A Model for Predicting the Melt Temperature in the Ladle and in the Tundish as a Function of Operating Parameters during Continuous Casting

A mathematical model for predicting the melt temperatures in the ladle and in the tundish during continuous casting has been developed. First of all, a chain of models was created for the following stages of the ladle cycle; the preheating of the empty ladle, filling of the ladle, period in the ladle furnace, waiting period prior to casting, the casting period, and, finally, the free cooling period of the empty ladle. Models, written in CFD code, were used in sequence so that each simulation continued from the results of the simulation of the previous stage. An intermediate model was constructed to estimate the outlet temperature of melt drained from the ladle. Then the work was continued by performing simulations in the tundish, using as input the temperature of the simulated melt feed from the ladle and, as an initial condition, the temperature field of the remaining melt in the tundish. The final model “TEMPARV3” was created and tested by means of measured tundish data received from a steel plant. By means of statistical analysis the coefficients of correlation between the test data and model data at the start, in the middle period, and at the end of casting were calculated to be 0.9, 0.92 and 0.87, respectively. So, the most effective predictive power of the model in the tundish by means of a sequential casting schedule is realized during the middle period of the casting process. The model is applied interactively by a user interface, which expresses the predicted melt temperatures numerically and with graphical curves. The predictive model can be used off‐line as a tool for scheduling the stage operations in advance. The program may be utilized on‐line to estimate the superheat needed and to control periods of the operation. In extreme cases, when the model alerts the operator about the danger of superheat loss having a critical effect on casting, the operator has a chance to take adjustment measures. In addition to production work, the model could be of benefit for studying changes in operating parameters, for training operators, and for use as a “low‐cost computational pilot plant” in process development in general.     

长水口对连铸中间包钢液保护浇注作用的研究进展

全球钢铁产品很大比例上是通过连铸工艺生产的,而中间包保护浇注是连铸生产高品质洁净钢的关键环节之一。长水口是连接于钢包和中间包之间的耐材质通道,长水口的发明和使用在连铸技术发展过程中起到了重要的作用,并与中间包的保护浇注效果有着紧密的联系,具体包括防止稳态和非稳态浇注过程中的二次氧化和来源于空气/渣/耐材/引流砂等的污染。本文基于中间包钢液污染的来源和形式,引申出了长水口在这些方面可以起到的潜在作用,并回顾了长水口在连铸发展早期的发明、工业实验效果和不断优化的历程。工业实践证实了长水口优良的保护浇注功能,但其实际效果与长水口的结构和操作工艺紧密相关。因此,分析了不同的长水口结构（包括工业化的长水口和一些新的设计理念）对保护浇注的影响,重点评述了喇叭型长水口在改善钢液洁净度和提高生产效率方面的优势。讨论了长水口的浸入深度和偏斜等操作工艺参数与保护浇注之间的关系。结合新时期炼钢?连铸的发展形势,指出了未来长水口结构功能一体化的发展方向,具体表现在长寿化、轻量化、多功能化和绿色化等方面。      

双通道感应加热中间包的三维磁流热耦合模型

 结合感应加热的中间包冶金是当前提升特殊钢连铸洁净度和质量稳定性的前沿技术。针对大方坯连铸用T型六流中间包,利用流动-传热耦合模型研究了控流装置对具有双感应加热通道中间包冶金行为的影响,首先获得了不开启感应加热工况下中间包的优化控流结构;进而通过对该结构进行电磁-流动-传热耦合模拟,研究了感应加热的控流和热补偿作用。结果表明,通过提高加热通道高度并配合双挡坝结构可进一步改善流体流动状况、提高各流一致性。其中,在不开启感应加热时,优化后中间包较原型死区比例由31.4%降低为17.6%,活塞区比例由19.1%提高为39.1%,平均停留时间标准差由99.6减小到40.3 s。开启感应加热后,中间包内流场有显著变化,通道出口钢液具有明显的上升流,这将有利于夹杂物的上浮去除。开启感应加热30 min后较未开启感应加热时中间包各出口平均温度由1 798.1升高为1 827.3 K,这表明感应加热可有效补偿钢水浇注过程中的热损失。这一功能有利于实现低过热度恒温浇铸,从而也有助于提高中间包控制铸坯洁净度和铸态组织一致性的综合冶金效果。     

Numerical Simulation for Effect of Inlet Cooling Rate on Fluid Flow and Temperature Distribution in Tundish

 The fluid flow in tundish is a non-isothermal process and the temperature variation of stream from teeming ladle dominates the fluid flow and thermal distribution in tundish. A numerical model was established to investigate the effect of inlet cooling rate on fluid flow and temperature distribution in tundish based on a FTSC (Flexible Thin Slab Casting) tundish. The inlet cooling rate varies from 0.5 to 0.25 ℃/min. Under the present calculation conditions, the following conclusions were made. When the stream temperature from teeming ladle drops seriously (for inlet cooling rate of 0.5 ℃/min), there is a “backward flow” at the coming end of casting. The horizontal flow along the free surface turns to flow along the bottom of tundish. The bottom flow shortens the fluid flow route in tundish and deteriorates the removal effect of nonmetallic inclusions from molten steel. Nevertheless, when the inlet cooling rate decreases to 0.25 ℃/min, the horizontal flow is sustained during the whole casting period. The present research provides theoretical directions for temperature control in teeming ladle and continuous casting tundish during production of advanced steels.     

RH精炼终点-中间包浇铸过程超低碳钢水增碳的影响因素

通过数据统计,分析了钢厂180 t RH精炼结束到45 t中间包浇铸过程中钢包衬、中间包涂料和覆盖剂等对MA超低碳钢水(≤0.005%C)增碳的影响。结果表明,连续浇铸第1炉增碳较大,增碳量5×10^-6~10×10^-6,其余炉次增碳量≤3×10^-6。通过第1炉缓缓加入覆盖剂控制中间包液面波动,加Al₂O₃减少钢包渣线侵蚀,减少钢包砖衬、中间包涂料和覆盖剂游离碳含量,可使RH精炼终点-中间包浇铸过程中钢水增碳量≤3×10^-6。     

Effect of holding time and surface cover in ladles on liquid steel flow in continuous casting tundishes

Mathematical modeling of fluid flow and heat transfer of melt in a typical two-strand slab caster tundish has been done for a complete casting sequence. The complete casting sequence consists of 1 minute of tundish emptying period during the ladle transfer operation followed by 1 minute of tundish filling period by the new ladle and pouring at the normal operating level of the tundish for 46 minutes. The effect of varying ladle stream temperature conditions on the melt flow and heat transfer in the continuous casting tundish has been studied. When the ladle stream temperature decreases appreciably over the casting period, corresponding to heat loss of the melt in the ladle from the top free surface, the incoming melt temperature becomes lower than that of the melt in the bulk of the tundish after about 30 minutes from the start of teeming. This results in melt flow along the bottom of the tundish instead of the normal free surface directed flow. The ladle melt stream temperature shows little variability when the ladle has an insulated top. Corresponding to this situation, the temperature of the incoming melt remains higher than that of the melt in the bulk of the tundish and the normal free surface directed flow is maintained throughout the casting period. The product cast under such condition is expected to have a uniformly low inclusion content. The heat loss condition from the top of the ladle has been shown to be the dominant factor in determining fluid flow and heat-transfer characteristics of the melt in the tundish rather than the holding time of the melt in the ladle. Formerly Graduate Student, Department of Materials Science and Engineering, Ohio State University     

Heat-loss calculation in ladle treatment of steel

A mathematical model permits calculation of the heat losses and temperature variation of liquid steel. The rates of variation in the heat losses and the integral mean temperature of the liquid steel are physically interpreted. A semiempirical formula that performs well in practice is used for the emissivity of slagmetal melt during discharge from a converter. Good agreement is found between the calculated and actual temperature values of the steel in a casting ladle for a continuous-casting machine.     

攀钢连铸高效化技术

介绍了高效连铸以及相关技术在攀钢的应用及效果。通过对钢包精炼的改进和中间包冶金技术的优化,提高了钢水洁净度;结合复合辊、低过热度浇注技术的采用和二冷技术与高速连铸保护渣的研制等新技术、新工艺的研究与应用,全面改善了高拉速条件下的铸坯质量,使攀钢板坯连铸机的铸坯产量、质量以及铸机作业率均有较大的提高。     

Hybrid Model of Molten Steel Temperature Prediction Based on Ladle Heat Status and Artificial Neural Network简

Aiming at the characteristics of the practical steelmaking process, a hybrid model based on ladle heat sta- tus and artificial neural network has been proposed to predict molten steel temperature. The hybrid model could over- come the difficulty of accurate prediction using a single mathematical model, and solve the problem of lacking the consideration of the influence of ladle heat status on the steel temperature in an intelligent model. By using the hybrid model method, forward and backward prediction models for molten steel temperature in steelmaking process are es- tablished and are used in a steelmaking plant. The forward model, starting from the end-point of BOF, predicts the temperature in argon-blowing station, starting temperature in LF, end temperature in LF and tundish temperature forwards, with the production process evolving. The backward model, starting from the required tundish tempera- ture, calculates target end temperature in LF, target starting temperature in LF, target temperature in argon-blo- wiag station and target BOF end-point temperature backwards. Actual application results show that the models have better prediction accuracy and are satisfying for the process of practical production.     

新型纳米级微孔隔热材料在炼钢生产中的应用

唐山中厚板材有限公司针对炼钢生产中钢水热量损失过大问题,在转炉、钢包和中间包上,系统采用了新型WDS纳米级微孔隔热材料,提高了耐火衬的蓄热量,在不影响耐火材料使用寿命的情况下,转炉的终点温度提高了7℃,从转炉、钢包到LF炉过程温降速度减小了0.3℃/min,采取降低LF炉出站温度5℃的方式,中间包后期钢水温度仍然能够满足连铸工艺需要,达到了节能降耗的目的,可以产生综合经济效益1480万元/a。     

中间包钢水温度控制研究及优化

为了提高中间包温度合格率,减少连铸机拉速波动,根据首秦现有工装设备条件,分析了中间包温度合格率较低的原因,研究了精炼周期、浇铸断面、工艺路线以及钢包状况对钢水温降的影响,同时总结出连铸中间包烘烤、开浇钢水温度变化以及浇钢过程钢水温度变化规律。通过提高优质钢包的周转数量、规范操作并精确控制精炼吊包温度、保持连铸中间包钢水温降稳定,使钢水中间包温度合格率达到92%以上,铸坯内部质量也得到一定改善。     

水平连铸过程热平衡实测与分析

本文通过水平连铸全过程钢水和铸坯温度变化及相关参数的实测，研究了水平连铸过程中钢的热平衡规律，并建立了铸坯凝固传热，中间包钢水温度，钢包钢水温度，包衬温度与吸热等数学模型。实测和分析表明，在该铸机上，钢水在钢包和中间包中分别损失了其热量的７％和１．２％，在结晶器和空冷段所传出的热量分别占１８％和２０％，切割时仍有５４％的热量保留在铸坯中。     

钢液过热度控制对连铸工艺和铸坯质量的影响

研究了25 t钢包炉和16 t中间包中GCr15、60Si2Mn、40Cr和20钢液的过热度控制。钢液过热度控制主要取决于钢包衬蓄热过程达到平衡状态时钢液温降速率-钢包和中间包钢液温降速率分别为≤1℃/min和≤0.5℃/min;钢液过热度为15～35℃时,200 mm×200 mm铸坯等轴晶率可达20%～30%,连铸拉漏率≤0.23%,铸坯质量良好。     

连铸铝镇静钢时中间包钢水氧含量预测模型

针对国内某厂６０ｔ中间包浇注低碳铝镇静钢的多次试验数据，从理论上建立了浇注过程中中间包钢水氧含量的预测模型，模型中综合考虑了钢包渣中ＦｅＯ及ＭｎＯ含量，耐火材料ＳｉＯ２含量，钢包到中间包钢水吸氮量，浇注时间，拉速，铸坯断面积等因素的影响，并对改进中间包操作进行了讨论。     

唐钢150tLF供中薄板连铸钢液温度改进实践

针对唐钢150t LF供中薄板连铸中间包钢液温度过高或过低的情况,通过对影响LF和中间包钢液温降的因素分析,经过优化相关工艺制度,提高了LF供钢离站温度的灵活性及中间包温降的稳定性,实现了中间包温度较高的可控性,在提高中间包温度合格率、降低生产事故及减少铸坯质量缺陷方面取得了显著成效。     

连铸中间包内钢液温度变化规律的研究

通过建立数学模型，研究了连铸过程中开浇、正常浇注、更换钢包、停浇等阶段的中间包内钢液温度变化规律，并分析了影响钢液温度变化的主要因素，为减少钢液温降和合理补偿钢液热量损失提供了理论依据。     

连铸中间包内钢液温度变化规律的研究

通过建立数学模型,研究了连铸过程中开浇、正常浇注、更换钢包、停浇等阶段的中间包内钢液温度变化规律,并分析了影响钢液温度变化的主要因素,为减少钢液温降和合理补偿钢液热量损失提供了理论依据。     

4流大方坯45 t中间包流场的物理模拟和冶金效果

通过几何相似比1:3的水模型对钢厂4流410 mm × 530 mm大方坯连铸机的不同结构的40～50t中间包进行流场、温度场以及流动特征的研究,并得出最佳控流装置。研究结果表明,为满足4流大方坯中间包对流场的要求,有通道式感应加热装置的中间包与无通道式感应加热装置的中间包优化出的最佳控流装置不同。对于无通道式感应加热装置的中间包,采用最佳方案(湍流控制器+带导流孔的"V"型挡渣墙+挡坝组合的控流方式),延长了近流水口响应时间及平均停留时间,各水口钢液的流动模式趋于一致,中间包内钢液的流动特征得到明显改善。生产40Cr钢实践表明,可连浇8炉,各水口最大温差为4℃,中间包钢液中T[O]约为10×10^-6。     

CAS OB精炼和连铸过程钢中夹杂物来源示踪研究

通过添加示踪剂研究CAS OB的精炼过程和连铸过程以及板坯钢样夹杂物来源。结果表明,精炼过程和钙处理后的钢中显微夹杂物均含有钢包渣示踪元素镧;中间包钢样中的显微夹杂物同时含有镧和中间包示踪元素铈;板坯中的显微夹杂物含有镧、铈、钾、钠中的几种,说明钢液脱氧产物与钢包渣、中间包覆盖剂、结晶器保护渣均产生了反应。板坯中大型夹杂物主要源于结晶器保护渣,其次源于钢包渣,少部分源于中间包覆盖剂;大型夹杂物同时含有钾、钠、镧、铈中的几种元素,说明大型夹杂物是脱氧产物与卷入钢液中的钢包渣、中间包覆盖剂、保护渣或中间包内衬蚀损产物相互反应的复杂夹杂物。     

Water model simulation of tundish flow under varying conditions

Water model studies have been conducted to characterise the flow conditions in continuous casting tundishes under conditions of open and submerged nozzles. In this investigation simulations of practical problems of flow interruptions from the ladle, thermal inversions due to uninsulated ladle, and pneumatic agitation near the tundish end wall were conducted. The studies showed that incorporation of suitable flow control devices brings about homogenisation of temperature and composition between strands in the above cases. This study also showed that agitation of the liquid at the end wall reduces the extent of stagnant zone in the tundish.