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By B. A. Peppley

The current most common method of hydrogen production for fuel cell systems, including SOFC systems, is autothermal reforming. Autothermal reformers have a number of advantages including fast start up and load following and ease of control. However, there are a number of problems inherent with the addition of air into a system connected to the anode feed such as dilution of the fuel with nitrogen and the potential for oxygen to reach the anode chamber directly. Pure steam reforming, which does not involve air addition, provides a richer fuel mixture to the SOFC anode and is inherently safer than autothermal reforming. Although in theory pure steam reforming can be shown to provide these advantages, a number of technical problems need to be overcome before such a system can be practical. In particular, issues such as catalyst degradation due to poisoning and thermal sintering, coking, as well as fuel-steam mixing need to be addressed. Experimental results from a prototype reformer will be presented to illustrate a number of these points. This paper will compare differences in system efficiency, safety and complexity between autothermal/SOFC systems versus a steam reformer/SOFC system. A system simulation will be utilized that is able to account for material and energy balances for a SOFC power generator operating on diesel fuel. The requirements for improved catalysts will be discussed and an analysis of the potential benefits of sulfur tolerance and lower temperature activity will be considered.

Jan 1, 2005

By Graham Bright

Up until a few years ago most of the electrical equipment used in the mines of this country was developed for industrial purposes and was adapted for use in mines by slight modifications. It became apparent, however, that mining conditions differed widely from most industrial applications and it became necessary to design and develop apparatus, particularly suited for use under mining conditions. Most of the electrical apparatus used in mines today, however, does not owe its success entirely to mining development, but in many cases developments in other branches have been taken and improved upon and modified to meet mining conditions. Power Plant: In the earlier days the power plant for the production of electric power usually consisted of fairly small belt driven direct current generators operated from reciprocating non-condensing steam engines. Today where possible the mines purchase power from central stations and where not possible it is ususally produced from turbine driven plants using non-condensing turbines for the smaller plants and condensing turbines for the larger plants. The bad water conditions at many of the coal mines in this country is, responsible in a large measure for the high cost of upkeep and repairs in isolated power plants. This feature with the type of labor available makes it difficult to operate an isolated plant condensing except in the larger mines where water conditions are good and the apparatus can be taken care of. The geared turbine is a particularly simple and rugged piece of apparatus and requires very little attention over long periods of time. Hoists: The first electric hoists to be installed used various types of motors designed for railway or industrial purposes, and the control furnished was far from satisfactory. Today most of the mine hoist motors are of the alternating current type, especially designed for hoisting service. The control for motors of 200 H. P. or over is usually of the magnetic of liquid rheostat type, and as built today will operate over fairly long periods with a very moderate cost of up-keep. Hoists of 1000 H. P. or larger are usually of the direct current type using field control and receiving power from a flywheel or synchronous M. G. set. Hoists of this type have made remarkable records in regard to continuity of operation and low cost of up-keep. Where high speed operation is desired in either coal or metal mines, the D. C. equipment using field control and a separate M. G. set to supply power to the hoist motor is not only the safest and most economical but in many cases is the only type of equipment capable of satisfactorily obtaining the output required. A number of improvements have been brought out with the field control scheme in connection with the acceleration, retardation, overfeed and overwind of the hoist. With these new developments the hoist operator can no longer abuse the hoist by improper manipulation of the control handle. Until a few years ago the matter of safety devices was not given much consideration when installing hoisting equipment. At the present time the safety devices are considered one of the most important items in connection

Jan 1, 1922

By H. Lind

Mining in Estonian oil shale deposit mainly takes place in the Ordovician, Keila-Kukruse aquifer. The aquifer is affected by mining and is fully dried out around the working mine areas (Perens and Savitski, 2008). The groundwater level is decreased down to 30 m, to the mine floor elevation using about 30 pumping stations (Lind, 2005). The pumping rate is very high - depending on the season, ranging from 10 up to 40 m3 per ton of produced oil shale (Reinsalu et al., 2006). The Estonian oil Shale Company mined 15.5 million tons of oil shale in 2007 (Source: Estonian Oil Shale Company). In order to predict the effects, and avoid the social and environmental impacts, there is a need to continuously monitor the situation and run software simulations aiming at decreasing the pumping rate. This becomes even more important since the environmental taxes on usage of groundwater resources increase every year. Therefore, it is necessary to monitor groundwater level and quality, and develop a groundwater model for the overview of the situation during mine operations and also for a number of years after mine closure.

Jan 1, 2008

The subject of government involvement in industry is, to say the least, a touchy one. For many it conjures up thoughts of socialisation or nationalisation. For others it is a desirable objective and is seen as a means of social reform by giving government a greater say in the control and distribution of human, financial and natural resources for the betterment of the community. Whatever your point of view, it is difficult to deny that government involvement exists to lesser or greater degrees in all industries. The mining industry is no exception and the degree of government involvement is probably greater than it is in other industries. I think it is important to remember when talking about government involvement in industry to recognise that there are different types of involvement and that all governments have a right, if they so desire, to become involved in whatever way they choose. The decision of a government to increase its direct or indirect involvement must, of course, be taken in the national interest. Governments, if we are still old fashioned enough to believe in ministerial and electoral responsibility, must make up their own minds about whether their actions are in the national interest and they must be prepared to accept the consequences of that action, good or bad. For instance, they must decide

Jan 1, 1975

By John D. Foulkes, David A. Curtis, Robert L. Lagace, John L. Rothery

An investigation is made of the feasibility of developing compact transmit antennas and/or other means to efficiently couple VLF to MF band radio energy between portable wireless communication units in coal mines. The completely wireless communication ranges between two portable radios equipped with practically-sized reference loop antennas in representative coal mine environments are estimated. Antenna technology is assessed with respect to transmit moment, range, intrinsic safety, battery and wearability requirements to deter- mine the most suitable antenna types for use by miners. It is concluded that air-core bandolier loop antennas, and perhaps ferrite-loaded loop antennas, having peak transmit moments of about 2.5 ampere-m5 will be the most effective antenna choices for portable units. This choice, however, will not allow the range goal of 1350 feet to be attained in mines having unfavorable signal attenuation and noise environments. Rectangular air-core loops are compared with grounded horizontal-wire and vertical-wire mode exciters for fixed station applications. The potential for significantly increasing the wireless communication range by inductively coupling to communications and power lines in a mine is evaluated and found to be considerable based on theoretical coupling equations. Lastly, the theoretical performance of a hybrid noise cancelling diversity receiving technique that utilizes both the electric and magnetic field components of the ambient noise to improve the receiver output signal-to-noise ratio under certain adverse conditions is estimated and shown to be favorable when the magnetic and electric field noise components are highly correlated.

Jan 1, 1977

By Subhash B. Bhagwat

No economic activity would take place without human ingenuity, driven by our needs and wants. Economic activity is made possible by the energy from fossil and other energy sources, our technological hardware, the buildings and infrastructure made from materials such as metals, plastics, wood, water, and numerous industrial minerals. Industrial minerals are difficult to define; however, they generally include utilitarian minerals other than metals and fuels. Some of the industrial minerals form an exception to this categorization and, as explained elsewhere in this book, belong to more than one category because of the manner in which they are used. Industrial minerals are so numerous, and their applications so ubiquitous that they often do not receive the attention given to metals or fuels. Nevertheless, without industrial minerals, many of our most fundamental economic activities such as construction of our cities and towns, control of floods, transportation of our people, the search for minerals, the smelting of metals, and the delivery of supplies of clean water would be impossible. How then do we assess the economic importance of such a variety of materials lumped together under the general designation of industrial minerals? The price per ton or the total amount consumed do not satisfactorily explain the relative value of these materials to the economy. For example, the current price of limestone is about $5/t and the price of fluorspar is about $190/t. However, nearly 1.1 Gt of limestone, valued at about $5.5 billion, are consumed in the United States annually, compared with 590 kt of fluorspar, valued at about $1 12 million. It would not, however, be accurate to conclude that the mineral with the higher total value is always more economically important. Many other questions must be answered before making judgments of this type. These questions include how many people are employed in the production, processing, and distribution of the mineral? How is the mineral used? Is it partly or entirely imported? Where do the imports come from? How is the mineral transported? Is the mineral considered critical to national security? Is there a substitute material available in case the mineral supply is interrupted? Where would the substitute be produced? What would be the basic material from which the substitute will be produced? Even when these questions have been answered satisfactorily, the economic importance of the mineral is not completely known until the consuming sectors are studied as well. For example, even though the manufacture of fighter aircraft is vital to the national security, it employs only a fraction of the number of people employed in the housing and construction industry or the automobile industry or the appliance industry. Mineral commodities consumed in these latter sectors of the economy are more significant than those consumed in the production of fighter aircraft, because nearly two-thirds of the Gross Domestic Product (GDP) depends on the purchasing power of individual consumers. In comparison, the entire defense budget accounts for only 6% of the GDP. There is no easy way to present the importance of industrial minerals to the US economy because most minerals have diverse applications and products made from industrial minerals often con- tribute to the production of other goods and services. One way of highlighting the value of a mineral would be to relate it to the GDP reported by categories such as construction, machinery, stone, clay and glass products, electrical and electronic equipment, paper and allied products, and chemicals and allied products. These GDP categories represent industries fundamental to the economy totaling $644 billion, or about 12% of the GDP in 1990. However, these categories are not convenient for discussion of the many minerals that are used in our complex economy. In a general way, minerals are the 5% of our economy that make the other 95% possible. This chapter, therefore, discusses a selected few industrial minerals to illustrate their importance to various sectors of the economy.

Jan 1, 1994

By Oleg I. Platonov

Method of high-temperature reduction of oxygen-bearing sulfurous gas has been developed at Copper Plant (CP) of MMC ?Norilsk Nickel? Trans-Polar Division (PD) with the aim of producing elemental sulfur from Vanyukov furnace? off-gas. Non-explosive reduction technology of oxygen-bearing sulfurous gas by methane utilized at Copper Plant has been designed to separate the processes of gas heating and sulfur dioxide reduction based on different kinetic of the reactions oxygen fixing and SO2 reduction. First, natural gas promptly reacts with oxygen contained in the process gas to heat a gas mixture up to the temperature of sulfur dioxide reduction (1200C). Then isothermal reduction takes place within 1 sec. Combustion chamber (pre-chamber) design developed based on the above principles is presented. Practical experience of the two reduction reactors operation at CP since 1996 proves high efficiency of the developed reduction process. The volume efficiency rises dramatically thanks to the fact that both fuel and reducing agent are fed into the reactor volume in the form of high-speed turbulent jets providing an intensive mixing of the reacting gases. On condition of equal internal volume of the reactors, the developed process offers higher efficiency of reagent interaction resulting in sulfur conversion exceeding 90%, as compared to the equilibrium one.

Jan 1, 2006

By P Clive Hart

DRA - BACKGROUND [MULTI MINERAL DESIGN & BUILD COMPANY FOUNDED 1984 ENGINEERING FOCUSED CORE ENGINEERING DISCIPLINES INCLUDE: ?PROCESS ?MECHANICAL ?E&I CONTROL PRIVATE COMPANY, INDEPENDENT & INTERNATIONAL]

Jan 1, 2006

By Rosa G. de Pena

From the MAP3S Precipitation Chemistry Network data bank five years of data from January 1, 1977 to December 31, 1981 have been analyzed. No definite trend has been observed in the concentrations and the total depositions in the analyzed period. Comparison between the weekly and event samples show that the weekly samples could underestimate the total deposition. Preliminary results show that there is a reasonably good correlation between the precipitation composition and the emissions feeding the air in which the precipitation is formed.

Jan 1, 1983

By Milton E. Wadsworth, W. Martin Fassell, William H. Dresher

A study of the rate of dissolution of molybdenite (MoS2) in alkaline solution was carried out under carefully controlled conditions. Effects of temperature, oxygen over-pressure, and KOH concentration were evaluated. Studies were made in the temperature range 100°C to 175°C and in the pressure range 0 to 700 psia of oxygen. Under these conditions molybdenite was found to leach according to a linear mechanism. Both oxygen over-pressure and KOH concentration were found to control the rate of leaching. The mechanism has been explained in terms of adsorption of oxygen at the molybdenite surface followed by configurational rearrangement of the adsorbed molecules. The hydroxyl ion dependency is believed to be diffusion-controlled. Laboratory batch studies have shown that molybdenite can be readily dissolved in alkaline solutions under moderate conditions of temperature and pressure. Commercial application of this process to the production of ferro-molybdenum and molybdenum chemicals is promising in view of the ease of dissolution of molybdenite and the relatively noncorrosive conditions involved in the process. HIGH temperature-high pressure techniques have long been used to great advantage in the organic chemical industry, the petroleum industry, and the paper industry. Only recently, however, have these methods been used to extract metals from their ores on a commercial scale. The Chemical Construction Corp., together with interested producers of nickel and cobalt, has done much to develop methods of producing nickel and cobalt powders by the use of high temperature-high pressure techniques.' The Howe Sound Co. is currently operating a plant near Salt Lake City in which the new Chemical Construction Corp. technique is applied to cobalt-arsenic sulfide concentrates. In this method the concentrates are leached in a dilute solution of sulfuric acid under air pressure at a high temperature. Near Edmonton, in Alberta, Canada, the Sherritt Gordon Co. is also using the new method in conjunction with its ammoniacal leach process.' National Lead Co., at Fredricktown, Mo., is operating a process similar to that of Howe Sound. In spite of the rapid growth of high temperature-high pressure hydrometallurgical processes, there has been very little work done on fundamental principles involved in this type of process. Conse- quently the literature lacks any significant data in this field. Oxidation of pyrite,3 phalerite,4 galena,5 and recently molybdenite" in alkaline solutions has been reported to some extent. This investigation was initiated, therefore, to broaden the application of high temperature-high pressure hydrometallurgy and also to contribute some insight into the basic mechanisms of oxidation in an aqueous medium under these conditions. In addition to the immediate consequences of these processes much valuable information remains to be learned about fundamental reactions when they are carried out at temperatures and pressures slightly higher than those normally encountered. Leaching of molybdenite by alkaline solutions under oxygen pressure has recently been reported in the Russian literature by E. S. Usataya,8 who found that leaching rate increased with an increase in the pH of the solution—the strongest effects being observed at a pH of 10—and also with an increase in temperature. Usataya also has reported the formation of a protective film on the surface of the molybdenite when the leaching solution was weakly alkaline, neutral, or acidic. He believes that this oxidation process explains the migration of Mo+ + in the oxidation zones of molybdenite ore deposits and the subsequent impoverishment of the ores. Equipment: The high temperature-high pressure reaction unit used in this work was especially designed for kinetic studies of this nature, emphasis being placed on accuracy of measurement and precision of control. As details of the unit's construction and operation have been discussed elsewhere,7 Only basic features and principles of operation will be discussed at this point.

Jan 1, 1957

Despite a long history of production of industrial minerals and rocks, New South Wales still offers significant opportunities for exploration for and development of these minerals. Exploration for opal, sapphires, and zeolites in the State has been particularly encouraged by pioneering geological studies by the Department of Minerals and Energy, which have resulted in the development of important new geological concepts and exploration techniques. Large areas with potential for these minerals have not yet been tested. In the case of sapphires, the studies have identified a new type of deposit which is'the source of most of the sapphires mined from alluvial deposits. Recent price increases for heavy minerals, a re-evaluation of previous exploration in coastal regions, and a recognition of suitable environments in inland New South Wales have stimulated renewed exploration both onshore and offshore and have led to increased production. Significant potential also exists for development of a number of other minerals, including: topaz, which occurs in large, unusual and perhaps unique deposits in northern New South Wales; dimension stone (particularly granite); bentonite; diatomite; and silica for metallurgical use. Potential also exists for development of construction material resources, particularly construction sand, which is in short supply in the Sydney region.

Jan 1, 1989

By Peter W. Scott

The Caribbean islands, with their very diverse geology, are a source of several industrial minerals both for their own domestic consumption and for export. The geology of the Greater Antilles, which comprises Cuba, Hispaniola, Puerto Rico, and Jamaica has a Mesozoic or pre-Mesozoic basement overlain by sediments and volcanics, the latter being dominantly island arc in character. Later granitoid intrusions were emplaced. Obduction of ophiolites also occurred variously from the mid- Cretaceous to the Palaeogene. Thick accumulations of limestones surround the older strata, along with Neogene and younger sediments. The Lesser Antilles islands form an arcuate chain, mainly of volcanic rocks of calc-alkali or sub-alkaline affinity with some younger limestones and siliciclastic sediments. Trinidad and Tobago have closer similarities with the South American continent in their geology. Tobago has a metamorphic complex, juxtaposed with a volcanic-plutonic complex, and limestones. Trinidad has very thick Cretaceous to Recent exposed sedimentary sequence. The current exploitation of industrial minerals in the Caribbean is dominated by construction raw materials (mainly sand and gravel, limestone, and cement), although there is extraction of gypsum, silica sand, marble, clay (almost entirely for construction use), pumice, and natural asphalt. Salt is obtained from solar evaporation of seawater. Limestone of high purity and high brightness, gypsum, pumice, and high-density igneous rock have potential for further development of their markets, particularly ex- ports. Potential new and undeveloped industrial-mineral resources include residual and sedimentary kaolin, bentonite, zeolites, magnesite, and talc. Cuba could be a source for many industrial minerals in the future.

Jan 1, 1999

By V. Tsyplakov

This article reviews factors of preg-robbing effect, occurring in the course of pressure oxidation of ore and concentrates, containing chloride compounds and so-called 'organic carbon'. The article also summarizes the main results of the studies and testwork conducted to overcome this effect. The following efficient preg-robbing mitigation methods have been noted: higher temperature of pressure oxidation process, preliminary removal of natural carbonaceous material from concentrate, chloride removal prior to concentrate pressure oxidation, and addition of water-soluble organic blanking agents, which suppress the adsorption activity of the native ore adsorbents. Keywords: preg-robbing, double-refractory gold concentrates, pyrite, arsenopyrite, blanking agents, pressure oxidation, autoclave leaching

Sep 1, 2012

By James E. Chapman

The observations here presented are not those of an expert accountant, but of one who, while he has seen considerable service in the accounting departments of large companies, has spent more time in engineering and operating. This paper is intended to cover, in a measure, mine accounting for small mines, as distinguished from the elaborate systems, requiring many persons in the accounting department. I shall attempt to outline a system embracing the essentials of accounting, and simple enough in form to permit one or two persons to carry it on from month to month, in sufficient detail to be able to tell quickly the grade of ore, the prices received for metals, costs per ton for mining and milling, costs per foot for development, upward or downward tendencies in costs, ore settled or in transit, cash on hand, stocks of supplies on hand, efficiency of labor, etc. As in all accounting, there are two main divisions: that of revenue received for what is sold, and that of disbursements made for what is bought, so in mine accounting we have to consider chiefly the income derived from sales of ore or concentrates, and the expenses incurred in producing the said ore or concentrates in a marketable condition. I. Income The revenue of a mining company from the sale of ore or concentrates comes in the form of remittances, accompanied by settlement sheets made out by the buyer of the mine product, such as a smelting company. It is the duty of the mine accountant (or the person to whom this is assigned in connection with other work) to check these settlement sheets, against both the mine weights and assays, and the schedules of prices arranged between the mine and the smelter. As a rule, quotations for silver, lead, zinc, copper and other metals enter into the settlements, and require checking, as do also bills of lading. Each step of the arithmetical calculation is also checked.

Jan 1, 1917

By Pak DL

Over the last decade computers have become an essential element in assessing the economic feasibility of mining new mineral deposits and in assisting a variety of related support functions. A broad overview is given of the many technical application areas where computers are contributing to the mining industry with reference to work being done on the evaluation of drill hole information, mineral inventory modelling, ore reserve estimation, financial analysis, process simulation, process control, workshop job scheduling, PERT applications, and com- puter aided drafting. In all these areas the computer has greatly reduced the manual effort involved in looking at alternatives. It has had a significant effect in eliminating delays in revising calculations, or rescheduling activities to incorporate new data or cater for changing conditions, while at the same time providing more accurate and prompt information for the management decision making Process.

Jan 1, 1980

By L. Katgerman, E. N. Straatsma, Suyitno

"Single-roll strip casting process is studied using computational fluid dynamics which takes into account fluid flow, heat transfer and solidification. The computational model is based on the conservation Jaws of momentum, energy and continuity. Correlation of strip thickness, solidification zone length, and puddle shape on single-roll strip casting of Al-1 %Mn is explored. Feeding pressure and roll speed are investigated. The results show that the··strip thickness slightly increases with pressure, similarly the length of solidification zone. The variations of strip thickness and solidification zone length with roll speed show a sharp decline for strip thickness and slight decline for the length of solidification zone with increasing roll speed. The constraint and free-jet flow have different feature in term of flow field. Severe turbulence is observed on the free-jet flow.IntroductionThe near-net shape casting of strip metals is a demand nowadays. The demand is particularly stimulated by the challenge to become more competitive through enhanced performance. The improvement in the existing processes and new innovative technologies are introduced by the metal industry to gain better product quality, more efficiency in energy consumption, low throughput, yield and operating costs [1-3].There are many advantages that can be obtained by the direct casting of strip. The most prominence is the elimination of hot rolling. Beside that the high rate of heat extraction associated with strip casting offers the possibility of a finer, Jess segregated cast structure. The microstructure will result in the improvement of mechanical properties compared to conventional material, or alternatively the opportunity of using grades of metal outside the normal range for continuous casting.The concept of single-roll strip casting has been difficult to commercialize, because of the complex interactions between fluid flow, solidification, shrinkage, and stress, which lead to serious quality problems. Besides that, the quality and the thickness of the strip are affected by the thermal properties of the strip, roll cooling conditions, roll geometry, and other process parameters. To understand how these parameters affect the strip formation, some researchers have modeled the process [4]."

Jan 1, 2004

By Michael H. Leon, John A. Organiscak

Controlling worker dust exposure on longwall mining systems is difficult because the working face area serves as an immediate return during the mining cycle and the amount of airborne dust generated is directly related to production. Since improvements in longwall mining technology have significantly boosted production levels, additional technology is needed to control the airborne respirable dust generated at present and future production levels. One concept to reduce longwall worker's dust exposure is to maintain two splits of air at the face -- a clean intake split in the workers walkway, and a return (dusty) split over the face conveyor. The U. S. Bureau of Mines has recently investigated a concept to overcome the visibility handicap of face partitions by utilizing a permeable polyester mesh. The mesh material was anticipated to provide adequate air-splitting capabilities as long as the pressure differential between the face and worker walkway was minimal. Initial testing of this concept at the Bureau's Lake Lynn Laboratory showed that notable reductions could be achieved with a 1/8 in (3.18 mm) and 1/16 in (1.59 mm) mesh opening size. Dust reductions at 100 ft (30.5 m) and 200 ft (61.0 m) downstream of source were 58 and 36 pct, respectively, for the 1/8 in mesh and 79 and 55 pct, respectively for the 1/16 in mesh. Longwall application of the 1/8 in mesh showed similar results to the Lake Lynn Laboratory tests. A flame retardant mesh was used underground with portable lighting mounted on the shearing machine for face side lighting.

Jan 1, 1993

By G du Toit, P L. Gillot, M Swanepoel

Randgold Resources’ Loulo-Gounkoto Complex is one of the largest gold mining operations in Mali, West Africa. The mine, which is situated on the western border with Senegal, treats more than 4 Mt/a of ore through a conventional three-stage crushing and ball milling circuit followed by a carbon-in-leach plant. Ore supply is achieved by a combination of open pit and underground mining, with the majority of the ore supply sourced from the Gara and Yalea underground mines situated approximately 2 km and 6 km respectively from the gold plant.In 2011, Randgold Resources commissioned Golder Associates to perform an evaluation study for providing structural backfill to both the Gara and Yalea underground mines using the current gold plant tailings. The test work performed as part of the evaluation study concluded the need for a tailings cycloning and dewatering facility capable of producing slurry at a solids concentration of 65 per cent with a particle size distribution that had minimum 25 per cent passing 20 µm and less than 5 per cent of -5 µm material. Tailings desliming was required to ensure a consistent feed quality to the paste preparation plants and to ensure that the system would be capable of handling variation in the feed composition from the gold plant.WorleyParsons, previously TWP Projects, was contracted by Randgold Resources to complete the engineering design for the slurry preparation plant, whilst Golder Associates was retained to complete the engineering design of the two paste preparation plants.This paper discusses the test work, design considerations and engineering design of the slurry preparation plant, termed the ‘intermediate plant’, as well as all ancillary facilities required for the delivery of the deslimed slurry to the paste preparation plants located at the two underground mines.CITATION:Swanepoel, M, du Toit, G and Gillot, P L, 2014. Case study – engineering design for a slurry preparation plant for a paste application in West Africa, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 477–486 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By Washington Martins da Silva Júnior

In stamping process, sliding between metal sheet and forming tool leads to wear of tool surface. Maintenance of stamping tools involves polishing the tool edge, or, in case of severe damage, replacement of the tool. Hard coatings have been applied on the stamping tool surfaces in order to reduce the maintenance cost causing a great economic impact in metal work industry. In this work, CrAlSiN coatings were applied by PVD onto SRV2W tool steel. The coating toughness was avaliated by the critical load in scratch tests. The following coating parameters were analyzed: 1- substrate surface finishing process; 2- coating architecture (multilayer or gradient); 3- chemical composition of the coating. AlSi concentration varied from the substrate/coating interface to the surface. Coatings were 3 µm thick. Scratch tests were carried out using a Vickers indenter. The applied normal load was varied from 0 to 13 N for a scratch length of 5 mm. In order to study the effect in the toughness, the substrate roughness was controlled by the finishing process before PVD coating. Samples subjected to polishing presented highest critical loads. Gradient coatings presented higher critical loads than those with a multilayer architecture. Coatings with higher concentration of AlSi near the surface supported higher loads before failure.

Jul 31, 2018

By J. W. Rutter, K. T. Aust

In previous studies of grain boundary migration in zone-refined lead, the authors used bicrystal specimens consisting of a striated crystal which was grown from the melt, and an adjacent striation-free crystal, introduced by artificial nucleation and growth.1 While this method permits the study of the motion of individual grain boundaries, it does not provide control of the relative orientations of the grains. The present note will describe a technique for controlling the orientations of the two crystals in this type of specimen. The technique consists essentially of placing a striated crystal and a striation-free crystal of controlled orientations end-to-end in a graphite trough, then melting a short zone at the junction of the two crystals and allowing it to freeze to form the desired grain boundary. The apparatus used to carry out this process is illustrated in Fig. 1. It consists of a trough milled from high-purity graphite,with grooves in the underside for the placement of thermocouples. The graphite piece fans out on one end at the level of the bottom of the trough; the sides of the trough are completed in this region by the attachment of a mating plate with a slot cut at any desired angle to permit reorientation of the crystal placed at this end of the assembly. The joint between the crystals is made at or near the point where the slotted plate joins the rest of the trough. The thermocouple slots are deepened in this region so that the thermocouples are separated from the melt by only 1/32 in. of graphite. An induction heater, with suitable temperature control, is used to obtain the molten zone. The two single crystals used are first chemically polished in a solution consisting of eight parts glacial acetic acid and two parts 30 pct hydrogen peroxide. They are then placed in the trough with the ends to be joined at the position of the thermocouples. Next, cooling is applied to the two crystals by means of air

Jan 1, 1962