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By George F. Crocker

Introduction The Helen mine and the Victoria mine of Algoma Ore Properties, Limited, in the Michipicoten district, Ontario, are 120 miles north of Sault Ste. Marie, on the north shore of lake Superior. They are on the Algoma Central railway between Hawk Junction and Michipicoten Harbour. Between them, these mines have produced 10,757,113 tons of iron ore. From 1900 to 1918, 2,823,369 gross tons of brown ore was shipped, and from 1939 to the end of 1949, 7,933,744 tons of siderite was produced from the open-pit operations and underground development. The finished product, known as 'Algoma sinter', is shipped to blast furnaces both in Canada and the United States. The iron-ore bodies are a part of a tabular shaped area of iron formation that extends over a length of more than 10,000 feet and has maximum width of 1,000 feet. The two siderite orebodies, known as the Helen and Victoria, are separated by two diabase dykes. The Helen orebody is 1,600 feet long with a maximum width of 250 feet and the Victoria is 1,200 feet long with a width comparable to the Helen. These orebodies are considered to be a replacement of the original rock by iron carbonate. The introduction of the iron-1bearing material probably occurred after the development of the major folded structures. The open-pit mining of siderite started in the Helen ore body in 1939 and continued until 1945. During this period, 3,853,395 tons of ore was mined. Open-pit mining started in the Victoria body in 1946 and is still being carried on. Underground development commenced in September, 1947. Diamond drilling and surface sampling had shown the Helen deposit to average 35.61 per cent Fe and 7.28 per cent SiO2, and the Vi.otoria deposit 33.73 per cent Fe and 10347 per cent SiO2?

Jan 1, 1950

By Pierre C. Vieillescazes

MIGA: Unique Multilateral Risk Mitigator ?A World Bank Group agency established in 1988 to promote and facilitate sustainable foreign direct investment in emerging coufacilitate countries ntries (north(north--south and southsouth south--south) ?Guarantees equity and debt and many other types of investments against non-commercial risk. ?Can cover the following type of risks: ?Expropriation ?Breach of Contract ?Currency Transfer and Inconvertibility ?War and Civil Disturbance ?Non-Honoring of Sovereign Financial Obligations

May 1, 2010

By E. Dernedde

Cell rooms of aluminium smelters have large openings in the sidewalls and in the roof. These openings provide a high ventilation rate, which removes heat and contaminants emitted by the reduction cells and thereby ensures acceptable working conditions inside the cell room. However the large openings make the airflows through the smelter building sensitive to the wind. In this study equations for the airflow through the openings of a smelter building exposed to crosswinds were developed and verified against plant measurements. The equations were then used to estimate the airflows through a two-storeyed smelter building containing VS Soderberg cells. Wind protection by wind-covers over the sidewall openings and by upwind buildings made the airflows through the building less sensitive to the wind. Physical and mathematical modelling showed that working conditions inside the wind-protected cell room would be acceptable for crosswinds at speeds up to 16 km/h. These predictions were confirmed by measurements taken in a VS Soderberg smelter.

Jan 1, 2007

"The United Nations, through the secretariat of the United Nations Economic Commission for Europe (UNECE) and its Ad Hoc Group of Experts on Harmonization of Fossil Energy and Mineral Resources Terminology, developed the Framework Classification.The UN Classification applies to fossil energy and mineral reserves and resources located on or below the Earth's surface. It aims to simplify reporting of energy and mineral reserves and resources in a globalized world and is intended to improve global communications regarding remaining quantities of non-renewable fossil energy and mineral resources. The UN Classification is not recognized as a Foreign Code under NI 43-101.SECTION I1.,The United Nations Framework Classification (UNFC-2009) applies to fossil energy and mineral reserves and resources located on or below the Earth' s surface. It serves the needs for classification at a global level (for energy and mineral supply studies), for governments (resources management and policy formulation), for industry (business process management) and for financial reporting.SECTION II2.,The UNFC is a generic system in which quantities are classified on the basis of the three fundamental criteria of economic and social viability (E), field project status and feasibility (F), and geological knowledge (G), using a numerical coding system. Combinations of these criteria create a three-dimensional system. Categories (e.g. El, E2, E3) and, in some cases, sub-categories (e.g. E1.1) are defined for each of the three criteria as set out and defined in Annexes I and II.3 The first set of categories (the E axis) designates the degree of favourability of social and economic conditions in establishing the commercial viability of the project, including consideration of market prices and relevant legal, regulatory, environmental and contractual conditions. The second set (the F axis) designates the maturity of studies and commitments necessary to implement mining plans or development projects. These extend from early exploration efforts before a deposit or accumulation has been confirmed to exist through to a project that is extracting and selling a commodity, and reflect standard value chain management principles. The third set of categories (the G axis) designates the level of confidence in the geological knowledge and potential recoverability of the quantities.4. The categories and sub-categories are the building blocks of the system, and are combined in the form of ""classes"". The UNFC can be visualised in three dimensions, as shown in Figure 1, or represented in a practical two-dimensional abbreviated version as shown in Figure 2."

Jan 1, 2003

By L. A. Ayres da Silva, J. P. G. Negri, A. L. M. Ayres da Silva

"Rock hardness is dependent on the type and quantity of the various mineral constituents of the rock and the bond strength that exists between the mineral grains. As the book “The Complete ISRM Suggested Methods For Rock Characterization, Testing and Monitoring:1974-2006” explains, hardness is a concept of material property. As such, the quantitative measure of hardness depends on the type of the test employed.Among the three types of tests that have been used to measure the hardness of rocks and minerals: 1) indentation tests; 2) dynamic and rebound tests; 3) scratch tests, the authors of this paper chose indentation tests, more specifically the Vickers test, and complementary verified the correlation between the results of the Schmidt sclerometer tests (rebound tests) and the Vickers microhardness tests in a set of the same 9 (nine) granite rocks.The objective of this research was to verif y the correlation of one created index, based on the Vickers test that can be able to represent the rock material hardness. We know that Vickers tests determine the microhardness of individual rock minerals. A pyramidal shaped diamond is applied to the surface with a specified force. The area of the permanent residual deformation divided by the applied force is a measure of the hardness. Using the relative participation of the mineral components of the rock, we established a hardness index denominated EVM (Equivalent Vickers Microhardness).The correlation of the EVM with others strength properties and application parameters like UCS (Uniaxial Compressive Strength) to study sawability of granite blocks have presented very good results. The association of equivalent microhardness with others strength parameters, allowed to find powerful algorithms for analyzes of the rock materials behavior under diversified circumstances, as the sawability of granite blocks, as we can see in Fig. 1.Other very interesting correlations were found as the EVM values and that were obtained by the use of the Schmidt impact hammer for the superficial hardness determination."

Jan 1, 2015

By L. A. Nazarova, M. Vandamme, L. A. Nazarov, R. I. Rodin

"The paper describes a new method of interpreting the “canister test” data for the quantitative estimation of gas-kinetic parameters of coal bed based on the developed model of gas emission from coal sample placed in a sealed container. The model accounts for grain-size composition of the sample, initial gas content S, as well as coefficients of diffusion D and mass transfer ?. The inverse coefficient problem is formulated to find S, D and ??from the data of pressure measurements in the sealed container. It is shown that the inverse problem is uniquely solvable if the pressure is dropped during the experiment. The method has been tested using the data from an underground coal mine in the Kuznetsk Basin.Based on the poroelastic model of a coal bed and Khristianovich’s concept about origination and evolution of the filtration zone F in the neighborhood of a degassing borehole the authors considered the corresponding direct problem on rock mass geomechanical state. It was offered interpretation method for data on pressure measurements in a plugged degassing borehole allows evaluation of the diffusion coefficient, the horizontal component of natural stress field and parameters of F. The related inverse problem of the mixed type is formulated, and the cost function is constructed. The analysis using synthetic input data has shown that the cost function has a number of local minimums arranged on the same straight line, one of the minimums being the inverse problem solution. INTRODUCTIONPre-mine degassing is an integral part of coal mining. It allows mitigation of induced accidents in mines (coal and gas outbursts, rock bursts) (Guide, 1990; Malyshev & Airuni, 1999; Seidle, 2011) and also furnishes an alternative and ecology-friendly energy source—methane (Rice, 1997; Nambo, 2001). Choosing an optimized pattern of degassing boreholes, as well as estimating degassing time and amount of gas recovered requires data on gas-kinetics indices of coal beds out of which the key parameter is a gas content S. According to the latest guidelines for coal mines in Russia (Ruban et al, 2012), mining is allowed if S in a coal bed section is under 7 kg/m3."

Jan 1, 2015

By Yanping Xiao, Ton van Sandwijk, Gus Van Weert, Larry McHugh, Thomas Zabev

"All attempts to remove significant amounts of arsenic from enargite via neutral or reductive pyro routes have required operating temperatures between 600 and 700 º C, too high to propose an equipment development program. Operating at reduced pressures, or using hydrogen or elemental sulphur as a sweeping gas did not help to lower these temperatures. Admixing iron powder gave excellent results, but still required 700 º C. By fortuity, in recent experiments to produce tennantite from an enargite mineral sample, it was observed that enargite was completely converted to bornite, chalcopyrite with minor residual tennantite within an hour at 400-450 ºC. This is believed to be due to the presence of pyrite in the mineral sample treated. All earlier decomposition work appears to have been done on predominantly enargite (i.e. low pyrite) samples, or at high operating temperatures, ignoring possible reactions at lower temperature. The decomposition of enargite into iron substituted tennantite plus some bornite under evolution of liquid elemental sulphur, followed by further decomposition of this tennantite into bornite and volatile arsenic sulphides, appears experimentally feasible at these low temperatures and mimics described ore genesis pathways at > 250 ºC in saline solutions. We suggest two pathways to describe the observed experimental results:20 Cu3AsS4 + 12 FeS2 ???5 Cu10Fe2As4S13 + 2 Cu5FeS4 + 31 S(l)31 S(l) ???31 S(g) (evaporation)5 Cu10Fe2As4S13 ???10 Cu5FeS4 + 10 AsS(g) + 5 As2S3(g)"

Jan 1, 2014

By L. Tong, D. Robinson

"The stirred milling of nickel laterites offers possibilities for improving liberation and selective size reduction of soft nickel-bearing minerals in laterites. Batch grinding tests were performed in a netzsch™ lME4 stirred mill on siliceous goethitic, goethitic, and saprolitic nickel laterites. Tests on the -2,000 µm sample displayed the effects of selective comminution. The -38 µm product of grinding the -2,000/+38 µm feed confirmed the effects of selective grinding and nickel upgrading. Size classification followed by stirred milling is recommended for nickel upgrading. The energy requirement in the stirred milling was also investigated.RÉSUMÉ le broyage par billes de latérites comportant du nickel offre des possibilités d’amélioration de la libération et de la réduction sélective de la taille des minéraux nickélifères tendres dans les latérites. Des essais de broyage en vrac ont été effectués dans un broyeur à billes netzschMD lME4 sur des latérites nickélifères à goethite siliceuse, à goethite et saprolitiques. Des essais sur l’échantillon -2000 µm présentaient des effets d’une comminution sélective. le produit -38 µm de l’alimentation -2000/+38 µm confirme les effets d’un broyage sélectif et du rehaussement de la teneur en nickel. Pour améliorer la teneur en nickel, il est recommandé de classifier le minerai en fonction de sa granulométrie, puis d’effectuer un broyage à billes. l’énergie requise pour le broyage à billes a aussi été étudié."

Jan 1, 2015

By P. Van Marcke, X. Sillen, G. J. Chen, I. Troullinos, A. Dizier, J. Leysens, X. L. Li, J. Verstricht

"In Belgium, Boom Clay is considered as one of the potential host formations for the disposal of the High Level radioactive Waste (HLW). The URL HADES at 223 m depth at Mol site was constructed in order to study the feasibility of HLW disposal in Boom Clay. Since 1995, the URL R&D programme has focused on large scale demonstration tests like the PRACLAY experiment.The PRACLAY in-situ experiments include a set of three tests: The gallery and crossing test, PRACLAY Heater test and PRACLAY seal test. The main aim of the Heater test is to study at a large scale the thermal impact of a HLW repository on the host rock. The test is housed in the PRACLAY gallery. A hydraulic seal, made of compacted swelling and low permeable bentonite annular ring was installed at the intersection between the heated and the non-heated part of the gallery. The primary objective of the seal is to provide undrained hydraulic boundary conditions for the Heater Test.The PRACLAY gallery was constructed in 2007 and the hydraulic seal was installed in 2010. The bentonite is hydrated by natural and artificial process. The swelling, total pressure and pore pressure of the bentonite are continuously measured and analysed by numerical simulations to get a better understanding of this hydration processes. The performance of the seal is tested systematically by means of gas injection breakthrough tests and permeability tests at interface bentonite / Boom Clay and in the Boom Clay around the seal.The PRACLAY Heater will be turned on at the end of Oct. 2014, since a sufficient seal swelling has been attained to fulfill its role for the PRACLAY Heater test. This paper will focus on the PRACLAY Seal test: How we understand the process behind the hydration of the bentonite and how we test the performance of the bentonite seal."

Jan 1, 2015

By Cristina Echavarría

MAIN POINTS ? The region: opportunities and limitations ? Overview of main issues emerging from MMSD in South America ? Who comprises the local community? ? What are the main challenges? ? Some suggestions for companies to improve their contribution to local sustainable development of mineral rich localities THE REGIONAL CONTEXT 1. The region is a producer of minerals contributing over 20% to world metal production. It consumes only 8% 2. Significant diversity of national contexts-both between countries and within countries 3. Variable but predominant need for strengthening of government and community institutions and governance, especially at the local level 4. Dearth of baseline information for decision making 5. Sustained social spending during early 90?s as a consequence of economic recovery and fiscal policy, produced important advances in education and health 6. Despite government efforts in most countries poverty continues growing 7. Highly inequitable distribution of wealth persists

May 1, 2002

By A. Probst, J. A. Finch

"Solids concentration (% solids) profiles and the clear liquid/slurry interface level (mudline) were determined from conductivity measurements in thickeners at Falconbridge' s Strathcona mill (Ni concentrate and non-mag thickeners) and Kidd Creek Division (Cu, Zn concentrates and final tails in the concentrator and thickeners in the Zn plant).The conductivity measurement system consisted of a probe 1.5 m in length with 24 electrode cells, a 24-channel relay, a conductivity meter and a computer. A conductivity profile is collected which locates the mud-line by the sharp change in conductivity. The conductivity measurements are readily converted to solids concentration profiles without need for calibration.The results from the conductivity measurements were compared with those from pressure profiles and direct measurements on local samples obtained using a modified Noranda sampler.It is concluded that the conductivity technique is applicable to locate the mud-line and to estimate the solids concentration profiles in thickeners. This on-line information could improve the operational efficiency of industrial thickeners.INTRODUCTIONAn automated, on-line technique for detecting the clear liquid/slurry interface (or mudline) and the variation in solids concentration with depth would enhance thickener operation and control. In some processes such enhanced control offers significant benefits. For example, in hydrometallurgical operations solid/liquid separation is often the process limiting step. Water treatment plants are increasingly expected to operate remotely and reliable sensing is vital.Current attempts to detect the mud-line include reflection of some signal (e.g. sonar), floats (Dahlstrom, 1985) and measurement of pressure (Rosenblum, 1991), and in one case, natural radioactivity of the solids (Johnston and Simic, 1991). A recent commercial development uses reflection from a vertical array of optical transmitters/sensors, which also gives local solids concentration (BTG Inc., 1991)."

Jan 1, 1993

By A. R. Hekmat

Hypereutectic Al-Si alloys are used in applications that require high resistance to wear and corrosion, hardness and low coefficient of thermal expansion, To maximize the properties of these alloys, semi-solid processing can be utilized to modify the solidification structure of the primary silicon crystals as well as to reduce microsegregation and porosity, The transformation and spheroidization of primary Si crystals by shearing in the semi-solid state are not fully understood as they precipitate in the presence of other alloy phases, The objective of the present work is the determination the rheological characteristics of A390 (Al-17%Si-4,5%Cu-0.5%Mg) alloy using a Couette type (Haake RV12) viscometer and examining the microstructural evolution during continuous cooling and isothermal shear rate experiments, The effect of shear rate, solid fraction (temperature) and morphological evolution of the silicon crystals are investigated.

Jan 1, 2005

By Nelson Hogg

"THE NOR-ACME gold mine is located close to the north shore of Snow Lake, at 54°53' north latitude and 100°03' west longitude. It is about 75 air miles east of Flin Flon, and 36 miles by road from Wekusko at Mile 81 from The Pas on the Hudson Bay Railway.The claims which contain the Nor-Acme orebodies were staked in 1927 by C. R. Parres, who, with his sons, held the ground until 1938 when Nor-Acme Mines Limited was incorporated. In 194 l, on the recommendation of F. Ebbutt (1), this property was optioned by the Howe Sound Exploration Company, Ltd. A program of 50,000 feet of diamond drilling resulted in the outlining of two orebodies containing an estimated 5,000,000 tons with an average grade of 0.15 ounces per ton to a depth of 1,000 feet.A period of inactivity during the war years was followed by the construction of a mining plant capable of treating 2,000 tons of ore per day. Milling started in March 1949, and to the end of 1954 has resulted in the production of 383,793 ounces of gold and 32,906 ounces of silver from 3,331,403 tons of ore.General GeologyThe general geology of the Snow Lake area is described by J. M. Harrison (2), and will not be discussed here except insofar as it affects the Nor-Acme orebodies. The orebodies occur in rocks of Precambrian age that have been classified by Harrison as the Snow group, comprising meta-morphosed sediments interbedded with acid and basic volcanic rocks. The volcanic rocks include pyroclastic types which are unique in the region, a fact which led to their classification in the Snow group rather than the more widespread Missi group that generally occupies the same stratigraphic position above the Amisk group (Figure 1)."

Jan 1, 1949

By Y. Duna

The reliability of mine ventilation systems is critical to normal and safe production in a mine and includes reliability of the following parts: ventilation system branch (or passage), ventilation structures, ventilation network, and the fan. Among these, the reliability of a ventilation branch may be considered the foundation of the whole ventilation system. The branch ventilation flow includes four parameters: air volume; toxic and hazardous gas concentrations; temperature, and dust concentration. The calculation model for the reliability of a branch was established based on the analysis of normal distribution of flows in any one branch. Then, the efficiency of the ventilation structures and fire risk compromising the reliability of branch was studied. The results obtained were as follows: if the air volume, toxic and hazardous gas concentrations, temperature and coal dust concentrations of the branch are within reasonable limits, set at any stable state and at the same time, then this branch is reliable.

Aug 1, 2013

By Christopher Boys

"Many water inflows in Saskatchewan potash mines are linked to salt anomalies. Potash ore and three anomalies in the PCS Cory potash mine in the Patience Lake Member of the Prairie Evaporite Formation were studied to understand the processes involved in their formation. Another goal was to find geological indicators of the proximity of anomalies. A geological model that relates the potash to the salt anomalies has been developed.Up to five post-burial facies may be recognized. These range from carbonate-mud collapse breccias to bedded sylvinite, and probably result from post-burial leaching. In this model, the same fluids that caused widespread recrystallization and possibly enrichment of the potash salts, started by dissolving huge cavities in the evaporites. The effects of the leaching were highly variable, indicated by selectively preserved delicate laminae and chevron textures, to deformed and totally dissolved salt beds. In at least two major events, Late Devonian and Cretaceous, collapse structures may have acted as conduits for overlying formation waters to cause pervasive leaching and recrystallization of the Prairie Evaporite Formation.Geological indicators of the proximity of an anomaly may include: a change in insoluble seam color from greenish-gray to mottled brown and greenish-gray, unusual local increases in ore grade, large patches (e.g., >200 cm2) of sylvite-poor potash crosscutting units near the top of the ore wne, and drops in topography > 10 m of the marker seams. Anhydrite was more common in an anomaly than in ore. The local abundance of anhydrite in ore may indicate the proximity of some salt anomalies. Once an anomaly has been encountered, indicators of a major collapse feature may include: stretched clay seams, folded beds, small collapse features (1 m to 20 m), numerous washouts, or split clay seams with injected salt. Any number, or none, of these indicators may be found close to a major collapse feature."

Jan 1, 1993

By P. -A. Bosse, J. Robitaille, P. Blatter

The LaRonde ore is a Cu-Zn-Pb ore with gold (3-4 g/t) and silver (60-100 g/t). The precious metals are recovered with copper concentrate, zinc concentrate and cyanidation of zinc tails via Merrill Crowe precipitation. Subsequent to a recent mill expansion, excessive gold was reporting to zinc concentrate with a concurrent decrease in gold to copper concentrate. Owing to the higher return obtained from the metal, the mill endeavors to recover additional gold and silver to the copper concentrate and minimize the placement of precious metals to the zinc concentrate. A gold deportment study showed that the gold occurs mainly as küstelite, with a moderate amount of electrum and a minor amount of native gold. It also showed that various sulfur-based Au-and/or Ag-bearing coatings on liberated küstelite and electrum were the major mineralogical factors that caused gold and silver to report to zinc concentrate. By frequency, such coatings were observed on 70-80% of total liberated gold particles reporting to the zinc concentrate. Based on the gold deportment and the chemistry of the coatings, the collector chemistry was reviewed and a new collector was added into the circuit which resulted in a significant increase in gold and silver recovery to the copper concentrate. The information obtained from the mineralogy confirmed and guided other process optimization. In this paper, the authors will describe the process mineralogy of the LaRonde ores, and in particular, the mineralogical evidence diagnosing the problem. Reference will also be made to the rationale behind how the problem was solved, the results achieved, and future steps in optimization.

Jan 1, 2005

Kahama Mining Corporation Limited (KMCL), a wholly owned subsidiary of Barrick Gold Corporation, operates the Bulyanhulu gold mine. The operation has been in commercial production since April 2001 and is the first modern underground mine to be developed on the Lake Victoria goldfield in Tanzania. Bulyanhulu is located in a major mineralised system along an emerging gold trend. This area, the Lake Victoria Greenstone belt, has been the focus of significant exploration and development programs since 1994, with over 34 million ounces of gold having been discovered and four new mines commissioned. The Bulyanhulu project has accounted for just over a third of the gold resources discovered during this period. From an initial exploration program, which outlined a resource of 1.37 million ounces of gold, Bulyanhulu now hosts a reserve of some 12 million ounces in a resource base, the limits of which are, as yet, undefined. The Bulyanhulu property is located approximately 56 km south of Lake Victoria, in northwestern Tanzania, eastern Africa. A Mining Licence issued by the Government of Tanzania on July 23, 1999 grants to KMCL the exclusive right to mine a concession area covering 51.48 km2. The property is reached via a 75-km road from the main road to Dar es Salaam. The nearest towns are Mwanza to the north on Lake Victoria, 155 km by road and ferry, Kahama, 86 km by road to the south and Isaka, 126 km by road. Isaka is on the rail line between Mwanza and Dar es Salaam and has facilities to receive heavy equipment, and a fuel depot. A gravel airstrip, 1,700 m long has been constructed at the property.

May 1, 2003

By Xueyi Guo

The total production of nonferrous metals in China is 31.35 million tons in 2010, which ranks first in the world for the past ten years. Large quantities of solid wastes including slag, residue, ash, and dust are produced every year in the production of nonferrous metals. These secondary resources are renewable, not only contain abundant valuable metals which can be recycled by metallurgical processing, but also could eliminate the pollution to the environment. In this paper, the status quo of the main nonferrous metals recycling in metallurgical industries in China was summarized, and the future development of waste processing and resource recycling was prospected.

Jan 1, 2011

By E. O. Magnusson

THE orebodies of the Preston East Dome mine show a considerable variation in size,? shape, dip, and ground condition. They vary from small and large irregular masses being mined by shrinkage, cut-and-fill, and square set-and-fill mining methods to narrow veins being mined by open stoping. Standardization of mining operations has necessarily been difficult. This considerable variation in mining condition prompted the development of a bonus system which would give more equitable bonus payments through-out the mine than those obtained by the usually accepted methods of calculating mine bonus. PRINCIPLES ON WHICH THE SYSTEM IS BASED Under an incentive bonus system, performance (efficiency) and a price per unit of work done are inter-related. It is in the application of this? principle to working conditions .in the Preston East Dome mine that the system to be described differs from the standard methods of calculating mine bonus. It was found that the method of paying a fixed price per unit of work done, under the 'contract' system, gave satisfactory results in development, less satisfactory results in timbering, and results which were not satisfactory in stoping. Under the fixed price system, bonus payments, in timbering and stoping particularly, were very erratic and did not necessarily represent fair payment for the work done. A fixed price in development is satisfactory because the work done, and the conditions under which the work is done, are uniform. The drilling and blasting cycle is completed in one shift, the size of heading is con-trolled, and a minimum number of holes are required in order to obtain a satisfactory break. The performance possible under these conditions has been found to be confined to a fairly narrow range. By performance in development is meant the efficiency of the working crew as expressed in terms of the two variables of feet of advance per round and pounds of ex-plosives consumed per foot of advance. A change in rock formation, how-ever, may alter to a marked degree the performance possible, quite independent of the skill and energy of the working crew. The changes in working conditions that affect development performance from the standpoint of bonus calculation are usually easily apparent and are satisfactorily met by establishing several fixed prices.

Jan 1, 1944

By M. Sahoo, P. Burke, Y. Fasoyinu, J. P. Thomson

The effects of grain refinement, mold temperature and chemical composition on the hot tearing resistance of aluminum alloys 535.0 and 206.0 has been studied by pouring constrained rod castings in metal molds. In addition, two prototype components that could be used in automotive applications were also poured from both alloys by gravity tilt-pour and low pressure permanent mold casting processes. This paper summarizes the results and issues encountered during the casting trials. It was shown that grain refinement and mold temperature ::::: 400°C reduced, and sometimes eliminated hot tear cracks in both alloys. The two prototype engineering components could be cast successfully from both alloys in metal molds. The metallurgical issues related to molten metal treatment and processing temperatures were well controlled. However, issues related to the control of hot tearing, casting and mold design must be addressed in future studies to guarantee the production of defect free castings.

Jan 1, 2006