水口类型对大方坯结晶器内钢水流动与凝固行为的影响

采用数值计算方法对比研究了直通式、4分径向以及新型4分切向水口对大方坯连铸结晶器内钢水流动与凝固行为的影响.结果表明,当前常用的直通式水口对坯壳无冲击,利于坯壳均匀生长,但钢水冲击深度大,易在弯月面处形成死区,不利于大方坯内部及表面质量的提高;改用4分水口浇铸时,结晶器宽、窄面冲击区附近都会出现不同程度的坯壳厚度零增长...     

大方坯径向水口旋流效应及其对凝固的影响

通过改变水口侧孔钢水流动方向可以控制结晶器内钢水流动与换热。采用流体动力学与凝固模拟方法对比研究了浸入式四分径向水口不同出流方向对大方坯连铸结晶器内流动、传热和凝固行为的影响。结果表明,侧孔方向对浇注过程结晶器内钢水的流动与凝固行为有显著影响。当水口侧孔水平旋转角度为30°时,结晶器内形成较好的水平旋流,可以有效降低侧孔出流钢水对坯壳的冲刷作用,并有利于结晶器内自由液面过热度的提高。比较不同侧孔出流角度发现,利用普通径向四分水口在一定安装角度下的旋流效应不仅对于初生坯壳的均匀生长以及自由液面的冶金效果产生有利影响,还可能在不改变水口结构条件下获得类似结晶器电磁搅拌的旋流效应。     

Numerical Analysis of Electromagnetic Field and Flow Field in High Casting Speed Slab Continuous Casting Mold With Traveling Magnetic Field

 A three-dimensional mathematical model for describing the electromagnetic field and flow field of molten steel in high casting speed slab continuous casting mold with electromagnetic level stabilizer (EMLS) system was developed, in which the effects of current intensity and frequency on the electromagnetic field and flow field were considered. Simulation results indicate that the electromagnetic force (EMF) along the mold width direction presents the centre-symmetric double-peak parabola distribution. The EMLS system leads to the flow velocity of molten steel decreases, especially near the free surface. Both the EMF increases with the current intensity and frequency (in the range of optimum frequency value), so the flow velocity of molten steel in the mold decreases obviously. As the current intensity increases from 800 A to 1000 A, the maximum free surface velocity decreases from 0.515 m/s without magnetic field to 0.155 m/s and 0.12 m/s, respectively. While the current frequency increases from 2 Hz to 6 Hz, the maximum surface velocity decreases from 0.177 m/s to 0.101m/s. The molten steel flow in mold is influenced obviously by the current intensity and frequency.     

多孔水口对轴承钢280 mm x325 mm铸坯结晶器钢液流场和温度场的影响

采用数值模拟的方法对比分析了直通式、四孔式以及五孔式水口对GCr15轴承钢280 mm×325 mm坯连铸结晶器内钢液流场和温度场的影响。结果表明,当前常用的直通式水口对坯壳无冲刷,利于坯壳均匀生长,但钢液冲击深度大,在弯月面处速度小,不利于大方坯质量的提高。当采用四孔水口时,钢液热中心上移,钢液面处温度可提高8℃,钢液向上漩流增强,有利于降低结晶器内钢水过热及保护渣的熔化,但由于钢液对结晶器宽、窄面坯壳的冲刷致使冲击区域附近坯壳出现不同程度的零增长区域。当采用五孔水口时,除了钢液热中心上移,钢液向上漩流增强,由于侧孔钢液流速减小,对坯壳的冲刷减小,有利于保护渣的快速熔化、过热度的快速降低,坯壳的均匀生长,显著提高大方坯的质量。     

立式组合电磁制动对CSP结晶器内钢液流动及偏流控制

紧凑型带钢(CSP)薄板坯连铸结晶器在浸入式水口下方设置水平式的全幅一段电磁制动器(Ruler-EMBr),在进一步提高薄板坯连铸拉坯速度的情况下,不能有效控制CSP结晶器自由表面的钢液流速和液面的稳定性.为此提出一种新型的立式组合电磁制动(VC-EMBr)技术,并利用商业软件ANSYS FLUENT数值模拟研究了全幅...     

电磁搅拌对特大方坯结晶器内流场及温度场影响

以某厂断面为410 mm × 530 mm的特大方坯结晶器为原型,利用ANSYS有限元软件建立三维数值模型,研究电磁搅拌对结晶器流场及温度场的影响。施加电磁搅拌后,钢液受到径向电磁力,液面呈现旋转流动趋势。结晶器内钢液最大切向速度随着电流的增加而增大,随着频率的增加而减小。电磁搅拌的电流大小由0 增加到500 A时,液面波动由1.21 mm增加到4.35 mm。电磁搅拌能够使钢水的高温区局限于连铸结晶器上部,钢水温度更加均匀。同时钢液的水平旋流能够抑制初生坯壳的生长,降低坯壳的生长速度,使结晶器出口处坯壳厚度变薄。综合分析,该厂在实际生产时合理的电磁搅拌的电流大小应为400 A,频率为1.5 Hz,此时钢渣液面波动约为2.73 mm,温度场较为均匀。      

板坯连铸充型过程流场温度场耦合数值模拟

利用CFD商用软件Flow-3d,对内外复合冷却结晶器内钢水充型过程流场温度场耦合作用下的 流动和凝固状况进行数值模拟,得到了流场温度场的分布图和充填过程中自由表面的位置和形状图。分析了 板坯连铸充型过程中流场温度场对钢水凝固的影响。结果表明内冷却器可改善钢水的流动,有利于钢液中的 夹杂物上浮,加快结晶器内钢液的凝固     

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

 The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product. The multiphase flow phenomena of molten steel, steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation, and the effect of electromagnetic brake (EMBR) and argon gas blowing on the process were investigated. The relationship between wavy fluctuation height near meniscus and the level fluctuation index F, which reflects the situation of mold flux entrapment, was clarified. Moreover, based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification, the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux, temperature and stress of shell in slab continuous casting mold were described.     

大方坯连铸结晶器电磁搅拌的数值模拟

对大方坯连铸结晶器电磁搅拌过程的流场和温度场进行了数值模拟,并讨论了搅拌强度对流场和温度场的影响。结果表明：在结晶器电磁搅拌下,搅拌器区域的钢液变为水平旋转,使从水口向下吐出的钢水与向上回流的钢水流股相冲突,流股侵入深度变浅,从而使轴向温度迅速降低,径向温度升高,提高了热区位置,有利于传热;搅拌强度越大,钢水的二次流现象越明显,热区位置越高。     

板坯连铸内外复合冷却流场和温度场耦合数值模拟

 针对1 240 mm×200 mm板坯连铸提出了一种钢水内外复合冷却技术，即在结晶器内设置内冷却器 U形管，起到提高传热效率改善铸坯内部组织之目的。运用流体力学分析软件，就内外复合冷却结晶器内钢水在流场温度场耦合作用下的凝固状况进行数值模拟，发现内冷却器可以使钢水的流动状态均匀和加快连铸坯的凝固速度。     

电磁场对软接触结晶器内钢液流动的影响

采用非交错网格和适体坐标方法数值模拟了电磁场对软接触结晶器内钢液流动的影响规律。讨论了感应线圈电流强度和电源频率等因素的影响。结果表明：电磁力能加强地晶器上部熔池的搅拌强度，并在上部区域形成一明显的回流区，同时还能减小射流的渗入深度;加大电流强度，能加强钢液的回流和对钢液的搅拌，减小射流深入深度。但电流强度有一个最佳控制范围；增加电源频率，射流渗入深度增大，弯月面附近的紊动能和钢液速度提高。电源频率应控制在20kHz左右。     

Analysis on Initial Defects Based on Mechanical State of Meniscus Shell

The meniscus shell plays an important role in slab quality and process operation for continuously cast steel.One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscillation and liquid steel flow to generate disturbance of casting.The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects.The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending.The formed crack may also expand and propagate due to the following secondary cooling and straightening behavior.The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of solidifying shell.The inter-dendrite bridging is also likely to be formed to produce other internal defects,such as air hole and solute enrichment in the residual molten steel located in the bridging area.     

An asymptotic model of the mold region in a continuous steel caster

A model is developed to simulate the solidification of the steel shell in the mold region of the continuous casting process. Conduction-dominated temperature fields in the mold, mold flux, steel shell, and molten steel regions are determined through the development of an evolution equation for the solidifying front. This equation is derived in the limit of small aspect ratio, mold width to height, using asymptotic methods. These results are coupled with a lubrication-theory model for the mold flux region. This model assumes a temperature-dependent viscosity for the mold flux and allows for solidification of the flux at temperatures below a critical value. System response to changing casting speeds, superheat, mold wall temperatures, and mold flux properties is investigated.     

宽厚板坯连铸结晶器流场、温度场及应力场的耦合数值模拟

利用Pro CAST软件对2400 mm×400 mm宽厚板坯结晶器建立三维动态模型,采用移动边界法实现结晶器内流场、温度场及应力场的耦合模拟.结果表明:考虑凝固坯壳的影响,下回流区位置向铸坯中心靠拢,真实反映了钢液在连铸结晶器内的流动情况.自由液面的钢液从窄面流向水口,速度先增大后减小,距水口约0.7 m处,出现最大表面流速,约为0.21 m·s-1.结晶器出口坯壳窄面中心厚度最小且由中心向两侧逐渐增大,最小厚度约为10.4 mm;受流股冲击影响较弱的宽面坯壳与窄面相比生长更均匀,宽面偏角部和中心的坯壳厚度分别为18.9 mm和27.6 mm.铸坯坯壳应力变化趋势与温度基本保持一致,表明初凝坯壳应力主要是热应力.结晶器内铸坯宽窄面上的等效应力均沿着结晶器高度下降方向呈增大趋势,铸坯角部、宽面中心及窄面中心位置的最大应力各约为200、100和25 MPa.      

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

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水口结构对连铸中低碳钢流场和温度场的影响

 为研究水口结构形状对连铸中低碳钢结晶器内流场和温度场分布的影响,采用有限容积法建立连铸圆坯三维数学模型,模拟了不同水口形状下圆铸坯的流场和温度场。结果表明,在水口浸入深度为80 mm、其他参数不变时,与直水口相比,旋流水口使钢水冲击深度降低,结晶器内涡流增强,弯月面温度和二冷区凝固率提高,且随着水口数量的增加,弯月面波高和结晶器出口温度降低;采用旋流水口并施加结晶器电磁搅拌(M EMS)时,结晶器中钢液温度升高,弯月面有卷渣行为,结晶器出口未形成凝固坯壳。在实际应用中,应避免同时使用M EMS和旋流水口,或使用旋流水口时采用低强度的M EMS。     

GCr15钢大方坯结晶器电磁搅拌工艺参数优化研究

摘要：为明确不同电磁搅拌条件对结晶器内钢液流动、传热行为的影响规律,对现场大方坯连铸结晶器电磁搅拌工艺参数的配置提供依据,采用ANSYS Fluent及Maxwell研究了320mm×280mm断面GCr15高碳轴承钢连铸过程中结晶器电磁搅拌工艺参数对结晶器内钢液温度场、磁场特性、注流冲击深度及液面波动的影响规律。研究结果表明,在M-EMS作用下,结晶器内钢液温度的耗散明显优于无电磁场作用工况,有利于改善结晶器内温度均匀性。注流的冲击深度随电流强度的增大而降低,而频率改变对钢液冲击深度影响不明显。当电磁搅拌电流强度一定时,随着搅拌频率增加,液面波动趋于平缓;当搅拌频率一定时,随着电流强度增加,液面波动变剧烈。对于320mm×280mm断面GCr15高碳轴承钢不同工艺进行工业试验,只改变结晶器电磁搅拌参数,从300A/2Hz调整到350A/3Hz,铸坯横截面中心碳偏析指数从1.06降低到1.01,铸坯纵截面中心碳偏析指数的平均值从0.98升至0.99,适合该钢种结晶器电磁搅拌工艺参数为350A/3Hz。     

Transport and Entrapment of Particles in Steel Continuous Casting

A particle-capture model based on local force balances has been developed, implemented into computational models of turbulent fluid flow and particle transport, and applied to simulate the entrapment of slag inclusions and bubbles during the continuous casting of steel slabs. Turbulent flow of molten steel is computed in the nozzle and mold using transient computational fluid flow models, both with and without the effects of argon gas injection. Next, the transport and capture of many particles are simulated using a Lagrangian approach. Particles touching the dendritic interface may be pushed away, dragged away by the transverse flow, or captured into the solidifying shell according to the results of a local balance of ten different forces. This criterion was validated by reproducing experimental results in two different systems. The implications of this criterion are discussed quantitatively. Finally, the fluid flow/particle transport model results and capture criterion are applied together to predict the entrapment distributions of different sized particles in a typical slab caster. More large particles are safely removed than small ones, but the entrapment rate into the solidifying shell as defects is still very high.     

Optimum Position of Electromagnetic Brake on Slab Caster

SymbolList　　B———Magneticfluxdensity ,T ;　　CD———Dragcoefficient;　　d———Diameter ,m ;　　g———Gravitationalacceleration ,m·s-2 ;　　h———Timestep ,s ;　　J———Currentdensity ,A·m-2 ;　　la,lb———Sizeofslabcross section ,m ;　　ln———Immersiondepthofnozzle ,m ;　　p———Pressure ,Pa ;　　t———Time ,s ;　　u→ ———Velocity ,m·s-1;　　vc———Castingspeed ,m·min-1;　　X→ ———Displacement ,m ;　　———Electricpotential,V ;　　ρ———Density ,kg·m-3;…     

连铸结晶器内钢液流动、凝固和夹杂物的分布

 建立并求解动量、热量和质量传输耦合模型,研究了连铸结晶器内钢液流动、传热、凝固、溶质输送和夹杂碰撞长大行为。数值结果表明,受钢液流动的影响,在连铸机内钢液温度、碳浓度和夹杂物的空间分布与钢水流动特征相似,也可分为上下两个循环区。但是其分布具有各自的特点。在涡心处,钢液温度较低,碳浓度较高,夹杂物体积浓度和数量密度较低。在弯月面处,钢液温度较低,碳浓度较高,夹杂物的体积浓度和数量密度较低。在结晶器出口处的凝固坯壳内,夹杂物的浓度和数量密度分布极不均匀,存在阶跃现象,这与冲击点处凝固坯壳的重熔有关。