Search Documents

By F. Field, R. Kirchain, J. Gregory

Utilizing alternative materials is an important tactic to improve the environmental performanceof products. Currently a growing array of materials candidates confronts today’s product designer. While life-cycle assessment (LCA) methods provide quantitative input into this selection decision, their implementations are evolving and disparate. The goal of this paper is to explore several major analytical variations of LCA implementations and the implications of these variants across a range of application contexts. Specifically, this paper examines analytical variations in valuation method and treatment of recycling by exploring allocation methods that affect product end-of-life. Case studies across a range of materials are presented, including materials that exhibit a spectrum in variation of environmental performance and material degradation between primary and secondary applications. Preliminary results indicate that the choice of analytical method can have real impacts on individual metrics and there are sets of analytical variation over which strategic results are strongly affected.

Jan 1, 2008

By Howard K. Worner

"In a rewarding career spanning nearly two thirds of a century, the author has worked at the frontier of such diverse fields as the creep of metals, structure properties and production of novel dental and surgical materials, molten salt electrolysis for titanium production, greatly improving the productivity of large iron blast furnaces and of oxygen steelmaking. While each of these has given great satisfaction, special thrills have derived from the development of new methods for the continuous production or refining of both ferrous and non ferrous metals. A rewarding segment was the evolution of various aspects of WORCRA technology. Unfortunately, several of these inventions have been ""ahead of their time"". Introduction""I am greatly honoured by the convening of this meeting to recognise my contributions to pyrometallurgy. My appreciation is the greater because this is the third Howard Worner Symposium; the first took place in the University of Newcastle in 1988, close to my 75th birthday. It was arranged by the local branch of The Australasian Institute of Mining and Metallurgy with the theme, ""Frontiers in Pyrometallurgy"". The second was organised by the University of Wollongong in conjunction with the Australian Academy of Science and the Australian Academy of Technological Sciences and Engineering; it celebrated my 80th birthday and, at my request, covered a broad range of topics under the heading of ""Recent Advances in Science and Technology"". Now, this very international meeting on ""Injection in Pyrometallurgy"" has been convened by the G K Williams Co-operative Research Centre for Extractive Metallurgy in my alma mater. I am both delighted and honoured that the cosponsors are the TMS (USA) and ISIJ (Japan).Dr Madhu Nilmani consulted me about the field to be covered and I readily concurred because ""injection"" has been of keen interest to me since the beginning of the 1960s when I began my pioneering work on sequential oxygen (or air) injection into flowing streams for both refining of blast furnace hot metal to steel and for the continuous smelting-converting of copper and nickel."

Jan 1, 1996

By B. G. Thomas

"Mathematical process models can be applied in several different ways to serve industry by inducing beneficial changes to process operation. This paper attempts to summarize the different uses, types, and attributes of these models, and to offer some ideas to consider when developing, using, and reporting on them. Process models range from empirical to mechanistic in nature and vary in complexity from simple analytical solutions to coupled, 3-D transient numerical simulations. They are classified here according to the way in which they are implemented in practice, viz. fully-online models, semi-online models, off-line models, and literature models. The purpose of the model should dictate how choices are made during its development. Ways to validate and compare the model with experiments are suggested. Examples are taken in the context of the author's experience in modeling the continuous casting of steel.IntroductionThe objective of this paper is to provide a partial introduction for this symposium by discussing some basic aspects of the application of mathematical process models in industry. Essentially, the aim is to explore how process models are used to benefit industry, and to offer some general comments and suggestions, based on the experience of the author, on how models can best meet this goal.This work is concerned with process models, which consist of systems of mathematical equations and constants that are solved on a computer to make quantitative predictions about some aspect(s) of the process. The specific variables required as input data and generated as output data are important features of the model. The equations often derive from a numerical solution to one or more differential equations and their boundary conditions. The model also includes the constants, which represent material properties, empirical relationships, and other knowledge about the process, and usually require considerable effort to obtain. Thus, general purpose commercial software packages, (ie. finite-element or finite-difference based codes), are not models in this context. They are useful tools, however, serving as frameworks for the development of process models."

Jan 1, 1994

By Nathaniel R. Quick

"Nd: YAG, KrF excimer, and Cu-vapor lasers are used in air to synthesize conductors and semiconductors as a second phase in silicon carbide and aluminum nitride. Conductor resistivities as low as 104 O-cm are formed in these substrates; the resistivities for the untreated substrates range from 10 11to 1014 O-cm. The silicon carbide conversion is relatively independent of wavelength while the aluminum nitride conversion shows a dependence on wavelength over the range 248 nm to 1064 nm. Silicon carbide conductors, evaluated over the range 15 K to greater than 300 K, exhibit metal like conductivity; resistivity increases with temperature. Silicon, carbon, and oxygen are identified as the principal chemical species associated with the conductor in SiC substrates while aluminum, nitrogen, and oxygen are identified as the principal chemical species associated with the conductor in aluminum nitride substrates. The silicon carbide system, which has the less complex phase diagram, is evaluated in more depth to explain the synthesis mechanism. Oxygen was principally on the surface and increasing SiC conductivity is associated with decreasing spacing between 5 µm, or less, diameter carbon globules. This technology is proposed as a replacement for metallization in electronic packages, sensors and devices. INTRODUCTIONCeramics are commonly used for multichip module, hybrid and multilayer electronic packaging; semiconductor device and sensor applications because of the insulating, conducting, semiconducting, or superconducting properties that these materials possess (1,2) The majority of ceramics, however, have not been known to exhibit conductive or semi conductive properties when exposed to rapid thermal heat processing. A ceramic and process which through selective conversion can combine two or more of these electrical properties to eliminate the need for metallization is of interest to both the commercial and military sectors."

Jan 1, 1994

By Germán Richter a

To comply with the chilean air quality regulation requirements, the Hernan Videla Lira Smelter which is a custom smelter having to cope with a wide variety of concentrates, has developed a two-step modernization plan. The main steps are: - A second acid plant of 80,000 Nm3/hr to be operating at the end of 1996. This will increase the sulphur capture from 43% to 701/o in association with the replacement of the Hoboken converter by a second PS-converter to reduce the operation problems resulting from the treating of high garde matte. - Oxygen enrichment, is going to be incorporated in 1998 in the Teniente Converter and PS-converters in association with tuyere injection of dry concentrates, increasing the sulphur capture to 90 - 93% of sulphur inputs. By this program, sulphur emissions will be decreased from 40,000 tpy today to less than 8,000 tpy and in this way to carry out the environmental regulations.

Jan 1, 1996

By Kandipati Sreenivasarao

Ion flotation is a promising separation process for continuously removing toxic metal ions from dilute process effluents. After treating the effluent with appropriate surfactant(s), the metal- bearing species adsorb onto the surface of rising gas bubbles and can be collected as foams. Suitable collectors have been identified for most of the elements of the periodic table. However, a better understanding of the thermodynamic, kinetic and engineering principles that determine the performance of ion flotation systems would facilitate commercial utilization of this technology. A model system of sodium dodecylsulfate-ethanol has been studied for the removal of Cu (11) from dilute solutions, using laboratory-scale flotation columns. This paper reports the effects of the air flow rate, solution height, foam drainage zone height and col1ector:metal ion ratio on the flotation kinetics, ultimate recovery of metal, flotation product grade, foam losses and effluent quality. Preliminary results for Pb (11) removal are also reported.

Jan 1, 1993

By G. A. Brooks

Reactive ball milling has been proposed as a new route for producing carbides from oxides through carbothcrmic reduction. It is claimed that through milling oxide and graphite powders to the nanoscale, amorphous materials with very high reactivity are formed, that allows for easy transformation of the starting material to another in a subsequent thermal process. Thermodynamic analysis of this proposed process suggests that unless particle sizes are reduced to below 10nm, then reduction in size alone cannot explain a change in the stability of oxides. Even with nanometer scale powders, the products formed need to have a lower total surface energy than the reactants before a chemical change will occur. A model developed by Bhattacharya and Arzt for predicting localized temperature changes based on milling conditions suggest that temperarure rises less than 400 K will be achieved in laboratory conditions. The present calculations suggest that nanometer scale powders formed through high speed ball milling (>10 mls) may have undergone a process analogous to melting and quenching. Further work is required to fully distinguish these features.

Jan 1, 2003

By Y. F. Jia

Arsenic constitutes a major contaminant for the hydrometallurgical industry. Its removal and immobilization from process effluents typically involves lime neutralization and co-precipitation with ferric iron (Fe (III)/As(V)>3). Alternatively, precipitation of scorodite (FeAsO4?2H2O (cr)) may be applied to arsenic fixation. The mechanism of arsenic fixation in the former process has been suggested to be surface adsorption. Unequivocal characterization of these products is difficult because of their amorphous nature hence a variety of methods need to be applied including the particularly powerful method, extended x-ray absorption fine structure (EXAFS) spectroscopy. In this study, we have investigated the preparation of arsenate-adsorbed ferrihydrite with the purpose to compare its structure to that of Fe(III)-As(V) co-precipitates and scorodite (both amorphous and crystalline). Furthermore the solubilities of these Fe(III)-As(V) solids are measured as a function of pH. Their structures are elucidated and correlated to their solubilities and thereby the application of these findings to the practice of arsenic removal and disposal is assessed.

Jan 1, 2003

By Muhammad Abid, Kh. .. S. Karimov

"In this study, design and investigation of biogas digester consisting of methane tank with built-in solar collector to utilize solar energy for the heating of the slurry prepared from the dung and heat exchanger is designed, developed and tested. The digester was laboratory type and consists of cylindrical metallic tank of size of 0.5 m in diameter; 1 m in height and 200 liters in volume. The surface of the digester from outside was covered by thermo insulated material a glass wool, except of south side (in northern hemisphere). This side played the role of built-in collector and was blackened to increase absorption of solar irradiation and covered under 45o by glass. In the blackened side of the digester on the different heights it was installed metallic pipes for the inlet and outlet of the air, connected with heat exchanger installed inside of the digester. The heat exchanger was fixed in the level above of the inlet pipe. The horizontal plane reflector concentrates solar beams to blackened side of the digester. In the winter period, it was found that the retention time of this digester is shorter on 15% and produced biogas volume is larger on 20% with respect of ordinary biogas digester. This digester is used for the demonstrative purposes and as a teaching aid presently and base on the results it may be used for the construction of large volume digesters for use in the farms, especially located in the remote and mountain areas where the climate in the winter period is cold. Introduction At present many experts around the world have focused their efforts to energy crises because energy is one of the most important factors for the development of the society. It is known that consuming energy is proportional to quality or standard of life. There is a close relationship between energy consumption and the Gross National Product (GNP). It is obvious that for further development of the country additional sources of energy is required, which are cheap, safe and environmentally compatible with respect to the action on possible wastes. Utilization of renewable energy is one route to help in solving the above mentioned problems. In particular, biogas as a source of renewable energy is produced by biotechnology and used wide on residential scale [1]. The biogas was produced for the very first time in 1814 by Deivy from organic wastes. In 1900 production of biogas was started in Bombay (India) [2, 3]. Biogas consists of 55-70% methane (CH4) and around of 27-44% carbon dioxide (CO2) and less than 1% H2 and H2S. At present biogas is used widely in some countries for lighting, machines, and vehicles, generators, cooking and heating. Biogas generation is suitable for small to large scale operation and at present is realized in a number of developed and developing countries as USA, Hungary, China, India etc. Since 1990s biogas projects construction in China has developed steadily by the end of 1998, there were altogether 6.88 million household biogas digesters [4]. In Russia biogas digesters are used for processing of hard dung into biogas [5]. Over the last few years the very first biogas digesters were constructed in Tajikistan as well [6,7] and it was found that the digesters can work with sufficiently high efficiency in mountain areas as well ."

Jan 1, 2008

By Ko-ichiro Ohno

It is recently recognized that the iron reduction and melting as well as the slag separation of a composite of granular iron ore and coal are completed in a very short period of about IO minutes when the composite is rapidly heated up to approximately 1673K. These phenomena are expected to be applied to a new iron-making process. The mechanism of iron ore reduction and iron-slag separation during rapid heating has not yet been revealed and the fundamental research has just started. Carburization of the reduced iron is regarded as one of the most important steps in this process. In the present work, the composite was prepared from four kinds of coal or graphite as a carbon source and electrolytic iron powder as a completely reduced iron ore. The temperature at which the liquid formation and iron carburization occurred was monitored. Direct observation of smelting reduction behavior was made by a confocal laser-scanning microscope combined with the infrared image-heating furnace to clarify the effect of molten ash on iron carburization. It was found that the meltdown temperature of composite became lower as the melting temperature of coal ash decreased. From the observed result, it was presumed that the liquid slag would act as an important media for the carbon transfer from coal to iron. The carburization mechanism during the smelting reduction was estimated as follows. When slag containing iron oxide melted down and contacted carbon, iron oxide in the slag was reduced and the formation of the metallic iron particle as well as the its carburization occurred simultaneously at the slag-carbon interface. Carburized iron particle was carried from slag- carbon to slag-iron interfaces due to the slag convection flow caused by the difference of the interfacial tension between the carbon-slag and iron-slag interfaces. Carburization of reduced iron could proceed with a repeat of the above-mentioned process.

Jan 1, 2003

By John Hollow

The Fort Knox Mine is an open-pit operation, located in Alaska, which started commercial production in March 1997. A conventional Mill processes 38,000 tpd of a low grade (1.0 g/t Au) free milling gold ore with a low sulphide component (below 1%). Gold production (11% from gravity and 89% from cyanidation) exceeds 400,000 ounces per year. Short retention time (20h), low temperature (7oC) and low grade make high leaching kinetics critical for the performance of the process. In April 2001, the treatment of True North ore, which represented 14.4% of the mill throughput and contained more sulphide in the form of pyrite, arsenopyrite and stibnite, resulted in a substantial drop in the average gold extraction from 87% to 72.6%. Laboratory investigations indicated that the addition of lead nitrate increased gold extraction to 91.7%. Further investigations were initiated to determine the leaching parameters and the nature of the problem. Subsequently, a lead nitrate addition scheme was implemented at the Fort Knox Mill that resulted in 2002 gold production being in excess of 31,000 ounces higher than that estimated for the non-lead nitrate reagent scheme. This paper presents the results of laboratory investigations and modifications in plant operating practices.

Jan 1, 2003

By Toshiro Kuji, Masakazu Fujita, Tetsuji Saito

"The magnetic properties of the magnetic materials were deeply dependent on the microstructures. In this study, the novel technique to produce the desired microstructures in a controlled manner was proposed. The technique consisted of the production of the amorphous alloys and the control of the crystallization process. The technique was applied to improve the magnetic properties of Nd-Fe-B permanent magnets. The microstructural control of the magnets exhibited the excellently high energy-products of higher than 430 kJm-1. The relationship between the magnetic properties and the microstructures of the Nd-Fe-B permanent magnets was discussed.IntroductionThe intrinsic properties of the materials are basically determined by the properties of the constituent elements or the compounds. However, it is often noticed the difference between the observed properties and the theoretical values expected from the intrinsic properties of the materials. This indicates that the observed properties of the materials are determined not only by the properties of the constituent elements. In other words, the observed properties of the materials are also strongly dependent on the morphology of materials. This means that the microstructural control may creates a great improvement of the properties of materials.In Nd-Fe-B permanent magnets, the superiority arises from the uniaxial intermetallic Nd2Fe14B compound which has a large saturation magnetization and a high anisotropy field [1,2]. The magnetic properties of the Nd-Fe-B permanent magnets are dependent on the microstructure, that is, the size, shape and degree of the crystallographic alignment of the Nd2Fe14B phase. Currently, the Nd-Fe-B permanent magnets have been produced by either sintering or melt-spinning [3,4]. In the sintered magnets, alignment of the Nd2Fe14B phase is achieved by the prior green compaction of the crushed ingot powders in an applied magnetic field [3]. In the melt-spinning approach, alignment of the Nd2Fe14B phase is achieved by hot deformation [5]. Amorphous melt-spun ribbons are comminuted and then are consolidated into bulk form by hot pressing before hot deformation. As-hot-pressed magnets have randomly oriented Nd2Fe1~ grains [6]. Subsequent die upsetting of as-hot-pressed magnets gives rise to the crystallographic alignment of the Nd2Fe14B phase."

Jan 1, 1998

By V. Gornitz

The Orphan mine uranium deposit, Grand Canyon, Arizona, is a cylindrical collapse-breccia pipe, 70 to 150 m in diameter and 500 m deep. Pipe fill was derived from the Supai Group, Hermit Shale, and the Coconino Sandstone. Uraninite, with Cu, Fe, Pb, Zn and Ni-Co sulfides is concentrated along the pipe boundary ring fracture (annular ring) and within the central porous sandstone matrix. There is some suggestion of vertical and lateral zonation of U with respect to Cu. Reduction of ferric oxide cement from red beds and recrystallization of carbonate, with formation of kaolinite preceded major ore deposition. Early Ni sulfides, arsenides and disseminated pyrite were followed by massive pyrite, and botryoidal uraninite, which in turn was suc-ceeded by Cu, Zn and Pb sulfides. A second, later generation of uraninite was closely intergrown with hematite and base metal sulfides. Oxidation of primary minerals may have been associated with Tertiary regional uplift. The paragenetic sequence closely resembles that of other Grand Canyon breccia pipes, except for the extensive development of the distinctive uraninite-hematite association. Mineral assemblages at the Orphan suggest possible mixing of the metal-bearing solution(s) with a more oxidized fluid, containing soluble uranyl complexes. Homogenization temperatures of fluid inclusions in calcite (GO-lIO?C) at the Orphan fall within the lower end of the range observed at other breccia pipes.

Jan 1, 1987

By Elli Miettinen, Markku Lahtinen, Ilkka Kojo

"The recent trends of decreasing energy consumption and environmental emissions and utilization of economies of scale are strong drivers favoring continuous copper converting processes. Flash Converting benefits from low off-gas volumes and low investment and operational costs for off-gas treatment. Separate matte and blister furnaces allow the adaptation to concentrate quality changes and flexibility in layout and maintenance.The stationary blister copper bath in Flash Converting furnace is less aggressive to the furnace linings than agitated processes, resulting in low refractory consumption, long campaign life and high on-line availability.Copper Flash Converting has been successfully applied in Kennecott with a campaign life now exceeding five years. A second FCF was started at Xiangguang Copper in China in 2007. The process itself is proven, as its features are similar to those in FSF, Direct-to-Blister and Direct Outotec Nickel Flash Smelting (DON), with one significant difference: it is the easiest of all to operate.The paper presents differences between continuous Flash Converting and conventional converting based on recent experiences and studies."

Jan 1, 2009

By David Tisdale, Phillip Mackey, Nagendra Tripathi, Matthew Kreuh, Pascal Coursol

Xstrata Nickel’s Sudbury smelter operation is based on fluid bed roasting of Ni-Cu sulphide concentrate, followed by electric furnace reductive smelting and Peirce-Smith converting to produce a Bessemer matte for electro refining, along with sulphuric acid produced from smelter gas. While the site dates back to the 1930s, the present smelter configuration has been operational since 1978, and currently has a nominal capacity of about 67,000 tpy of contained nickel and is investigating options to expand in future up to 85,000 tpy. As part of a review of plant capacity options, a new metallurgical model of the plant was developed in order to examine a number of processing alternatives. Based on the METSIM™ platform, the present model includes the ability to examine the impact of a number of plant parameters on potential plant performance including; for example, the following: percent of sulphur elimination in roasting, matte grade, degree of matte metallization, temperature, coke requirements, sulphuric acid production, CO2 emissions and overall energy requirements. The process model also includes a number of special features adopted; for example, approaches to effectively model the complex Ni-Cu-Co-Fe-S-O matte system. This paper provides a description of the model and gives an overview of the results. As well as presenting the results of the present study, the applicability of this modeling approach to pyrometallurgical systems in general is also briefly discussed in the paper.

Jan 1, 2009

By Zhenyang Wang, Yiran LIU, Xiangdong Xing, Jianliang Zhang, Zhengjian Liu

Basic characteristics of marine placer were systematically studied by chemical analyze, scanning electron microscope and X-ray diffraction in this paper. It could be found that the marine placer mainly consists of titanomagnetite and titanohematite. A series of experiments were performed to investigate reduction-magnetic separation for Fe and Ti from the marine placer. Effects of reduction temperature, reduction time, carbon ratio, magnetic density, and grinding fineness on the reduction-magnetic separation process were investigated. And the optimal process parameters were obtained as follows: the reduction temperature 1300, the reduction time 30 min, the carbon ratio 1.1, the magnetic density 50mT, and the grinding fineness of 0.074μm 86.34%. Under such conditions, the metallization rate, iron grade of magnetic substance and iron recovery reached to 94.23%, 97.19% and 90.28% respectively, and the titanium grade in non-magnetic substance and recovery of was 57.94% and 87.22% respectively. The effective separation of iron and titanium could be achieved in reduction-magnetic separation process.

Jan 1, 2015

By Min Xiaobo

As for treatment of zinc-containing wastewater, traditional SRB (Sulfate Reducing Bacteria) process was used, however, there exist two defects, like toxicity of heavy metal ions and high effluent COD (Chemical Oxygen Demand) value. In this study, a new technique, called ISIS process (Immobilized SRB sludge beads with Inner cohesive carbon Source), in which SRB sludge is embedded in carrier of PVA (Polyvinyl Alcohol) with carbon source that adsorbed on certain material, is put forward for the first time to overcome the two defects existing in traditional SRB process. Furthermore, it has been shown that compared to traditional SRB process, ISIS process increases average zinc removal rate up 30%, average sulfate reduction rate up20%, and decrease average effluent COD value to meet discharge standards. If activated carbon is selected for carbon source adsorption and fixing material, and PVA for immobilization material, the zinc removal rate can reach above 98% under the conditions of 35 and pH 6. Meanwhile, the mechanism of zinc removal has been determinated according to the results from SEM (Scanning Electronic Microscope) and XRD (X-Ray Diffraction).

Jan 1, 2006

By Leo Brewer, Kazuyoshi Shimakage, Mamoru Mitomo, Toshiyuki Nishimura, Yoichiro Uemura, Shinji Hirai

"In the synthesis process of ß -La2S3 via the sulfurization of La2O3 powder using CS2 gas, La2O2S was formed. This occurred at an initial stage of the reaction for sulfurization temperatures below 973K, and ß -La2S3 was also formed at a shorter period for higher sulfurization temperatures. It was found that the oxygen content in ß -La2S3 powders decreased gradually with an increase in sulfurization temperature. On the other hand, the carbon content in these powders increased gradually with an increase in the sulfurization temperature. Though it has been reported that ß -La2S3 was transformed to Y -La2S3 at 1723K± 50K, the sintered compact of double-phase Y -La2S3 and ß. -La2S3 was formed at a rather higher temperature of 1973K when the synthetic powder of ß -La2S3 containing a high amount of oxygen was used. However, phase transformation of -La2S3 to Y -La2S3 progressed preferentially with a decrease in the oxygen content of synthetic ß -La2S3 powder. The Seebeck coefficient of the sintered double-phase Y -La2S3 and -La2S3 was higher than that of the single-phase Y -La2S3, reported previously.Introduction La2S3 exists in three polymorphic forms that are similar to a series of Ce2S3, Pr2S3 and Nd2S3: a, ß , and Y'. The a -La2S3, which is stable at low temperature, is irreversibly transformed to ß -La2S3 of various compositions in the solid-solution range between La2S3 and La3S4, at 923 ± 50K. The -La2S3 may also be an oxysulfide of La10S14O2. Moreover, the ß .-La2S3 phase is transformed to Y -La2S3 ,which has a Th3P4 structure, at 1573 ± 100K. The melting point of Y -La2S3 is 2398 ± 30K where this temperature is similar to those of common refractory materials such as silica and alumina. Therefore, it can be predicted that y -La2S3 which has a high melting point and a thermodynamic stability due to the strong affinity of La for S, would have &high refractory character and chemical inertness in many molten metals. The y -La2S3, colored vivid faint yellow is stable up to 623K in air, where oxidation starts. y -La2S3 is frequently used as pigments for plastics and paints3. Furthermore, Y -La2S3 which is a semiconductor, is considered to be useful as a thermoelectric conversion materials, because it has a high Seebeck coefficient."

Jan 1, 2000

By R. G. Robins

Metal separations based on the selective precipitation of phosphates have a potential application in many hydrometallurgical processes. This paper reviews the literature on the solubility of a number of both divalent and trivalent metal phosphates and presents the result of some additional experimental measurements. The systems examined have been modelled to obtain free energy of formation data for the various species. Computer generated solubility diagrams which are described can be useful in predicting a variety of metal separations.

Jan 1, 1991

By J. L. Hill, M. A. R. Sharif, J. Lin

"A numerical algorithm has been developed to simulate the movement, breakup, and entrapment of the oxide film inclusions encountered during the mold-filling processes of aluminum castings. The flowfield is solved using the well-known Marker and Cell (MAC) method by a time marching process. The Volume of Fluid (VOF) method is used to track the free surface boundaries. A kinematic approach is employed to track the movement and breakup of the oxide films on the free surface or in the bulk liquid metal. The computer program based on the proposed algorithm is able to model the flow behavior and oxide film movement, breakup, and entrapment in mold cavities for aluminum castings.IntroductionMetallographic and fractographic studies of the aluminum castings show tangled networks of oxide films in the castings. These oxide films can form in the furnaces or during the mold filling processes. Green and Campbell [I] concluded that the oxide film defects dominate the strength of aluminum castings. The main cause of oxide film entrapment into the bulk molten metal during the casting processes is the surface turbulence. In film-forming alloys, if the surface breaks, due to a drop, a fountain, or a breaking wave, then the surface film is folded over and incorporated into the bulk liquid. The incorporation of surface films leads to cracks in the casting and other defects that are nucleated by the presence of the folded films, such as porosity and hot tears. Campbell [2] estimated that up to 80% of scrap in light-alloy casting is the result of surface turbulence."

Jan 1, 1999