Search Documents

By Joachim Klein, Frank Reimann

Nodular-graphite cast iron (GGG) is a material similar to steel, and one which exhibits excellent properties, in particular for components exposed to pressure. GGG cast iron has been used in many cases when sinking mine shafts with conventional tubbing. With linings made of cast iron tubbings (the backfill concrete is not integrated into the calculations, and merely serves as bedding) the properties of the cast iron can be made full use of, provided the tubbing is made to the appropriate cross-section. Calculations have shown that better static values can be arrived at when using cross-sections other than those of tubbings made to conventional German standard. The cross-sectional design of the new types of shaft lining made from GGG is to be developed on these lines irrespective of the cast iron structure being only stressed component or its restistance function being combined with the one of concrete. GGG 50 is used for the first time to make the reinforcing inner liner of a main shaft currently sunk in Germany. The physical properties of nodular-graphite cast iron, strength and deformability, suggest that, in the future, its application will not be restricted to shaft support but also in tunneling. New moulding techniques with better three-dimensional modelling resulted in new tubbing designs as installed e.g. for the Hannover underground at present. Shield-driven tunnels have to withstand earth and water pressure, apart from axial machine loads. In this field time is money as well. Therefore easy handling and quick installation are necessary for successful, use. Last but not least, safety is of first-order importance for work in shaft sinking and tunneling. Cast iron lining systems, accordingly, are adequate systems, in particular for excavations underneath water for transport systems and for goods and passengers.

Jan 1, 1987

By W. E. Coxe

In 1857 the Philadelphia and Reading Railroad Company, whose main line extended from Philadelphia to Pottsville, Pennsylvania, with branches into the coal regions of Schuylliill County, made a contract with the Fairmount Rolling Mill, at Philadelphia, for the rerolling of some four thousand tons of iron rails. The essential features of the agreement were that the old rails should be piled with puddled iron and rolled into flats for the rail pile, which latter was • to be of a section seven inches square, and after being heated, and reduced, by rolling, to a bloom of a section about fire inches by six inches, was to be reheated, before being finished into the rail of the T pattern, four inches high, weighing sixty-four pounds per yard. Great care was exercised in the execution of this contract, and the rails being distributed over all parts of the road, gave general satisfaction by their excellent wear. Five years afterward, the principal proprietor and manager of the Fairmount Rolling Mill was elected President of the Reading Railroad, and very many of the rails made under his supervision were still in use in the tracks of the company, of which he had just assumed the management. His first efforts were, therefore, directed to the procuring of more rails of the same quality wherewith to replace those worn out. Here he encountered some trouble, makers refusing to bid because of the details in the specification, the required reheating being the objectionable feature, for which it was generally intimated they would not be sufficiently remunerated for the increased labor, extra coal consumed, and the changes necessary from the established methods of working. Most of the new rails were, therefore, bought, and the old rails rerolled without regard to any particulars as to the manner of piling, heating, etc., each manufacturer furnishing what he deemed the best article possible for the money. As a consequence, rails of all imaginable grades were placed in the tracks, some giving out in six

By W. E. C. Coxe

IN 1857 the Philadelphia and Reading Railroad Company, whose main line extended from Philadelphia to Pottsville, Pennsylvania, with branches into the coal regions of Schuylkill County, made a contract with the Fairmount Rolling Mill, at Philadelphia, for the rerolling of some four thousand tons of iron rails. The essential features of the agreement were that the old rails should be piled with puddled iron and rolled into flats for the rail pile, which latter was to be of a section seven inches square, and after being heated, and reduced, by rolling, to a bloom of a section about five inches by six inches, was to be reheated, before being finished into the rail of the T pattern, four inches high, weighing sixty-four pounds per yard. Great care was exercised in the execution of this contract, and the rails being distributed over all parts of the road, gave general satis¬faction by their excellent wear. Five years afterward, the principal proprietor and manager of the Fairmount Rolling Mill was elected President of the Reading Railroad, and very many of the rails made under his supervision were still in use in the tracks of the company, of which he had just assumed the management. His first efforts were, therefore, directed to the procuring of more rails of the same quality wherewith to replace those worn out. Here he encountered some trouble, makers refusing to bid because of the details in the specification, the required reheating being the objectionable feature, for which it was generally intimated they would not be sufficiently remunerated for the increased labor, extra coal consumed, and the changes necessary from the established methods of working. Most of the new rails were, therefore, bought, and the old rails rerolled without regard to any particulars as to the manner of piling, heating, etc., each manufacturer furnishing what he deemed the best article possible for the money. As a consequence, rails of all imaginable grades were placed in the tracks, some giving out in six

Jan 1, 1877

By M. M. Moghaddam

Charge motion is of prime importance in the efficiency of comminution in tumbling mills. Since direct observation of charge shape and its motion in industrial mill are not possible, a combination of analytical and physical studies was used to determine charge trajectory. Software packages, which predict charge motion such as the GMT (Grinding Media Trajectory) only consider the outermost layer of charge (single ball) and ignore the interactions of grinding elements. In this research, the measured charge trajectory in a 1m-diameter mill with the transparent end, called model mill, was compared with that of the GMT. Four types of polyurethane rings were accurately machined to scale down the liners arrangements at two industrial mills. To explore various charge shapes and trajectories, the model mill was operated at 55, 70 and 85% of critical speed for five levels of mill filling (10, 15, 20, 25 and 30% by volume). The angular displacement of the toe, toe departure, shoulder and charge impact point were determined from the photographs taken from the model mill. New relationships to predict charge shape and charge impact points were introduced to modify the GMT results. The relationships were validated by the model mill using the new liner of the Sarcheshmeh copper complex SAG mill. The relative error of prediction was found to be 1.1%. The results indicated that when the lifter face angle increased from 7 to 30º, the distance between the charge impact point and the toe decreased from 52 to 31º for 25% filling. This meant increasing the probability of charge impacting the toe not the liner which favoured more efficient comminution practice. After converting AG mills to SAG mills on account of liner profile change, 31% increase in throughput (from 419 to 548 t/h) in addition to 4% decrease in the product size (from 516 to 496 µm) were realized which was a significant contribution in the plant performance improvement.

Sep 1, 2012

By George H. Hanna

THE importance of the Donets coal field (the Donbas) to the national economy of the Soviet Union is well known. Great as was the significance of this tremendous deposit of coal in prewar days it is destined to become an even greater factor in the economic life of the country now that the tremendous havoc wrought by the Germans is being remedied. Since the war began, new coal fields have been extended; for example output of the Moscow and Karaganda (Kazakhstan) fields has become considerably larger while new mines are producing coal in several parts of Uzbekistan and Kirghizia. The huge West Siberian coal field, the Kuznetsk Basin, is producing more coal than ever before to supply the industries of that region and of the Urals. But so great has been the development of industry to meet war needs, especially in those districts of the Soviet Union that lie to the East of the Urals, that the coal obtained, eked out by such locally-won fuels as peat and wood, is still barely sufficient to meet industrial requirements. The main burden of the coal supply for the restored industries of the West, therefore, will fall on the Donbas.

Jan 1, 1945

By S. Krishnannair

Singular Spectrum Analysis (SSA) is an effective data-adaptive multimodal tool for monitoring chemical processes. However, monitoring multiscale signals using principal component analysis obtained from the multilevel decomposition of process signals using basic SSA assume the upper control limits of monitoring charts (" ) to have a Gaussian distribution. This assumption deteriorates the performance of basic SSA when applied to the monitoring of nonlinear processes. To address the issue in this paper, the kernel density estimation (KDE) was used to estimate upper control limits of monitoring charts for basic SSA based nonlinear process monitoring techniques. The monitoring performance of the resulting basic SSA-KDE approach was then compared with a basic SSA approach of which upper control limits of the monitoring charts were determined based on a Gaussian distribution. Application on nonlinear dynamic simulated process and base metal flotation plant chemical processes showed that the SSA-KDE approach provided better overall performance than the SSA approach with Gaussian assumption-based upper control limits for its monitoring charts. Keywords: Fault detection, singular value decomposition, singular spectrum analysis, kernel density estimation

Jan 1, 2020

By Greg Beckstrom

On Oct. 1-3, SME?s Twin Cities chapter (SME TC), in cooperation with the University of Minnesota ? Duluth?s Precambrian Research Center (UMD-PRC), cohosted a symposium on silica sand mining and processing. The conference was held at the Earle Brown Heritage Center near Minneapolis. The symposium was followed by a day-long field trip to operating mines, processing plants and loading facilities located in southwestern Wisconsin. Speakers and attendees at the symposium included university professors, industry experts, regulators, mining company representatives, equipment suppliers, consulting engineers and service companies. Approximately 320 people attended the conference. In addition, about 50 people who oppose mine development and the oil and gas industry showed up to voice their displeasure with the event and those companies that operate in this space.

Jan 1, 2012

By R. M. Hardgrove

PULVERIZED coal was first used for firing cement kilns about 45 years ago, with such success that it has continued in general use. Based on cost, pulverized coal is usually the most economical fuel. In some localities natural gas or oil is cheaper, but 85.5 per cent of all cement kilns at present are fired with pulverized coal. The pulverized-coal flame is well suited to kiln conditions. Its soft, luminous nature gives it a high radiating property and the length of the flame can be readily varied to suit conditions in a kiln of any length. Ash and slag cause most of the difficulties incident to the burning of coal. In a cement kiln, however, the ash, being similar in composition to the raw mix and being deposited uniformly in the mix and clinker, occasions no difficulty as long as it remains constant in quality and quantity. Until 6 years ago almost all cement kilns using pulverized coal employed the bin system. The coal was dried and pulverized in a separate plant and delivered into a bin at the kiln. Thus the bin system requires driers, storage-type pulverizers, conveying systems, individual kiln bins, pulverized-coal feeders and primary air fans. The direct-fired system requires only a pulverizer and a blower. Fig. I shows typical plants. The first installations of direct-fired pulverizers were of the impact type but fineness of pulverization was both inadequate and variable. About 1927 a few direct-fired installations employing tube-type pulverizers were made, which were much more satisfactory. As more efficient pulverizers were developed from 1934 on, equipment for direct firing was installed at a large number of plants, until now 196 of about 900 kilns in use in the United States are direct-fired. Most of these replaced antiquated bin systems. PROCESS OF BURNING CEMENT CLINKERS The process of burning cement clinkers is fundamentally one of heat transfer. In boilers and other heat-exchange apparatus the area of the surface receiving heat from the gases is the best unit for comparing output. This seems to be equally true for kilns. The inside kiln surface is the heat-receiving surface and its area is used as the unit of kiln size in the following comparisons. Heat input is based on British thermal units in the fuel. E. G. Bailey,1 in his work on boiler-furnace heat absorption, has used the unit "B.t.u. available." This is the practical calorific power of the fuel, plus the heat in the air used for combustion. In other words, it is the heat available for useful work in the furnace or kiln. The unit of kiln output is barrels per hour. The composition of the raw mix, the percentage of water in the slurry of wet plants and hardness of burning all affect the output. These conditions, however, are hard to evaluate and probably have less effect on the output than irregularities of raw feed and clinker discharge and inexpert control of combustion. WET VS. DRY PLANTS The study presented here covers 88 plants, of which 41 are wet and 47 dry. Of

Jan 1, 1941

By Douglas Muir, Chas. A. Chase

The Aztec mine is not widely known, by reason of its isolation and the relative insignificance of its tonnage; financially, however, it has an enviable record and geologically it is extremely interesting. The town of Baldy, Colfax County, the mine camp, at an elevation of 10,000 ft. (3048 m.) is 8 mi. west of Ute Park, the terminus of a branch of the A. T. & S. I?. Ry. The mining tract was designated by the Maxwell Land Grant Co. as the Aztec Reservation, and lies on the east slope of Mt. Baldy, the summit of which, 12,491 ft. (3807 m.), is one of the highest in the state. Rich copper float was found on the northeast slope of the mountain in 1865, and discovery work was begun the next year. At the same time, gold placers were found on Willow Creek, on the southwest side of the mountain, and the Elizabethtown settlement followed shortly. Gold washing lasted many years. In 1867, placer gold was found also on Ute Creek, the tracing of which to its source led to the locating of the Aztec mine by Lynch, Dogherty, and Fosley in the following year. The early production came from the contact of shale and sandstone or from sandstone immediately above the contact. Exact record of production is lacking, but L. C. Gratonl gives estimates ranging between $1,250,000 and $1,500,000, of which about $1,000,000 was taken out in the first four years. After the exhaustion of the early bonanza, production continued intermittently until 1909, when the Maxwell Land Grant Co, undertook systematic development, through four adits at intervals of 75 ft. vertically or approximately 100 ft. on the dip of the contact, which was thought to contain generally a quartz-pyrite vein. The two intermediate adit? almost immediately reached ore, the most southeasterly in Fig. 2. This ore, however, was not mined until 1911-12; its grade was about $20 and

Jan 1, 1923

By Douglas Muir, Chas. A. Chase

The Aztec mine is not widely known, by reason of its isolation and the relative insignificance of its tonnage; financially, however, it has an enviable record and geologically it is extremely interesting. The town of Baldy, Colfax County, the mine camp, at an elevation of 10,000 ft. (3048 m.) is 8 mi. west of Ute Park, the terminus of a branch of the A. T. & S. I?. Ry. The mining tract was designated by the Maxwell Land Grant Co. as the Aztec Reservation, and lies on the east slope of Mt. Baldy, the summit of which, 12,491 ft. (3807 m.), is one of the highest in the state. Rich copper float was found on the northeast slope of the mountain in 1865, and discovery work was begun the next year. At the same time, gold placers were found on Willow Creek, on the southwest side of the mountain, and the Elizabethtown settlement followed shortly. Gold washing lasted many years. In 1867, placer gold was found also on Ute Creek, the tracing of which to its source led to the locating of the Aztec mine by Lynch, Dogherty, and Fosley in the following year. The early production came from the contact of shale and sandstone or from sandstone immediately above the contact. Exact record of production is lacking, but L. C. Gratonl gives estimates ranging between $1,250,000 and $1,500,000, of which about $1,000,000 was taken out in the first four years. After the exhaustion of the early bonanza, production continued intermittently until 1909, when the Maxwell Land Grant Co, undertook systematic development, through four adits at intervals of 75 ft. vertically or approximately 100 ft. on the dip of the contact, which was thought to contain generally a quartz-pyrite vein. The two intermediate adit? almost immediately reached ore, the most southeasterly in Fig. 2. This ore, however, was not mined until 1911-12; its grade was about $20 and

Jan 1, 1923

By J. Peterson, P. G. McKneight, R. W. Riggle

"In today’s tough mining environment, the key difference between surviving and thriving is how effectively miners optimize their mining operations. This paper explores the compounding effects material fragmentation has on mining costs and productivity. Starting with Drilling & Blasting and moving through Loading, Hauling and Crushing, we will illustrate the opportunities to improve operating costs and thus reduce the Total Cost of Ownership (TCO) of the total mining system. Material size and volume requirements are defined by the needs of the mill or plant, and drive the rest of the mining operation from the bench through the primary crusher. At the start of the cycle, where the rock mass is drilled and blasted, the degree of fragmentation and the muck pile configuration is determined, as are the effects on cost and productivity of all subsequent operations. The cost of managing oversize material, including secondary handling, overloading, reduced diggability, higher load factors, extra pass loading, increased wear factors and reduced throughput rates are all opportunities for improvement. INTRODUCTION Having visited many mine sites, customers are asking about the end to end mining value stream from loading to the crusher and how to measure the cumulative effects on each part of the mining value chain. All too often improvements with the drilling and blasting may impact fragmentation but do not improve the diggability so the net change on cycle times or fill ratios is perceived to be negative at the point of loading but they may have a measured improvement going through the primary crusher. This makes it imperative to measure performance at each segment of the overall cycle and not just to the crusher but thru it. The mine material process originates with solid rock, in-situ, and progresses to the output of the primary crusher. Once the material has passed the primary crusher the fragmentation size will be fairly consistent and promote consistent throughput of the plant or mill. In late 2015 a team was conducting a reassessment visit to a mining site where we had conducted the original assessment the previous year. Though many recommendations had been implemented some had been so recent they had not resulted in the expected improvements. Several of our discussions kept returning to the impact fragmentation has to both the individual components of the mining cycle but also the effects compounded throughout the end to end process. Let’s move on to the big picture before we zoom in on any specific operation. To get from native solid rock in the ground to a concentrate or a saleable rock product we have the same steps from one end of the chain to the other. We start with a good geological understanding of the rock type, characteristics and structure to design a program to drill and blast the rock. The height of the bench is relevant to the annual production requirements and the specific digging equipment models best sized to make that production possible. The equipment selection influences the bench height which has a minimum and maximum hole diameter to maintain a safe blasting operation. The diameter of hole burden and spacing all contribute to a good distribution of explosives in the rock mass that maximize the fragmentation and preconditioning of the rock when blasted. The timing and sequencing of hole initiation will yield a fragmentation ratio and diggability factor. Fragmentation size adjustments will change the meters drilled per cube and the explosives consumption will change accordingly. Drill cost is measured by meter drilled so a direct relationship exists between cost and fragmentation sized achieved."

Jan 1, 2017

By R. M. Hardgrove

PULVERIZED coal was first used for firing cement kilns about 45 years ago, with such success that it has continued in general use. Based on cost, pulverized coal is usually the most economical fuel. In some localities natural gas or oil is cheaper, but 85.5 per cent of all cement kilns at present are fired with pulverized coal. The pulverized-coal flame is well suited to kiln conditions. Its soft, luminous nature gives it a high radiating property and the length of the flame can be readily varied to suit conditions in a kiln of any length. Ash and slag cause most of the difficulties incident to the burning of coal. In a cement kiln, however, the ash, being similar in composition to the raw mix and being deposited uniformly in the mix and clinker, occasions no difficulty as long as it remains constant in quality and quantity. Until 6 years ago almost all cement kilns using pulverized coal employed the bin system. The coal was dried and pulverized in a separate plant and delivered into a bin at the kiln. Thus the bin system requires driers, storage-type pulverizers, conveying systems, individual kiln bins, pulverized-coal feeders and primary air fans. The direct-fired system requires only a pulverizer and a blower. Fig. I shows typical plants. The first installations of direct-fired pulverizers were of the impact type but fineness of pulverization was both inadequate and variable. About 1927 a few direct-fired installations employing tube-type pulverizers were made, which were much more satisfactory. As more efficient pulverizers were developed from 1934 on, equipment for direct firing was installed at a large number of plants, until now 196 of about 900 kilns in use in the United States are direct-fired. Most of these replaced antiquated bin systems. PROCESS OF BURNING CEMENT CLINKERS The process of burning cement clinkers is fundamentally one of heat transfer. In boilers and other heat-exchange apparatus the area of the surface receiving heat from the gases is the best unit for comparing output. This seems to be equally true for kilns. The inside kiln surface is the heat-receiving surface and its area is used as the unit of kiln size in the following comparisons. Heat input is based on British thermal units in the fuel. E. G. Bailey,1 in his work on boiler-furnace heat absorption, has used the unit "B.t.u. available." This is the practical calorific power of the fuel, plus the heat in the air used for combustion. In other words, it is the heat available for useful work in the furnace or kiln. The unit of kiln output is barrels per hour. The composition of the raw mix, the percentage of water in the slurry of wet plants and hardness of burning all affect the output. These conditions, however, are hard to evaluate and probably have less effect on the output than irregularities of raw feed and clinker discharge and inexpert control of combustion. WET VS. DRY PLANTS The study presented here covers 88 plants, of which 41 are wet and 47 dry. Of

Jan 1, 1941

By B. Dyck, C. Rodgers

ABSTRACT Cameco Corporation is revitalizing its Key Lake Operation uranium mill in northern Saskatchewan. The mill currently uses ammonia stripping in solvent extraction (SX) and ammonia yellowcake precipitation. As part of the revitalization, the company considered installing strong acid stripping in solvent extraction (used at its Rabbit Lake Operation), which would lead to using hydrogen peroxide for uranium precipitation. As part of the process evaluation, tests were carried out to study how the drying temperature in indirect fired dryers would affect the uranium peroxide yellowcake precipitate properties. This paper discusses the test work results, including the relationships between drying temperature and product reactivity with water, product colour, product grade, and energy input requirements.

Jan 1, 2012

By RALPH HAYES SWEETSER

IRON ore and bituminous coal are the two basic raw materials for the whole iron and steel industry. The ore furnishes the iron and is absolutely necessary-all iron and steel products come directly or in- directly from the iron ores. The bituminous coal furnishes the carbon needed for the smelting of the ores and for the fuel used in all the processes of iron and steel manufacture. The necessary carbon could be furnished in some other form besides bituminous coal. In fact, it is only since the Civil War that bituminous coal has been the chief source of the carbon for metallurgical fuel. For many years only charcoal made from the forests furnished the carbon for smelting iron ores. About 90 years ago, anthracite coal was first used as blast-furnace fuel and for many years continued to be the chief blast furnace and steel making source for carbon. Even in my own blast-furnace experience, I have used charcoal in Canada and anthracite in Pennsylvania for smelting ores in an iron blast furnace. Bituminous coal, now almost exclusively the source for the carbon used in smelting iron ores, also furnishes most of the heat used in the steel-making processes. It is seldom used in blast furnaces in its natural condition, hut is first coked in beehive, or in by-product coke ovens; such bituminous coal is called "coking coal." Bituminous coal that is suitable for making the producer gas used in the open-hearth steel process is called gas coal. Any bituminous coals suitable for making blast-furnace coke or foundry coke, or that can be satisfactorily used for making producer gas, are classed as metallurgical coals and as such are to be considered in my proposed plan for the evaluation of metallurgical coals. According to Bureau of Mines Bulletin No. 449 these coals comprised 22 per cent of the bituminous coals mined in this country in 1923.

Jan 1, 1926

By Qixing Yang, Björn Haase, Fredrik Engström, Anita Wedholm

"MiMeR, the Minerals and Metals Recycling Research Centre at Luleå University of Technology, Sweden, started industry-related research work to stabilize an EAF slag from Höganäs AB with of CaO/SiO2 values near to 3.2. The intention was to determine the suitability of the EAF slag as construction material after stabilization. Some of the stabilizers effective for preventing disintegration of AOD slag were examined in laboratory tests for stabilization of the EAF slag. The EAF slag samples were mixed together with stabilizers for melting at 1600ºC and then cooling in a crucible system. With a laboratory granulation system, the liquid EAF slag was cooled rapidly using air. Samples from the tests were characterized by different techniques, including XRD and SEM. Some of the results from the work may be useful for preventing slag disintegration and, thus, enhancing utilization of the EAF slag as construction material, thereby saving valuable natural resources.IntroductionAt steel plants of some MiMeR member companies, steel grades with low carbon contents were produced in Electric Arc Furnaces (EAF). EAF slag was tapped out of the furnace to slag pots for transport to slag yards, where the slag was poured on the ground. Very often, the EAF slag disintegrated during cooling on the ground. Fines from the slag disintegration were often difficult to handle and use as material for road construction [1, 2]. The EAF slag disintegration was rather similar to the disintegration occurring in the slag tapped from some AOD (Argon Oxygen Decarburization) converter heats.Literature studies show that formation of dicalcium silicate (C2S) is the main reason for the disintegration or dusting of AOD slag from production of stainless steel [1-4]. The C2S can form while the content ratio of CaO to SiO2 of the slag, CaO/SiO2, exceeds 1.4 [1]. Values of CaO/SiO2 for the AOD slag are often near to 2.0, making the C2S a predominant slag component. The ß phase of C2S, ß-C2S, transforms into its low temperature ? form in the temperature range of 400-500°C, inducing a volume expansion of nearly 12% [1-4]. The volume expansion disintegrates the AOD slag."

Jan 1, 2008

The income of the Institute is derived from dues, subscriptions to Mining and Metallurgy and sale of publications. These sources are fortunately supplemented by the interest from invested funds now amounting to over $500,000, a considerable portion constituting endowments for especial purposes. Aside from the medal funds the principal endowments are the James Douglas Fund for support of the Library, the Rocky Mountain Fund and the Seeley W. Mudd Memorial Fund. The income from the two last named is available for the support of research and a variety of other purposes, It is allocated by the Board of Directors upon recommendation of standing committees in each case. An active effort is being made to increase the endowments of the Institute, it being felt that unusual opportunities exist for research and public and professional service through the organization and at a minimum of expense. J. V. W. Reynders is chairman of the Endowment Committee. Seeley W. Mudd Memorial Fund THE Seeley W. Mudd Memorial Fund, consisting of $100,000, was given the Institute in 1929 by the family of Colonel Mudd who had served the Institute as Director, Vice-president and on many important committees. His long career of distinguished professional and public service is fittingly commemorated by this fund. The income is available for support of research and other special purposes. In view of Colonel Mudd's life work with the nonferrous metals and his keen interest in the younger men of the profession it is purposed to apply the fund particularly to the benefit of these two. Control of income is exercised by the Board of Directors on recommendation of a Committee consisting of the President and Secretary, ex officiis, together with three others selected by the Board. The Committee consists at present of the following members: W. H. Bassett, President; H. Foster Bain, Secretary; Harvey S. Mudd serving until October, 1931; Edgar Rickard serving till October, 1932; George Otis Smith serving until October, 1933. On recommendation of this Committee the Board has authorized as a first project the preparation of a series of small books designed especially to be helpful to the Junior Members. These are now being written and it is hoped will be available for distribution in 1931. The list includes: A Brief History of American Mining, by T. A. Rickard; Mining Costs, Why and What, by Arthur Notman; Introduction to Mineral Economics, by H. Foster Bain and T. T. Read; Choice of Methods—A Record of Experience in Making Decisions, with chapters by W. H. Bassett, F. W. Bradley, E. DeGolyer, Howard N. Eavenson, A. B. Parsons, J. V. W. Reynders, L. D. Ricketts, Robert E. Tally, Pope Yeatman and others. One other book is projected but final selection has not been made. The purpose of these books is to afford the younger men who now come into a highly specialized profession some substitute for the broad

Jan 1, 1930

By Elaine T. Cullen

Safety training materials appropriate for specific underground noncoal operations in the United States are often outdated or nonexistent. The Spokane Research Laboratory (SRL) of the National Institute for Occupational Safety and H ealth has developed several new training tools, including three videos on common underground activities, software that will allow trainers to create a virtual training mine using their own mine map, and toolbox training materials. SRL is working closely with industry in the development of these tools. Teams of safety professionals are involved in the early stages, and actual mines and miners are involved throughout the production phase. This presentation describes the development process and results of SRL’s safety training projects.

By A. D. Randolph

Comminution represents one of the major costs of mineral recovery from low-grade ores. Efficient mineral recovery in a typical low-grade ore grinding-flo¬tation process depends on grinding the ore small enough to liberate mineralization without producing excessive slimes, which would result in higher power and flotation reagent costs. Size criteria for efficient grinding should be stated in terms of the distribution of mineralization sizes, but as the mineralization-size distribution is difficult to determine, less desirable criteria of absolute particle-size distribution (PSD) are used in practice. Thus, there is considerable incentive to be able to analyze and predict the PSD performance of grinding circuits for control and optimization of the process. Any realistic model of a grinding circuit must account for recycle of oversize material; such oversize recycle adds to the total mill load and limits total production rate. Simulation of such closed-circuit operation to study grind factors affecting total throughput can be done in a straightforward fashion provided recycle calculations can be added to an accurate input-output model of PSD in the grinding mill itself. Such a total simulation of mill performance is of obvious practical value in assessing the practicality and benefits of various over-all mill control schemes and/or modes of operation. For example, considerable interest has been shown in the development of continuous on-line particle-size sensors and such instruments should be an operating reality in a few years. A total closed-circuit PSD model of this type would be invaluable in the utilization of, and in predicting the pay-out from, such an on-line particle-size sensor. The purpose of this paper is to present a new approach to the development of an input-output PSD model of a grinding mill. The model is continuous in the par¬ticle size coordinate, L, and is based on the principle of a particle population balance along the particle size coordinate. Most previous studies of the grinding unit operation attempt to relate power

Jan 1, 1971

By Milton R. Pickus, Earl R. Parker

THE modern theories of creep¹-4 in general have been based upon the concept of generation and migration of dislocations, with the generation process normally assumed to be rate controlling. The theories are generally deficient in that they fail to take into account many factors that are known to influence creep. The influence of the state of the surface of the test specimen has been almost completely overlooked; yet the present report shows that the nature of the surface may, in certain cases, govern the creep characteristics of a specimen. In the period since Taylor" applied the concept of dislocations to a study of metals, a school of thought has developed that closely relates the plastic deformation of metals to the generation and migration of dislocations through the crystal lattice. It might be expected that the thermal energy required for the generation of a dislocation would be different from that for migration of the dislocation through the lattice. Furthermore, the activation energy for generation would be expected to vary for different parts of the solid metal. It has been predicted that dislocations would be generated most easily at external surfaces, but could also be activated at certain internal surfaces such as grain or phase boundaries. Within the body of the metal a range of values for the activation energy might be expected because of different degrees of disorder at such regions as grain boundaries, impurities, and second-phase particles. The particular value of the activation energy that was rate determining could then depend on the specific conditions of a test. If, for example, the surface atoms were by some means constrained, the generation of dislocations in the body of the metal might become the important factor. On the other hand, other conditions may favor generation at the surface. It is possible then that the creep behavior may not be completely determined by the inherent properties of the metal. Even the environment in which a test is carried out could have a significant effect. In fact it is conceivable that in order to obtain the maximum creep resistance from a given alloy, the surface atoms must be so constrained that the activation energy for generating dislocations on the surface is at least equal to that required for generation in the body of the metal. On the basis of such considerations, and in view of the limited number of publications discussing this subject, it seemed that an investigation of the influence of the state of the surface on creep might yield information of both theoretical and engineering interest. Experiments on single crystals, demonstrating a variation in the mechanical properties due to alterations in the surface layer, have been reported by several investigators.6-13 he results of these experiments have been briefly summarized;14 consequently, the earlier work will not be reviewed here. As an example of these findings the observations of Cottrell and Gibbons may be cited. They reported the critical shear stress of a lightly oxidized cadmium single crystal is greater by a factor of 2½ than a specimen with a clean surface. Materials and Methods Single crystals M in. in diam and 8 in. long were prepared from Horse Head Special zinc, melted under an atmosphere of helium in a large pyrex test tube, and drawn up into a long ½ in. diam pyrex tube by means of a vacuum pump. The cast zinc rods thus produced were cut into convenient lengths and sealed in evacuated pyrex tubes. Single crystals were grown by gradual solidification of the remelted rods. Cleaving the ends of the single crystal specimens chilled by liquid nitrogen proved a simple method for determining orientations from the exposed basal plane from the markings left on the cleaved surface that gave the slip directions with sufficient accuracy for the experimental work. The specimens chosen for the experiments were those having the angle between the basal plane and the specimen axis within the range of 15" to 65". Since zinc single crystals are quite delicate, it was necessary to devise an appropriate method of gripping the specimens in order to suspend them in the furnace and apply the load. Stainless steel collars were prepared having an inside taper, the smaller end of the taper being of such a size that the specimen could just pass through freely. The tapered hole did not extend the full length of the collar; a sufficient thickness of metal remained so that a hook could be attached to provide a means of applying the load and suspending the specimen. One of the collars was slipped over the upper end of a specimen which was supported vertically in a steel jig. The collar was then heated electrically until the end of the crystal melted and filled the collar with molten zinc. At this point the application of heat was discontinued, whereupon the molten zinc quickly solidified, due to the chilling effect of the jig. The specimen was then inverted and the second collar applied in a similar manner. The jig served several purposes: limiting the length of specimen that was melted, providing excellent alignment of the collars with respect to the specimen axis, and protecting the specimen from mechanical damage. Once the specimen was suspended in the furnace and loaded, it was desired to accomplish the surface treatment with a minimum of disturbance of the specimen. Around the specimen was a long pyrex tube, the upper portion of which was approximately 1 in. in diam, and in it was a copper coil of such a diameter to fit snugly against the tube. A specimen, approximately ½ in. in diam and 4 in. long, was suspended by means of a stainless steel rod so that it hung within the copper coil. The lower portion of the glass tube was approximately ¼ in. in diarn, and passing through it was a 5/32 in. diam stainless steel rod which hung from the lower specimen collar. This portion of the glass tube and the stainless steel rod extended through the bottom of the furnace. A T-connector, with suitable packing, was attached to the lower end of the stainless rod to provide a water-

Jan 1, 1952

As the 2009 George Fox Conference neared its conclusion, Arthur Silber, project chief of the Mass Transit Tunnel (MTT) project was able to pull away from the constant buzzing of his Blackberry long enough to give a short presentation and a significant piece of news to the record 318 attendees at the Graduate Center, City University of New York regarding the MTT project. ?As the former administration (The Bush administration) was leaving office, we were told that Congress was notified of the FTA?a (Federal Transit Authority?s) intent to issue final design construction approval to us,? Silber said of recent advancements concerning the $7.2-billion dollar project. It will add passenger rail service from New Jersey to New York City as part of the Access to the Region?s Core project in the form of the Trans Hudson Express Tunnel (THE tunnel). ?That 10-day waiting period ended yesterday (Jan. 26).? In days leading up the Fox Conference, those involved in the tunneling industry, and the MTT in particular, had a lot to be optimistic about. The MTT received environ-mental approval on Jan. 14 (see page 9) and, with the acceptance of the final design, the multi-billion dollar project moved that much closer to a ground-breaking ceremony. So close, in fact, that before leaving his office for the conference, Silber posted the contract documents and plans for the Manhattan Tunnel project online at www.arctunnel.com (an indepth look at the project from Silber is on page 22). While many were interested in the progress of the project, Silber also spoke about the new plans for the cavern complex at the New York Penn Station expansion. The original plans called for two lines that would come into a large cavern complex with a north and south cavern to access the trains. After numerous core samples were taken from the streets of Manhattan, it was deter-mined that this design was not feasible and changes were made that will include a deeper cavern under Sixth Avenue, with 14-m (45-ft) of cover with a 30-m (96-ft) wide cavern that resides entirely under 34th Street. The cavern was also moved 20 m (60 ft) to the west to remain at least 61 m (200 ft) away from New York City Water Tunnel #1. The new design will include three-over-three track arrangement. The mezzanine will be 46 m (150 ft) below street level at 8th Ave, Silber said.

Jan 1, 2009