炼钢短流程工艺国内外现状及发展趋势

全废钢连续加料电弧炉内长电弧作为炉内主要的能量来源,对废钢熔化及钢液升温至关重要。采用磁矢量势的磁流体动力学方法建立了电弧炉内电弧的数值模型,并基于该数值模型对电弧炉内电磁场、温度场和流场进行耦合求解,研究了电流大小、弧长对电弧炉内电弧的温度、速度、压力及气体剪切力特性的影响。结果表明,全废钢连续加料电弧炉内电弧等离子体呈“长钟型”分布,电弧柱较细长;随着电流增大,电弧有效作用范围增大,阳极表面电弧压力和气体剪切力增大;随着弧长增加,电弧有效作用范围减小,阳极表面的电弧压力和气体剪切力减小。短弧操作对熔池冲击剧烈,长弧操作熔池较为平稳,合理控制电流和弧长能有效提高电弧热效率。     

Acoustic characteristics of electric arc furnaces

A mathematical model is constructed to describe the appearance and development of the noise characteristics of superpower electric arc furnaces. The noise formation is shown to be related to the pulsation of the axial plasma flows in arc discharges because of the electrodynamic pressure oscillations caused by the interaction of the self-magnetic field with the current passing in an arc. The pressure in the arc axis changes at a frequency of 100 Hz at the maximum operating pressure of 66 kPa for an arc current of 80 kA. The main ac arc sound frequencies are multiples of 100 Hz, which is supported in the practice of operation of electric arc furnaces. The sound intensity in the furnace laboratory reaches 160 dB and is decreased to 115–120 dB in the working furnace area due to shielding by the furnace jacket, the molten metal, and the molten slag. The appropriateness of increasing the hermetic sealing of electric furnaces and creating furnaces operating at low currents and high transformer voltages is corroborated.     

Analysis of electric arc furnaces efficiency via frequency spectrum-based arc coverage detection

We introduce the analysis of variables measured outside a direct current electric arc furnace that are related to the arc coverage and its electric energy efficiency. We derive an on-line reference to the arc coverage suitable for control decisions. In order to do so, we study the furnace shell vibration frequency spectrum as structure-borne sound sensed by a microphone. The data is analysed using real time software tools to obtain the sound signal spectrum associated with arc coverage likewise related to the optimal performance of the furnace. A statistical test is performed to prove the relationship between sound and electric energy efficiency.     

A mathematical model of gas tungsten arc welding considering the cathode and the free surface of the weld pool

A two-dimensional axisymmetric numerical model, including the influence of the cathode and the free surface of the weld pool, is developed to describe the heat transfer and fluid flow in gas tungsten arc (GTA) welding. In the model, a boundary-fitted coordinate system is adopted to precisely describe the cathode shape and deformed weld-pool surface. The current continuity equation has been solved with the combined arc plasma-cathode system, independent of the assumption of current density distribution on the cathode surface, which was essential in the previous studies of arc plasma. It has been shown that the temperature profile, the current, and the heat flux to the anode show good agreement with the experimental data. Moreover, the current and the heat-flux distributions may be affected by the shape of the cathode and the free surface of the weld pool.     

Process dynamics of electric arc furnace during direct reduced iron melting

A phenomenological mathematical model to simulate steelmaking operations in an electric arc furnace (EAF) has been developed. This model has been validated with industrial data from a Mexican company that employs direct reduced iron (DRI) as the main iron unit. The slag and steel composition can be predicted in real time with the aid of several components integrated into the simulator. The model starts with the optimization of mass and energy balances that yields the requirement of materials to produce a given quality of steel with the minimum cost. The rate of reduction of iron oxide is computed based on two reactions occurring between the FeO and carbon dissolved in the metal and FeO with the carbon particles injected into the slag. A mechanism of consumption of carbon particles has been completed, which includes the effect of surfactant species in the slag and operational variables of the industrial practice of carbon injection. A new concept, called dynamic foaming index, (DFI) is proposed to quantify the actual foaming behavior of industrial slags throughout a commercial heat. The results prove the versatility and robustness of the present mathematical model and provide a knowledge base to assist in the design, operation, and optimization of metallurgical practices for EAF steelmaking.     

Characteristics of electric arc furnaces powered by a low-frequency alternating current

The changes in the parameters of a DSP-100 electric arc furnace that are induced by a decrease in the current frequency are considered. It is shown that the related decrease in the current lead resistances causes an increase in the arc power and voltage, a decrease in the reactive power, and an increase in the electrical efficiency and the power coefficient. The heat indices are expected to be significantly improved.     

Modeling of fluid flow and heat transfer in the plasma region of the dc electric arc furnace

A mathematical model describing the transport processes in the plasma arc in dc electric arc furnaces has been developed. The equations of conservation of mass, momentum, and energy are solved numerically in conjunction with Maxwell's equations of the electromagnetic field to calculate the velocity and temperature distributions in the plasma region. The heat transfer from the arc to a rigid anode surface is calculated. The model is applied to obtain quantitative results on the relative importance of the various modes of heat transfer from the electric arc to the anode surface. Computational results were obtained for varying arc current magnitudes and anode-cathode distances. The model predicts higher arc jet velocity and a broader arc core at higher arc current. The shorter arc length is more efficient for transferring heat to the anode.     

Relationship between furnace voltage signatures and the operational parameters arc power,arc current,CO pressure,and electrode gap during vacuum arc melting INCONEL 718

Transfer of metal during vacuum arc remelting creates a signature on the voltage waveform called a drop short, and subsequent arc reignition sometimes creates a signature called an anode spike. The frequency of these events is used forin situ control of electrode gap and, at the present time, their use is limited to melting at conditions of constant current and CO pressure. Statistically designed experiments were conducted in a production melt shop to evaluate the influence of the independent variables arc power or current, CO pressure, and electrode gap on the frequency of these events. Approximately 5000 kg of INCONEL 718 alloy 0.406 m diameter electrodes were vacuum arc remelted into 0.457 m diameter ingots. The experimental results produced regression models which show a three way interaction of the independent variables to be the dominant term with increases in each independent variable producing a power-law reduction in frequency. The inverse nature of these relationships is created by the behavior of the cathode spots, system geometry, and unresolved physics. The models perform accurately at gaps <25 mm and exhibit considerable error at gaps >25 mm. Implications of the results are discussed from the standpoint of arc furnace control.     

Fluid Flow Modeling of Arc Plasma and Bath Circulation in DC Electric Arc Furnace

 A mathematical model describing the flow field, heat transfer and the electromagnetic phenomenon in a DC electric arc furnace has been developed. First the governing equations in the arc plasma region are solved and the calculated results of heat transfer, current density and shear stresses on the anode surface are used as boundary conditions in a model of molten bath. Then a two dimensional time dependent model is used to describe the flow field and electromagnetic phenomenon in the molten bath. Moreover, the effect of bottom electrode diameter on the circulation of molten bath is studied.     

Designing of an electric regime for an arc steel-melting furnace using a heat-exchange model for an arc

New methods for choosing the operating current and the electric circuit parameters of a designed ASF, which are based on a heat-exchange model of an electric arc, are considered.     

Concept of dynamic foaming index and its application to control of slag foaming in electric arc furnace steelmaking

Abstract

To sustain a foam in steelmaking processes, two basic requirements should be fulfilled, i.e. appropriate physical properties of the slag such as high viscosity, low density, and low superficial tension, and the generation of sufficient reaction gas. To date, foaming indexes have been focused on the physical properties of refining slags. In the present paper a dynamic foaming index (DFI) that involves both above requirements is proposed, using a kinetic model of the electric arc furnace process to calculate the generation rate of reaction gas, mainly CO. When the arc distortion, as affected by electrode submergence in the foam, is compared with the DFI, calculated via the kinetic model, it is observed that both parameters follow very similar trends. This finding indicates the feasibility of knowing the foaming conditions of a heat in advance, or of using the kinetic model online to control the foaming phenomena. Furthermore, experimental results relating to dynamic behaviour of the slag chemistry are well simulated using the kinetic model. To take into account the effect of size distribution of carbon particles injected into the slag to reduce FeO, a Monte Carlo simulation has been integrated into the process simulator, allowing a more realistic prediction of the current steelmaking process.     

Influence of non-uniform material properties and water cooling on current density and temperature profiles in arc furnace electrodes

The influence of the simplifying assumption of constant electrical conductivity on the modelling of current density and temperature profiles in arc furnace electrodes is investigated in comparison with calculations taking into account the complete interdependence of electrical and thermal effects. With respect to the accuracy of the calculated values for UHP arc furnace electrodes it is shown that the classical theory for the skin effect using the approximation of constant electrical conductivity is inferior to an exact numerical evaluation, especially concerning the current distribution. A two-dimensional thermal analysis is performed for combination electrodes consisting of a water cooling shank and a graphite wearing part, in order to demonstrate the cooling effect for the reduction of graphite consumption. In the electrodes considered here, the cooled region in the wearing part covers an axial distance in the order of one electrode diameter.     

Ti2AlNb合金锭真空自耗过程宏观偏析的数值模拟

Ti₂AlNb合金锭的真空电弧重熔(VAR)是一种超高温且不透明冶金过程,很难对这一过程中的熔体流动行为和宏观偏析的形成过程进行试验研究。发展了基于欧拉多相流的电磁场、温度场、流场、溶质场的多场强耦合数学模型,研究了真空自耗过程中的多物理场相互作用机制,对Ti₂AlNb合金锭中成分偏析形成过程及分布规律进行了预测。模拟结果表明,电磁力主要分布于熔池表面,自感电磁力推动金属液由中心向下流动而加深熔池;搅拌电磁力的离心效应则大幅提升熔池的温度场均匀度,促使熔池内金属液中的溶质混合均匀。尽管铸锭外围和中心分别形成了大范围的正、负偏析区,但区域内的成分较为均匀。在搅拌和沉降的作用下,金属熔池中的等轴晶极大地缩短了铸锭中的柱状晶区。该模型的模拟结果在熔池深度与宏观偏析分布方面与试验结果吻合良好,可进一步应用于预测和研究工业级大型铸锭中的成分偏析。     

Innovation approaches to controlling the electric regimes of electric arc furnaces

The processes of current passage in an ac electric arc furnace (EAF) are subjected to industrial experiments and mathematical simulation. It is shown that, when a charge is melted, arcs between charge fragments exist in series with main arc discharges, and these arcs influence the stability of the main arc discharges. The measurement of instantaneous currents and voltages allowed us to perform a real-time calculation of the electrical characteristics of a three-phase circuit and to determine the θ parameter, which characterizes the nonlinearity of the circuit segment between electrodes. Based on these studies, we created an advanced system for controlling the electric regime of EAF.     

Arc voltage distribution properties as a function of melting current, electrode gap, and CO pressure during vacuum arc remelting

An industrial vacuum arc remelting experiment was carried out at Cytemp Specialty Steel Corp. (Titusville, PA) during which a 0.432-m-diameter Alloy 718 electrode was remelted into a 0.508-m-diameter ingot. The purpose of the experiment was to investigate the response of the arc voltage distribution properties (mean, standard deviation, and skewness) and the drip-short frequency to melting current, electrode gap, and CO pressure. The responses were characterized by recording and analyzing changes in the temporally averaged properties. Each independent variable was systematically varied in accordance with a modified Yates order factor space experimental design within the following ranges: melting current, 5000 to 11,200 A; electrode gap, 0.004 to 0.056 m; and CO pressure, 0.40 to 14.7 Pa. Statistical models were developed describing the correlation between the averaged arc voltage distribution properties and the independent variables. The models demonstrate that all of the voltage distribution properties, as well as the drip-short frequency, are directly related to electrode gap. An arc column model is presented to account for the mean arc voltage properties and the model is used to estimate the arc column pressure. The potential usefulness of the distribution properties as process diagnostics and control responses is evaluated.     

Numerical analysis of metal transfer in gas metal arc welding

The present article describes a numerical procedure to simulate metal transfer and the model will be used to analyze the transport processes involved in gas metal arc welding (GMAW). Advanced Computational fluid dynamics (CFD) techniques used in this model include a two-step projection method for solving the incompressible fluid flow; a volume of fluid (VOF) method for capturing free surface; and a continuum surface force (CSF) model for calculating surface tension. The electromagnetic force due to the welding current is estimated by assuming several different types of current density distribution on the free surface of the drop. The simulations based on the assumption of Gaussian current density distribution show that the transition from globular to spray transfer mode occurs over a narrow current range and the size of detached drops is nonuniform in this transition zone. The analysis of the calculation results gives a better understanding of this physical procedure. Comparisons between calculated results and experimental results are presented. It is found that the results computed from the Gaussian assumption agree well with those observed in experiments.     

Numerical study of dc arc plasma and molten bath in dc electric arc furnace

Abstract

A numerical study of the arc plasma and molten bath in a dc electric arc furnace (EAF) is useful for understanding and improving the production process of the dc EAF. In the present paper, a mathematical model based on conservation equations of mass, momentum and energy along with Maxwell's equations is developed to describe the flow field and heat transfer in the arc and molten bath regions of a dc EAF simultaneously. The governing equations are solved using the PHOENICS software package. The calculated results show good agreement with those of previous studies, giving a useful insight into the factors of arc heat transfer and bath circulation.     

多电飞机断路器电弧机理及灭弧技术研究综述

多电飞机指次级功率从机械能、液压能、气压能等传统的多能源体制统一为电能体制的飞机,具有系统结构简单、可靠性高、可维护性高和能源利用率高等优点,其电力系统最先进的架构为360～800 Hz变频交流电源和270 V直流电源,目前已在空客A380、波音B787、F-22等多电飞机中应用。但随着用电功率的增加,多电飞机的配电、用电网络以及线缆布局将变得更复杂,发生短路等电气故障的概率明显加大。故障电流产生的电弧不仅严重影响线缆和用电设备的寿命、可靠性和安全性,还将限制航空电力系统扩容和飞行性能提升。多电飞机断路器是灭弧的关键器件,通过分析断路器中电弧放电过程的复杂机理,可有助于提升其灭弧性能。为深入推进多电飞机电力系统中断路器电弧理论与灭弧技术研究的开展,首先分析了民用和军用多电飞机电力系统的结构以及电气故障保护的难点,然后分别归纳了航空变频交流断路器和270 V直流断路器中电弧理论与灭弧技术的研究现状,最后预测了未来航空保护电器灭弧技术的发展趋势。      

Large arc voltage fluctuations and droplet formation in electric arc wire spraying

Abstract

The diameter of droplets in electric arc wire spraying is critical in determining the microstructure, porosity and oxide content of the resulting sprayed coatings. Droplet diameter controls dynamic and thermal behaviour in the spray, and the splashing and spreading behaviour of droplets at deposition. In electric arc wire spraying, the droplet diameter is determined by a combination of the melting behaviour of the feedstock wires in a direct current arc, combined with primary and secondary atomisation processes under the action of a high velocity atomising gas. The high frequency arc voltage variations during electric arc spraying of Fe-0·8C have been investigated and arc voltage fluctuations related to atomisation events occurring at the wire tips during spraying. A simple analytical model has been proposed which allows the diameter of primary droplets produced by atomisation to be calculated from the wire feedrate and the average time period for material removal, which was obtained from the voltage traces. Primary droplets were then assumed to undergo secondary atomisation according to correlations from the literature, and resulting droplet diameters were compared with diameters measured by experiment. Despite uncertainties in some of the thermophysical data and dynamic conditions during atomisation, predicted droplet diameters were in good agreement with experimental mass mean droplet diameters obtained under a range of atomising gas pressures, arc voltages and wire feedrates.