Numerical simulation on the multiphase flow and reoxidation of the molten steel in a two-strand tundish during ladle change

A 3D mathematical model was proposed to investigate the molten steel–slag–air multiphase flow in a two-strand slab continuous casting(CC)tundish during ladle change.The study focused on the exposure of the molten steel and the subsequent reoxidation occurrence.The exposure of the molten steel was calculated using the coupled realizable k–εmodel and volume of fluid(VOF)model.The diffusion of dissolved oxygen was determined by solving the user-defined scalar(UDS)equation.Moreover,the user-defined function(UDF)was used to describe the source term in the UDS equation and determine the oxidation rate and oxidation position.The effect of the refilling speed on the molten steel exposure and dissolved oxygen content was also discussed.Increasing the refilling speed during ladle change reduced the refilling time and the exposure duration of the molten steel.However,the elevated refilling speed enlarged the slag eyes and increased the average dissolved oxygen content within the tundish,thereby exacerbating the reoxidation phenomenon.In addition,the time required for the molten steel with a high dissolved oxygen content to exit the tundish varied with the refilling speed.When the inlet speed was 3.0 m·s^(-1)during ladle change,the molten steel with a high dissolved oxygen content exited the outlet in a short period,reaching a maximum dissolved oxygen content of 0.000525wt%.Conversely,when the inlet speed was 1.8 m·s^(-1),the maximum dissolved oxygen content was 0.000382wt%.The refilling speed during the ladle change process must be appropriately decreased to minimize reoxidation effects and enhance the steel product quality.

Optimization of flow control devices for a T-type five-strand billet caster tundish: water modeling and numerical simulation

The optimization of flow control devices(FCDs) for a T-type five-strand billet caster tundish was carried out by water modeling and numerical simulation. In water modeling experiments, flow characteristics of the bare tundish and tundish conf igurations with designed U-type baff les and a round turbulence inhibitor were analyzed using residence time distribution(RTD) curves. Mathematical models for liquid steel in the real plant tundish were established using the fluid dynamics software package Fluent. The flow field, the temperature field, and the RTD curves of liquid steel in the proposed tundish conf igurations were obtained. The results of numerical simulation and water modeling were validated with each other by the predicted and experimental RTD curves. The results of flow field and temperature field were used to ref lect the actual state of a real plant tundish and to choose the optimal FCD. Finaly, from the whole performance of the multi-strand tundish, the optimal scheme was determined by combining the results of water modeling and numerical simulation. With the optimal tundish equipped with U-type baffle with def lector holes and round turbulence inhibitor, not only was the flow characteristic of each strand improved, but also the difference of flow characteristics between multiple strands was smaller.

Parameter Design of Current Double Closed Loop for T-Type Three-Level Grid-Connected Inverter

To reduce current harmonics caused by switching frequency,T-type grid-connected inverter topology with LCL filter is adopted.In view of the disadvantages of the slow response speed of the traditional current control and the failure to eliminate the influence of the LCL filter on the grid-connected current by using current PI control alone,a current double closed loop PI current tracking control is proposed.Through the theoretical analysis of the grid-connected inverter control principle,the grid-connected inverter control model is designed,and the transfer functionmodel of each control link is deduced,and the current loop PI regulator is designed at last.The simulation results show that the control strategy is feasible.

中间包等离子体加热技术研究进展及应用

在钢铁行业面临转型升级的新常态形势下,借助智能装备驱动钢铁产业向绿色高端化发展,有望实现钢铁生产组织的最优化。连铸中间包实现恒温、低过热度浇铸可有效改善钢材质量,为此发展中间包加热技术十分必要。针对近年来日益受到重视的中间包等离子体加热技术的相关热点问题,系统阐述了其加热原理和设备特点,介绍了等离子体加热技术国内外设备、冶金功能研发以及应用进展状况,重点分析了等离子体加热技术对中间包内钢液流场、温度场、夹杂物去除、钢液化学成分的影响,以及实际应用冶金效果。基于对等离子体加热技术研究和应用的深入认知,探讨了国内自主研发新型中空石墨电极加热过程发现的新问题,以及进一步提高其冶金效果的途径。分析表明,国内自主研发的中空石墨电极等离子体加热装置,更好的适配了国内钢铁行业变革需求,是解决浇铸钢水过热度不稳定、钢水洁净度水平低和钢水组织成分不均匀问题的有效途径,补齐精准定位“一键加热”中间包的智能化短板。

板坯连铸机中间包内钢液流动的物理模拟研究

依据相似原理,建立包钢双流板坯连铸机中间包几何相似比为1∶4的物理模型,采用物理模拟的方法研究控流装置对中间包内钢液流动状态的影响。结果表明,板坯中间包采用优化的控流装置,中间包内钢液的峰值时间和平均停留时间增加,中间包内钢液的死区体积降低,钢液的峰值时间增加比率为240.98%,钢液的平均停留时间增加比率为2.37%,死区体积减少了7.56%,优化了中间包内钢液的流动状态,促进夹杂物在中间包内碰撞、聚集、上浮、去除,保证了钢液的洁净度。

Design of a distributed power amplifier based on T-type matching networks

The impedance characteristics of distributed amplifiers are analyzed based on T-type matching networks, and a distributed power amplifier consisting of three gain cells is proposed. Non-uniform T-type matching networks are adopted to make the impedance of artificial transmission lines connected to the gate and drain change stage by stage gradually, which provides good impedance matching and improves the output power and efficiency. The measurement results show that the amplifier gives an average forward gain of 6 dB from 3 to 16. 5 GHz. In the desired band, the input return loss is typically less than - 9. 5 dB, and the output return loss is better than -8.5 dB. The output power at 1-dB gain compression point is from 3.6 to 10. 6 dBm in the band of 2 to 16 GHz while the power added efficiency （PAE） is from 2% to 12. 5% . The power consumption of the amplifier is 81 mW with a supply of 1.8 V, and the chip area is 0.91 mm × 0.45 mm.

TUNDISH METALLURGY AND ITS DEVELOPMENT

The research on tundish metallurgy has focused mainly on taking countermeasures to avoid and remove inclusions and the recent developments on tundish metallurgy were surveyed.The authers'advices for future development of tundish metallurgy were given in summary section.

感应加热中间包钢液氢含量控制

重轨钢氢含量是影响质量的关键因素之一。包钢感应加热中间包运行初期,重轨钢等钢种常常出现首炉氢超标的现象。基于此,本文详细分析了感应加热中间包钢液氢含量超标的主要原因,并对中间包材料、耐火材料和连铸工艺进行了优化改造。研究发现,中间包感应加热上线后,预制件数量较多,常规烘烤方式很难实现有效烘烤,这是导致包钢钢液氢含量偏高的主要原因;通过改进耐火材料材质,使用PVC管替代铁皮作为通道模具,利用下线铸坯和中间包的余热以及外置烧嘴对流钢通道预烘烤,烘烤时添加烘烤喷嘴,同时提前对预制件进行烘烤、浇注前氩气置换以及浇注工艺优化等方式,有效实现了浇次首炉氢含量低于2 ppm的目标。中包感应加热运行后生产了154个浇次不同钢种,氢含量全部满足目标要求,同时碳偏析指数平均降低了0.013,提高质量的同时获得了显著的经济效益。

微孔白云石加入量对镁钙质中间包干式料性能的影响

以白云石为原料,采用二步煅烧法制备的致密镁钙砂是镁钙质中间包干式料常用的耐火原料。然而二步煅烧法工艺复杂,资源耗费大,且致密镁钙砂不利于中间包干式料隔热性能的提升。以一步煅烧法(1400℃保温3 h)制备的微孔白云石和电熔镁砂为主要原料,分别于1100、1550℃热处理后制备了镁钙质干式料试样,研究了微孔白云石加入量(质量分数分别为0、15%、30%、45%和60%)对试样性能的影响。结果表明:随着微孔白云石加入量的增加,1100℃热处理后试样的线收缩率和体积密度呈减小趋势,常温耐压强度先增大后减小;1550℃热处理后试样的线收缩率先减小后显著增大,显气孔率增加,热导率大幅降低,但常温耐压强度和抗渣性能降低。当微孔白云石加入量为60%(w)时,1550℃热处理后试样在800℃下的热导率为2.410 W·m^(-1)·K^(-1),与传统镁质干式料相比下降了51.9%,同时常温耐压强度为26.0 MPa,在力学性能略微降低的情况下表现出优异的隔热性能。

真空连铸中间包多场耦合对夹杂物去除影响研究进展

真空感应熔炼过程中连铸中间包内温度梯度与钢液流动对固体夹杂物的去除有重要作用,其直接影响钢液的纯净度。分析了连铸中间包内温度场、流场及应力场耦合数值模拟计算的现状,基于此,总结了多场耦合作用下夹杂物去除数值模拟的问题,介绍了热流耦合、流固耦合以及流固热耦合模拟方法,最后提出了流热固耦合下夹杂物去除数值模拟的建议。合理地控流装置组合和耐材选择可提高钢液质量。

高拉速连铸中间包耐材防护优化与应用

高拉速浇钢会造成中间包较严重的冲刷侵蚀,为进一步实现连铸高效率生产,满足高拉速长寿命中间包要求,通过优化中间包冲击区和迎钢面修砌方式、Al_(2)O_(3)-MgO护板材质、永久层预埋冲击板、稳流器安装方式等防护技术,提高在高拉速工况下中间包的使用寿命和安全系数。在小方坯连铸机4.5 m/min的高拉速工况下,中间包使用寿命由20 h提高到45 h,使连铸机具备长寿命高拉速的生产能力,实现了连铸直供棒材轧制生产的工艺条件,满足连铸浇注周期与轧制品种、设备维护相匹配的工艺要求。

八流方坯中间包控流装置的优化

以某钢厂八流方坯中间包为研究对象,采用物理模拟与数值模拟相结合的方法,基于中间包的流场、温度场及钢水停留时间分布等参数评价原控流方案下中间包钢水流动存在的问题;分析挡墙导流孔数量、孔径、位置和倾角对中间包钢水流动特性的影响,优化中间包控流装置。结果表明:原控流方案下中间包钢水存在死区体积较大、各流一致性较差及温度场不均匀等问题;优化控流方案为在挡墙侧墙减小2个导流孔孔径并提升其位置,在中间墙增加带偏角(43°)和仰角(15°)的小导流孔。优化方案的中间包流场和温度场得到大幅改善,死区体积比例由原方案的19.04%降至7.06%,活塞流和全混流体积比例均有所增加,且各流滞止时间、实际平均停留时间和峰值时间一致度均提高到80%以上,各流一致性得到大幅提升;优化方案中间包最大温差为16.004 K,比原方案下降2.182 K,且各流出口钢液最大温差为0.616 K,比原方案下降0.944 K,整个中间包温度场更均匀。

Tundish工艺在铁液球化处理中的应用

介绍盖包法(Tundish)球化处理工艺的特点。与冲入法工艺比较,盖包法的优点是:(1)铁液不会直接冲到球化剂上,能减少球化剂烧损,因而球化剂加入量从1．4％降低到1．05％,并且球化效果比较稳定;(2)球化处理反应在密闭的处理包内进行,能减少镁光和烟雾,有利于环保。

中间包涂料对GCr15轴承钢洁净度的影响

分析了某钢厂GCr15轴承钢生产过程中,在真空处理前后及中间包的钢水中夹杂物演变规律,结果表明,钢水中全氧含量在中间包中大幅度上升,镁铝尖晶石类夹杂物在RH软吹及中间包中有不同程度的上升,在中间包中数量上升明显。用后中间包涂料工作层中MgO骨料颗粒大量减少,部分MgO颗粒溶于钢水中造成钢水中氧含量上升。通过热力学模拟分析,论述了不同SiO_(2)含量对中间包涂料高温物相的影响,提出将SiO_(2)控制在4%~6%,并加强中间包砌制管理,可减少中间包涂料中高温低熔相的生成,可有效提高GCr15轴承钢头炉探伤合格率。

中间包IF钢桶状取样器提取样夹杂物分布研究

IF钢的洁净度控制对产品质量至关重要,中间包内夹杂物的数量、尺寸及分布等特征是IF钢洁净度控制的重点,取样器提取的样品中夹杂物分布不均会影响对钢液洁净度测定的准确性。采用桶状取样器对国内某钢厂IF钢中间包进行取样,对钢样不同高度上的夹杂物类型和数量进行了统计对比,分析夹杂物在样品高度上的变化。结果表明:样品中氧含量随着样品高度的增加逐渐上升,氧化物夹杂的数量也随着高度的增加逐渐增加;钢样中的夹杂物主要以Al_(2)O_(3)及Al-Ti复合夹杂为主,直径大多在20μm以下,数量密度随高度的上升呈增加趋势;尺寸大于20μm夹杂物数量较少,存在于样品上部,有上浮去除的倾向;研究不同尺寸夹杂物应取不同高度样品,小尺寸夹杂物在提桶40 mm以下的分布更稳定,大尺寸夹杂物考虑上浮,应在上部取样;样品上部还存在少量卷渣夹杂物。

ER70S-6焊丝钢连铸全保护浇注工艺优化实践

唐钢公司长材事业部在拉拔生产ER70S-6焊丝钢时因氮质量分数高出现脆断情况,对此从焊丝钢连铸全过程保护浇注工艺改进以及连铸长水口、中间包密封、覆盖剂、浸入式水口和保护渣设计优化等方面采取措施,提高焊丝钢连铸保护浇注效果,降低焊丝钢氮质量分数(氮质量分数整体下降0.0012%),增强塑性和变形能力,避免焊丝钢因氮质量分数高导致其在拉拔和加工过程中金属流动性差造成的脆断现象。

新型环保无碳中间包干式料的研究与应用

采用新型无碳结合剂取代酚醛树脂研制出一种新型环保无碳干式料,并研究了无碳结合剂加入量对干式料性能的影响。结果表明:偏硅酸盐加入量为8%时,干式料综合性能较为优异。引入橄榄砂能够有效降低干式料热膨胀性能及烧结性能,但是抗渣性能较镁质材料略差。研制的环保无碳干式料可以满足钢厂浇注超低碳钢的使用要求,不会使钢水增碳,环境友好,弥补了树脂结合干式料在低碳、环保方面的不足。

超低碳IF钢冶炼过程炉渣对夹杂物控制研究进展

超低碳IF钢板主要应用于汽车面板等超深冲部件,其面临的主要质量问题是夹杂物、卷渣、气泡造成的炼钢缺陷,因此全生产流程中所采用的炉渣性质对控制炼钢缺陷具有重要作用。分别从炉渣的物化特性以及所在工序炉渣特性两个角度归纳总结了炉渣对夹杂物控制产生的影响,发现炉渣对夹杂物的吸附溶解与炉渣的物化性质和夹杂物的尺寸相关。RH精炼渣主要控制目标是低氧化性和合适的w(CaO)/w(Al_(2)O_(3)),TFe质量分数一般控制在2.0%~8.0%,w(CaO)/w(Al_(2)O_(3))控制在1.2~1.8,此外精炼渣碱度一般控制较高为4.0~10.0。中间包覆盖剂和结晶器保护渣首先要防止钢液增碳,其次是防止渣中SiO_(2)造成钢液的二次氧化,同时它们还应拥有良好的吸附夹杂物的能力。超低碳IF钢中间包高碱度覆盖剂一般碱度为2.9~11.5,w(CaO)/w(Al_(2)O_(3))控制在1.0~2.5,(FeO+MnO)质量分数控制在1.9%~4.0%。而超低碳IF钢结晶器保护渣的碱度一般控制较低在0.85~1.0,w(CaO)/w(Al_(2)O_(3))控制在5.0~8.5,(FeO+MnO)质量分数小于1%。

提高连铸机中间罐连浇炉数的生产实践

唐钢新区炼钢部通过生产实践,采取了降低小浇次个数、提高转炉周期及连铸机拉速、优化炉机匹配、规范生产计划管理、优化生产组织等措施,有效提高了连铸机中间罐连浇炉数,降低了生产成本。

采用气幕挡墙感应加热中间包的模拟研究

为了研究气幕挡墙对感应加热中间包内传输行为的影响,根据实际单流双通道感应加热中间包数据,通过数值模拟的方法,建立三维非稳态数学模型研究了气幕挡墙对感应加热中间包内流动、传热及夹杂物传输行为的影响规律。结果表明,气幕挡墙能够使感应加热中间包浇注区内流场分布更合理,钢液成分更均匀,更有利于夹杂物的上浮去除;浇注区内钢液的温度场分布更均匀,温差不超过1 K,温度较低区域进一步缩小;使用气幕挡墙后夹杂物的去除率较使用前明显提高,去除率提高约41%。