Search Documents

By J. McKelliget, J. Szekely, Oreper. G. M.

"1. INTRODUCTIONThis paper is concerned with heat and fluid flow phenomena in arc welding operations. Fig. 1 shows a schematic sketch of a typical arc welding arrangement. It is seen that an arc is being struck between an inert electrode and a metal surface and that the resultant current and energy flow will case the formation of a molten weldpool.It is clearly appreciated that the weldpool shape and the nature of circulation in the weldpool may play an important part in determining the ultimate weld quality. It is known, furthermore,· that the weldpool behavior in turn will be affected by the spatial distribution of the current and the heat flux it receives from the arc. Indeed, the inherent coupling between the arc and the weldpool is a key feature of welding operations.Up to the present useful work has been done on the modelling of heat transfer and melt circulation in weldpools (1,2,3,4) and also on the description of arcs, including welding arcs (5,6,7,8). However, the coupling between these two sets of phenomena is relatively unexplored in a qualitative sense. The purpose of the present paper is to examine the interaction between welding arcs and weldpools. The actual material will be presented under the following headings:"

Jan 1, 1986

By Wayne Bell, Xiaodi Huang, Matthew Andriese, Jiann-Yang Hwang, Zhiwei Peng

"The equations for determining microwave field attenuation length and half-power depth in magnetic materials were derived from Maxwell’s equations. The microwave field attenuation length and the half-power depth for a magnetite concentrate were calculated and the temperature dependence of them was determined. It is demonstrated the microwave field attenuation length and the half-power depth highly depend on temperature and decrease with increasing temperature up to 900 °C. The variations of field attenuation length and the half-power depth with temperature indicate the microwave power attenuates much faster than the field strength in materials. The evaluations of field attenuation length and microwave half-power depth can be used to characterize the microwave dissipation behaviors in the sample and optimize the dimensions of the material in microwave heating.IntroductionMicrowave has been applied in materials processing for its distinguished advantages including rapid heat transfer, volumetric and selective heating [1,2]. However, most research work involving microwave heating are confined to non-magnetic materials (e.g. ceramics), with limited attention paid to the heating of mixed property materials (e.g. magnetite and other ferrites) under microwave irradiation [3-5]. Since many magnetic materials exhibit good and even better microwave absorption capability than non-magnetic counterparts, it is quite necessary and deserved to take advantage of this property and then improve the heating efficiency. To achieve this aim, further understanding on the microwave heating mechanism, especially the microwave propagation/dissipation behaviors in magnetic materials is required.The dissipation behavior of microwave in materials has been identified as one of the key factors that affect the efficiency of heating under microwave irradiation and this behavior can be characterized by several parameters. Apart from traditional penetration depth (TEM power penetration depth, Dp = 1/(2*a), where a is the TEM field attenuation factor), two other parameters, field attenuation length (Df) and half-power depth (Dh), are also applied to indicate the microwave dissipation in materials [6].The accurate determination of such parameters can help in optimizing the dimensions of the load in a microwave furnace, producing more uniform heating under microwave irradiation and avoiding thermal runaway."

Jan 1, 2011

By Shoji Taniguchi, Lifeng Zhang

"In this paper, firstly the 3D single-phase turbulent steady fluid flow in a vessel with four baffles stirred by a single impeller is mathematically simulated. Turbulence is modeled by using the standard k - e model. Sliding-grid method is used to model the impeller. The flow domain is divided into two cylindrical, the inner one rotates at the same speed as the impeller, and the outer one is fixed with the baffles. Results indicate that the high-speed zone is near the paddles, and larger stirring speed generates larger fluid flow velocity. The calculated stirring intensity data are used to analyze the experimental results. Secondly the effects, such as filter pore size, gas flow rate and NaCl concentration, on bubble size are studied by experiment. For the particle removal rate by bubble flotation in this vessel, first order kinetics is adopted. The effects of initial number of the particles, gas flow rate, particle and bubble size, stirring speed and surface condition, on the removal rate constant are discussed, and an empirical equation is derived by experimental data. At last, a simple model is developed to study the particle attachment probability on bubble surface under turbulent flow conditions. IntroductionIt is well known that inclusions have a bad effect on steel quality. Trying to remove inclusions from liquid steel as many as possible is one of the main objects for the metallurgical workers. Lots of ways are developed to remove inclusions from liquid steel. Gas injection is an effective one. This technique is used to achieve homogeneity in the temperature and metal composition and to assist in the removal of second phase and dissolved impurities from molten steel. Gas injection is commonly applied to the secondary metallurgy processes and continuous casting, for example the ladle argon gas treatment, RH vacuum degassing, and the gas injection in the Submerged Entry Nozzles (SEN) of continuous casting mold, etc. The development of these processes focuses on achieving two conditions: fine bubbles and good mixing. Fine bubbles provide a large gas/liquid interfacial area and a high attachment probability to inclusions, and good mixing enhances the efficiency of impurity transfer."

Jan 1, 2000

By J. L. Sanchez

Using a special double-zone transpiration reactor, the vapor transport chemistry of vanadium pentoxide in the presence of water vapor has been investigated. Three possible volatile hydroxides above V,O,(s) are reported in the literature: VO,(OH),, V,O,(OH),, and VO(OH),. In the present study, it was established that VO(OH), is the principal gaseous hydroxide species formed. The predominant reaction was found to be: { } The vapor pressure of VO(OH), was measured as a function of temperature, water pressure, oxygen pressure and flowrate. The results have been used to determine the Gibbs free energy of the above reaction as a function of temperature: { } The results of the present work were combined with thermodynamic data reported in the literature to obtain expressions for the AGO for the reaction above V,0,(1) and the AGO of formation (units in cal/g-mole).

Jan 1, 1993

By A. Navarra

Within conventional copper and nickel-copper sulfide smelters, ladles of molten matte are fed into converters. These converters blast oxygen-enriched air into the matte, thereby eliminating iron and sulfur. The converting reactions are exothermic and, indeed, the converter heat balance is often a limiting consideration on the smelter throughput. If a portion of the matte were fed in solidified (granulated) form, this would support higher oxygen enrichment, and lower volumes of converter offgas, allowing higher throughput. This approach is not applied in conventional smelters, partly because of the copious amounts of water that must be evaporated in typical granulators, as in the Kennecott-Outotec process. The current paper recalls a waterless matte granulator that had been pioneered in the 1990’s, and is applicable to conventional smelters. A mathematical formulation is presented that can be used in the context of simulation-based optimization, to estimate the size and impact of waterless matte granulation.

By Garry W. Warren

The brass foundry industry produces a significant amount of waste sand containing Cu, Zn and Pb which is often classified as a hazardous waste due to Pb content. The potential application of a hydrometallurgical process to treat the sand by extracting metal values and thus detoxifying the material has been investigated. The process involves leaching of metal values followed by cementation. The emphasis of this investigation was on the leaching step, although some preliminary cementation experiments have been performed. In order for any alternative treatment scheme to be successful, the smaller size fractions of the sand must be addressed. Experiments have been performed on five individual size fractions using various lixiviants HCI, acetic acid and HCI/NaCI. Cu extraction was found to be slower than either Zn or Pb. Results obtained in this investigation indicate that copper is present in two forms, an oxide form which dissolves rapidly and is insensitive to the level of oxygen, and a less soluble form, probably metallic which dissolves more slowly and requires an oxidizing agent. The presence or absence of oxygen had no influence on the rate of Zn dissolution indicating that zinc is present mostly in oxide form. Toxicity Characteristic Leaching Procedure (TCLP) tests showed that residues could be produced which meet the toxicity limit for lead. Preliminary cementation experiments have also demonstrated the feasibility of Cu and Pb recovery.

Jan 1, 1991

By W. K. Tolley

The Bureau of Mines is investigating hydrometallurgical processing techniques to recycle metals from semiconductors and other advanced materials. Cadmium and tellurium were recovered from CdTe scrap produced in the manufacture of infrared optic devices. Sulfation, ferric chloride leaching, and oxygen-pressure leaching have been tested. Cadmium dissolution was achieved using oxygen-pressure leaching in dilute sulfuric acid. However, no satisfactory scheme for dissolution of the higher valued tellurium has been devised. Leaching the ground CdTe for 75 min at 110°C in 1.1M H2S0, under 120 psig 0, yielded 99.5% Cd extraction. Tellurium remained in the leach residue as TeO, and elemental tellurium; residual cadmium was less than 0.5%. The cadmium in the leach liquor was purified of coextracted metals such as gallium and iron by adjusting the pH. The cadmium was recovered as cadmium sulfate crystals by evaporating the solution. Recovery of by product metals, notably gallium, is possible.

Jan 1, 1991

By M. Bhattacharya, A. Dutta, P. Barat

"Pinning of dislocations at nanosized obstacles like precipitates, voids and bubbles, is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often explored at fundamental level by means of analytical tools, atomistic simulations and finite element methods. Nevertheless, such studies fail to predict the effect on the overall plasticity on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here we propose a new statistical approach, where the statistics of pinning at idealized spherical obstacles is explored by taking into account the generalized size distribution of the obstacle along with the dislocation density within a three-dimensional framework. The application of this approach has been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel.IntroductionPresence of nanoscale obstacles like precipitates, voids and bubbles play a crucial role in determining the deformation behavior of a crystalline solid on account of the interactions between the line defects and such localized obstacles. In the context of the glide motion of dislocations, the obstacles can offer resistance to a moving dislocation, thereby causing a hardening effect [l-3]. In some other cases, inclusions like voids and bubbles can affect the rate of dislocation climb through diffusive [4] and non-diffusive [5] mechanisms. Over the last few decades, numerous studies have been performed to gain an insight of the dislocation-obstacle interactions at a fundamental level. These include the interactions responsible for the hardening effect, in addition to those pertaining to the non-conservative motion of dislocations.Although the elementary mechanisms of the various dislocation-obstacle interactions have been vastly explored and understood by means of analytical theory and numerical simulations, it remains difficult to quantitatively understand their effects on the macroscopic deformation behavior. This is due to the fact that their influence on the gross plastic deformation of a bulk sample would be the collective outcome of a large ensemble of such interactions. As a result, it becomes infeasible to predict the bulk deformation behavior of a material until the statistics of pinning of the dislocations at the localized obstacles is available. In the context of precipitate hardening, some well known attempts to extract the pinning-statistics were made by Friedel-Fleischer [6] and Mott [7] by analytical means, which were later tested through simplified 2-dimensional in-silica modeling [8]."

Jan 1, 2014

By Alicia E. Ares, Carlos E. Schvezov

In the present work it was observed the nucleation and growth of grains in the equiaxed zone of metal matrix composites (MMCs) samples directionally solidified wit the presence of columnarto- equiaxed transition (CET) in the samples. In order to do so, first, it was defined the difference between the real temperature at a given instant, which it is used in the analysis, its variation and furthermore, the variation in the solid fraction with time between the beginning and the end of solidification. It was determined a growth law assuming a lineal variation of equiaxed grain radius as a function of time, and also, it was expressed a law of grain density as a function of time, considering the presence of SiC and Al2O3 particles in the matrix. Finally, the results obtained were validated with measured values of grain density at each position of the thermocouples in the equiaxed zone of the solidified samples.

Jan 1, 2015

By B. Q. Li, S. P. Song

"This paper describes an on-going research on developing coupled boundary element and finite element algorithms for the solution of thermal and electrodynamic problems relating to materials processing. The coupled methods are uniquely suitable for field problems involving composite regions, in which detailed information on field distributions within one particular region is of more interest and yet the solution can be obtained only if the effects of other regions are all considered. Problems of this type include heat transfer in multiple regions and also magnetic induction involving an infinite boundary. The hybrid boundary and finite element formulation, algorithm development and the applications are discussed. Two examples are given to demonstrate the capability and accuracy of the coupled algorithm for heat transfer problems. Various treatments of corner discontinuity are discussed. It is found that the double flux treatment is an ideal choice amongst those tested as it is easy to implement and also gives the most accurate solution. 1. INTRODUCTIONElectrodynamic and transport problems occur frequently in materials processing systems. Accurate solution of these problems is of great importance not only for our fundamental understanding of physical principles governing these phenomena in the processing systems but also for optimization of the existing processes as well as development of new processes. For this purpose, many numerical algorithms have been developed. These computational schemes in general can be classified into three categories, that is, the finite element and finite difference schemes and the boundary element scheme. The former two are domain based numerical algorithms while the latter the boundary-based algorithm.The finite element method, which is based on the variational calculus, is a very useful and yet popular engineering numerical method for boundary value problems defined over irregular boundaries. The use of the method requires the discretization of the entire domain. It can be applied to solve both linear and nonlinear problems, but is particularly powerful for nonlinear problems that involve the field variables defined within the computational domain. On the other hand, the boundary element method, with its root in the Green's function method, is very efficient for linear boundary value problems or nonlinear problems that involve field variables only along the boundaries. The primary advantage of the boundary element method lies in the fact that only the boundaries of the computational domain need to be discretized, and hence the dimension of the problem is reduced by one, compared with the finite element method."

Jan 1, 1994

By A. A. Hejja

"Liquidus temperature and electrical conductivity data measured on synthetic slags were modelled by the use of neural nets (NN). In this work the applied multilayer feedforward NNs were trained by a conjugate-gradient optimisation for which a three layer formulation was used. Very good fits were obtained for both the liquidus temperature and the conductivity data. The synthetic slags were prepared from pure oxides to represent a wide range of compositions likely to be encountered in ferromanganese and silicomanganese smelting. The slag constituents were in the following range: Mn0;5-30%, Ca0;20-35%, Mg0;5-15%, Si02;27-58%, Al20 3;5%. Liquidus temperatures varied from 1300° to 1380° and increased with increasing basicity ratio. The electrical resistivity of slags decreased with the increase of basicity ratio from 0.55 to 1.1 but above 1.1 basicity ratio the resistivity tended to increase depending upon the MnO content.Neural NetsVarious neural net (NN) topologies such as Hopfied nets, Hamming nets, Carpenter/Grossberg classifiers have been discussed in some detail by Lipmann (1). In this work, the applied multilayer feedforward NNs are not trained by backpropagation (BP) using the generalized delta rule (2) (GDR), but by a conjugate-gradient optimisation [3,4] - a procedure similar to that proposed by Barnard and Cole [5]. A neural net is capable ·of learning the non-linear functional relationship existing between a set of inputs and outputs [ 6]. In this capacity a neural net is used to determine the functional relationship that exists . between N dependent and independent variables, which characterize the system under consideration For a three layer neural net [1] the following function may be formulated, which relates X; inputs to the output Y 0 from node o:"

Jan 1, 1997

By M. Z. Sukiennik

A static method for vapor pressure measurement up to 1450 K and above 1 hPa is presented. The method is designed for equilibrium and kinetic studies of metallic systems, including those with a chemical reaction. Application examples are given for determination of activities in condensed phases, and heterogeneous reaction rates and equilibrium constants.

Jan 1, 1993

By Kazuteru Tozcwa

The oxidation of several sulfide minerals in aqueous ammoniacal solution is discussed thermodynamically. The region in which Cu(NH3)2 4+ is stable has been estimated as a function of pH and concentration of total ammonia, {[NH3) + [NH4)}. In ammonia leaching when copper in sulfides is assumed to be extracted in the form of Cu(NH3)2 which will be rapidly converted to cupric ammine, thermodynamic data predict that such minerals are oxidized readily in the following order, CuS, Cu2S, CuFeS2, ZnS, NiS, Ag2S. This agrees with investigations on ammonia leaching of sulfide minerals, reported previously. The leaching of copper sulfide concentrate has been examined experimentally. Copper in a copper sulfide concentrate, in which the main constituents were chalcopyrite and pyrite, was effective¬ly extracted. The copper extraction was affected by factors such as (1) agitation intensity, (2) oxygen partial pressure, (3) NH3/Cu molar ratio, (4) leaching temperature and (5) addition of ammonium sulfate. From the results obtained in this work, it is concluded that mass transfer of oxygen plays the most important role in ammonia leaching of copper sulfide minerals.

Jan 1, 1976

By Haibin Wang, Kaile Tang, Chenn Q. Zhou, Guangwu Tang, Zhixiang Cui, Ping Zhou, Armin K. Silaen, Hongjie Yan, Zhi Wang

The submerged lance smelting furnace (SLS) for copper smelting has been developed and used by Dongying Fangyuan Nonferrous Metals Co., Ltd. The technology has shown advantages such as high oxygen enrichment, good feed adaptability, short processing time, high SO2 concentration for acid plant, and auto-thermal operation. In this study, computational fluid dynamics (CFD) was used to investigate the gas/matte two-phase flow characteristics and the chemical reactions in the SLS during typical operational conditions. The Eulerian-Eulerian approach was employed to model the phase interactions. The chemical reactions were modeled by calculating the mass transfer coef ficients and using the eddy-dissipation model. The simulation was conducted using the commercial software ANSYS Fluent®. The developed CFD model is able to predict the flow, temperature, and species distributions inside the SLS under various operating conditions.

Mar 1, 2018

By B. Ozturk, K. Ito, R. J. Fruehan

"A simulation model for bath smelting processes for the production of iron was developed which predicts the coal, flux, ore, and oxygen consumptions and the off gas volume, temperature and composition. The model is comprehensive in that it takes into account all of the important variables including coal composition, metal composition, ore composition, slag basicity, post combustion ratio, (PCR), prereduction degree (PRO), heat transfer coefficient (HTC) , flux, scrap charge, and heat losses. Four basic cases were considered: I. 30% PRO-50% PCR; II. 90% PRO-O% PCR; III. 60% PRO-30% PCR; and IV. 0% PRO-50% PCR. Several different coals were considered and a sensitivity analysis of the critical variables was performed. The model also estimates the sulfur content of the metal. The major conclusions included:1. Post combustion significantly reduces coal consumption but above 20% PCR little reduction of FeO to Fe can be performed with the off gas.2. Prereducing to FeO (Case I) and having as much post combustion as consistent with good heat transfer is an attractive process. This process only requires a simple pre reducer, uses less coal, and is relatively insensitive to the type of coal used.3. High off gas temperatures may pose a potential problem. The off gas temperature can be reduced by using an 02-Air mixture for post combustion, limiting post combustion or adding water to the gas.4. The use of CaC03 in place of CaO or of supplemental electricity does not appear attractive.5. The melting unit is theoretically an energy efficient scrap melter. For Case I using 200 kg of scrap as part of the charge the coal consumption decreases by about 80 kg.6. With PCR > 30% the FeO content of the slag is expected to be 2-5%, and the metal will not be saturated with carbon. These factors and the increased sulfur load since coal is the fuel indicate the sulfur content of the metal may exceed 0.25%"

Jan 1, 1988

By R. Moreau, V. Uspenski, K. Messadek, Y. Delannoy

Experiments and numerical simulations have been carried out to investigate the properties of quasi-2D turbulence. A new mercury model experiment has been built and tested in a uniform magnetic field up to 6T, (Ha~ 1000), ensuring a better two-dimensional behaviour than earlier versions (Alboussiere et al., 1997), limited to 0.2T. The quality of the experimental results has been improved in order to get wave number spectra (instead of frequency spectra) and higher signal over noise ratio (due to the higher magnetic fields). In parallel, some two-dimensional "direct" numerical simulations were performed using a commercially available code to solve a 2-D motion equation involving a source term to model the Hartmann layer. This term is derived from the condition of closure of the electric current, which allows to transfer the Hartmann effect into the 2D-core flow without simulating the layer itself (Sommeria & Moreau, 1982). No subgrid scale modelling is needed in such a two-dimensional situation where most of the energy is carried by the large scales.

Jan 1, 1999

By Hongfa Hu, Stavros A. Argyropoulos

"This paper describes a mathematical model which simulates numerically reaction driven fluid flow phenomena. The driving force of this reaction is an exothermic heat of mixing. In addition, the model predicts the heat and mass transfer phenomena where both heat source and heat sink co-exist in close proximity. The heat source is generated by an exothermic reaction. The heat sink is formed by a moving boundary such as the melting of a solid. This type of phenomena occur quite often in various metal processing operations in which exothermic additions are immersed in liquid metals. The model is based on the SIMPLER algorithm and uses an enthalpy method to predict the fluid flow, temperature, and concentration fields. The results indicate that the exothermic mixing reaction was responsible for an abrupt rise in temperature around the moving boundary. The intensity of this reaction was also found to be responsible for the enhanced convection of fluid and the acceleration of the moving boundary. The modelling results were also verified by experimental work which included velocity and temperature measurements in a low temperature physical model. IntroductionAlloying additions are used extensively in the treatment of liquid metals during metallurgical processes. The alloying additions introduced into liquid metals can be classified into various classes, each of which follows its own route[l]. As a major group, the exothermic additions follow two different steps during their assimilation into liquid metals. In the first step, upon immersion, a metal shell solidifies around such additions, and then melts back. At this point, the second step commences. During this second step, due to the mixing of the addition with a liquid metal, an exothermic reaction occurs, which liberates large amounts of heat, resulting in an enhanced convection in the liquid metal surrounding the addition."

Jan 1, 1994

By Donald I. Bleiwas

World primary nickel production in 1987 is projected to be 770,000 mt, slightly higher than that in 1986. Market economy country (MEC) production in 1987 is projected to be about 524,000 mt, an increase of almost 5 pct over 1986 production. Production cutbacks and closures at Japanese ferronickel plants in 1987 resulted primarily from the strong yen and higher energy prices. Cutbacks also caused reductions in ore production from Indonesia, New Caledonia, and the Philippines. Technical problems affected production, to varying degrees, in Botswana, Indonesia, and Yugoslavia. World primary nickel production for 1988 is projected to be 787,000 mt, of which 536,000 mt will be produced in MECs. Increased production is projected from Botswana, Canada, Cuba, and possibly Greece and Yugoslavia, while slight production decreases are projected for Indonesia, New Caledonia, the Philippines, and Zimbabwe. .. South African nickel production in 1988 could be severly curtailed by social strife. In the early 1990's Brazil and China could be major economic competitors to Western nickel producers.

Jan 1, 1988

By Robin M. Forbes. Jones, Suhas V. Patankar, Ramesh S. Minisandram, Jr. Carter, Kanchan M. Kelkar

"The nucleated casting process currently under development has the potential for production of Ni-base superalloy preforms that possess superior microstructure to product made by conventional casting processes, primarily for gas turbine applications. In this process, electroslag remelted (ESR) clean (i.e., free of ceramic inclusions) molten metal is conveyed via a watercooled copper Cold-walled Induction Guide (CIG) to a gas atomizer. The spray of clean metal droplets is then directly cast into a water-cooled crucible for ingot production. The microstructure of the resulting ingot preform evolves within the length scale of the individual droplets and is a function of the thermal state of the incoming metal droplets. This, in turn, depends on particle size, flight time and heat exchange with the gas phase.In the present study, computational models is developed for the analysis of the flow and heat transfer in the gas-metal spray system under axisymmetric and steady-state conditions. The gasphase flow is analyzed using an Eulerian framework and turbulent mixing within the gas phase is modeled using the two-equation k-e model. The dynamics of the metal particles is analyzed using a Lagrangian framework that involves calculation of the trajectories of the metal droplets. A two-way coupling is considered whereby the transport and heat transfer in the gas and the metal phases influence each other.The analysis is developed at two levels. The spray model performs a detailed calculation of the spray dynamics in the vicinity of the spray and is intended for predicting the temperature and mass flux distributions of the metal spray depositing into the mold. The chamber model enables prediction of gas flow and motion of metal particles in the entire spray chamber."

Jan 1, 2004

By Shoji Taniguchi, Lifeng Zhang, Kaike Cai

"In the present paper, based on the two-phase (Eulerian-Eulerian) model, the 3D fluid flows in gas-stirred systems, i.e., air-stirred water vessel and argon-stirred liquid steel ladle, are simulated. In the Eulerian-Eulerian two-phase model, gas and liquid are considered to be two different continuous fields. The phases are assumed to share space in proportion to their volume fractions. The exchange between the phases is represented by source terms in conversation equations. Turbulence simulated by the k- e model is assumed to be the property of the liquid phase. The following effects of mathematical treatments and operational factors on the fluid flow are discussed, such as interphase drag force, turbulent model, the size of bubble, and gas injection mode.Some interesting results are derived. Except the interphase drag force, the interphase lift force should be taken into accounted in order to exactly simulate the fluid flow in gas-stirred systems. Suitable turbulent model and drag coefficient have effect on the mathematical simulation. Injecting small bubbles can realize a well mixing flow condition. The distance between the two gas-injection nozzles has effect on the fluid flow."

Jan 1, 2000