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Important factors in dredge design are the estimation of total head, and the determination of flow in and around suction nozzles and in pipe lines. Total head for the dredge pump is calculated from velocity, static, and friction heads. Flow into suction nozzles depends on whether hydraulic jets or mechanical cutters are used, and on nozzle shape. Design of pipe lines depends on the transportation characteristics of the pulp, skin friction, swirl, and the avoidance of cavitation. Measurement and control of flow is important.INTRODUCTIONEconomic deposits of heavy minerals along the east coast of Australia occur in frontal dunes, which are normally unconsolidated and granular, or in hind dune areas which may contain indurated seams interspersed with loose material. In working frontal dunes, dredging depths are usually shallow since values do not persist for more than a few feet below sea level. However, the controlling factor in dredging the hind dune areas is the level of the water table and suction dredges may be designed to mine to depths of 120 ft, or even more, if necessary.In previous applications of suction dredges in the industry attention was directed primarily towards production and there was only limited research on fundamental techniques. However, with lower grade deposits now forming the major ore reserves, production levels and profit margins will fall unless more efficient dredges are developed.For satisfactory design of dredges it is essential that the total head be accurately estimated and that detailed information of the principles of flow in and around suction nozzles be determined. This paper presents information gained from field experience and laboratory investigation on these aspects.

Jan 1, 1962

By C P. Kramers

The need to provide a sufficient quality and quantity of backfill continues to increase in South Africa, particularly as related to the increasing depth of mining. More and more applications require well designed fill systems either as classified or cemented backfill, and in some applications even tailings/aggregate based backfills. The paper discusses developments in backfill technology in South Africa with special emphasis on reliable system designs and operations, particularly as related to the preparation and hydraulic transportation aspects. Approaches for the alleviation of previous problems associated with premature pipe failures in vertical shaft columns for the distribution of tailings based backfills are discussed. Resulting from CSIRÆs developmental work, reliable full-flow systems, which can operate at low system pressures, have become a common practice, provided that backfill flowrates and internal pipe sizes are well matched. This aspect is reviewed. With regard to the tailings/aggregate based backfills the paper reviews some of the results of comprehensive in situ monitoring and the development of such systems. It is shown that a thorough understanding of the effects of aggregate top size, fines content and slurry relative density is required in order to ensure the restartability of temporarily shut-down pipelines. Some innovative technologies for the comminution of development waste underground to yield aggregate products potentially suitable or hydraulic transportation and backfilling, are briefly discussed.

Jan 1, 1998

By MARK J. VANARELLI

Estimating ground-water inflows in rock deep tunnels is critical to the safety of personnel constructing the tunnel and the cost of construction. This paper presents two case studies, including the Chattahoochee and Nancy Creek tunnels, for estimating steady-state ground-water inflows into deep rock tunnels. Statistical methods were applied to packer test data obtained from exploratory borings during geotechnical site investigations, and a semiempirical procedure was used to estimate ground-water inflows. The Chattahoochee and Nancy Creek tunnels are deep rock tunnels that exhibit radial flow conditions. For the radial flow condition, a statistical analysis presented in this paper indicates that the semiempirical procedure works well; however, variations in the procedure and/or an insufficient amount of testing could lead to underestimations of the inflow quantities. Modeling using Monte Carlo simulations was observed to be an effective tool for removing data distribution irregularities and incorporating high-end permeability data to derive reasonable ground-water inflow estimates.

By Tukkimies M

During the late-1980s crawler-mounted crusher units established their position in the aggregates industry. Between 1986 and 1994 about 700 units were delivered to customers all over the world for surface operations, mainly in Scandinavia and central Europe. The crawler-mounted units are popular among smaller crushing operators because they are versatile and easy to move between sites. In large quarries the greatest benefit is obtained by combining a primary crawler-mounted crusher unit with mobile belt conveyors which eliminates the need for costly haulage by dump truck. Savings of up to 40 per cent in production costs prior to secondary crushing have been achieved. Today the environmental aspect in quarrying is assuming ever greater importance. Besides being costly the dump trucks are also the major source of dust and exhaust fumes within a quarry. A complete face crushing system consisting of a crawler-mounted crusher unit and mobile belt conveyors can be electrically driven and can be equipped with dust encapsulation and dust collectors. A mobile crushing unit is not a new idea. From the mid-1950s onwards the mobile and self-propelled units have been built equipped with crawlers, tyres or walking mechanisms, with weights usually of 500-1000 t. Due to their massive size these unit are not mobile in the same way as the today's mobile units. It is not feasible to move them more than a few times a year unlike today's fully mobile units which are often relocated once an hour. This means that the massive units can not continuously follow the production face and their loading always requires a certain amount of haulage. Today the mining industry is facing new challenges. With low mineral prices and high labour costs, increasing productivity is essential for survival. New standards are also being set for the labour safety and the environment. Large research programs have been launched to meet these challenges. However, technology which can partly solve these problems already exist and is only waiting to be introduced into underground applications as well - the mobile crushing unit followed by belt conveying. As in surface operations the elimination of truck haulage also brings considerable savings in operating costs in underground mines and reduces the amount of dust and exhaust gases generated. An additional benefit especially in underground applications is improved safety. In an underground mine most accidents are caused by moving vehicles.

Jan 1, 1995

By S. M. Shelton, M. M. Fine, T. L. Johnston

"INTRODUCTION The Bynum property is about 15 miles west of Gadsden and 1 mile north of Walnut Grove, Etowah County, Ala. The ore lies in layers and as irregular masses and pockets in the clay residue from decomposed quartzite and limestone formations to the district.The property has been developed by means of numerous shallow shafts sunk to water level - about 25 foot. Operations are confined to small-scale, selective mining of pockets of high-grade ore. The ore is marketed directly, without beneficiation. The property does not yield a large amount of manganese ores. No estimates of reserve ore tonnages are available.A 206-pound sample was furnished for test. It was taken at random from a stock rile estimated to contain 130 tons of ore. The sample con¬sisted of a mixture of manganese oxides, iron oxides, and siliceous fragments in clay. The manganese occurred largely as soft, unconsolidated pyrolusite and wad. Some hard, crystalline pieces of psilomelane were distributed through the soft material. Small amounts of iron oxides were associated with the manganese oxides. Chert, quartzite, and clay comprised the gangue minerals.Dry analysis of the sample was as follows: 36.0 percent manganese, 6.1 percent iron, 2: .0 percent silica, 1.5 percent calcium carbonate, 0.36 percent phosphorus, 3.0 percent alumina, 2.2 percent barium, and 0.31 percent zinc."

May 1, 1942

By M. Woodie

INTRODUCTION Information such as application review to choose the proper style of vibrating screen, parameters that determine the proper size of vibrating screen, engineering design information that governors proper screen design, review of topics that govern proper isolation from structural steel and other topics that dictate proper screen selection for applications will be presented in this paper. Topics like process and application information review to choose the style of screen and how material size and type influences proper type of screen selection (multi-slope, incline, horizontal, linear incline or dewatering) will also be discussed. Parameters will be reviewed that help size the screen for the application. The total amount of surface area to size a screen is critical to the overall success of a screen installation. Once proper style of screen is determined there is an engineering process that is required to design the screen to operate correctly in the environment it will be used. Finite Element Analysis, Dynamic Modeling, Field Vibration Analysis and other engineering tools will be reviewed to best implement a successful vibrating screen installation. TYPES OF SCREENS Multi-Slope Multi-Slope vibrating screens are used where sizing large amounts of tonnage on surface areas that would be smaller than conventional screening where roughly 6” (150mm) minus material is required to be sized. Occasionally larger particle sizes can be screened on the Multi-Slope machine but the effectiveness of the machine can be diminished with larger particle sizes and larger than 4” (100mm) screen opening. The most common and effective size range of screening with these machines is 2” (50mm) minus material. The Multi-Slope screen is used where particle size is not extremely important. Mineral processing, hard rock mining and industries where exact material size is not critical are best suited for this equipment. Because the aggregates industry requires very specific material sizes, the Multi-Slope screen is not suited for most aggregate screen applications. The key to the success of a Multi-Slope screen is proper material presentation at the feed end of the screen. This allows for the material to stratify quickly and disperse the fines through the screen quickly with a relatively thin bed depth at the feed end which allows the undersize material through the screen quickly.

Jan 1, 2019

By Güven Önal, Gülay Bulut, Mustafa Özer, Yunus Emre Benkli, Olgaç Kangal, Mustafa Tarkan

There are various types of natural zeolite deposits in Turkey. Naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential. In this paper, the beneficiation of natural zeolite, taken from western part of Turkey, was investigated. According to X-Ray Diffraction (XRD) and mineralogical studies carried out on the representative ore sample, the natural zeolite was found to be in the forms of clinoptilolite and heulandite. Clinoptilolite forms as a devitrification product of volcanic glass in tuffs. Quartz, clay minerals, orthoclase, plagioclase, biotite, seruzite-muskovite and epidote were observed as impurities. Several types of mineral processing methods were performed in order to remove impurities from the natural zeolite sample to produce high purity zeolite. Gravity separation methods such as shaking table and superpanner were carried out for separating heavy minerals, while high intensity dry magnetic separation was used for discarding magnetic minerals.

Jan 1, 2003

By Strathmore R. B. Cooke, Thomas E. Bam

The paper discusses the mineralogy, structure, and strength of magnetite pellets fired in air and in a neutral atmosphere at various temperatures. The information obtained from this investigation is used to explain the origin of the structures occurring in pellets produced by pilot-plant operation. MUCH experimental work has been performed on i-VL the mechanism of agglomeration and pelletiz-ing of moist ore and concentrates and on the process of firing agglomerates, but except for the work of Tigerschiold and Ilmonil much of the published information is empirical, and the literature contains no information concerning the structure of fired pellets. Results of a preliminary study of the micro-structures occurring in pellets produced both in the laboratory and on a pilot-plant scale are presented in this paper. Most of the results were obtained from pellets prepared from Mesabi magnetic taconite, but through the courtesy of the staffs of the Minnesota Mines Experiment Station and the Bethlehem Steel Co., fired pellets produced from limonite and hematite ores and from Lebanon magnetite have also been examined. The work has been restricted almost entirely to pellets produced without additives, the exceptions being those in which coal was added to the filter cake before rolling. Schwartz has described the microstructures occurring in ore sinters produced under reducing conditions.' Many of the structures and constituents he describes are common to fired pellets, but the constituents normally occur in markedly different proportions. His statement that "in all satisfactory sinter the amount of hematite is small, perhaps not over 2 or 3 per cent" is inapplicable to pellets produced by pilot plant operation or by any process in which air is not deliberately excluded. Pilot plant pellets contain over 90 pct by weight of hematite, and those produced in the smaller furnaces of the Minnesota Mines Experiment Station contain more than 80 pct of that constituent. Preparation of Specimens It is difficult to examine unfired pellets microscopically because of their insufficient coherency to withstand sectioning and polishing. Fired pellets sometimes lack coherency and frequently contain holes which are troublesome during polishing. Impregnation of both air-dried and fired pellets is readily accomplished by the use of methyl metha-crylate monomer." The dry pellets are covered in a test tube with excess monomer, to which a small amount of accelerator has been added. When the test tube is placed in a cooling bath and evacuated with an aspirator, most of the entrapped air is removed, and disruption of weak pellets by boiling of the monomer is reduced to a minimum. Polymerization is then effected by immersion of the test tube in a water-bath at about 45"C, this temperature being held for 4 or 5 days. The test tube may then be broken away from the solidified mass and the pellets sectioned by a carborundum wheel or a diamond saw. Where time is important, impregnation is carried out at a higher temperature by Meyer's method.' Air-dried pellets must be impregnated with especial care; otherwise swelling occurs and the solids are displaced. It is more important to be certain that the monomer forms a reasonably complete network throughout the specimen than that all entrained air is removed, and for this reason the vacuum technique may be omitted. Impregnated agglomerated products and pellets are extremely coherent, section well, and may be polished either by hand or by machine. Hand polishing is not satisfactory for the examination of conditions existing at the boundaries of grains, and for this machine polishing must be used. The Graton-Vanderwilt machine gives excellent results, provided that pressure on the specimen is considerably in excess of that recommended by the manufacturer. Mineralogy of Fired Pellets Only two opaque iron minerals, magnetite and hematite, have been recognized in pellets. The complete identity of, these artificial minerals with their corresponding natural counterparts is shown by their mineralographic characteristics and their X-ray structures. Wiistite has not been found. Slag is the most common transparent constituent of fired pellets. Occasionally conditions have been appropriate for the crystallization of fayalite from the slag, and at other times another crystalline sil-

Jan 1, 1953

By Strathmore R. B. Cooke, Thomas E. Bam

The paper discusses the mineralogy, structure, and strength of magnetite pellets fired in air and in a neutral atmosphere at various temperatures. The information obtained from this investigation is used to explain the origin of the structures occurring in pellets produced by pilot-plant operation. MUCH experimental work has been performed on i-VL the mechanism of agglomeration and pelletiz-ing of moist ore and concentrates and on the process of firing agglomerates, but except for the work of Tigerschiold and Ilmonil much of the published information is empirical, and the literature contains no information concerning the structure of fired pellets. Results of a preliminary study of the micro-structures occurring in pellets produced both in the laboratory and on a pilot-plant scale are presented in this paper. Most of the results were obtained from pellets prepared from Mesabi magnetic taconite, but through the courtesy of the staffs of the Minnesota Mines Experiment Station and the Bethlehem Steel Co., fired pellets produced from limonite and hematite ores and from Lebanon magnetite have also been examined. The work has been restricted almost entirely to pellets produced without additives, the exceptions being those in which coal was added to the filter cake before rolling. Schwartz has described the microstructures occurring in ore sinters produced under reducing conditions.' Many of the structures and constituents he describes are common to fired pellets, but the constituents normally occur in markedly different proportions. His statement that "in all satisfactory sinter the amount of hematite is small, perhaps not over 2 or 3 per cent" is inapplicable to pellets produced by pilot plant operation or by any process in which air is not deliberately excluded. Pilot plant pellets contain over 90 pct by weight of hematite, and those produced in the smaller furnaces of the Minnesota Mines Experiment Station contain more than 80 pct of that constituent. Preparation of Specimens It is difficult to examine unfired pellets microscopically because of their insufficient coherency to withstand sectioning and polishing. Fired pellets sometimes lack coherency and frequently contain holes which are troublesome during polishing. Impregnation of both air-dried and fired pellets is readily accomplished by the use of methyl metha-crylate monomer." The dry pellets are covered in a test tube with excess monomer, to which a small amount of accelerator has been added. When the test tube is placed in a cooling bath and evacuated with an aspirator, most of the entrapped air is removed, and disruption of weak pellets by boiling of the monomer is reduced to a minimum. Polymerization is then effected by immersion of the test tube in a water-bath at about 45"C, this temperature being held for 4 or 5 days. The test tube may then be broken away from the solidified mass and the pellets sectioned by a carborundum wheel or a diamond saw. Where time is important, impregnation is carried out at a higher temperature by Meyer's method.' Air-dried pellets must be impregnated with especial care; otherwise swelling occurs and the solids are displaced. It is more important to be certain that the monomer forms a reasonably complete network throughout the specimen than that all entrained air is removed, and for this reason the vacuum technique may be omitted. Impregnated agglomerated products and pellets are extremely coherent, section well, and may be polished either by hand or by machine. Hand polishing is not satisfactory for the examination of conditions existing at the boundaries of grains, and for this machine polishing must be used. The Graton-Vanderwilt machine gives excellent results, provided that pressure on the specimen is considerably in excess of that recommended by the manufacturer. Mineralogy of Fired Pellets Only two opaque iron minerals, magnetite and hematite, have been recognized in pellets. The complete identity of, these artificial minerals with their corresponding natural counterparts is shown by their mineralographic characteristics and their X-ray structures. Wiistite has not been found. Slag is the most common transparent constituent of fired pellets. Occasionally conditions have been appropriate for the crystallization of fayalite from the slag, and at other times another crystalline sil-

Jan 1, 1953

By V. Panayotov

Flotation practice usually uses the Sheridan-Grizvold selection method, where zinc minerals are activated by addition of copper sulphate and depressed by addition of sodium cyanide, ferrous sulphate, zinc sulphate or various mixtures of these reagents. The method is suitable for the flotation of sulphide ores, which, do not bear precious metals, such as silver and gold. When classical technology with cyanide is applied to depress zinc minerals, the precious metals, which are contained mainly into lead minerals, are dissolved into the solution, which represents a technological loss. In order to avoid this process, we have made use from the knowledge on the semiconducting properties of lead and zinc sulphide minerals. We have changed the surface charge of minerals by means of an electrochemical impact realized by direct current application and specially designed set of insoluble or semi-soluble electrodes. Thus, flotation separation of lead and zinc sulphide minerals was achieved, at increased recovery of lead, zinc and silver. The technology proposed was implemented in a Bulgarian flotation factory; it worked over 5 years providing significant, positive economic, technological and environmental impact. Silver recovery was increased by 0.8-1.0 %, and lead and zinc recovery was increased by 0.8-1.0 %. The technology is easily controllable and adaptable to raw materials and parameters of the technological process. It can be paid back for 6-8 months after the implementation. Keywords: lead-zinc flotation separation, electrochemical impact

Sep 1, 2012

By Matthew Thurley

Optimisation and control of comminution, pelletization, and agglomeration processes is a complex task with large potential for gains in productivity, energy efficiency, and particle size distribution quality. One factor in realising these gains is the requirement for fully-automated online particle size distribution measurement. Moreover, online particle size distribution measurement that is based on the particles on the visible surface and can avoid or mitigate substantial errors that result from under-sizing overlapped particles and over-sizing areas of fines particles. Literature review indicates a body of substantially 2D photographic based particle size measurement systems that suffer from a large number of significant errors except in the simplest case of a monolayer of particles under good illumination with limited color variation in the material. In order to measure the visible particles on a pile there are a number of requirements including; avoiding particle delineation errors due to variation in material color and shadows, detect overlapping versus non-overlapping particles, and identify areas of fine particles as fines and not large rocks. Results are presented using a fully-automated online measurement system of crushed rock on conveyor belt using a 3D surface laser profile. The system provides continuous online measurement and results are shown on over four hours of production after the primary crusher. Size distribution results are calculated using volumetric estimation of the particles on the surface of the pile. The results show a strong capability to discriminate size variation especially in the 10% and 20% passing values. Furthermore results show that if areas of fines are misclassified as large rocks, and overlapped particles misclassified as small rocks, then a near complete loss of discrimination occurs for the P10 and P20 values which become largely constant values.

Jan 1, 2014

By Knut Conradsen

In the study 208 heavy mineral concentrates (pan samples) from Jameson Land, East Greenland, are considered. Each concentrate has been analysed (by spectroscopy) for the content of (approx.) 25 elements. Furthermore the exact sampling position and the geological characteristics of the environment have been registered. In the study is shown how different multivariate methods combined with geological knowledge of the area can be used in the interpretation and classification of the data. Special emphasis is put on the problem of finding reliable expressions for the background level of the element concentrations in the area. This is done by means of severel discrimination procedures. The other main subject is a demonstration of the applicability of isoscore maps - originating from factor analyses - in the evaluation of the co-variability of the data, and thus give another way of classifying the individual samples according to the content of different elements.

Jan 1, 1977

By S. Narasimha Rao

Significant amounts of lateral load may act on pile foundations supporting structures such as transmission line towers, tall structures, bridge abutments, offshore platforms, quay wails, harbour structures and anchorages for water front structures. There were several theoretical and experimental studies conducted on laterally loaded piles in clays to determine ultimate lateral capacity and deflections under working loads. Under a lateral load, a pile deflects in the direction of load application and the soil in front of the pile offers resistance to this movement. The ultimate lateral resistance of a pile can be estimated considering the statics of the pile for a known distribution of soil resistance with depth. In this paper, considering the contributions from both lateral shear drag and frontal passive earth pressure, a method has been proposed to estimate the ultimate lateral capacity of rigid piles in clays. The lateral shear drag has been estimated in terms of adhesion and shape factor. A few load tests were conducted on model piles subjected to lateral loading and these experimental values are used in verifying the proposed method. The reported results obtained from both model tests and field tests were used in support of the predictions made. In all the cases, there is a good agreement between the predicted and measured capacities.

Jan 1, 1996

By Donald R. Simon

Money... not many subjects are as personal or as emotional. Hessiod said it well in 700 B.C. "Money is life to us wretched mortals". Are you getting paid enough? Does your company reward its top people? Does coal or copper pay more? Production or engineering? How is the synfuels industry going to influence mining salaries? Do high salaries attract and retain the best people? Do modern compensation systems ensure fairness or destroy entrepreneurial spirit? With our tax system and high standard of living why are we so salary conscious? Salary is not only important for what it can purchase but it is also a yardstick, measuring how well we are doing. We all need money to pay the bills and maintain our standard-of-living, but once we reach a certain point the psychological ramifications become more important than the purely practical side. Even necessary payments like the mortgage and the car are a function of our egos. Are our choices of cars and homes based on simple transportation and shelter?

Jan 1, 1980

By T. Gerritsen, A. Matyas, F. Stober, I. Candy

This paper describes developments in ferro-nickel furnace technology, specifically improvements to cooling methods, furnace controls, and high voltage furnace operating regime. The evolution of these technologies is briefly presented, as context for describing the current state of the art that has enabled ferro-nickel furnace operation at over 75 MW and specific energy consumption of less than 400 kWh/t dry ore. Examples from existing operations are used to illustrate present best practices, and potential future trends are discussed. The paper begins with an overview of the fundamental aspects of pyrometallurgical treatment of lateritic ores that drive ferro-nickel furnace design. Furnace wall cooling methods are related to the requirements resulting from specific furnace process conditions, including slag and metal compositions, as well as arc and bath power. The benefits of high productivity and low specific energy consumption resulting from high voltage (shielded-arc) operating practice are discussed, along with the furnace controls and electrical power train that enable such operation even with captive power generation.

Jan 1, 2004

By David Schlain

"IntroductionThe purpose of this investigation was to study the characteristics of the high-acid electrolytic manganese cell with the idea of fitting it into one of the flow sheets being worked out by the Metallurgical Division of the Bureau of Mines for the recovery of manganese from low-grade domestic ores.In construction, the high-acid cell 3/ differs from the low-acid type in that the cathode and anode compartments are separated by a diaphragm of relatively low porosity, such as alundum. This is necessary because in the high-acid cell the two electrolytes are circulated separately. The anolyte is 15 to 30 percent H2SO4. The catholyte consists of a solution of ammonium sulfate and manganese sulfate with a OH of 4 to 3. The only mixing of electrolytes is that resulting from flow through the diaphragms. In the low-acid cell the two electrolytes are not circulated separately and do not differ so widely in hydrogen-ion concentration. Hence, the canvas diaphragm is sufficient.During operation of the cell, manganese is deposited on the cathode, and sulfuric acid is produced in the anode compartments. Various other reactions take place in the cell. There is considerable decomposition of water; hydrogen is evolved at the cathode, and oxygen is liberated at the anode. When lead anodes are used, some hydrated oxides of manganese are formed at the anodes. The quantity of oxides formed is not as great as it is in the low-acid cell, because fewer Mn++ reach the vicinity of the anodes."

Jul 1, 1942

By Gabriela Pereira de Miranda

Os aços avançados de alta resistência do tipo dual phase (DP) são aplicados na indústria automobilística, principalmente, em componentes estruturais. Alguns desses aços são revestidos com zinco e suas ligas, visando maior resistência à corrosão. Atualmente, o processo de união de aços mais utilizado em veículos é a soldagem por pontos. O emprego inadequado de parâmetros de soldagem pode provocar trincas por fragilização por metal líquido (LME, do inglês liquid metal embrittlement) em regiões de soldas a pontos de aços de alta resistência revestidos com zinco. O metal líquido, neste caso, consiste em ligas de Zn-Cu provenientes da combinação de cobre dos eletrodos de soldagem com o zinco do revestimento, que penetra em contornos de grãos, reduzindo a sua energia coesiva. Sob solicitação mecânica, tal fragilização pode ocasionar origem às trincas. Neste trabalho foram investigadas as condições de formação de trincas por LME na soldagem de aços DP da classe de 600 MPa de limite de resistência galvanizado por imersão a quente (HDG - GI). Verificou-se, em todas as condições de soldagem avaliadas, a penetração do metal líquido na superfície da solda. A ocorrência de trincas, no entanto, só foi constatada em condições de soldagem que implicaram na geração de tensões. Tais tensões foram intensificadas com refrigeração inadequada, causada por diferentes vazões de água nos eletrodos inferior (1,5 l/min) e superior (7,5 l/min), e/ou soldagem sequencial. Não foram observados efeitos prejudiciais de trincas por LME nas resistências estática (cisalhamento por tração) e dinâmica (fadiga sob cisalhamento).

Oct 30, 2017

By Chi-Mun Song, Seok-Hyun Choi, Seok-In Hong, Han-Kee Jang

Accurate measurement and evaluation of hand-transmitted vibration from a power tool is an important issue for tool manufacturers, because they are obliged to develop low-hazard power tools for workers. The International Standard ISO 5349(1) dictates a systematic procedure for the measurement and evaluation of hand-transmitted vibration. However, the uncertainty in this measurement is too large for manufacturers to apply such data to the design and modification of power tools. There can be several sources of this uncertainty in such measurements; e.g., operator-dependent, power tool-dependent, and operational conditions (see Table 1). For a manufacturer to characterize the exposure of a power tool’s use to a given level of vibration, the relationship between these uncertainty factors and the measured vibration must be elucidated. In this study, we investigated the effect of several factors on the uncertainty in measurements. [ ] Methods In this study, some of the factors in Table 1 were selected for examination, and their effect on the measured variation was quantitatively investigated. Three tools from the same manufacturer were sampled at random in our experiments, and each of five of the same type of insert (disks or tips) was installed into each tool. Although each of the tools and inserts were of the same design and were made by the same production process, they differed from one to another, which can be a source of the variation in the measured vibration. Three human subjects participated in our experiments, which were carried out as stated in ISO 5349. The subjects were asked to maintain their posture, and the applied force was kept as constant as possible. The applied force was monitored using an indirect method, where vibration energy was displayed in real time during the experiment using a three-axis accelerometer attached to the work piece at a specified point. The appropriate range of the applied force was predetermined to cover the range of real work operations. The engineering tolerance between the inner diameter of a grit disk and the outer diameter of the tool shaft leads to an eccentricity of the mass at the center of the disk. The degree of eccentricity varies with installation, and this is another source of uncertainty. In our study, the effect of this eccentricity was investigated by carrying out repeated assembly and disassembly of an insert.

Jan 6, 2006

By YANG TSANQ WOO

THE method of making coke that has been adopted at the Kaiping and other collieries in northern China resembles, to some extent, the familiar bee-hive oven process of the United States, except that a kiln with permanent sides is used instead of a closed oven, and the products of combustion are drawn off at the bottom, In building coke-kilns in China, two circular holes, 8 ft. 6 in. in diameter at the bottom and 13 ft. in diameter at the top, are excavated in the ground, both being .connected at the bottom by a flue as shown in Fig. 1. The sides and bottom of the kiln are lined with fire-bricks, and covered with a layer of fire-clay, and a rectangular opening, 6 in. by 8 in., connects the bottom of each kiln with the main flue. Around the edge of the hole, and overlapping the lining, is a wall of fire-brick extending .2 ft. 6 in. above the level of the ground. An open space 5 ft. wide is left in this wall, through which the coal is carried into the kiln and the resultant coke removed. This space, of course, is bricked up during the time that the coking operation is being carried on. The wall is pierced with nine flue-openings uniformly placed around the circumference, each intervening space in the wall being strengthened with a brick buttress, as is shown in Figs. 2 and 4. The floor of the kiln, as well as the main flue, is lined with fire-brick. Before charging the coal, it is first placed in shallow bamboo sieves, 2 ft. in diameter, and immersed in a trough 10 ft. long, and 3 ft. wide, fed with pit-water; in which it is washed by hand. Fig. 3 shows the manner in which the washing is done. From 25 tons of good " dust" coal, 22.5 tons of washed coal are obtained. When ready to charge the coal into the kiln a temporary cone-shaped flue of fire-wood and lump coal is first built to a

Nov 1, 1905

By William A. Hustrulid

A technical and economic evaluation of the potential for improving mining productivity through the use of underreamers in blastholes, specifically in relation to Minnesota taconite, Arizona surface copper and in situ mining operations is presented. Included are (1) a review of the drilling and blasting practices presently being used, (2) a discussion of current underreamer technology. (3) the presentation of a general economic cost model for underreaming, (4) the application of the model to surface taconite, surface copper and in situ mining, and (5) a summary discussion including required performance specifications, potential overall benefits, and recommendations for further development.

Jan 1, 1977