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By k. Lebecki, S. Trzcionka

The prototype and test results of the instrument for quick determination of incombustible content in deposited dust as a protection against coal dust explosion propagation are presented. Presently existing methods do not permit to obtain quick information about incombustible content, needed for the proper protection of workings. As the operating principle for the e instrument the dependence of reflection of infrared radiation intensity on incombustible content in the sample is chosen. The construction is based on the modern electronics. The measurement will be done at the sampling site. The range of the instrument is 0-100% of incombustible, direct reading, autonomous supply, weight no more than 0.5 kg, and is intrinsically safe according to EN Standards. During the Conference the instrument will be commercialized.

Jan 1, 2003

Contribution by F.S.A. de Frey The authors are to be congratulated on a job well done by making, in their paper, such a pool of information available to mining engineers. I would like to comment on the following statement: 'As an alternative to the commonly used deep-level mining methods, consideration should also be given to pillar mining at great depths as a logical extension of the current methods. For example, a 75 per cent extraction Or Ryder's discussion The moderate levels if average pillar stress (APS) (320 MPa) are consistent with pillar stability. Squat 10:1 pillars should never 'fail' in themselves, and foundation strengths are also not exceeded (the stresses are well below the 2 ½ x UCS rule-of-thumb provided the foundations comprise normal strong 200 MPa quartzites). Authors' reply We thank Dr de Frey for his contribution to our paper on shallow hard-rock pillar systems. To considerable extent, we share his enthusiasm the potential role of squat pillars in deep-level mining, although we harbour reservations concerning strata control, mining economics, other issues. We agree wholeheartedly that further research, together with carefully planned field trials, is warranted in pursuit of this potentially highly rewarding concept. .

Jan 1, 1995

By P. N. Harris

The Colloquium on 'Recent Mining and Metallurgical Developments in the Orange Free State' was held at the Civic Centre in Welkom on the 4th and 5th May, 1983. The Chairman of the Orange Free StatejKlerksdorp Branch of the Institute and Acting General Manager of Unisel Gold Mining Company, Mr D. A. Parfitt, opened the proceedings, and Professor A. N. Brown gave the welcoming address. Mechanization of mining The South African Institute of Mining and Metallurgy is to hold a one-day colloquium on 'Developments in the Mechanization of Mining Operations' during September 1984. Surfac,e mining and quarrying The Second International Surface Mining and Quarrying Symposium is being organized by The Institution of Mining and Metallurgy in association with the Institute of Quarrying.

Jan 1, 1983

By Donald J. Murdock

Column flotation has been developed over the past ten years as an alternative to conventional flotation. It has been used mainly in the cleaning applications of sulphide flotation, where its ability to wash the froth of entrained gangue and produce a higher-grade product has given it a distinct advantage over other technology. The benefits of column flotation can be summarized as follows: Improved concentrate gradeby 2 to 5 per cent . Significantly lower operating costs . Savings in capital investment . Superior control. Since the initial development of the equipment, a number of design improvements have been developed that now form the basis of the Cominco column-cell design. The purpose of this article is to discuss some of those design innovations, and present some typical industrial results.

Jan 1, 1991

By G. Iabichino, M. Cravero, F. Nacci, L. Rinaldi, L. Vigliero

ABSTRACT: The proposed paper is aimed at analysing the failure of a steep cliff slope that, in the past, was exploited for open pit mining operations. A volume of over 400,000m3 of gneissic aplitic rock was involved in the slope failure. An evaluation of possible failure mechanisms is given, based on a structural description of the rock mass, a mechanical characterisation and on computation methods. The block theory and limit equilibrium techniques for sliding and block toppling were applied and a comparison is given with the result obtained by using DEM models. RESUME: Le document proposé vise l’analyse des mécanismes de rupture d’une falaise qui a été intéressée dans le passé par une mine à ciel ouvert. Un volume supérieur à 400.000 m3 de aplite-gneiss a été concerné par la rupture de la falaise. Le document fournit une évaluation des possibles mécanismes de rupture, basée sur une description structurale de l’amas rocheu, une caractérisation mécanique et des méthodes de calcul numérique. L’analyse a été développée à l’aide de la théorie des blocs et de la technique de l’équilibre limite, soit pour le glissement que pour le basculement des blocs, et une comparaison avec le résultat obtenu par application des modèles DEM a été effectuée. ZUSAMMENFASSUNG: Die vorgeschlagene Arbeit zielt darauf ab, den Einsturz einer steilen Felswand zu analysieren, an der in der Vergangenheit eine Mine im Übertageabbau betrieben wurde. Der Einsturz betraf ein Volumen von über 400000 m3 an Gneis und Aplit. In der Arbeit ist eine Einschätzung des möglichen Mechanismus angegeben, der zum Bruch geführt hat, und sie basiert auf einer strukturellen Beschreibung der Felsmasse, einer mechanischen Charakterisierung sowie auf der Anwendung von Berechnungsmethoden. Angewandt wurden die Blocktheorie und die Methode der Gleichgewichtsgrenze für das Abrutschen und Kippen von Blöcken. Darüber hinaus wird ein Vergleich mit den Ergebnissen angestellt, die unter Verwendung von DEM-Modellen erzielt wurden.

Jan 1, 2003

By G. M. Evans, S. Mitra, G. J. Jameson, M. M. Hoque, E. Doroodchi, R. Moreno-Atanasio

In this study, the detachment behaviour of 314 μm diameter silica particles from a single 3 mm diameter bubble rotating in a confined cavity connected to a cross-flowing water channel was investigated. The liquid cross-flow generated a rotating flow inside the confined cavity, which was quantified using 2D particle image velocimetry (PIV) measurements. The fluctuating (x-y) velocity components inside the cavity for each cross-flow velocity, U, were then used to estimate the corresponding time/volume average turbulence intensity values, Ti. Turbulence intensity ranged from 9.3-16.2%. In the absence of a bubble, the rotating vortex within the cavity created a pressure field which decreased towards the centre of the vortex; wherein the lowest pressure zone was located at the centre of the cavity. The vorticity into the cavity was found to increase with increasing the turbulence intensity. A bubble, both without and with particles attached, was introduced into the cavity under different flow conditions and its motion was tracked using the shadowgraphy technique. Experimentally, it was found that the bubble-particle aggregate was trapped at the centre of the cavity (low-pressure region) following a spiral trajectory. An interface resolved 3D computational fluid dynamics (CFD) model was developed to predict the particle detachment conditions within the confined cavity. CFDpredicted vorticity in the absence of a bubble agreed well with experimental observation. The CFD analysis indicated that the vorticity inside the cavity was not significantly changed when a single bubble was introduced. On this basis, the computed vorticity was utilised in describing the force balance applied to the attached particle. Computationally, it was found that the critical turbulence intensity, beyond which the particle was detached from the bubble, was 14%. This value was consistent with the experimental observation of detachment at Ti at 15.7%, and above, but not at lower values. Keywords: Bubble, particle, turbulence intensity, vorticity, particle detachment, CFD, PIV

Jan 1, 2020

By C. H. Wyndham, N. B. Strydom

INTRODUCTION Acclimatization of the labour force to heat is an integral aspect of gold mining in South Africa. A recent survey revealed that about 250,000 Bantu mine workers require to be acclimatized to heat each year. Until 1965 men were acclimatized by means of one of the Chamber of Mines methods (introduced by the Human Sciences Laboratory in 1953). This type of acclimatization was carried out underground where men shovelled rock in hot stopes under careful supervision. However, it has become increasingly difficult in the last few years for mines to provide underground the conditions of work and environmental heat required for adequate acclimatization to heat. In examining an alternative to acclimatization in underground hot stopes, the Human Sciences Laboratory carried out a trial in 1965 of acclimatization in an air-conditioned climatic room on the surface of a mine. The new procedures developed from this trial have been so successful that there are today 26 climatic rooms on different mines. These rooms have been built following a design proposed by Mr Hodgson of the National Mechanical Engineering Research Institute1. Approximately 85 per cent of the total number of men being acclimatized each year are put through the new procedures in these climatic rooms. This paper gives an account of the problems which arose and how they were solved, the inter-relationship between physical conditioning and climatic room acclimatization, the prodecures developed for elimination of labourers with low maximum oxygen intakes, and the advantages of climatic room acclimatization. CLIMATIC ROOMS The majority of the climatic rooms (twenty) have been built on the surface, but a number (six) of mines preferred to establish their acclimatization centres underground in order to decrease the initial costs involved in the construction of such facilities. These underground climatic rooms are usually located near shaft stations in redundant haulages and they can accommodate from 200 to 400 labourers, thus eliminating the need for multiple acclimatization shifts. Figs. 1-4 illustrate various aspects of a surface climatic room. PROBLEMS WHICH AROSE IN INTRODUCING CLIMATIC ROOM ACCLIMATISATION There were four main problems which arose in connection with the introduction of the new method. These were: (i) The type and rate of work to be used. (ii) The air conditions required to obtain optimum acclimatization. (iii) The duration of exposure to heat each day and the total number of days of acclimatization. (iv) The methods of cooling labourers with high body temperatures. Shovelling rock would have been the desirable type of physical work to employ, but the air-conditioned space required to accommodate large numbers of men and the difficulty in standardizing the work rate in shovelling led to the decision to employ instead the work procedure used by the Human Sciences Laboratory in acclimatizing men in the Laboratory. This is the lifting of the body weight against gravity when men step on and off a bench. It has the advantage that large numbers of men can work physically at the required rate in a relatively small space (120 men can be accommodated in an area of 70 ft by 21 ft) and the cost of construction and ventilation of the climatic rooms is thereby reduced. Also the work rate can be standardized by varying the height of the stepping benches in relation to the individuals' body weights. The next problem was the air condition to be used in the climatic rooms. The Laboratory's research experience in acclimatization led it to choose an air temperature of 89°F (with the air almost saturated with water vapour) and an average velocity of air movement of 100 fpm. This air condition was combined with a work rate of 1,560 ft lb/min (oxygen consumption 1.0 litre/min) on day 1, and the work rate was increased gradually over the period of acclimatization to reach a work rate of 3,120 ft lb/min (oxygen consumption 1.6 litres/min) on day 9.

1. Book reviews Dislocations and properties of real materials, edited by M.H. Loretto. London, The Institute of Metals, 1985. 392 pp. Reviewer: F.R.N. Nabarro Au &Ag heap and dump leaching practice, edited by J.B. Hiskey. AIME, 1984. 162 pp. $20 (member), $15 (student member), $30 (non-member) plus $3.50 for postage and handling. (Order from SME Books, Caller no. D, Littleton, CO 80127, U.S.A.). Reviewer: R.A. Snodgrass The cost and availability of Colombian coal, by Eric D. Jamieson, with the assistance of Kathleen Jamieson. London, lEA Coal Research (14/15 Lower Grosvenor Place, London SWl W OEX). £50 (in member countries), £100 (in non-member countries). Reviewer: W.C. Mather Extraction Metallurgy '85. London, The Institution of Mining and Metallurgy, 1985. £42. Reviewer: R.A. Snodgrass 2. Recent publications Mining annual review 1985. London, Mining Journal, Jun. 1985. 600 pp. £26.50 (surface), £39.50 (air). High heat production (HHP) granites, hydrothermal circulation and ore genesis. London, The Institution of Mining and Metallurgy, 1985. 593 pp. £27 (members), £30 (non-members). Potential mineral resources of Egypt. 144 pp. US$10. Available from Bendix Field Engineering Corporation-MPGAP, Box 1237, Grand Junction, CO 81502, U.S.A. 3. Mintek reports Report M212 South African costs of equipment for the metallurgical industry (1984). Report M213 The response of as-rolled 3CR12 steel to heat treatment. Report M214 A computer programme for use in the development of multi-element X-ray-fluorescence methods of analysis. Report M221 Commodity profiles for selected metals. Report MIO7D Upgrading of alaskite rock to feldspathic sand. (First issued Jun. 1983; reissued Nov. 1985). IMM awards Given below are details of the trust funds to which applications are invited for grants, etc., payable in 1986. Application forms, which must be returned to the Secretary before 17th March, 1986, are available on request. Applicants should note that, in general, preference will be given to members of the Institution.

Jan 1, 1986

By M. Hakala

A computer program was developed to simulate transient strains and stresses during an overcoring in the situ stress measurement. The solution is based on superpositioning of elastic stresses. The measured strains can be compared with the calculated ones to check if the measured transient behaviour is accordant with the interpreted in situ state of stress. If not, the in situ state of stress can be calculated based on any transient or final strain values. The transient stresses can be compared with the strength envelope of intact rock and thereby estimate the core damage potential. Technically, the developed code fulfilled all the objectives, and the numerical error was found to be less than 5%. The basic idea can be applied also for different overcoring probes with minor modifications and recalculation of stress tensors. The analysed case studies showed clearly the advance of having an objective and practical quality control method to study the reliability of the in situ stress measurement data. The study was set up and funded by the nuclear waste management companies Posiva Oy ( Finland ) and Svensk Kärnbränslehantering AB ( Sweden ). Un programme informatique a été développé pour simuler des tensions et des contraintes passagères pendant la mesure in situ de contrainte de surcarottage. La solution se fonde sur une superposition de contraintes élastiques. Les contraintes mesurées peuvent être comparées avec celles calculées pour vérifier si le comportement passager mesuré correspond à l'état de contrainte in situ interprété. Sinon, l'état de contrainte in situ peut être calculé à partir de n'importe quelle valeur de contrainte passagère ou finale. Les contraintes passagères peuvent être comparées avec l'enveloppe de force de roche intacte et ainsi il est possible d'évaluer le potentiel de dégâts au noyau. Techniquement le code développé a rempli tous les objectifs, et le taux d'erreur s'est révélé être inférieur à 5 %. L'idée de base peut être appliquée aussi pour différentes expériences de surcarottage avec des modifications mineures et le recalcul de tenseurs de contrainte. Les études de cas analysées ont montré clairement l'avantage d'avoir une méthode de contrôle de qualité objective et pratique pour étudier la fiabilité de données de mesure de contrainte in situ. L'étude a été fondée et financée par les sociétés de gestion de déchets nucléaires Posiva Oy (Finlande) et Svensk Kärnbränslehantering AB (Suède). Es wurde ein Computerprogramm entwickelt, um Transient-Beanspruchungen und Spannungen während eines Überentkernens in situ-Spannung-Messung zu simulieren. Die Lösung beruht auf Superpositionierung von elastischen Spannungen. Die gemessenen Beanspruchungen können mit den berechneten Daten verglichen werden, um nachzuprüfen, ob das abgemessene Transient-Verhalten mit dem interpretierten in situ-Zustand der Spannung übereinstimmt. Wenn nicht, kann der situ-Zustand der Spannung auf irgendwelchen Transient- oder endgültigen Beanspruchungswerten berechnet werden. Die Transiet-Spannungen können mit dem Stärke-Umschlag des intakten Felsens verglichen werden und dadurch ein Kernbeschädigungspotential kalkulieren. Technisch erkannte der entwickelte Code alle Ziele und hat gefunden, dass die numerische Fehler weniger als 5 % waren. Grundsätzlich können auch verschiedene Überentkernen-Untersuchungen mit kleineren Modifizierungen und Wiederberechnung des Spannung-Tensors angewandt werden. Die analysierten Fallstudien zeigten deutlich den Fortschritt, objektive und praktische Qualitätskontrollmethode zu haben, die Zuverlässigkeit in Situ-Spannung-Messung-Daten zu studieren. Die Studie wurde aufgestellt und durch Atommüll-Management-Firmen Posiva Oy (Finnland) und Svensk Kärnbränslehantering AB (Schweden) finanziert.

Jan 1, 2003

By B. Z. Weiss, N. R. Comins, F. Blum

The effect of microstructure on the deformation and fracture properties of 3CR12 steel was investigated at different strain rates in the temperature range -196 to 200°C. The yield stress of the as-received steel, showing a banded dual-phase microstructure, was much lower than that of the flake-like dual-phase microstructure produced by heat treatment. The heat treatment also resulted in an increase in the volume fraction of martensite. The fracture toughness of the as-received 3CR12, on the other hand, was significantly higher than that of the heat-treated material. These changes in both yield stress and fracture toughness were attributed to the effect of microstructural parameters on the constraints imposed on the deformation and subsequent failure of the ferritic phase in the as received and heat-treated steels. The exceptionally low resistance to crack extension in a plane parallel to the roiling plane of the as-received material was ascribed to the delamination process, which is typical for controlled-rolled steels. The yield stress and fracture toughness were found to depend on temperature and strain rate. The appearances of the fracture surfaces were found to be consistent with the mechanical properties.

Jan 1, 1992

NIM reports Report No. 1615 Fluorspar pellets. A survey of the world market and an assessment of future South African production. Report No. 1621 Correction for matrix effects in the analysis of solutions by X-ray-fiuorescence spectrometry. Notices Questionnaire on Technicians The Department of National Education's committee of enquiry into the education, training, utilization, and status of engineering technicians in the Republic of South Africa was established as a result of Resolution 6.3 taken at the Sixth Conference on Engineering Education: The Education and Training of Engineering Technicians. Vraelys oor Tegnici Die Departement van Nasionale Opvoeding se komitee wat ondersoek instel na die opleiding, gebruik en status van ingenieurstegnici in die Republiek van Suid-Afrika is gestig as gevolg van Besluit 6.3 wat geneem is tydens die Sesde Konferensie oor Ingenieursopleiding: Die Opleiding van Ingenieurstegnici. Competition for Student Members of the South African Institute of Mining and Metallurgy Each year the Institute offers a prize (or prizes should the entries warrant it) of up to R100 for the best paper or dissertation on a topic appropriate to the interests of the Institute. The competition is open to all Student Members of the Institute.

Jan 8, 1974

By R. A. Snodgrass

Heap leaching is a topic that is gradually generating more interest in South Africa as more non-Witwatersrand gold deposits are being investigated. This was evident from the number of delegates (85) who supported the SAIMM School on Heap Leaching, which was held at Mintek from 29th February to 3rd March, 1988.

Jan 1, 1988

By P. R. Beeley

Metal founding - a modern perspective The recent development of metal founding is reviewed in the context of basic requirements for the successful manufacture of cil;5ti,ngs.Progress has been related to the two interdependent fields of process technology and product characteristics. . After a brief review of the growth of the traditional industry. various features of the modern industry are discussed. Reference IS made to current trends in process technology and to the introduction of new techniques affecting production engineering, product quality. and the general nature of the industry. Metallurgical aspects of metal founding are considered, and modern techniques for the control of casting conditions are examined. These aspects are related to the structure and quality of cast metal and to the development of newer types of cast material and product.

Jan 9, 1976

The aspect ratio (mill diameter/mill length) of autogenous and semi autogenous mills varies widely and can be as high as three or as low as 0.5. The literature on the subject of what effect aspect ratio has on grinding mill performance or energy efficiency is almost non-existent. However, at the design stage of many grinding circuits the subject is often vigorously debated amongst metallurgists. In this paper the performance characteristics of mills with different aspect ratios are examined to determine whether process performance characteristics are a function of aspect ratio and whether high aspect ratio mills are any more or less energy efficient than low aspect ratio units. Data from both pilot and full-scale mills are used for this purpose in open and closed circuit configurations.

Jan 1, 2007

The International Colloquium on Developments in Froth Flotation, which replaced the Annual University of Cape Town (UCT)/University of Stelenbosch (US) Minerals Processing Symposium, was held at the Van Riebeeck Hotel in Gordon's Bay on 3rd and 4th August, 1989. The Colloquium attracted 150 delegates from the mining, metallurgical, and chemical industries, including 9 from overseas.

Jan 1, 1989

By N. B. Prenn, R. H. Robinson

"The model described is a design and economic planning tool for analyzing surface mineral deposits. Mineralization, topography, costs and significant geologic features are input to the model. The results are:(i) final pit limits yielding the maximum total profit,(ii) annual cut-off grades and plant sizing yielding the maximum present value, and(iii) annual maps of the pit and annual production statistics for the mine, concentrator and smelter.Additionally, summaries are printed of the block mining sequence and cash flow. A special feature is an option to include dump-leaching operations. Stockpiling of material can also be simulated by the model. The model is built around theories of dynamic cut-off grades and a pit design algorithm. The dynamic cut-off grades maximize present value by examination of all economic and physical constraints for the optimum combination. The pit design algorithm is a set of rules formulated to find the maximum value from a special graph. The graph is different from graphs of analytical geometry, being made up of points and arrows connecting some of the points. These graph elements describe the relationship between any point in the deposit and the material which must be mined to get at that point. The model was designed to bring together the interdependent theories of economics, pit design and production scheduling."

Jan 1, 2014

By H. Matsuoka, M. Kawata, K. Mitsuhashi, C. Tokoro, T. Kato

Copper sulfide minerals generally have high floatability, but their floatability decreases when surfaces are oxidised under some conditions. Sodium hydrosulfide, NaHS, is known both as an activator and as a depressant for copper minerals. NaHS at low concentrations activates copper oxides by sulfurising surfaces, but at high concentrations depresses copper sulfides by interfering with the adsorption of collectors. In this paper, we applied NaHS to activate oxidised chalcocite and bornite and focused on the conditions of NaHS treatments such as dosages and pH, and the effect of these conditions on the floatability of those minerals. The pure minerals treated with NaHS were analysed using zeta potential analyser and X-ray photoelectron spectroscopy. Analyses indicated that the reactions of NaHS and the products on the mineral surfaces after the reactions (i.e. oxidation, pH change) depended on whether NaHS reacted with copper or iron, and the reactions between NaHS and iron depend on NaHS concentration and pH. Flotation tests using a small column cell were performed with a single pure mineral, and using a Denver-type flotation machine with a copper sulfide ore. The results of each flotation test were utilised to clarify the floatability. The relation between flotation behaviours and analysis results were also discussed. Keywords: Chalcocite, bornite, NaHS activation, flotation, floatability

Jan 1, 2020

By Z. Song

Real-time monitoring makes it possible to detect any disturbance occurring in production, while decision instruments can efficiently assist decision-makers to optimize production, reduce iterative workload, obtain better solutions, and preview possible results. Technologies for the above already exist and have been proven in the process industry, i.e. refining and smelting. Optimization is also essential for profitable and stable mining production. Real-time monitoring has already taken hold in mining operations, especially in surface mining, while optimization techniques have also been widely used in underground mining, particularly for planning and scheduling. This review is limited to the hard-rock mining production of metallic ores such as gold and copper. It reviews optimization techniques developed for mine planning and scheduling, and communication technologies suitable for underground applications. It also presents control features for individual operation units, and discusses the technical viability of a mining production real-time optimization (MPRTO) system for underground mines, with possible benefits and challenges. Operational disturbances always occur in mine production. An MPRTO system can be useful to maintain operational effectiveness and efficiency by allowing quick changes to short-term plans. This paper briefly describes the MPRTO system, including the input, output, and basic algorithms. The technical prerequisites for the system specified here are already available. Further studies that are required to improve the system are discussed. Keywords real-time optimization, underground mining, production, operation.

Dec 1, 2013

By J. Manchisi

Laboratory investigations were conducted to establish the feasibility of bioleaching a mixed copper oxide/sulphide rougher concentrate from Nchanga Mine on the Zambian Copperbelt. The objective was to determine the kinetics and extent of copper extraction for this material. Batch experiments were conducted under different solution conditions in stirred tank bioreactors. The progress of (bio)leaching was monitored through measurements of soluble ferrous and ferric iron, copper, pH, and redox potentials, while bacterial activity was monitored online through 02 and C02 gas utilization rates. About 20 per cent copper was solubilized within 2 hours in all cases of non-oxidative (abiotic), oxidative (abiotic), and bioleaching experiments. This was attributed to the dissolution of mainly copper oxides. Subsequently, bioleaching experiments resulted in an overall copper extraction of 93 per cent, with up to 8 g.L-1 copper after six leaching days, compared to 58 per cent copper extraction in the abiotic oxidative acid leaching experiments. However, there was little effect of time (i.e. poor dissolution kinetics) on copper recovery for abiotic non-oxidative acid leaching of the material. Hence, the rate of sulphide leaching increased due to the activity of bacteria. Thus, the material is potentially bioleachable under mesophilic conditions. However, more exhaustive test work needs to be conducted to establish the effect of bioleaching variables and heat requirement.

Jan 1, 2012

By M. A. El-Sayed

"Double oxide films (bifilms) are significant defects in light alloy castings that occur when, during melt handling, the oxidized surface of the melt is folded over onto itself and then entrained into the liquid metal, encapsulating a portion of the local atmosphere. These defects create crevices in the final castings and have been shown to decrease tensile and fatigue properties, and also to increase their scatter, making casting properties unreproducible and unreliable. This paper reports on two different experiments performed to study the behaviour of such defects in Al alloys. In the first experiment and as a proxy for a bifilm, air bubbles were held in an Al-5Mg alloy melt for varying periods of time before the melt was allowed to solidify. The composition of the gas content of the bubbles was subsequently analysed using mass spectrometry to ascertain how it changed with time. In the other experiment the influence of the age of bifilms on the mechanical properties of Al-5Mg castings was assessed by holding castings in the liquid state for different times before solidification, followed by mechanical property testing and SEM and EDX studies of the fracture surfaces of tensile test bars. This research could provide a better understanding of the behaviour of double oxide film defects, and may lead to the development of new techniques by which these defects could be eliminated, or at least deactivated, in light alloy castings. Introduction One of the major structural defects affecting the reproducibility of mechanical properties of aluminium castings is the double oxide film defect (El-Sayed and Essa, 2017; El-Sayed and Ghazy, 2017). This type of defect is usually created as a result of poor filling system design. Owing to the very high reactivity of liquid Al-Mg alloy with oxygen in the air, the surface of the liquid metal can be considered to be permanently coated with an oxide film (Weigel and Fromm, 1990). As a consequence of surface turbulence, the oxidized metal surface can become folded over onto itself, but not fused, and then submerged into the bulk liquid, with a portion of the mould atmosphere being entrapped within it (Campbell, 2003; Al- Sayed, 2016; El-Sayed, Hassanin, and Essa, 2016)."

Nov 1, 2018