高频磁场作用下软接触电磁连铸初生坯壳的变形行为

结晶器内初生坯壳的变形行为直接决定着连铸坯的表面质量。笔者运用Reynold润滑方程推导出渣膜内的动压力分布,建立了初生坯壳的二维弹塑性变形有限元模型,研究了施加电磁场前、后坯壳的变形行为。研究结果表明：高频磁场(20kHz)下的感应加热作用会降低保护渣的粘度;电磁压力将增加渣缝的宽度,使施加电磁场后连铸坯初生坯壳的变形行为受到影响,进一步解释了软接触电磁连铸技术改善坯壳表面振痕的机理。     

钢的软接触电磁连铸技术的研究进展

钢的软接触电磁连铸技术(SoftContactElectromagneticContinuousCasting)是利用高频交变电磁场在结晶器内铸坯初始凝固区施加电磁压力来减少钢液与结晶器壁的接触压力,从而减小结晶器振动对铸坯表面质量的影响,降低拉坯阻力和减弱初始凝固点的传热来提高铸坯表面质量。分析了实现钢的软接触电磁连铸在结晶器结构、材质以及电磁场参数等方面需要解决的问题,并介绍了该技术的最新研究成果:高频调幅磁场及无结晶器振动的电磁连铸技术。     

连铸结晶器内大方坯的热力耦合分析

针对攀钢大方坯连铸机投产初期铸坯表面角部纵裂缺陷,建立了大方坯连铸结晶器内铜板与铸坯问的热力耦合模型,应用模型分析了大方坯连铸结晶器内的传热过程和坯壳的应力分布.在传热模型中,以稳态模型分析结晶器的传热过程,以瞬态模型分析铸坯的传热过程;在力学模型中,考虑铸坯和结晶器的接触边界以处理结晶器角部的气隙,以热弹塑性模型分析铸坯的变形和应力场.2种结构的连铸结晶器中大方坯温度场和应力场计算结果表明,结晶器倒角从25 mm×45°变为12 mm×45°时,可改善铸坯角部的传热条件,降低凝固坯壳角部温度,增加凝固坯壳厚度,有利于减轻和防止铸坯角部裂纹.     

纵向细沟槽结晶器改善初生坯壳传热的模拟实验

 连铸坯初生坯壳厚度的均匀程度直接影响其表面质量。通过铋热态模拟浸渍实验,对比表面光滑和表面刻划纵向沟槽水冷铜板的初生坯壳性状,研究沟槽内壁结晶器改善初生坯壳传热的效果。实验结果表明,水冷铜板表面刻划纵向沟槽,可明显均匀初生坯壳厚度。     

高频调幅磁场下无结晶器振动电磁连铸技术的实验研究

为了在连铸过程中用电磁力的振动代替结晶器的机械振动,成功研制了可以产生方波、正弦波、三角波3种波形的高频调幅磁场发生器,并对其在结晶器内产生的磁场进行了测量.进行了3种波形高频调幅磁场下的无结晶器振动电磁连铸实验,结果表明①在方波、三角波和正弦波调幅磁场作用下的无结晶器振动电磁连铸过程中,当调制波频率略低于系统固有频率时,弯月面与结晶器器壁间断接触距离最大,保护渣润滑效果最好,连铸过程拉坯阻力最小,连铸坯表面质量相对较好.②在3种高频调幅磁场中,从减小拉坯阻力和改善铸坯表面质量的角度讲,正弦波在整体上要稍优于三角波和方波.     

板坯连铸热顶结晶器研究

连铸热顶结晶器对改善结晶器传热状况影响显著。在结晶器热面弯月面处热镀低导热性材料,增加热阻、降低热流密度、提高初生坯壳均匀性,从而改善铸坯表面质量。数值预测每增加1 mm镀层厚度,热面温度提高10~15 K;现场在线热电偶监测数据证实,热顶结晶器能够降低铜板温度5~15 K;热顶结晶器能够降低结晶器进出口水温差(即平均热流密度),促进初生坯壳均匀生长。将热顶结晶器应用到高碳钢连铸生产,显著降低了连铸纵裂发生率。     

大方坯连铸结晶器冷却制度优化研究

在分析攀钢大方坯连铸现行结晶器冷却能力的基础上,优化调整了结晶器冷却制度。结果表明,增大结晶器冷却警度,强化结晶器传热,结晶器出口坯壳厚度由14．5～15．0mm增至19．0～20．5mm;合理匹配结晶器宽窄面水量分配,可以促进结晶器区域凝固坯壳均匀生长,宽面、窄面坯壳厚度一致,有利于减少因初生坯壳厚度偏薄或厚薄不均产生的铸坯表面角部纵裂或凸包缺陷。     

圆坯钢电磁软接触连铸的实验研究

为确定工业实验基本参数,对电磁软接触连铸结晶器进行了优化设计计算,设计制作了φ100 mm圆坯电磁软接触连铸结晶器,利用Sn-Pb-Bi合金实验研究了结晶器内的弯月面行为,并进行了w(C)为0.22%钢坯的电磁软接触连铸实验。结果表明,电磁软接触连铸结晶器内磁场和弯月面变形具有不均匀性,切缝数为12时,磁场周向分布和弯月面变形较均匀。输入功率增加,弯月面高度增高,液面波动加剧。对于100 mm圆坯电磁软接触连铸系统,功率可控制在50~60 kW左右。实际应用中,浇注液面应控制在线圈中心偏上位置。较低的电源频率可获得较高的弯月面,频率应控制在20 kHz左右,可获得较高的周向均匀的磁场。获得了表面质量改善的电磁软接触连铸钢坯。随功率增加,铸坯表面依次会出现环状振痕、无振痕和波纹状振痕等3种振痕形态。     

包晶钢结晶器液面周期性波动原因及控制

针对鞍钢股份有限公司鲅鱼圈钢铁分公司板坯连铸在生产包晶系列钢种时．连铸结晶器钢液面周期性剧烈波动的原因进行了分析。包晶钢液在凝固过程的包晶相变造成初生坯壳的不均匀生长是导致结晶器出现液面周期性剧烈波动的主要原因。通过调整结晶器冷却水强度和控制保护渣传热性能,有效地控制了结晶器液面周期性波动,提高了铸坯质量。     

圆坯电磁软接触连铸结晶器高频磁场分布

通过实验检测和数值模拟方法研究圆坯电磁结晶器切缝形式、切缝宽度、切缝数量及切缝长度对圆坯电磁软接触结晶器内高频磁场分布的影响,为软接触结晶器优化设计提供磁场理论依据.结果表明:切缝数增加可提高透磁性和均匀性;增大缝宽对透磁性影响不明显,但降低均匀性;缝长只在一定范围内对透磁性有影响.     

Numerical Simulation of Heat Transfer and Deformation of Initial Shell in Soft Contact Continuous Casting Mold Under High Frequency Electromagnetic Field

  Heat transfer and deformation of initial solidification shell in soft contact continuous casting mold under high frequency electromagnetic field were analyzed using numerical simulation method; the relative electromagnetic parameters were obtained from the previous studies. Owing to the induction heating of a high frequency electromagnetic field (20 kHz), the thickness of initial solidification shell decreases, and the temperature of strand surface and slit copper mold increases when compared with the case without the electromagnetic filed. The viscosity of flux decreases because of the induction heating of the high frequency electromagnetic field, and the dimension of the flux channel increases with electromagnetic pressure; thus, the deformation behavior of initial solidification shell was different before and after the action of high frequency electromagnetic field. Furthermore, the abatement mechanism of oscillation marks under high frequency electromagnetic field was explained.     

小方坯连铸机喷淋结晶器的研究

建立小方坯喷淋结晶器凝固传热数学模型，模拟计算了铸坯温度场、坯壳厚度、热流场，坯壳与铜壁间气隙厚度。计算坯壳厚度与实测坯壳厚度基本吻合；与普通水缝式结晶器相比，铸坯温度场均匀，坯壳厚度均匀，冷却强度有所提高。     

Effect of Induction Heat on Initial Solidification During Electromagnetic Continuous Casting of Steel

 Aiming at the process of electromagnetic continuous casting (EMCC), a three dimensional finite element model on electromagnetic field and temperature field was developed through the commercial software ANSYS to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in soft contact mold under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases of exciting current frequency and density make the effects of induction heat on solidification process increased remarkably. Especially, with the increase of exciting current frequency, the early solidification process and shell growth become non-uniform in billet circumferential direction. Morever, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is decreased greatly.     

Solidification in Soft-Contact Continuous Casting Mold with Alternating Electromagnetic Field

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提高亚包晶钢板坯拉速对结晶器传热的影响

通过对提高亚包晶钢AQ钢种230 mm×1200 mm板坯拉速试验过程中结晶器冷却水参数、铜板测温等数据进行适时记录,并与数学模型及ANSYS商业软件相结合,研究了提高拉速对结晶器平均热流、局部热流、铜板温度场以及坯壳厚度的影响。结果表明,拉速由1.3m/min提高到1.5m/min时,平均热流增加0.1 MW/m²左右,宽边弯月面区域局部热流增加0.13 MW/m²,但均在合理范围内,这与采用高碱度高结晶温度的试验保护渣有关;结晶器窄/宽面平均热流比超过0.9,应适当减少结晶器锥度;宽面坯壳厚度平均减薄4 mm左右,应严格控制结晶器传热强度,以保证连铸工艺稳定和铸坯质量。     

Effect of exciting current of high frequency electromagnetic field on initial solidification of steel during electromagnetic continuous casting

Abstract

A three-dimensional finite element model of the electromagnetic field and temperature field of electromagnetic continuous casting (EMCC) process was developed. The aim was to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in mould under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases in exciting current frequency and density make the effects of induction heat on solidification process increase remarkably. Especially, with the exciting current frequency increase, the early solidification process and shell growth become non-uniform in billet circumferential direction. Furthermore, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is greatly decreased. As a conclusion, the effects of induction heat on initial solidification process must be considered when the exciting current frequency and density are adjusted during the electromagnetic continuous casting process.     

高速连铸结晶器内凝固传热行为及其均匀性控制

从分析高拉速包晶钢板坯连铸结晶器内凝固传热行为特征入手,首先阐明拉速对结晶器内的界面热阻、凝固坯壳的温度与应力分布的影响规律,研究发现拉速超过1.6 m·min?1时,界面热阻明显增加,拉速由1.4 m·min?1提升至1.6 m·min?1和1.8m·min?1时,出结晶器坯壳厚度相应减少约10%,其发生漏钢的危险不断增加;在此基础上,阐述了结晶器的内腔结构、保护渣、振动与液面控制等控制结晶器内坯壳凝固均匀性的相关技术。要实现高速连铸,首要应考虑结晶器内腔结构的优化设计,使其能更好地迎合凝固坯壳的生长,研制适合包晶钢等凝固特点的专用连铸保护渣至关重要,铸坯鼓肚控制也是保障高拉速液面稳定的关键。      

380mm×280mm大方坯连铸结晶器电磁搅拌的数值模拟

利用有限元分析软件,建立了380 mm×280 mm大方坯结晶器电磁搅拌的三维数学模型,系统研究了电磁搅拌工艺参数(电流250～500 A,频率1.5～3.0 Hz,结晶器铜板厚度34～40 mm)对结晶器内电磁场的分布影响。结果表明,结晶器内磁感应强度沿铸流轴向呈"两端小、中间大"分布;电流从350 A增大到500 A,搅拌器中心的磁感应强度呈线性递增;频率由1.5Hz增大到3.0Hz,搅拌器中心磁感应强度仅减小0.001 5 T;随着结晶器铜板厚度的增大,铸坯宽面、窄面和角部的磁感应强度都减小。在实际连铸U71Mn重轨钢中,电流应该维持在400 A以上。     

A Study for Initial Solidification of Sn-Pb Alloy During Continuous Casting: Part II. Effects of Casting Parameters on Initial Solidification and Shell Surface

The initial shell solidification of liquid steel in the mold has significant influence on both surface and internal quality of the final slab, and it is mainly determined by the high transient high temperature thermodynamics occurring in the mold. This study investigated the effects of casting parameters like casting temperature, mold oscillation frequency, and stroke on the initial solidification of a Sn-Pb alloy through the use of a mold simulator to allow the clear understanding of the inter-relationship between irregular shell solidification, heat transfer, negative strip time (NST), and casting conditions. Results suggested that the shell surface oscillation marks (OMs) are strongly depending upon the fluctuations of meniscus responding temperatures and heat flux. An abrupt sudden fluctuation of high frequency temperature and heat flux at the meniscus during the NST would deteriorate the shell surface and leads to deep OMs. The fluctuations of responding temperature and heat flux are determined by the NST, meniscus solidification, and oil infiltration, which in turn are influenced by casting conditions, like casting temperature, oscillation frequency, stroke, etc.