Melting Furnace Research Articles

Basics and applications of microporous insulation for aluminum melting furnaces

Basics and applications of microporous insulation for aluminum melting furnaces

Solidification and recovery of Cr from hazardous Cr-bearing steel slag: Selective solidification, super-gravity separation and crystal characterization

Massive hazardous Cr-bearing steel slag is produced from the electric furnace smelting process of stainless steel, while the soluble poisonous hexavalent chromium (Cr(VI)) seriously limits the sustainable utilization of the slag. In this study, a novel method of selective solidification and super-gravity separation was proposed to recover Cr resources from Cr-bearing steel slag safely and efficiently. Firstly, Cr elements were selectively solidified into Cr-spinel in Cr-bearing steel slag with wt.%(MgO) = 6.00, and the high-purity Cr-spinel crystals ((Mg0.43Fe0.28Mn0.29)(Cr1.67Al0.33)O4) were effectively recovered from the molten slag via super-gravity separation with a significant Cr2O3 content of 58.08 wt% and a high Cr recovery rate of 88.58 %. On this basis, the chemical formulas and crystal structures of various high-purity Cr-spinel crystals were characterized and the solidification mechanism of Cr in Cr-spinel was determined, to verify that Cr3+ was accordingly substituted by Al3+ when Fe2+ and Mn2+ were substituted by Mg2+, and Cr elements were efficiently solidified and recovered into the Cr-spinel in stable trivalent chromium (Cr(III)) based on the XPS results. Thus the effective leaching amount of Cr in Cr-spinel was as low as 0.011 mg/L, which provided a basis for sustainable utilization of Cr-bearing steel slag.

Enhanced Supercapacitive Properties of Mixed Oxide Nanotubes Grown by Anodization of Ti–Fe Alloys

Like titanium metal, nanotube array films can be grown on Ti alloys by anodization in fluoride‐containing electrolytes. Further, the anodization of Ti alloys provide a unique pathway to dope TiO2 nanotubes with the alloying element. However, the details of anodization behaviors of Ti alloys and the obtained nanotubes for application in supercapacitors remain poorly understood. Herein, three Ti–Fe alloys containing different amounts of Fe element (10, 15, and 20 wt%) are fabricated by using a vacuum arc melting furnace. Their anodization behaviors are systematically investigated. The nanotube array films can be achieved on these alloys, which are composed of TiO2, Fe2O3, and Fe‐doped TiO2. Their electrochemical behaviors are completely different from both the pure TiO2 and the pure Fe2O3. The mixed oxide nanotubes on Ti–15 wt%Fe have the maximum capacitance among the three Ti–Fe alloys, which is 3.75 times higher than that of pure TiO2. Moreover, the mixed oxide electrode exhibits high rate capability and excellent cycling stability with only 5.7% loss in capacitance over 10 000 cycles. The presented results suggest that the alloy anodization is an efficient strategy for enhancing the performance of TiO2 electrode materials for supercapacitors.

A clean and efficient utilization of fly ash with a focus on the strengthening decomposition mechanism of mullite

A novel method of comprehensive disposal of low temperature and high-efficiency reduction of fly ash to produce ferrosilicon without slag under the action of Fe2O3 was proposed in this paper. In addition, the promotion of Fe2O3 on the reduction and decomposition of fly ash at a low temperature and the strengthening mechanism of the reduction and decomposition of the mullite phase were systematically studied. The thermodynamic analysis shows that the decomposition reaction of mullite can be carried out only after the free SiO2 in fly ash is exhausted. Combined with the thermodynamic prediction of the equilibrium phase concentration of reduction products, the phase evolution of reduction products and the results of SEM microanalysis, it is proposed that the carbothermal reduction process of fly ash and the decomposition mechanism of mullite are as follows: iron oxide reduction, mullite decomposition into aluminum–silicon oxide and aluminum–silicon oxide deep decomposition and complete release of Al2O3, while the final products of reduction decomposition are ferrosilicon phase and alumina. According to the mineralogical characteristics of reduction decomposition products, a novel idea of preparing ferrosilicon and alumina/calcium aluminate byproducts by electric furnace melting is proposed, which lays a theoretical foundation for the large-scale, slag-free and high-value utilization of fly ash.

Формирование микроструктуры типа «ожерелье» методом ковки в сплавах Гейслера системы Ni-Mn-Ga-Si как способ повышения механических свойств

The standard technique for melting Heusler alloys involves melting in an argon-arc furnace on a water-cooled copper crucible. As a result of intensive crystallization of the ingot, large elongated crystals are formed in the structure. The thermo-mechanical treatment of such a structure is ineffective, since microcracks are formed along the boundaries of large crystals as a result of internal stresses and martensitic transformation, along which then, during processing, cracks develop and the workpiece is destroyed. It is shown that additional heat treatment by the vacuum induction remelting makes it possible to eliminate this effect. As a result of the treatment, an equiaxed granular microstructure with a grain size of about 200 μm is formed. However, as a result of remelting in a quartz crucible, silicon atoms diffuse into the bulk of the ingot. Its content varies in the range of 1-2% depending on the duration of exposure in the molten state. A uniform distribution of silicon, without the formation of additional phases is shown by energy-dispersive analysis. Thus, the Ni54.1Mn19.6Ga24.6Si1.7, Ni56.2Mn18.8Ga23.2Si1.8, Ni57.4Mn18.2Ga22.7Si1.7 and Ni56.5Mn20.1Ga22.3Si1.2 alloys were obtained. A partially recrystallized structure of the "necklace" type was formed in the alloys by the multiaxial isothermal forging at 950-973 K and the true degree of deformation e=1.9...3.9. The initial large grains with a size of 100-200 microns are surrounded by a layer of fine-grained structure. The thickness of the interlayer at the periphery of the workpiece is about 5 grains. In the center of the workpiece, the proportion of the fine-grained structure may prevail over the coarse-grained structure. The study of cyclic and fatigue strength was carried out by the method of three-point bending during cyclic tests in the temperature range of martensitic transformation using the example of the Ni54.1Mn19.6Ga24.6Si1.7 alloy in the initial state and the Ni57.4Mn18.2Ga22.7Si1.7 alloy in the forged state. It is shown that the “necklace” type microstructure, compared to the equiaxed microstructure, demonstrates a twofold advantage in cyclic strength and a fivefold advantage in fatigue strength.

Numerical modeling of gas-solid two-phase flow in a plasma melting furnace

Due to the low leaching rate of heavy metals and high energy utilization, the plasma melting furnace is widely used in the harmless treatment of waste incineration. In this paper, the gas-solid two-phase flow in the plasma melting furnace was numerically modelled by means of Euler-Lagrange approach. Conclusions can be drawn that the raw fly ash should be pelletized in order to successfully participate in the melting reaction and effectively avoid the collisional erosion with the graphite cathode. The velocity and temperature fields in the furnace showed asymmetry due to the interaction between the flue gas and slag particles. The heat-up degree of fly ash was much greater than that of SiO 2 particle while the speed discrepancy was small. The average temperature of slag particles in the effective melting region was relatively higher, which is more beneficial to the melting reaction. In addition, three evaluation indicators were established to analyze the distribution of slag particles on the bath surface. The mass proportions of different slag particles in the effective melting region were >40%, the maximum value of their radial distribution can be obtained in the radius range of 0.9–1.0 m, and the mass ratios of fly ash and SiO 2 particles in the same radius domain were overall closer to that of entering the furnace. Finally, the collisional erosion effect of slag particles on the graphite cathode was discussed in detail. • Particle flow in the plasma melting furnace is studied by Euler-Lagrange approach. • Fly ash pelletizing facilitates melting reaction and avoids collisional erosion. • Distribution of particles on bath surface can be evaluated by three key indicators. • High portion of particles in the effective melting region benefits melting reaction.

An efficient and clean utilization technique for red mud based on fluidized bed carbon monoxide reduction

In order to simulate the pre-reduction behavior of ore powder by coal gas produced by smelting reduction of coal-based electric furnace, an efficient and clean utilization technique for red mud based on fluidized bed carbon monoxide reduction was developed in the present study. Experimental results indicated that a metallization rate of 68.08 % and reduction degree of 78.72 was obtained under the optimal conditions of reduction temperature of 800 °C, CO concentration of 85 %, and reduction time of 30 min. Pre-reduced materials can be used as raw materials for electric furnace melting reduction. The order in which iron oxides were reduced is only related to temperature, and at 800 °C, iron oxides were reduced in the order of Fe2O3 to Fe3O4 to FeO to Fe. During different stages of prereduction, the surface structure of ore particles changes, which is related to the metallization rate of iron oxides in red mud.

High Manganese TWIP Steel with Increased Corrosion Resistance

The paper describes the development of austenitic steel with the TWIP effect, which is alloyed with chromium to increase corrosion resistance. The experimental heat of this steel was cast in an experimental melting furnace and subsequently subjected to hot and cold rolling. After cold rolling, the appropriate recrystallization annealing temperature was applied to obtain the optimal austenitic grain size. X-ray diffraction proved that the steel contains a fully austenitic structure. After recrystallization annealing, the sheets achieved a TS of more than 950 MPa with an elongation of 40%. The corrosion resistance of this steel is increased with the addition of chromium.

Quantitative characterization of secondary copper flue dust and guidance for separating valuable and toxic elements via low-temperature roasting and selective leaching

Secondary copper flue dust (SCFD), produced by secondary copper reduction smelting in blast furnaces, contains valuable metal elements (e.g., Zn, Pb, Cu, Sn, and Bi) and various toxic elements (e.g., As, Cd, F, Cl, Br, and Tl). The H2SO4 roasting-water leaching process is widely employed to pre-separate target elements. However, due to the complexity of raw materials, the mineralogical factors that affect the removal efficiency or leaching separation of some elements are unclear. In this study, the quantitative characterization of valuable and toxic elements in SCFD was first investigated through mineralogy methods. Then, the distribution and occurrence of all elements in products from the low-temperature H2SO4 roasting-water leaching process were clarified. The results indicated that the phases in SCFD were complex, including ZnO, PbCl2, Cu2S, metal Pb, Zn2SnO4, Cu-sn-Ni alloy, and C. They also indicated that the formation of Pb3(AsO4)2 was negatively correlated with the removal of As. The encapsulation of newly formed PbSO4 and copper film to large-grained Cu2S affected its transformation to CuSO4. Furthermore, the adsorption of siliceous colloid on Cd2+ impeded the leaching of Cd. Based on the mineralogical factors, guidance for process optimization was proposed. The optimized process realizes the deep removal of toxic elements and efficiently selective leaching of valuable metals.

Influence Factor Analysis and Prediction Model of End-Point Carbon Content Based on Artificial Neural Network in Electric Arc Furnace Steelmaking Process

In this manuscript, we consider the accuracy of end-point carbon content prediction affected by oxygen injection in multiple stages of electric arc furnace (EAF) melting process. Such a prediction would help to further evaluate process control strategies and optimize overall operation of the electric arc furnace. Principal component analysis (PCA) was used to normalize the 13 input variables affecting the endpoint carbon content. log-sigmoid and tan-sigmoid functions were used to verify the same sample, and it was found that the Mean squared error(MSE) of the model under logsig + logsig function was smaller, indicating that the model was more stable. At the same time, different hidden layer nodes were tried, and finally the structure of the model was determined as 13 × 10 × 8 × 1, and the activation function was logsig + logsig. Using historical smelting data to train and test the neural network model, the correlation coefficient (R) of the verified model is 0.7632, the model prediction is in the range of ±0.03%, the hit rate of the model is 64.5%, and the hit rate of the model is 42% in the range of ±0.02%. Combining the verification basis of the model with the metallurgical reaction principle of the EAF steelmaking process, a pretreatment method of phased input of total oxygen is proposed. The oxygen is divided into three stages, which are the oxygen consumption volume of 0–5 min, 5–30 min and more than 30 min and other variables are kept unchanged. The same neural network is used to train and verify the same data. After verification, the R of the oxygen staged model is 0.8274. The model prediction is in the range of ±0.03%, the hit rate of the model is 78.5%, and the hit rate of the model is 58% in the range of ±0.02%. Finally, an on-line carbon content prediction system based on artificial neural network model is developed and applied to actual production. Running results illustrated that the hit rate of end-point carbon content is 96.67%, 93.33% and 86.67%, respectively when the prediction errors are within ±0.05%, ±0.03% and ±0.01%, the improved neural network model can effectively predict the end-point carbon content, which provides a good basis for the carbon content at the end point of EAF steelmaking process.

The use of vacuum refining to separate Ca, Al, and P from crude metallurgical grade silicon

Crude metallurgical grade silicon (C-MG-Si) is produced by electric furnace smelting and must be purified before being used to produce organosilicon monomers and polysilicon. In this paper, the separation of Ca, Al and P from C-MG-Si by vacuum refining was studied. First, the direct vacuum refining of C-MG-Si was carried out at 1723 K and 3 × 10−3 - 5 × 10−3 Pa. After refining for 2.5 h, the removal efficiency of Ca, Al, and P reached 82.56%, 52.91%, and 79.17%, respectively. The combination of Ca, Al, and O was stable under the experimental conditions, and oxidized CaAl2Si2O8 eventually reacted with Ca and transformed into CaSiO3, which was deposited in the products. The oxidation refining pretreatment of C-MG-Si was carried out before vacuum refining and removed 91.24% Ca and 77.08% Al, including elemental and oxidized Ca and Al. Then, the same vacuum refining procedure was carried out on the MG-Si produced by pretreatment, and the cumulative removal efficiency of Ca, Al, and P reached 98.08%, 83.85%, and 79.17%, respectively. This study shows that vacuum refining can replace or complement oxidation refining to purify C-MG-Si.

Decarburization and ash characteristics during melting combustion of fine ash from entrained-flow gasifier

Disposal of gasification fine ash (GFA), a by-product of coal gasification, is still dominated by stockpiles, increasing land and environmental problems. To explore ways to reduce and reuse GFA through combustion, our research team used the circulating fluidized bed to modify the less reactive GFA through preheating and achieved the secondary use of GFA under high-oxygen and high-temperature reaction conditions. Through this experiment, we explored the effects of equivalent ratio and oxygen concentration in a melt furnace on carbon conversion and ash characteristics. The increase of oxygen concentration in the melt furnace unit benefited decarbonization of the preheated GFA. The increased oxygen concentration in the melting furnace unit was not conducive to the generation of mineral phase structures and pore structures in the products. The mineral phase structures and elemental contents of the coarse slag, fine slag and fly ash produced by the melt furnace unit differed. Reduction of the equivalent ratio did not significantly affect the morphology of the coarse slag products. However, the morphology of the fine slag and fly ash changed more significantly. Moreover, the carbon conversion capacity decreased significantly along with the drop of equivalent ratio and the change of the reaction atmosphere.

Effect of Basicity on the Reduction Swelling Performance of Pellets Prepared from Bayan Obo Iron Ore Concentrate Based on Microscopic Characterization

The development of blast furnace smelting technology with a high proportion of pellets is an important means for improving the utilization rate of complex co-associated mineral resources. The effect of basicity on the reduction swelling performance of pellets prepared from Bayan Obo iron ore concentrate is characterized by the aspects of microscopic morphology, element distribution and weight-loss behavior. The results show that with the increase in basicity, the reduction swelling rate and the weight-loss rate of pellets follows the change rule by first increasing and then decreasing. With a basicity of 0.8, the pellets have the largest swelling rate (75.743%) and the largest weight-loss rate (24.77%). The reduction swelling rate is proportional to the porosity and inversely proportional to the amount-of-liquid phase. In the first stage of reduction, pellets with a basicity of 0.8 changed from tabular to granular, and there were a large number of cracks. In the third stage of reduction, pellets with a basicity of 0.8 had coarse iron whiskers. In the same reduction stage, the amount of K and Na elements in the pellets with a basicity of 0.8 entering the iron oxide lattice was much larger than that in the pellets with a different basicity. As the reduction progresses, the ability of alkali metals to enter the iron oxide gradually increases.

Production of pre-reduced sinter based on sensible heat updraft of sinter

Utilization of pre-reduction burden in the blast furnace ironmaking process is an important measure for realizing low-carbon operation. In this paper, a new process for the production of pre-reduced sinter based on sensible heat updraft of sinter was put forward. The effects of sinter temperature and reducing gas composition in the pre-reduction cooling section on metallization rate and sieve size distribution of pre-reduction sinter were studied. The results showed that the metallization rate and proportion of 10–12.5 mm particle size of pre-reduction sinter increase with the increase of sinter temperature. When the sintering temperature was 950 °C and the reducing gas was the mixture of H 2 and CO, the metallization rate of the pre-reduced sinter was up to 35.5%. When the sintering temperature was lower than 750 °C, the carbon deposition reaction between H 2 and CO reduces the proportion of 10–12.5 mm particle size of the pre-reduced sinter significantly. The metallurgical properties of pre-reduced sinter with different roasting systems under hydrogen-rich smelting in blast furnace were studied. The results showed that compared to the traditional sinter, the reduction degradation index, reducibility index, and softening-melting properties of pre-reduced sinter were improved, and the permeability and maximum differential pressure of the stock column were reduced, which was beneficial to the improvement of blast furnace production efficiency. Based on the comprehensive effects of sinter temperature and reducing gas composition on the metallization rate, sieve size distribution, and metallurgical properties of pre-reduced sinter, the quality of the pre-reduced sinter was better when the sintering temperature was higher than 750 °C and the reducing gas was a mixture of H 2 and CO. In addition, the new process could organically combine sinter sensible heat utilization, flue gas circulation, and denitrification to form a complete technological process, which had a good development prospect. • Production of pre-reduced sinter based on sensible heat of sinter was proposed. • Metallurgical properties of pre-reduction sinter were systematically studied. • The process can organically combine with flue gas circulation and denitrification. • Process route of production of pre-reduced sinter was schematically mapped.

Thermodynamic analysis of interactions between furnace burden components in the process of obtaining metallurgical silicon

The theoretical foundations of the recovery process and the technology of silicon smelting in electric arc furnaces are considered. The results of a study of thermodynamics, reaction kinetics, and mechanisms of the melting process are presented. Production issues are covered: charge preparation, smelting, refining, gas purification. Physicochemical models of the carbothermal process were developed, proposed and tested under industrial conditions (Tau-Ken-Temir LLP), which made it possible to assess the influence of the specified technological parameters of the smelting (chemical composition and loading coefficients of charge components, temperature) on silicon recovery and grade. To obtain the base material, metallurgical grade silicon is used, obtained by melting in ore-thermal furnaces (RTP). In this regard, the research goal is determined, which consists in studying ways to improve the quality (chemical purity) of silicon, and methods for achieving it at this stage of the study - modeling the carbothermal process for producing silicon.The article describes the main mechanism for the recovery of silica in the furnace, presents one of the designs of the furnace and the technological scheme for the production of silicon. The author suggested studying the process of producing metallurgical silicon in RTP using the HSC Chemistry software package. A model of silicon smelting in RTP was formed, which adequately describes the technological process for producing metallurgical silicon.

Temperature Prediction Model for a Regenerative Aluminum Smelting Furnace by a Just-in-Time Learning-Based Triple-Weighted Regularized Extreme Learning Machine

In a regenerative aluminum smelting furnace, real-time liquid aluminum temperature measurements are essential for process control. However, it is often very expensive to achieve accurate temperature measurements. To address this issue, a just-in-time learning-based triple-weighted regularized extreme learning machine (JITL-TWRELM) soft sensor modeling method is proposed for liquid aluminum temperature prediction. In this method, a weighted JITL method (WJITL) is adopted for updating the online local models to deal with the process time-varying problem. Moreover, a regularized extreme learning machine model considering both the sample similarities and the variable correlations was established as the local modeling method. The effectiveness of the proposed method is demonstrated in an industrial aluminum smelting process. The results show that the proposed method can meet the requirements of prediction accuracy of the regenerative aluminum smelting furnace.

ANALYSIS OF DEVIATIONS DURING THE BLAST FURNACE SMELTING IN THE BLOW-IN PERIOD AND MEASURES TO PREVENT AND ELIMINATE THEM

The work of blast furnaces during their blow-in period after major repairs is analyzed, the individual deviations from the normal operating mode are noted and the causes of their occurrence are investigated. It is shown that in three or four out of ten start-up campaigns, immediately after the ignition of coke, there is an abrupt increase in the
 temperature of the top gas in the gas outlets to values exceeding 800 °C and representing a serious issue to the metal structures of the top. At the same time, with approach to the melting zone of the charge of fluxed coke and the “ore” charge, the thermal state of the furnace decreases. Therefore, on the one hand, the location of the melting zone is determined by the composition of the charge, and, on the other hand, by the amount of the hearth gas heat involved in the heat exchange with the charge. At a high total speed of convergence of oncoming heat flows, the factor of residence time of
 iron ore materials in the zone of active reduction acquires a fundamentally important role. With “cold” blows, the reduction of iron not only continued in the lower coke deadman, but did not even complete: the FeO content in the slags of the first tapping reached 5–10% or more, and the silicon content in the pig iron decreased to the minimum values. The presence of increased moisture in the coke nozzle leads to the impossibility of normal processing of smelting products, since the heat consumption for moisture evaporation does not allow heating the slag to a good fluidity temperature, and it also leads to cooling of the hearth and disruption of the communication channels of the tuyere zone with the metal receiver. It is noted that blow-in using multicomponent charges is accompanied by the increased energy consumption, which is due to both the peculiarity of the heat exchange during the blow-in period and an increased degree of direct reduction. Minimizing the risks of technological disruption associated with the loss of the drainage capacity of the hearth during the blow-in period is possible through the implementation of measures to minimize the moisture content in the coke deadman
 before starting the blast furnace after the major repairs.

Determination Some Physical Properties of Ground NiMnCoSn Magnetic Shape Memory Alloy Powders

In this study, NiMnCoSn alloy was produced in the arc melting furnace and then grounded into small powder particles. After this procedure, particles of alloys were pelletized and heat treatment was applied to pellet alloys for 3 different temperatures (500 oC,700 oC and 900 oC). Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and physical property measuring system (PMMS) were used for determining physical properties of samples. The biggest feature of NiMn-based shape memory alloys is that they are magnetically based. The feature that distinguishes magnetic shape memory alloys from traditional ones is that the shape memory effect is magnetic. For this reason, studies of NiMn-based alloys are becoming very popular. It was observed that, grounding procedure is effected all physical properties of NiMnSnCo shape memory alloys, seriously.

Development of a low cost portable aluminium melting furnace for laboratory use

A lot of research is going on metal matrix composites. Many permutations and combinations are made in the fabrication of MMCs (Metal Matrix Composites). The variations are made in the type of base metal and reinforcement, the percentage of reinforcement in the matrix, the form of reinforcement like powder, fibre, flakes, the type of fabrication like stir casting, squeeze casting etc. Then the mechanical properties, along with microstructures are tested for desired applications. Casting plays an important role in the fabrication of MMC. Here melting of metals, alloys in small quantity for experimental purpose is needed. Therefore a portable, low cost aluminium or any other metal/alloy having melting temperature in the range of 600–750 °C is developed in this research work. Infrared heater is used to melt aluminium in graphite crucible. The melting electricity cost for this infrared furnace (IR Furnace) for melting 250 gm of aluminium in 55 min is estimated as Rs. 13.50. The furnace is fabricated using standard parts instead of going for manufacturing special parts, which considerably reduced the cost of furnace and estimated Rs. 15080/-

Influence of copper on the deformation behavior of NiTi shape memory alloys in isothermal compression

NiTi alloys are more commonly employed in engineering and medical applications because of its appealing shape memory and superelastic qualities. Recent efforts have been made to increase their thermal memory, mechanical capabilities, and corrosion resistance by alloying, heat treatment, and other means. NiTiCu alloys are the most often utilised ternary alloy in actuator applications. However, there is a scarcity of literature on the hot deformation properties or deformation process maps of NiTiCu shape memory alloys. To make cylindrical ingots, elemental forms of high purity nickel, titanium, and copper were melted in a vacuum induction melting furnace. These ingots were homogenised at 900 °C, quenched in water to room temperature, then machined to achieve a length-to-diameter ratio of 1.5, which is appropriate for doing hot deformation tests in a Gleeble thermo-mechanical simulator. The samples were exposed to strain rates of 0.01, 0.1, 1, and 10 s−1, respectively, and the data acquired was used to build a deformation processing map. The zones of instability were defined, and the dominating operational mechanisms in various regimes were projected and reported.