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.     

直流电弧炉钢棒式底电极传热与流动数学模型

 为了深入了解直流电弧炉水冷钢棒式底电极的传热过程，根据底电极的炉底结构结合相应的边界条件，建立了基于流动的二维轴对称固液相变传热数学模型。推导了考虑水冷铜套和电极之间空气隙影响的等效对流换热系数以及通电时的径向和轴向电磁力方程。模型中考虑了底电极从固态300 K到液态2 000 K过程中钢的物性的连续变化。利用所建模型，可以数值模拟直流电弧炉单炉冶炼、双炉冶炼的非稳态传热过程以及考察计算参数和结构改变影响的稳态传热过程，为改善电弧炉的安全性、提高工作效率提供理论依据。     

直流电弧炉底电极的设计与应用

本文由电工学、传热学及触针风冷底电极特点，推导出触针底电极根数、直径与最大直流电流的关系式，结合上钢五厂１０ｔ直流电弧炉底电极的设计，说明关系式的应用、注意事项以及底电极冷却所需气体量的确定等。底电极尺寸确定过程虽然是以触针风冷底电极为例，但同样适合于棒式水冷电极尺寸的确定。     

A novel numerical model for billet reheating furnace

A numerical model of billet reheating furnace is proposed, which includes heat fluxes calculation around four billet surfaces and two-dimensional conduction calculation inside billet. Radiation and convection heat fluxes on top and bottom surfaces are calculated simultaneously, based on quartic and linear difference between furnace gas and billet surface temperatures, while furnace gas temperature is determined according to thermocouple values along furnace length together with billet surface temperature. Lateral fluxes are also calculated considering angle factor on billets interval. Two-dimensional partial differential equation is acquired for billet conduction to determine temperature distribution, which is discretised and solved by Alternating Direction Implicit and TriDiagonal Matrix Algorithm. Two embedded thermocouple experiments were carried out to verify furnace gas temperature, the effect of billet interval on lateral heat flux calculation as well as billet temperature. It met agreement well with experiments on billet temperature, which could be a better prerequisite for further reheating furnace automatic control.     

Rotor Lorentz force as a parameter for the estimation of vortex flows in a DC electric arc furnace with different bottom electrode positions

This article is devoted to researching a simple parameter which can predict the electrovortex flow in a liquid conductor under a Lorentz force. This is provided by a numerical simulation of the electrovortex and convection flows in a DC electric arc furnace with the bottom electrode in different positions. The electromagnetic, temperature and hydrodynamic distribution parameters are given. It is shown that lifting the bottom electrode above the fettle surface by the electrode radius leads to the decrease of shear stress on the fettle area by 30%, while putting the bottom electrode lower than the fettle surface by a distance equal to the electrode radius and its expansion by the same distance reduces stress by 10%. A good correlation between the shear stress on the fettle area and a rotor Lorentz force provide possibility to use rotor Lorentz force as a simple electromagnetic parameter for the estimation of the vortex flow influence on the increased wearing of the fettle.     

Modeling of Vortex Flows in Direct Current (DC) Electric Arc Furnace with Different Bottom Electrode Positions

This article is devoted to the numerical modeling of electrovortex and convection flows in the direct current (DC) electric arc furnace with a different position of the bottom electrode. The electromagnetic, temperature, and hydrodynamic distribution parameters are given. The shear stress on the fettle area is offered as a criterion for the estimation of vortex flow influence on the increased wearing of the fettle. It is shown that lifting the bottom electrode above the fettle surface at the electrode radius leads to the decrease of shear stress on the fettle area by 30 pct. Putting the bottom electrode lower than the fettle surface by the distance equal to the electrode radius and its expanding by the same distance reduces the stress by 10 pct.     

Modelling of electrovortex and heat flows in dc arc furnaces with bottom electrode

Abstract

The article is devoted to the investigation of interaction between electrovortex and heat flows of liquid metal in dc arc furnaces with a bottom electrode. A mathematical model of liquid steel flows in a dc arc furnace with a bottom electrode was developed, and an algorithm of a three-stage solution was produced based on standard software packages. The results of electromagnetic, heat transfer and hydrodynamic analysis in industrial dc arc furnaces are given. It is shown that the Lorentz force makes up ～30% of the volumetric gravity force and makes the main contribution to vortex flow of liquid metal in a dc arc furnace. The convection flows with the maximum heat power of furnace make a significant contribution to the vortex flow of liquid metal, and the maximum value of the vortex flow velocity is ～1·5 times more than the movement without convection. The verification of results has been carried out by comparing them with general electrovortex flows theory, experimental data and results of similar software packages.     

直流矿热炉熔炼硅锰合金温度场-电磁场数值模拟

采用直流供电成为电弧炉熔炼硅锰合金的发展方向.由于直流供热强度增加,炉衬的温度分布及传热规律需要重新考察及设计.建立了炉衬与炉内熔池耦合的三维非稳态传热模型,研究给定不同外加电压时直流矿热炉炉内的温度场和电磁场.研究表明,外加电压由100 V增大到300 V后,电弧区的最高温度增大了 150％.底电极中心与炉壁的温差T...     

推钢式板坯加热炉炉底水梁节能改造

通过对推钢式板坯加热炉炉底水梁振动现象进行分析研究,找出原因并实施技术改进,显著降低了炉底水梁在钢坯运行中的振动,提高了水梁包扎料及炉体耐材的使用寿命。通过对炉底水梁布置形式和耐热滑块等优化设计,降低了炉内水梁面积及水冷热损失。对推钢式加热炉炉底水梁节能优化改进,不仅降低了能源消耗,同时还提高了钢坯加热质量,应用效果良好。     

GCr15钢喷射成形沉积坯孔隙形成及致密度的分析

GCr15钢(1.01%C、1.48%Cr)经100kg中频感应炉熔化至1 580℃,金属液流经炉底导液管喷嘴处被高压氮气流在雾化室雾化成微米级液滴,在基底形成沉积坯。通过使用金相显微镜、扫描电镜对GCr15钢喷射成形试样的孔隙分布、微观组织和密度进行比较分析。结果表明,沉积坯截面上有宏观孔隙,在整个截面上也存在一些形状不规则的孔隙;沉积坯整体平均相对致密度为85.51%。     

The effect of rapid heat treatment on the high-temperature tensile behavior of superplastic Ti-6Al-4V

The effect of rapid heat treatment on the microstructure and elevated-temperature tensile behavior of a Ti-6Al-4V sheet has been studied. Nonequiaxed secondary α phase, introduced by rapid heat treatment, increased the flow stress and changed the stress-strain behavior. A finer scale of the microstructures produced by rapid heat treatment, however, resulted in a stress-strain behavior that differed from that reported in the microstructures obtained from a slower, furnace heat treatment. These fine structures exhibited higher values of m, greater elongation, and lower flow stresses. The stress-strain behavior was found to be dependent on the prior-β grain size; this effect was not observed when the material was furnace heat treated in the β-phase field. The stress-strain curve gradually changed from exhibiting continuous strain hardening to exhibiting a peak stress followed by strain softening, i.e., the superplastic behavior of the as received material gradually diminished as the prior-heat-treatment temperature increased.     

直流电弧炉钢棒式底电极热状态数值模拟

 采用Fluent软件和文献建立的二维传热模型,对底电极稳态和非稳态的传热过程进行了数值模拟。计算中考虑了底电极物性随温度的变化、空气隙的等效对流换热系数、底电极内部电磁力和焦耳热的影响等,并采用UDF函数加以实现。通过数值模拟,研究不同底电极结构、电流强度以及绝热/绝缘材料熔损对底电极热状态的影响。计算得到的冷却水进出口温差随冶炼时间的变化与现场实测结果吻合,进一步验证了所建模型和参数选择的合理性。计算结果表明,底电极周围绝热/绝缘材料熔损和电磁力对底电极的热状态和熔化深度起着重要的作用。     

蓄热式加热炉提高加热能力探讨

蓄热式加热炉投产后,通过采取改进炉体材料及实炉底材料、蓄热体材料、缩短均热段实炉底长度、改变纵水管工艺布置、改变纵水管滑道与钢坯接触部位等技改措施,实现了加热能力的提高.     

步热式加热炉坯料摆放最佳间隙的研究

本文从炉内辐射传热角度出发,阐述了步进式炉坯料摆放最佳间隙的确定方法。实例分析结果表明,利用该方法确定料坯的摆放间隙是合理的,可使步进炉获得最大热效率。     

On the development of a three-dimensional transient thermal model to predict ingot cooling behavior during the start-up phase of the direct chill-casting process for an AA5182 aluminum alloy ingot

The control of the heat transfer during the start-up phase of the direct-chill (DC) casting process for aluminum sheet ingots is critical from the standpoint of defect formation. Process control is difficult because of the various inter-related phenomena occurring during the cast start-up. First, the transport of heat to the mold is altered as the ingot base deforms and the sides are pulled inward during the start-up phase. Second, the range of temperatures and water flow conditions occurring on the ingot surface as it emerges from the mold results in the full range of boiling-water heat-transfer conditions—e.g., film boiling, transition boiling, nucleate boiling, and convection—making the rate of transport highly variable. For example, points on the ingot surface below the point of water impingement can experience film boiling, resulting in the water being ejected from the surface, causing a dramatic decrease in heat transfer below the point of ejection. Finally, the water flowing down the ingot sides may enter the gap formed between the ingot base and the bottom block due to butt curl. This process alters the heat transfer from the base of the ingot and, in turn, affects the surface temperature on the ingot faces, due to the transport of heat within the ingot in the vertical direction. A comprehensive mathematical model has been developed to describe heat transfer during the start-up phase of the DC casting process. The model, based on the commercial finite-element package ABAQUS, includes primary cooling via the mold, secondary cooling via the chill water, and ingot-base cooling. The algorithm used to account for secondary cooling to the water includes boiling curves that are a function of ingot-surface temperature, water flow rate, impingement-point temperature, and position relative to the point of water impingement. In addition, a secondary cooling algorithm accounts for water ejection, which can occur at low water flow rates (low heat-extraction rates). The algorithm used to describe ingot-base cooling includes both the drop in contact heat transfer due to gap formation between the ingot base and bottom block (arising from butt curl) as well as the increase in heat transfer due to water incursion within the gap. The model has been validated against temperature measurements obtained from two 711×1680 mm AA5182 ingots, cast under different start-up conditions (nontypical “cold” practice and nontypical “hot” practice). Temperature measurements were taken at various locations on the ingot rolling and narrow faces, ingot base, and top surface of the bottom block. Ingot-based deflection data were also obtained for the two test conditions. Comparison of the model predictions with the data collected from the cast/embedded thermocouples indicates that the model accounts for the processes of water ejection and water incursion and is capable of describing the flow of heat in the early stages of the casting process satisfactorily.     

Effects of alloy composition and casting speed on structure formation and hot tearing during direct-chill casting of Al-Cu alloys

Effects of casting speed and alloy composition on structure formation and hot tearing during direct-chill (DC) casting of 200-mm round billets from binary Al-Cu alloys are studied. It is experimentally shown that the grain structure, including the occurrence of coarse grains in the central part of the billet, is strongly affected by the casting speed and alloy composition, while the dendritic arm spacing is mostly dependent on the casting speed. The hot cracking pattern reveals the maximum hot-tearing susceptibility in the range of low-copper alloys (1 to 1.5 pct) and at high casting speeds (180 to 200 mm/min). The clear correlation between the amount of nonequilibrium eutectics (representing the reserve of liquid phase in the last stage of solidification) and hot tearing is demonstrated. A casting speed-copper concentration-hot-tearing susceptibility chart is constructed experimentally for real-scale DC casting. Computed dimensions of the solidification region in the billet are used to explain the experimentally observed structure patterns and hot cracking. Thermomechanical finite-element simulation of the solidifying billet was used as a tool for testing the applicability to DC casting of several hot-tearing criteria based on different principles. The results are compared to the experimentally observed hot tearing. It is noted that hot-tearing criteria that account for the dynamics of the process, e.g., strain rate, actual stress-strain situation, feeding rate, and melt flow, can be successfully used for the qualitative prediction of hot tearing.     

直流电弧炉几种型式炉底电极的比较与评价

从安全、导电、绝缘、搅拌、偏弧、炉子吨位，冷却方式与允许电流密度，砌筑与维修方式，起动方式，炉底电极寿命及费用等十几个方面对直流电弧炉不同型式炉底电极进行了综合比较与评价，指出每种型式炉底电极都各有优点和缺点，绝对肯定或否定哪种型式都不恰当，用户可以根据自己的认识与工厂的实际情况选择合适的炉底电极型式。对我国直流电弧炉的发展提出了几点建议。     

无水冷滑轨加热炉的设计及应用

介绍了加热高温合金钢坯的推块式加热炉,炉底采用无水冷滑轨结构,既能加热方坯又能加热圆坯,投入生产后取得较好的使用效果。     

电弧炉炼钢技术若干问题的实践与认识(1)

简要评述了近20年来电弧炉炼钢技术的发展趋势并将其归纳为4个方面,即改进供电系统、多元化的能量利用技术、主原料多样化及加强环保措施.基于宝钢的实践与认识,讨论了直流电弧炉的某些技术点,包括电能质量、电极消耗及底电极技术等,特别就近期直流电弧炉受冷遇的原因作了较详细的分析.