昆钢小方坯铸机中间包、结晶器水模试验优化研究

【作者】 陈伟；

【导师】 施哲； 苏鹤洲；

【作者基本信息】 昆明理工大学 ， 冶金工程， 2008， 硕士

【摘要】 近年来,随着连铸技术的发展和优化,对铸坯的质量要求越来越高。研究表明,连铸中的大型夹杂物主要来源于中间包,中间包内钢液温度和成分不均匀、夹杂物上浮不充分与铸坯的表面质量、内部质量有很大的关系。结晶器内钢水质量决定于钢水在结晶器内的流动与凝固过程,它与结晶器初生坯壳的形成、保护渣、浸入式水口插入深度和结晶器液面波动等因素密切有关。因此,深入了解和控制中间包和结晶器内的钢液流动行为则是保证连铸工艺稳定顺行、提高铸坯质量的关键。近年来,国内外炼钢工作者通过中包水模试验开展研究了中间包内部形状、注流对多流浇注的影响;通过结晶器水模试验对结晶器液面卷渣机理、对影响结晶器液面波动的主要因素如水口内径、水口浸入深度、拉速等进行了研究,一些研究结果已应用于生产实际,并取得了一定成效。昆钢炼钢厂7~#方坯铸机改造后,采用了多种先进的工艺装备和工艺质量控制手段,但中间包没有合适的控流装置、浸入式水口插入深度不合理,生产过程中钢水夹杂物上浮不充分,钢液成份不均匀及各流之间温度差较大等缺点较为突出,生产45、60、TS800U等品种钢时铸坯夹杂、裂纹等质量缺陷较多,制约了产品质量的进一步提高。本文根据7~#方坯铸机改造后的实际情况,建立了中间包、结晶器水力学模型,采用反应器理论系统研究了不同中间包控流装置对平均停留时间、死区及活塞区比例的影响,并用夹杂物的上浮率进行模拟验证;选择结晶器液面的波动和液位差作为衡量铸坯表面发生裂纹几率的指标,结晶器表面的卷渣情况和冲击深度作为衡量结晶器内卷渣和夹杂上浮的指标,对浸入式水口插入深度进行了优化研究。通过中间包水模试验,找到了最优的控流装置和结构:中包无控流装置时存在一定的短路流和旁路击穿流,此时流体混匀效果、钢水洁净度差,为改善中包流场,有必要在中包内加入控流装置;中间包内加设单挡墙时,2~#单挡墙为最佳方案,最佳放置位置为距出渣口710mm处;中间包内加设多孔挡墙时,3~#挡墙为最佳方案,最佳放置位置为距出渣口710mm处。通过结晶器流场研究,找出了分节式浸入式水口合理的插入深度控制在100-125mm。根据水模试验研究结果对7~#铸机中间包、结晶器控流装置进行了优化调整:浇铸普钢时,中包采用2~#单挡墙方案;浇铸优钢时,中包挡墙采用3~#多孔挡墙方案;浇铸过程中分节式浸入式水口插入深度控制在100-115mm。水模试验结果应用于生产实践后取得了显著效果:连铸工艺进一步稳定顺行,铸坯浇成率由99.22%提高到99.65%,溢漏率由0.09%降至0.04%;铸坯质量得到明显改善,品种钢铸坯合格率由97.5%提高到99.2%;经济和社会效益显著,试验结果应用于生产实践后减少废品损失10795t,创造经济效益达2667万元,7~#铸机每年可多产钢材约12500t,进一步减少矿石和煤炭开采量、节约用水用电,有利于改善环境污染、保护生态平衡。更多还原

【Abstract】 In recent years, along with the development and optimization in continuous casting technologies, higher quality requirements for casting products have been put forward. The research shows that large size inclusions of casting products are mostly originated in the tundish. Surface and internal quality of casting steel are closely related to characteristics of liquid steel in the tundish, such as uneven temperature and chemical compositions. And also steel quality depends on flow patterns and solidification process of liquid steel in the mould, it’s intensively related to several main factors, such as shell growth in the early stage of solidification, mould powder behaviors, immersion depth of SEN (submerged entry nozzle) and mould level fluctuation etc. Therefore, it is very important to know more about liquid steel’s behaviors in the tundish and mould in order to ensure a steady casting operation and enhance quality of casting products. At present, by carrying out hydraulic simulation experiments, researchers involved in steel-making home and abroad have studied the influences of tundish internal shape and pouring flow on multi-strand casting; and they’ve learned flux entrapping mechanism and how level fluctuations are affected by SEN inner diameters, SEN immersion depth and casting speed. Some of the findings are successfully applied into practice and better results have been achieved.Although No.7 billet caster in the steel-making plant of KISC has been equipped with many advanced devices and quality control measures after modification, some shortcomings of the tundish are still obvious, for example, flow control devices are not suitable; SEN immersion depth isn’t optimized; non-metallic inclusions couldn’t float up to the surface efficiently; compositions of liquid steel is uneven and there’s sharp temperature differences between different tapping holes etc. Thus some defects have showed up, particularly inclusions and crack have been found during 45, 60 and TS800U steel casting, which is becoming the restriction to further improve steel quality. Based on actual conditions of No.7 billet caster, hydraulic simulation models for the tundish and mould have been set up; by adopting the theory of reactors, this paper systematically analyzes the influences of different tundish flow control devices on average residence time, dead zone and stopper flow zone, and simulation results have been verified by floating rate of inclusions; By analyzing relations between level fluctuation and crack defect occurrence rate, and inspecting flux entrapment conditions and impact depth of stream, the optimization study of SEN immersion depth has been made.The optimum flow control devices and structures have been found by carrying out hydraulic simulation experiments in the tundish: the short circuit and by-pass breakdown flow occur in tundish without barricade, turbulence flow will result in worse cleanliness of steel due to uneven stirring of fluids; in order to improve flow field, it is necessary to install flow control devices in the tundish. In case of simple barricade, option 2# with the barricade installed 710mm away from the tapping hole is the best option; In case of multihole barricade, option 3 with multihole barricade installed 710mm away from the tapping hole is the best one. A range of 100-125mm SEN immersion depth is found reasonable by hydraulic simulation experiments.The flow control devices of the tundish and mould for No.7 billet caster are optimized and adjusted based on hydraulic simulation experiment findings: option 2# with simple barricade is applied for carbon steel casting; option 3 with multihole barricade is applied for quality steel casting; SEN immersion depth is to be controlled at 100-115mm during casting. Obvious progress has been made after applying experimental findings into practice: casting process is becoming steady and reliable, the casting success rate of billet increases from 99.22% to 99.65%, the breakout rate reduces from 0.09% to 0.04%; the quality of billet improves greatly, the qualified rate of quality steel billet increases from 97.5% to 99.2%; great economical and social benefits are achieved, the loss of defective products decreases 10,795t, therefore 26.67 million yuan profit has been created; No.7 billet caster is able to produce additional 12,500t annually after optimization of flow control devices, so it can save more ore and coal resources, as well as water and electricity. It’s good for environmental protection and ecological balance.更多还原