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By A. E. WALKER

SOME eighty years have elapsed since the discovery of the Clifton magnetite deposit. For a few years about the time of the Civil War it was mined for iron ore. most of which was smelted on the property. Since risen the small exposures of ore in the old cut. test pits, and on the dumps have been examined by various prospectors. The M. A. Hanna Co. first became interested in the possibilities of the deposit when we discovered the large area of strong magnetic anomalies caused by the margnetite bed, indicating a size that would support a commercial operation. In 1940 we made a detailed magnetometer survey of the area. and the deposit was diamond-drilled. The main ore lied was found to be 1500 ft. long, to average 60 ft. thick, and to dip southeast at an angle of about 40 deg. The thickness of the bed is irregular in wavy folds both along the strike. and down the dip. Faults occur at both raids of the main deposit.

Jan 1, 1943

By G. M. Brownell

THE Falcon Lake stock is a small igneous mass, 2.6 square miles in area, which has intruded a belt of older lavas and metamorphosed sediments. It is well exposed and the entire area of its outcrop is taken up with surveyed mining claims, the claim lines forming a grid which makes ideal conditions for a detailed petrographical study of the unusual variations which are found in the composition of this unit (see Figure 1). The study of this mass, which has revealed features of both scientific and economic significance, began in the summer of 1939 when trainees in a Prospectors' Training Camp, a Do-minion-Provincial youth-training project under the writer's supervision, were, detailed to map rock outcrops on various mining claims. Microscopic study of rock specimens taken on a line across this stock were made during the following winter and proved to be of such interest that a special trip was made the following summer for the purpose of gathering more data, the results of which are presented here. Location The stock is close to the southeast corner of the province of Manitoba, about three miles from the Ontario boundary. It lies between Falcon and West Hawk lakes and less than a mile south of the Trans-Canada highway. It is easily accessible by motor car, as a branch road from the highway leads to the Sunbeam Kirkland gold mine, which is within the inner core of the stock. Previous Work This area was the first in the Province to receive attention from prospectors, who entered it from the adjacent Lake of the Woods district during the days of the mining boom in the 1890's. Small occurrences of gold, copper, molybdenum, and tungsten ores were found, but to date there has been no production from the district, except for small shipments of gold ore. The regional geology has been mapped by the Manitoba Department of Mines and Natural Resources, the Falcon Lake stock being shown and recorded as of "varying composition". The more detailed work involved in preparing the accompanying map has necessitated only minor changes in the outline as previously mapped.

Jan 1, 1941

By W. R. Ingalls

THE propaganda in favor of the adoption of the metric system of weights and measures in the United States is founded upon the idea of compulsory adoption. There can be no argument about this, for the metric system has been legal, by Act of Congress, in the United States since 1866. Nobody ought to oppose an educational movement, and if pro-metric activities were confined to that there might be no reason to gainsay them. I do not propose to enter into any discussion of 'the relative merits of the metric and the English systems of weights and measures. The simple case is that the metric system not having made much headway in the United States after more than 50 years of legality, 'it is now aimed to force it upon the people by legislative compulsion. The main arguments in favor of such compulsory adoption are that it would- simplify the education of our children and would promote our foreign trade, for the reason that more countries of the world, with which we do business, use the metric system than the English system. I am going to disregard,' in this contribution, the first of these arguments, for it is largely conjectural." Not so with the other, which is specific, and being so its speciousness can be, proved. It is true that the metric system is used by more countries of the world than the, English system. It is commonly stated that of the Indo-European nations only the United States, Great Britain, and her colonies, and Russia have failed to adopt it. However, if with "colonies" we equate Canada, Australia, New Zealand, Tasmania and South Africa, we have a longer list of non-metric countries, and it comprises not only the most populous, but also the most industrial nations of the world.

Jan 1, 1921

By Lauri Gregg

The implementation of Energy Management within the global mining industry has advanced significantly during the past 20 years. Consequently, the industry?s knowledge of energy efficiency improvement opportunities, more energy efficient technologies, renewable energy technologies, energy procurement practices, and most importantly, practical approaches for integrating the energy management best practices into business processes and operational procedures has improved greatly. Based on 25 years of experience leading the management of energy in mining operations and the Canadian mining community, the author discusses the key building blocks in the evolution toward becoming an energy efficient mining facility. Sustainable energy management depends on the internalization of the behaviors related to the effective energy use by a mining organization. The paper outlines the typical business drivers that stimulate top management commitment to allocate the resources necessary for this to happen. It also explores the barriers that mining companies must overcome to maintain the commitment. Additionally, it will advocate the need for the application of the principles of organizational change management as part of the energy management implementation process. The question regarding how energy management can be made to happen in a way that is practical for an established organization is answered by providing the details of the framework for energy management, the methodology for controlling energy use, and the roadmap for integrating energy as a key business parameter and production process input variable. An Energy Management System standard developed within the Mining Association of Canada?s ( MAC ) Towards Sustainable Mining ( TSM ) initiative has played an important role in increasing the capacity of the Canadian mining industry to manage energy. The impact of the application the MAC TSM Energy/GHG Management Protocol by Canadian mining companies will be discussed. In June of 2011, the international ISO 50001 Energy Management Systems standard was finalized and published for use. The structure of ISO 50001 will be outlined along with its applicability to the mining industry. Opportunities for practically improving mining energy performance along with the most appropriate current new technologies will be identified. A brief discussion of case studies will be included that demonstrates the successful implementation of Energy Conservation Measures ( EAC?s ) and economic benefits. In conclusion, thoughts on important areas of research and development related to increasing mining energy efficiency will be provided.

Aug 1, 2013

By J. D. Galloways

The northern part of the P. G. E. railway traverses and opens up that part of the province known as the Cariboo district, comprising the Cariboo and Quesnel Mining Divisions, which are a part of the Northeastern Mineral Survey District. Williams lake, a divisional point on the P. G. E. is near the southern boundary of the Quesnel Division and from this point the railway runs northerly to Quesnel, its present terminus. From Quesnel the railway is projected and partially constructed to Prince George on the Canadian National railway; therefore its general trend is northerly through the heart of the Cariboo district. Early History There is no need to outline at any length the early history of mining in the Cariboo. It is sufficient to say that the great gold rush to the Cariboo, in the early sixties, was practically the commencement of mining in British Columbia. These early placer mining operations centred around the old towns of Quesnel Forks, Keithley Creek, Barkerville and Van Winkle, the latter now called Stanley. Many millions of dollars of placer gold have been taken out and the end of production is not in sight yet. The maximum yearly production was reached about 1863, after which there was a gradual decline in output. During the war years production was at a very low figure but a steady, even if small, increase has occurred in the last three years and prospects are encouraging for a much greater output.

Jan 1, 1925

By C. P. Crawford

Bureau of Mines Technical Paper 172, by S. H. Katz and H. C. Porter, entitled "Effects of Moisture on the Spontaneous Heating of Stored Coal", says at the outset, "Spontaneous fires in storage piles of bituminous coal' have been the source of trouble and loss since the industrial utilization of coal began. In Europe the idea arose that spontaneous combustion is more liable to happen during wet weather than during dry. Statements favoring or opposing this idea have crept into the literature. Conflicting conclusions, based on experiment as well as opinions based on observations of various degrees of reliability, are given in most of the recorded discussions of the subject. "Because of the uncertainty of the effect of moisture and its seeming importance among the conditions that affect spontaneous combustion in stored coal, the work described in this paper was undertaken by the Bureau of Mines. The experiments showed that a coal from Illinois oxidized faster when dry, whereas a sample of Pittsburgh coal oxidized faster when moist. These discordant results and similarly inconsistent results from the observations of different investigators may be coupled with the fact that under actual conditions of, storing, both coal and air always contain a considerable amount of moisture." The foregoing report of the investigations of the Bureau demonstrates that the mystery of spontaneous combustion has not yet been solved. This fact adds to the fascination of the subject. I became interested in the matter about ten years ago in observing what was probably one of the best exhibitions of this phenomenon. The old dump at Castle Gate No. 1 Mine contained boney coal and track cleanings generally. In winter when snow fell upon this old dump, the snow was soon melted by the heat of the dump which was comparatively warm at all times. Within 48 hours afterward little blue flames were in evidence on the surface of the pile. Few of the gas feeders were sufficiently constant to maintain a steady flame at any given point, but shifting emissions of gas were ignited one by another, resulting in a continuous popping and apparent running about of the flames. Another interesting exhibition of spontaneous heating was to be seen a few years ago in the storage coal piles of the local sugar factories. This coal was piled in concrete lined pits and the latter were filled with water. However, or this occasion the coal extended above the surface of the water. At every plant where this condition existed the coal was affected heating, and in each case the affected area was in a plane horizontal to and from 8 to 1.4 inches above the water level. The height of the hot area above the surface of the water appeared to be affected by the fineness of the coal. It is well known that oily rags have a tendency to heat when allowed to accumulate in some location protected from free air circulation. For some reason, as yet unknown, this does not apply to petroleum or its derivatives. Now, the most common explanation of spontaneous combustion is that the combustible material oxidizes by being brought into contact with air in the presence of moisture, the theory being that the moisture acts as a catalytic agent. My theory is that spontaneous combustion is due to oxidation of combustible matter by free oxygen carried in solution by a liquid, the oxidation taking place only as, when, and at the place where this oxygen is released from solution by the evaporation of the liquid. Also, this oxidation takes place to some degree regardless of the condition of the combustible-whether it be lump coal, coal dust, straw, wheat flour, coke, or any other combustible but, as the speed of oxidation is directly influenced by temperature, it follows that spontaneous combustion only becomes noticeable or serious in cases where the resulting heat' cannot escape as fast as it is generated.

Jan 1, 1925

By George E. Roberts

The maintenance of the common gold standard is the most important cooperative undertaking in the world. The war broke up this relationship and brought about a state of great disorder in the currencies and exchanges. After the war the countries all began to grope their way back to the gold standard as the best means of establishing trade and financial relations with each other. With this movement began a general decline in commodity prices. The question has been raised whether the world's return to the gold standard was not forcing prices back to the prewar level. Also, the question is raised whether the world has not outgrown the supply of gold as the basis of credit. Because Europe readjusted its monetary units to conform to the higher level of prices there is no pressure on prices on this account. Furthermore, a large amount of gold formerly in hand-to-hand circulation passed out of circulation and has been added to the central bank reserves. The gold reserves of 36 countries increased approximately 100 per cent from the outbreak of the war to June 30,1930. The increase is much larger than the average increase of prices in any of the important countries, at any time since 192.5. As gold in the central banks of issue is far more effective for all business purposes than gold in circulation, the gold scarcity argument has little basis as applied to this time. The abnormal distribution due to the war was to the disadvantage of business everywhere. Credit was scarcer and dearer in some countries. The inflation in this country might have been greater had the production of gold been greater. The argument supporting the theory of a scarcity of gold assumes as fundamental that general price changes must be accounted for by changes in the price equation on the side of money. This is disproved in every period of business depression. A downward price movement is characteristic of every period of business recession. Important discoveries of gold must be made even to maintain present gold production, in the face of which the world's business is bound to continue increasing. It cannot be doubted that some way will be found

Jan 1, 1931

By M. Piard

The scarcity of literature referring to mines in the Rockies has compelled the writer to co-ordinate information and advice taken at the very source. Help was gladly given by active inspectors and mine bosses. Although the field is unimportant at the present time, due to its distance from markets for raw coal, it is quite worthy of the attention it is receiving from two continents; for, with the commercial synthesis of liquid fuels, it would become the largest fuel laboratory in the world, provided, of course, that freight cost drops to a low comparative level. As explained below, there are no obstacles to economical and safe operation under anything like the typical outcrop shown in Figure 1. Although coal dust is probably more dangerous in the Rockies than anywhere else, the damp outcrops afford means of control. The abundant gas may be bled to the open air, and the rigid roof will settle gradually under a wide span of opened outcropping. The Panel Retreating Wall The Measures: Coal measures having an attitude similar to that shown in cross-section in Figure x are characteristic of the active coalfield on the Alberta side of the Rockies, and they are also found on large tracts of undeveloped land west of the divide. The small anticlines, not shown in the cross-section, do not affect the progress of a pillar line, provided their crests are connected to the atmosphere by drainage bore-holes.

Jan 1, 1928

By Janos de Warga

"After a short introduction to the history of the semi-conductor theory, the paper describes the principles of electron and hole flow in the semiconducting materials, the operation of the PN junction, and the rectification process in multi-layer devices (diodes and SCR's). The various methods of purification and zone-refining of the silicon are illustrated prior to the discussion on the most commonly used junction-forming processes (alloying, diffusing, etc.). Modern device fabrication and packaging operations are illustrated. Factory testing, evaluation, electrical parameters and guaranteed rating characteristics are listed. It is explained in this paper how the various device parameters affect the electrical performance of the finished unit and how the finished unit characteristics (turn-on, turn-off time, etc.) will influence the equipment rating. In concluding, some typical items of equipment are highlighted, and the applications of these semiconductor rectifiers in the chemical, mining, pulp and paper, and steel industries, etc., are dealt with."

Jan 1, 1967

By H. A. D. Kirsten

The skills differential between manpower supply and demand is due to deeply rooted socio- and politico-educational misconceptions that can be remedied only by a concerted cooperative effort on the part of the general public, the State, organized industry, organized engineering, and engineering education. This will require the general public to recognize that the reasons for the shortages in engineering manpower should be regarded as critical. Public perceptions of engineering, of the vocational and educational prospects in engineering, and of the skills required are poor. The spectrum of engineering vocations, the corresponding function profiles, the interaction between the vocations and the relative proportions of the vocations in the engineering team are in general not adequately appreciated. The recruitment and training of students and teaching staff, teaching facilities, educational curricula, practical training, qualifications, professional registration, and financing are aspects of engineering education that should be brought to the attention of all concerned. . In addition, the educational curricula for the various vocations need to be specified clearly and definitively if the overall mission of engineering education is to be properly appreciated. The uncertainties between university and technikon education and the pursuant vocations need to be resolved. This can be done only by defining the respective curricula in terms of the mental skills and scientific techniques required. The remedial actions with regard to the rationalization of engineering education comprise informing of the public; establishment of an active political lobby; revision of existing education policy; rationalization of existing educational infrastructure; promotion, development, and guidance of engineering student intake; financing of engineering education; accelerated creation of new employment opportunities; and monitoring of the supply and demand of high-level manpower. The parties required to nitiate these remedial actions are various State departments and corporations involved in engineering and industry, various departments of education, the Directorate of Technology of the Department of Trade and Industry, organized engineering education, organized engineering, organized industry, and the Human Sciences Research Council. Only if these interest groups actively initiate the various actions under the coordinated guidance of organized engineering wil the required results be achieved. The South African Engineering Association has proposed a comprehensive programme as strategy to solving the problem, and has obtained broad consensus from various State departments, organized engineering education and research, and the private sector. A joint venture between the Foundation for Research Development, the South African Engineering Association, and organized industry has been charged by the State President with the task of launching the programme.

Jan 1, 1991

By L. O. Howard

THERE are three active mines in the Chewelah-Colville district, the United Silver Copper near Chewelah, and the Old Dominion and the Chloride Queen near Colville. The Admiral near Valley is also doing development work. The Chewelah district is in the south central part of Stevens County in the Colville Valley. Chewelah, a thriving town of 1600 people, and the scene of operations of the Northwest Magnesite Co., is about the center of the district. It is situated in a farming community on the Spokane-Nelson branch of the Great Northern railway, about 65 miles north of Spokane. Only two or three of the mines in the district have been extensively developed, although many have been prospected. The general elevation of the valley, is about 1600 or 1700 ft., that of the mountain ranges on each side about 3000 to 4000 ft., with gentle slopes and rounded glaciated tops. Prospecting is often difficult because of much glacial debris.

Jan 1, 1925

By William Campbell

In the olden days the making of alloys was an art, and the secrete of the craft were jealously guarded. To-day it has become a science, though the old ideas in regard to the secrets and formulæ are dying hard. Modern progress may be attributed to scientific research and testing of materials, and the substitution of chemical analytical control for " cook-book " methods. We know to-day a great deal about the constitution of alloys, the reasons of the change in structure and physical properties by heat and mechanical treatment; and this new knowledge is due for the most part to the physical chemist and metallographist, who have shown us that alloys are simply solutions, and as such obey definite laws. The application of the theories of solutions and of the phase rule tells us what ought to happen when our alloys are in a state of equilibrium. The working-out of the temperature-composition diagram (thermal diagram) for numerous alloys has thrown a light on the structure and constitution which has dispelled most of the darkness in which we labored before the advent of metallography. The work began with the determination of the freezing-point curves, and here the research of Le Chatelier,' Gautier,2 Roberts-Austen,3 and the other pioneers broke the ground. Next the physical chemists, Tammann,4 Rooseboom,5 Bancroft,6 and their colleagues, showed us the complete thermal diagram and its meaning. Then the researches of Heycock and Neville7 on the Cu-Sn series and of Shepherd 8 on the

Jan 1, 1913

By J. M. Goris

The U.S. Bureau of Mines, in cooperation with the Homestake Mining Co., and the University of Utah, is conducting a field demonstration to evaluate the behavior of rock masses supported with cable bolts. One of two rock masses being studied is supported with both conventional and birdcage cables. This rock mass is located between the 6500 and 6650 levels of the 45-4BN stope. 21 ledge. The second rock mass is the hanging wall of the D-limb stope between the 3500 and 3650 levels near the Ross Shaft and is supported with conventional cables. The primary objectives of the project are to monitor the behavior of the two rock masses during mining using extensometers and cable support strain gauges, after which the rock will be modeled using the finite-element code UTAH III. Field data will be used to verify the modeling. In addition. a comparison between the effectiveness of conventional and birdcage cables will be made.

Jan 1, 1991

By IRENE AITKENS

The Mining Law of 1910 , with amendments of 1914 and 1928 , is at present in force in the Dominican Republic . The first and basic mining law of the Republic was passed in 1876 , and although numerous changes and amendments have been made from time to time , the new laws and amendments thereto have not changed the original or basic law materially . However , these enactments have materially changed the legal methods governing the exploitation of the mineral resources of this country and have added new regulations and requirements to those concerning certain specific minerals , etc. The original or basic law still exists as it was first promulgated to protect the rights of the Dominican Republic itself , the rights of the landowner , and the rights of prospectors in general . The Mining Law of 1876 remained in force , without amendment , until it was superseded by the law of May 25 , 1904 , an enactment modeled after the Mexican mining law and designed especially to encourage the investment of

May 1, 1931

By Francis Church Lincoln

I. Situation and Surroundings, The Promontorio mine is situated at the northern end of the Sierra San Francisco de Coneto, in the town of Promontorio, Partido of El Oro, State of Durango, Mexico. As shown in the sketch-map, Fig. 1, the nearest railroad station is Chin-acates on the Mexican International Railroad, 82 miles north of the city of Durango. The mine is 16 miles north of the sta-tion by air-line. It is reached by means of a good wagon-road which first crosses the Guatimapé Plain, passing the ranches of San Antonio and San Julian, to Estacion—a distance of about 15.5 miles—and then entering the mountains crosses the Sierra to Promontorio—a further distance of 11.5 miles— making in all a distance of 27 miles by road from railroad to mine. Promontorio is just beyond the summit of the range, at an elevation of about 8,000 ft. above sea-level, or 1,350 ft. above the Chinacates station. The Castillo de San Francisco, the highest peak in the Sierra, has an altitude of 10,000 ft., and the Promontorio road crosses the summit of the ridge at an elevation of 9,000 ft. by a pass just below this peak known as the Puerto del Almagre. The Promontorio mill is situated at Santa Inés, 2 miles by tram or 3 miles by wagon-road to the north of Promontorio and about 600 ft. lower. The Sierra San Francisco de Coneto decreases in height towards the north and west till it comes to an end at the Mel-chor Arroyo on the ranches of Melchor and Ramos. Beyond this arroyo another range, the Sierra de la Candela, begins. In the vicinity of the Promontorio mine the hills are very rugged and the surface is furrowed by ravines which contain running streams during the rainy season-—July, August and

Jan 1, 1908

By Jerry A. Steding

How many times have you heard "You can't drive piles because of the vibration."? You hear these words come out of the mouths of owners, engineers, and contractors. When a piling contractor hears this, he can almost always do a psychological profile of the individual uttering these words of wisdom. If the owner makes the statement, we know the odds are about 95% that the owner owns the building next door or he wouldn't care what happens to it; or the guy next door has threatened to sue the owner if he even so much as walks across the site of the proposed new building. If the owner owns the building next door to the new construction you can also be just as certain the old structure has undergone settlement. If the statement comes from the mouth of the contractor, it is usually just a case of him being inexperienced.

Jan 1, 1988

By Jose Antonio Silva Souza, Emanuel Negrao Macedo, Iara Ferreira Santos, Otacilio Dias, Luis C. A. Venancio

"The Bayer process alumina production generates 0.7 to 2.0 ton of bauxite residue (BR) and an average of 1.0 ton of C02 per ton of alumina produced. The direct reaction of exhaust gases to reduce the alkalinity of the BR may allow a triple gain: improve the storage conditions, open a range of new applications for BR and sequester from 16 to 102 kg of C02 per ton of alumina. This paper shows the measurement of C02 captured during a pilot scale reaction of a suspension of BR in water with flue gas, produced from direct oil burning. Three different types of reactors were used: one spray tower and two packed columns. The inlet and exhaust gases were analyzed using electrochemical and non dispersive infrared sensors. The pH of the suspension was monitored during and after the reaction to evaluate the buffer effect.IntroductionAlumina is mainly produced from refining bauxite using the Bayer process. This process consists of extracting the aluminum oxide through its dissolution in caustic soda and the separation of insoluble residues. The remaining bauxite residue (BR) although not particularly toxic, poses risks to the environment due to the large volume and its reactivity. According to the latest technology it is stacked on sealed deposits specially constructed. To date the vast majority of the bauxite residue that has been produced was stored and were not incorporated into any existing production processes to significant amount with exception to some extent of the sintering process residue at Russia and China [l]. On the other hand, a strategic goal was set in 2010 by the Bauxite and Alumina Committee of the International Aluminium Institute (formed by the majority of the industries) to reuse 20% of BR in 2025 [2]. China has established the same objective for 2015[1].This paper is a sequel of two others presented at TMS 2010/2012 [3-4] and describes:• A pilot plant assembled for testing the carbonation process of BR with gaseous effluents similar of the refining process.• The methodology used to measure the amount of C02 captured during the carbonation process.• The results of the carbonation process, the C02 capture and the buffering effect of the pH.This process is studied in order to consume minimal power and use the effluent as efficiently as possible in different reactors from low cost to ultra high performance. The process is designed for minimizing the power consumption and equipment investment."

Jan 1, 2013

By E. T. Tuzcu

Microscale information about single particle fracture can be incorporated into the macroscale model of the whole size reduction process in the mill. The ultrafast load cell (UFLC) device provides a substantial amount of information about fracture characteristics of a particle under impact loading. UFLC captures high-resolution compressive force signals during particle breakage. The measurement of the compressive force at the instant of fracture of the particle allows computation of a number of comminution-related particle properties, as well as the energy absorbed during fracture. In the current study, limestone particles 50 mm in size were fractured to obtain specific fracture energies. Then, based on the experimental data, two models were proposed to quantify the fracture process. The specific fracture energy distribution of the particles in the range of 6 to 50 mm was defined by the well-known Weibull distribution. The other model is a probabilistic fracture model. This model is a link between energy events occurring in a grinding mill and the breakage rates of particles. The impact energy spectra or energy events occurring in a grinding mill can be obtained with a discrete element method (DEM) simulation. One can model the breakage rates of the mill material by combining the energy spectra with the probabilistic fracture model. This novel approach for the modeling of breakage rates via DEM and UFLC is shown here.

Jan 1, 2011

By Winton Gale

"Rock and coal fractures and micro seismic vibration are common occurrences during development mining. It is very uncommon for coal and rock to be propelled into the roadway during normal mining operations. However, such occurrences do occur and appear to require significantly more energy than is available from strain energy release during coal cutting. The sources of energy, which can contribute to the propulsion of coal from the face or ribs, are typically strain energy from the surrounding ground, seismic energy from a rapid rupture of the ground in the vicinity, or rapid expansion of gas from within the burst source area.The aim of this paper is to briefly review the bursts that could be related to strain energy or seismic energy. However, the greatest emphasis is placed on the effect that gas within the coal could play in moderate to gassy mines.It has been found that the bursts related to the expansion of gas can occur in coal and stone. The volume of gas involved in coal bursts is typically lower than in gas outbursts; however, the process is generally similar.INTRODUCTIONA coal burst is defined as a rapid expulsion of coal (and potentially gas) from the boundary of the roadway. The volume of a burst can be variable, but volumes above 10-50m3 are noted and cause significant disruption to operations.Rock and coal fracturing is common about roadways, particularly under the influence of elevated stresses, either tectonic or related to mining abutment stress. Shear fracture is very common; however, it is very uncommon that the coal is propelled from the face or ribs as a result of fracture of the material. The nature of rock fracture about roadways under elevated stress is presented in Figure 1.A burst requires energy to propel the coal or rock from the rib or face of the roadway. The depth of material impacted may vary from 0.5m to greater than 3m inside the roadway boundary. The strength of the ground in this zone is variable depending on the nature of the coal seam (or surrounding material). Typically, this material has significant residual strength as confinement increases into the ribside.The energy required to propel this material is typically in addition to that which is associated with normal fracturing about the roadway."

Jan 1, 2018

By E. A. Werner, W. Liebfahrt, J. Blaha

"The influence of the composition and the microstructure on the plane strain fracture toughness of five cold work tool steels all processed via the powder metallurgical route is investigated using 3-point bending specimens. The steels differ in composition and therefore possess different volume fractions of carbides. The amount, size and distribution of the carbides in the matrix are estimated by quantitative image analysis on a plane parallel to the fracture surface without discrimination of the carbide type, since the carbides are always much harder [1,2] than the matrix, irrespective of their composition. Due to the production of the steels via the powder metallurgical route almost all carbides are spherical in shape. The mechanical in-situ properties of the matrix are characterized by indentation tests performed with an ""UltraMicro"" -indenter in a scanning electron microscope.IntroductionCold work tool steels are used as tools in applications where excellent wear resistance and high hardness are required. Examples are cutting, woodworking, thread rolling, wire and deep drawing, cold extrusion and pressing of parts at process temperatures below 200°C. For such applications the steels must show an optimum combination of hardness, wear resistance and toughness while offering good machinability. Hardness and wear resistance are controlled by the amount of carbon and carbide forming elements such as molybdenum, tungsten, vanadium, chromium and niobium. These elements are present in the MC-, M6C and M7C3-carbides and are also responsible for the precepitation of secondary carbides during tempering. In this report attention is paid to the influence of the primary carbides only, while the very small ~~nm) secondary carbides will be treated as constituent of the homogeneous matrix. Increasing the amount of carbides (alloying elements) usually results in a decrease of the material's toughness which is caused by the presence of clusters and/or bands of carbides. To achieve an optimum combination of hardness, wear resistance and toughness many of the today's cold work tool steels are processed via the powder metallurgical (PM) route, which helps to prevent non-uniform element/carbide distribution because of the rapid solidification of the powders used. The resulting microstructure of the tool steel then consists of a tough matrix with uniformly distributed hard carbides· of globular shape. This shape of the carbides is also desirable instead of blocky carbides present in non-PM tool steels, since they improve the machinability of the steel. An additional advantage of PM-steels lies in the possibility to produce near net shaped tools thus lowering the costs of machining."

Jan 1, 2000