H. J. French

WITHIN the past few years, particularly because of the rapid growth of the airplane industry during the war, considerable attention has been paid to the manufacture of light-wall cold-drawn seamless and welded steel tubing for structural purposes. While the manufacture of such tubing is not, in itself, a difficult matter, some difficulties have. been encountered in producing the same under specifications requiring definite physical properties. It is the purpose of this paper to describe the methods of manufacture and the properties that may be obtained by such methods for tubing coming within about ½ to 2 in. (12.7 to 50.8 mm.) outside diameter and 10 to 22 Birmingham wire gage (0.134 to 0.028 in. wall thickness). Such tubing is largely used as structural material in the aircraft industry, and it is of the utmost importance that the physical and chemical properties should be known, and also that the various factors entering into the manufacture should be under such control as to allow these properties to be varied and held within definite limits. In general, tubing may be divided into four classes: namely, specialty tubing, such as riveted-sheet or plate, lock jointed, etc.; brazed tubing; welded tubing; and seamless tubing. Welded tubing may be divided into hot product, such as lap welded and butt, welded, and cold product, such as acetylene and electric welded. Seamless tubing may be hot rolled or cold drawn.

Jan 9, 1919

By Anthony Sharkey

Introduction In Europe, longwall mining accounts for over 95% of coal produced from deep mines, whereas in the U.S.A., longwall accounts for less than 5% of deep mine coal production. There are many reasons for the difference, but in general: a. U.S. mine operators have invested heavily in continuous mining or conventional equipment which continues to produce acceptable results; b. There 1s a reluctance to change from, a familiar (and proven) mining method to an unfamiliar one, despite promises of huge production increases,; c. Multi-seam mining in Europe has made longwall the only really viable mining method, whereas In the U.S.A. multi-seam mining (particularly in "below-drainage" mines), is relatively rare; d. Although some spectacular results have been achieved by longwall in the U.S.A.(I), the general performance of longwall in this country has not been good enough to generate much enthusiasm for its wide application; e. The much higher level of investment in face equipment required for longwall when compared to alternative methods (approximately $7.5 million for a medium seam longwall installation and $1 million to $1.5 million for a continuous miner section). However, declining productivity, national energy requirements and safety legislation are creating a situation in which longwall as a viable mining method is being examined more closely and in more places than hitherto. This paper, therefore, attempts to identify some of the principal criteria needing examination in any assessment of the feasibility of longwall application, the limitations of information for those criteria in the decision making process and the need for further research and development to assist the mine operators make the decisions.

Jan 1, 1981