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By Joner O. Alves

The disposal of scrap tires has been a serious environmental problem. The treatment of this waste by pyrolysis and combustion has advantages since the landfill space is dwindling and the production of fuel becomes of technological interest. However, that processes needs a rigid control of emissions. This work presents a study of the light hydrocarbon gases (HC) generated during the burn of waste tire chips in a two-stage laminar-flow horizontal furnace. Different temperatures in the primary and secondary stage of the furnace were tested, and the oxygen/nitrogen percentage was also varied during the combustion process. A gas chromatograph was used to identify and quantify the components of the gaseous products of combustion and pyrolysis. The results showed the behavior of the gases during the burn of tires, providing valuable information to the control of hydrocarbon emissions.

Jan 1, 2010

By B. P. Sereda

The properties, characteristics and phase structure of chamotte refractories produced with the usage of mullitecorund chamotte and caoline have been given. The comparison of new refractory C-45 obtained by us and refractory C-43 produced by traditional method has done. The physical-chemical properties of refractories is reviewed. The visual porosity, density and pore characteristics of given refractories was calculated. It is established that C-45 has the less gas permeability then C-45 that gives melting units more stability. The petrographical microstructures of refractories have been done. The main phase structures and their influence on refractories properties have been observed. It is established that refractories with mullitecorund chamotte adition has more advantages then refractories gained by traditional method and can be applied to melting units.

Jan 1, 2010

By N. M. Komkov

The main operation of obtaining zinc from sulfide raw materials by hydrometallurgical technologies is the oxidation roasting of zinc concentrates in fluidized bed furnaces. The technical-economic parameters are determined by the parameters of the roasting process, which depend on the composition of the initial raw materials, the temperature of the bed and on other factors. The predetermined roasting temperature is maintained due to the change of specific efficiency as well as to the quantity of the heat removed from the bed. The efficiency of caissons depends at a high degree on the composition and the thickness of the accretion formed on the surface of the caissons. Forecasting the roasting results is impossible unless we know the mechanism of the accretion formation. The aim of the present paper is the thermodynamic analyses of the behavior of the charge compositions under roasting and the determination of the potential mechanism of the accretion formation. The thermodynamic analyses show that under conditions of the oxidation roasting the thermodynamic probability of the formation of zinc sulfate is higher than the probability of the oxide formation until a temperature of873 OK is reached. The thermodynamic probability of the formation of the lead sulfate is higher than the probability of oxide formation in the entire temperature range of roasting. The probability of formation of ferrites and silicates of zinc decreases only insignificantly the sulfate stability. The results of the investigation of the accretions composItion formed under roasting of concentrates with particle sizes less than 0.02 J..lm (60%), containing 65% of sphalerite (ZnS), 12% of pyrite and chalcopyrite (FeS2 and CufeSz) each, 3% of galenite (PbS), 7% of silica and other non-ore minerals, have shown that the composition of accretion varies depending on the depth of the accretion layer. The accretions on the caissons and the thermo-siphons consist mostly of zinc sulfate (more than 50%). The accretions of forehamber consist mostly of zinc oxide. They also contain ferrites and silicates. The formation of the sulfate zinc accretion in the cold parts of the fluidized bed furnace (the caissons and thermo-siphons) may be explained by a lower temperature on the surface and probably by a catalytic influence of the present oxides in the formation of S02 and sulfates. The nature of the structure of the accretion in the hotter parts of the furnace may supposedly be explained by the formation of elemental vaporous zinc during roasting.

Jan 1, 2003

By Takashi Ikeda, Masafumi Maeda

"Demand for solar cells is increasing linearly throughout the world. Last year production totaled 3000 tons worldwide. The market size of solar silicon is expected to increase further because of international ""political"" demand to reduce carbonaceous emission from energy consumed. Most elemental silicon is produced by the carbon reduction of Silica in an electric arc furnace. Purity of silicon at this stage is 90-99%. Major impurities are Fe, Ti, Ca· and Al, and minor ones are P, B and carbon. The oxidizing metallurgical process is no longer effective to remove transitfon metals because those are less noble to silicon. Nonmetallic impurities such as phosphorus and boron must be reduced to 0.001ppm for semiconductor use. The most common process for high purity silicon is the Siemens C process, which is basically distillation of hydro-chlorinated silicon followed by CVD of SiHCl3. The cost of such silicon is expensive to allow its popular use in solar cells. Currently scrap silicon -of semiconductors is used for this; however, the supply-of that scrap is limited to just a portion of semiconductor production.In this paper world demand for silicon will be reviewed and some of the processes proposed summarized.IntroductionSilicon is element 14 in atomic number and has an atomic weight of 28.0855. Little elemental silicon is found in the earth, and it is mostly found as oxides or silicate. The Clark number of silicon is very large and the second in its number. If we were discussing the volatility of silicon element on the globe, we would never worry about it. However, it is very difficult to obtain pure elemental silicon because a high purity silicon compound is very rare. In most cases these are silica (silicon oxide SiO2). As shown in Table 1, there are many grades of silica ore classified mainly by their content of iron and alumina."

Jan 1, 2000

By Yuanbo Zhang, Zhixiong You, Daoxian Duan, Guanghui Li, Tao Jiang

"Manganese is mainly consumed by steel and battery industries. In recent years, it is essential to utilize the low-grade manganese oxide ores with total manganese grade below 25%, as the high quality manganese ore resources are becoming scarce with the rapid development of the steel industry. Conventional pyro-metallurgical processes for utilizing manganese oxide ores are characterized by high production cost and energy consumption, low productivity, serious environmental pollution, etc. In this study, reduction thermodynamic of MnO2 reduced by sulfur was firstly carried out. Then, a novel process of reduction roasting with sulfur followed by acid leaching was developed to recover manganese from the very low-grade manganese oxide ores. Effects of main factors, including temperature, reduction time and S/Mn mole ratio, were investigated, and a high leaching efficiency of Mn above 95% was obtained under optimal conditions.IntroductionHigh/middle-grade manganese oxide ores are generally used in the metallurgical industries, particularly in steel plants and ferro-alloy units. The consumption of metal manganese in the ferro-alloy industry accounts for 85- 90% of the total Mn demanded [1]. Therefore, high quality manganese ore resources are becoming scarce with the rapid development of steel industry. It is essential to make good use of large quantity of low-grade manganese ores (TMn < 25%) presently available."

Jan 1, 2012

By J. D. Law

The presence of long-lived radionuclides presents a challenge to the management of radioactive wastes. Separation of the radionuclides from the waste solutions has the potential of significantly decreasing the costs associated with the immobilization and disposal of the waste by minimizing waste volumes. Several solvent extraction processes have been developed at the Idaho National Engineering and Environmental Laboratory for the separation of transuranic elements (TRUs), 90 Sr, and/or 137 Cs from acidic radioactive waste solutions. The TRUEX and POR processes for the separation of TRUs, the SREX process for the separation of 90Sr, the cobalt dicarbollide process for the separation of 137Cs and and a universal solvent extraction process for the simultaneous separation of TRUs, 90Sr, and 137Cs have all been developed in centrifugal contactors using actual liquid radioactive waste solutions and simulated dissolved calcine waste solution. In addition, the behavior of metals with each of the solvent extraction processes was evaluated. This article summarizes the most recent results of the each of the flowsheet demonstrations and provides Information on the centrifugal contactor equipment used for the testing.

Jan 1, 1999

By Ying Li, Xuling Chen, Xiaohui Fan

"In the sintering process, the behavior and performance of iron ores is extremely complex. Different minerals have different sintering properties. In order to use iron ores rationally and effectively, multilevel fuzzy evaluation method is used to establish the comprehensive evaluation model of iron ores. Because of the relative independent characters of iron ores in sintering process, the characters can be divided into physical and chemical properties, granulation performance, and sintering properties, are divided, and together with iron ores prices as the first level index for judging, which are used as the second level index for judging. Using the analytic hierarchy process (AHP) to determine the weight of each index, which is used as the second level index. The relative membership matrix is determined by triangular membership function, the comprehensive evaluation model is established.IntroductionIn China, sintering is the main method for iron ores agglomeration. Sinter accounts for more than 80% of the blast furnace. Sinter production in the iron and steel enterprises in China plays an important role[l-2]. As the main raw material of iron ores sintering, the objectivity and integration of iron ores evaluation is essential. The iron ores evaluation methods include of metric ton price evaluation method, iron grade of a single iron ores sintering, acid-base balance method, composition assessment method and other methods which are based on the chemical composition and physical properties of iron ores to measure the quality of iron ores[3]. The high-temperature mineralization is an important process in sintering process, which affects the structure and mineral composition of the sinter, and has a close relationship with the quality of the sinter[ 4]. Therefore, in consideration of the physical and chemical properties, granulation properties, mineralization performance and sintering properties, the iron ores are evaluated by multi-level fuzzy comprehensive evaluation. The multi-level fuzzy comprehensive evaluation method makes a comprehensive evaluation, applying fuzzy transform principle and maximum membership degree principle, considering a number of factors related to the things which are evaluated. The method has lower requirements for the amount of data, and which integrates qualitative with quantitative judgment. It has a unique advantage to make up for the deficiencies of traditional evaluation methods. It also can comprehensively evaluate the iron ores in a relatively short period, reduce a lot of experiments, improve efficiency and guide the sinter production[5-6]."

Jan 1, 2013

By Pengfu Tan

A thermodynamic model of KIVCET lead smelting process has been developed. The model has the capability to predict the distribution behaviors of Pb, Zn, Fe, S, O, As, and heat balance in KIVCET direct lead smelting furnace. The compositions of lead bullion, matte, slag and gaseous phases, and heat balance are calculated. The effect of the ratio between oxygen and feed on the chemistry of the smelt and heat balance of the coke checker has been simulated and discussed. The thermodynamic model also helps to understand the tapping issue of the lead bullion. In this paper, some applications of this model in the industry have been presented.

Jan 1, 2006

By Yuanbo Zhang, Yingming Chen, Zijian Su, Bingbing Liu, Jun Chen

Iron, tin-bearing tailings is a kind of hazardous solid waste generated from cassiterite dressing operation. It is difficult to utilize the tailings by present mineral processing methods due to the complex dissemination characteristics. In this study, a process of gas-based magnetizing roasting followed by magnetic separation was studied for separating and recovering iron from the tailings. The effects of roasting and magnetic separation parameters on the recovery of iron were systematically investigated. The optimum parameters were proposed as follows: CO/(CO+CO2) content of 5%, roasting temperature of 850 C, roasting time of 60 min, grinding particle size of 90% less than 45 μm and magnetic field intensity of 800 Gs. Under these conditions, the magnetic concentrate containing 68.5% Fe and 0.06% Sn was achieved, which can be used as high-quality raw materials for direct reduction iron production.

Jan 1, 2016

By Upali Siriwardane, Tushar V. Kudale, Naidu V. Seetala

"Cellulose acetate (CA) membranes with 25% triethyl citrate (TEC) as plasticizer were prepared with varying thickness for CO2 gas separation from water-gas-shift (WGS) reaction products. The AFM analysis of the CA membrane showed that the uniform coating had fewer and smaller pores as the film thickness increased, and corroborated by gas permeability studies. The CO2 permeability has decreased faster than CO permeability with the CA/TEC membrane thickness, and findings support that the CA membrane could be used to entrap CO2. Several CA/TEC membranes were also staked to increase the separation efficiency. Positron Annihilation Lifetime Spectroscopy (PALS) was used to estimate the nano-porosity (pore size and concentration) changes of CA/TEC films. PALS results show a decrease in pore size with increasing CA-TEC concentration in acetone, while the pore concentration increases. The PALS results are correlated with the CO2/CO permeability variations as the CA-TEC concentration change.IntroductionHydrogen is one of the main energy sources available for the future advancement of clean fuel technologies especially for fuel cells. Generation of hydrogen and CO2 from Water Gas Shift (WGS) reaction mixtures of CO and H2O is of interest to many researchers since it allows a large scale production of hydrogen [1, 2]. Once hydrogen is produced using the WGS reaction, the output products contain mixture of CO, CO2, H2, and water vapor. Metallic membranes have been used as hydrogen separation membranes [3-6]. As H2 is separated from the mixture using the metal membranes, we need to separate CO2, and find ways of sequestration of CO2 to avoid environmental problems by greenhouse gasses. Polymeric Membranes have been used for CO2 separation [7]. Plasticizer can control the micro-structural properties such as pore size and concentration of polymer membranes [8], which influence the size/molecular weight dependent diffusion rates of the gas molecules. We have used cellulose acetate with triethyl citrate as plasticizer to separate CO2 from the WGS reaction products. Positron annihilation lifetime spectroscopy (PALS) is very sensitive and able to identify different kinds of defects and their agglomerates such as vacancies, vacancy loops, and voids [9, 10]. PALS has been successful in determining the free volume in polymers that influence the properties of the polymers [11, 12]. Microscopic properties of the free volume obtained from PALS have been correlated to macroscopic properties [13, 14]. We used PALS to study the nanoporosity (pore size and concentration) and fractional free volume changes of CA/TEC films, and used to understand the variations observed in the CO2/CO permeability as the CA-TEC concentration in the membranes change."

Jan 1, 2014

By Zhuokun Cao

Manufacture of aluminum foams still suffer from nonuniformity and poor reproductively for there is lack of basic knowledge of foaming process. In this paper, carbon fibers are used as novel stabilizing additive for aluminum foams, and the structure evolution of aluminum foams with different fiber content was studied. A laser rangefinder was used to detect the expansion rate of different al foams. Al foam samples are solidified at different foaming time to determine its relative density and cell size distribution. Results indicate that the cell size of foams linearly increases with the decrease of density, and the slope of the line is influenced by fiber content. The relationship between expansion ratio, density and cell size of the foams is discussed. It is concluded that the density of resulting foam is influenced by the rate of gravity driven drainage, and its cell size is determined by expansion ratio and foaming time.

Jan 1, 2010

By F. Ríos

Fundamental research, at laboratory scale, on the biomass adsorption capacity of a liquid mining effluent has been done. The biomass used corresponds to a Chilean seaweed called Gracilaria chilensis. The waste water effluent corresponds to clear water coming from thickeners of a Chilean copper mining operation. The biomass was dried, washed, treated with an acid solution, and then reduced in size. A characterization of Zeta potential was made, finding negative values in a wide pH range with a ZPC equal to 2.5 1. Adsorption tests were made- in an agitated system containing an artificial solution of CuS04 at a controlled temperature of 25 degrees Celsius; also, the effect of pH over the copper adsorbed was studied. Maximal adsorption of copper was found at pH equal to 6, and the Langmuir model indicated values for saturation of 52.08 mg/g and for standard free energy of about -21 KJ/mol. Kinetic adsorption was very high and fitted very well with a second order model equation, finding that 90 per cent of the adsorption occurred during the initial 10 minutes. After stoichiometric when 1 mol of copper is adsorbed, 2 mol hydrogen are released, showing that the main mechanism to remove heavy metals is the ionic exchange, and the seaweed ensures total discharge of copper adsorbed when the pH value is about 1. Experiments done with real waste water from thickeners lead us to conclude that optimal results for copper and molybdenum adsorption are at pH around 3.25 and the remaining treated water may be partially discharged into the water currents, thus showing that Gracilaria chilensis can be used to remove heavy metals easily from liquid effluents in the copper mining industry.

Jan 1, 1999

By Biswadeep Saha, Meenakshisundaram Ramanathan, Chai Ren, Sivaraman Guruswamy

"Fe-Ga alloys have a large low-field magnetostriction and these alloys are attractive candidates in energy conversion and harvesting applications. Small additions of W also increase the magnetostriction of Fe. In this paper changes in magnetostriction by W substitution for Ga in various Fe-x at.% Ga alloys are presented. Fe-Ga-W single crystals were grown using vertical Bridgman Growth technique. [001]-orientated single crystal samples were prepared with faces within 1 degree off <100> orientation. The samples were annealed at 1150 °C in the alpha-phase region and water quenched. The magnetostriction coefficient (3/2)A-100 measurements were made on these Fe-Ga-W single crystals. The result on the effects of W substitution and annealing on the magnetostrictive behavior of these alloys are discussed.*Support of this work by NSF-DMR under the award DMR-0854166 is gratefully acknowledged.IntroductionMagnetostrictive materials changes their dimension exhibit reversible strains and changes in elastic properties in the presence of an applied magnetic field or the reciprocal effect of changes in the magnetic properties with the application of stress [IJ and are very important in sensor, actuator device, linear motor, magnetomechanical devices, microelectro- mechanical devices, active vibration dampening devices application areas. The discovery of an order of magnitude enhancement in the magnetostriction of Fe with Ga addition coupled with low saturation magnetic fields, and excellent mechanical properties opened up the possibility of obtaining larger magnetostriction values in other low-cost ductile a-Fe phase based alloys with alloying additives that are less expensive than rareearths such as Tb and Dy [2·4l_ The magnetostriction values observed in Fe-Ga single crystals are sensitive to thermal history and composition. The formation of second short range ordering phases and local defects inside crystal structure can also cause a dramatic change to this alloy's magnetostriction behavior [5-9l_"

Jan 1, 2012

By Björn Hinzel, Joachim Rösler

"The most important characteristic of open-pored metals is porosity, since it enables all of their functional applications as filters or sound absorbers. Due to the notch effect of the pores, mechanical properties of porous metals are better than the ones of comparable structures made of polymers or ceramics. Consequently, only open-pored metals can be used in aircrafts to reduce flow noise or noise resulting from the core engine by acoustic absorption. Absorption properties depend highly on pore size and porosity of the material, which must be characterized as precisely as possible in order to analyze the correlation between morphology and noise reduction performance. Here, a line segmenting method is explained in order to characterize pore size and porosity of absorber materials using image processing based on two dimensional microscopy images, including sample preparation and specification of the set-up. Then, the influence of the pore structure on the measured absorption behavior is discussed. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined.IntroductionSignificant noise loads affect everyone causing anxiety, depression, insomnia and other effects which impair health and productivity [1],[2]. Due to the rising number of flights and aircrafts, air traffic noise increases dramatically. To counter this development, various approaches have been developed to reduce the different noise sources resulting from airframe, jet or engine [3],[4],[5],[6]. One approach to reduce this noise is the application of noise reducing liners in the hot gas path [7]. This is especially important, since the engine is becoming the dominant noise source of modern airplanes during take-off [8]. Due to the elevated temperatures and high fatigue loading in this part of the aero-engine, conventional passive absorber materials cannot be used. Polymers would not be able to bear the heat and ceramic fibers would crack under the mechanical loading due to the notch effect. Consequently, this study focuses on metals with open pores, which can resist elevated temperatures and fatigue loading and additionally resemble geometrically conventional passive absorbers. Based on the production processes, e.g. sintering of metal fibers [7], powder processing using a foaming agent [9], coating of polymer foams [10], or using melt infiltration techniques [11], the characteristic dimension of the porosity is usually in the range of 0.01-10mm. In this work, sintered metals and metal sponges are analyzed after the theory of sound absorption is briefly outlined. Then, measurements of the acoustic absorption of metal sponges and sintered metals in an impedance tube are performed. To understand and predict the acoustic properties of metals with open porosity, it is necessary to characterize the materials as precisely as possible. This is explained in detail using a line segmenting technique, followed by a discussion of the connection of pore characteristics and acoustic absorption. Finally, a conclusion is given."

Jan 1, 2012

By Neng-Wen Yu, Shau-Jun Zhu, Ji-He Wei

The desulfurization process by powder injection and blowing in the RH refining of molten steel and its mechanism have been considered and analyzed. Based on the two-resistance mass transfer theory and the mass balance of sulfur in the system, a kinetic model for the process has been developed. The related parameters of the model, including the mass transfer coefficients and the effective amount of powder in the molten steel being treated for desulfurization, have been more reasonably determined. Modeling and predictions of the process of injecting and blowing the lime-based powder flux under assumed operating modes with the different initial contents of sulfur and amounts of powder injected and blown in a RH degasser of 300 t capacity have been carried out using the model. The relevant circulation rate of the liquid steel and the powder injection and blowing rate were taken to be 100 t/min and 150 kg/min, respectively. The initial contents of sulfur in the liquid steel to be treated and the amounts of powder injection and blowing were respectively assumed to be 0.007, 0.006, 0.005, 0.004, 0.003, 0.002 mass-% and 10, 8, 6, 5, 4, 3 kg/t-steel. The total treatment time for desulfurization under each mode was set up at 24 min, equivalent to eight circulation cycles of the liquid steel to be treated. The results indicated that the predictions made with this model are in good agreement with some data of the industrial experiments and practice. Injecting and blowing the lime-based powder flux with the composition of 85 mass-% lime (CaO) + 15 mass-% fluorspar (CaF2) of 3-5 kg/t-steel, it is possible to decrease the sulfur content in the molten steel to ultralow level below (5-10)x10·4 mass-% from (60-80)x 10·4 mass-%. The total treatment time needed will appropriately be 12-20 min. Intensifying the powder injection and blowing operation and increasing the circulation rate of the liquid steel may effectively' raise the rate of the process in RH refining. The model may be expected to offer some useful information and a reliable basis for determining the reasonable process parameters and help in optimizing the technology of desulfurization by powder injection and blowing in the RH refining of molten steel.

Jan 1, 2000

By Peter Ehren

Global Geoscience is developing a Rhyolite Ridge project, a shallow boron-lithium resource deposit, located in Nevada about 25 km from Albermarle’s Silver Peak operation. The main minerals of interest are the boron mineral searlesite (40%wt) and lithium containing clay minerals. These minerals are found among principally calcite, feldspar, muscovite, dolomite, and quartz. The equivalent commercial value is about 7–9% boric acid (H3BO3) and 0.8–1.0% lithium carbonate (Li2CO3) equivalents. Selective agitated leach tests at SGS Lakefield laboratory showed that searlesite can be acid leached between 20 and 75 °C and at a pH lower than 4. On the other hand, lithium can be leached between 20 and 75 °C and at a pH lower than 1. In other words, lithium can be recovered at low temperatures if sufficient free acid is available, which gave the motivation to investigate heap leaching of the mineral. The PLS contains boric acid, magnesium, sodium, lithium, potassium aluminium, and iron sulfates.

By Taegong Ryu

Nanosized tungsten powder was synthesized by the hydrogen reduction of ammonium paratungstate (APT) in thermal plasma. The effects of operating conditions on the product composition and particle size were investigated. The particle size of synthesized W powder was less than 30 nm in all cases tested. The sintering behavior of the synthesized powder (25 nm average size) was then investigated and compared with those of commercial W powder of 500 nm average size and W powder of 23 nm average size produced by milling the commercial powder. The sintering was done at 1400oC with various holding times. The hardness of the resulting compact from the synthesized W powder (315 VHN) was similar to that from the milled W powder (309 VHN), but the plasma-synthesized powder had a much lower tendency to form cracks. The compacts of both nanopowders were significantly harder than that of the commercial powder (192 VHN).

Jan 1, 2009

By San-chuan Tang, Wen Chen, Shun-ming Ning, Kan-ping Yu, Qiang Zhao, Xue-yong Xing

"A new type of desilication agent (PA-2) was selected by experiment based on the analysis of the characters of silica gel, and the influence of desilication type, desilication dosage, pH value, temperature and aging time on the desilicating effect was studied. The test results showed that on the conditions that pH was 2.0, temperature was 20""C, aging time was12 hours and the dosage of desilication agent was 0.23%, the desilication rate was higher than 93% in solution.IntroductionVanadium is an important strategic resources, which applies to steel industry and petrochemical industry. The main materials for vanadium product are steelmaking vanadium slag, stone coal and containing vanadium waste catalyst, etc. And stone coal is a low-grade carbonaceous silicified vanadium resource, which is unique material for vanadium extraction in China. Meanwhile, our stone coal reserves is No.l throughout the world.The silica acid solution containing vanadium is produced by acid leaching of raw stone coal or its roasted ore. The silica content of this solution is mostly high, besides, when pH is higher than 2 , the solution is unstable. Furthermore, it is very easy to generate gel substance with the increasing of pH value and standing time. 'Ibis silica gel is composed of colloidal particles with the size in 0.001 - 0.1 um. As a result, it is very hard even impossible for the following operation of solution."

Jan 1, 2013

By A. Christlo

Short circuit detection in 1984 involved nine inspectors for production rates of 43,000 tpa. Trials indicated the feasibility of applying cell voltage monitoring to short circuit detection and improving operational efficiency. A computerised cell voltage monitoring system was commissioned in February 1986, to read voltages from 648 cells. The system incorporates 16 evenly distributed work face units which communicate with a central computer system. Provision has been made in the computer program for the automatic adjustment of cell reference voltages. This allows for the effect of polarization and other process variables which might other wise interfere with short circuit detection. The work face units can continue to work independently for several days should this become necssary. Current efficiencies have been maintained and the number of inspectors reduced from nine to five.

Jan 1, 1987

By Yong J. Kim, J. M. Park

"Solid/melt interface shape during continuous casting process has a strong influence on the resulting microstructure of the ingot. The interface shape is primarily governed by the heat flow condition between the molten metal and mold (or container). The roll of the microstructural transition resulting from various solid/melt interface shapes is discussed using the Sn-22.6wt%Pb alloy. Three different types of mold such as cold mold, resistantly heated mold, and electromagnetically heated mold were used to generate those interfaces having different curvatures. Experimental measurements of complete temperature profile along the axis and surface of the ingot during downward continuous casting are presented to determine the solid/melt interface geometry. The results provide an explanation of the ingot property with emphasis on microstructure.IntroductionA large scale of continuous casting process of alloys often has a rather deep V channel type of solid/melt interface resulting from a limited heat flow condition. As a result, the deep V type solid/melt interface shape entraps defects such as pores and inclusions and also creates canter segregation. In order to reduce the defects concentration, electromagnetic stirring(EMS) mechanism has been applied to the melt in the channel[l]. Speith and Bungeroth introduced first experimental EMS device to the continuous caster in 1952.[2] Today, with wide ranges of benefit, a large variety of such technique is available. Electromagnetic field on the melt can be divided into three aspects. First, eddy current is induced on the metal surface by alternating magnetic field with high frequency, which results in heating the metal. Second, electromagnetic body force which is generated by the magnetic field and the eddy current reduces the melt pressure on mold or support the melt not to contact with the mold[3,4,5]. This force is used for electromagnetic casting process(EMC). Finally, it causes stirring in the melt. Many research efforts have been done on the EMC process to improve surface quality of slab[6] and control meniscus shape where three phases such as melt, solidified metal, and mold powder coexist[7,8]. However, the eddy current heating effect on the surface of the ingot was less considered. It is worth noting that induced eddy current on the surface of slab melts the solidified shell and thus changes the heat flow condition between the mold and melt. Mold heating effect was first proposed by A. Ohno[9] and its processing conditions were identified in details[ 10, 11]. The so-called Ohno process is based on the fact that by keeping the mold temperature slightly above the melting temperature of the liquid, no grain can be nucleated on the mold wall[12]."

Jan 1, 1998