【作者】 张林涛；

【导师】 赫冀成； 王恩刚；

【作者基本信息】 东北大学 ， 热能工程， 2008， 博士

【摘要】 电磁软接触连铸技术通过施加高频磁场控制钢液的初始凝固过程来提高铸坯的表面质量。高频磁场作用下结晶器内的磁场和金属液弯月面变形特性是衡量电磁软接触效果的重要指标,而电磁软接触结晶器的结构型式和参数设计对软接触效果具有决定性的影响作用,它也是电磁软接触技术能否推向工业应用的关键技术之一。研究和探讨不同坯型(方、扁、圆)和不同切缝形式和参数下的软接触结晶器内的磁场、金属液弯月面变形和凝固传热特性,认识其变化规律,是设计工业用电磁软接触结晶器,推广电磁软接触技术的重要技术基础。本论文以此为选题,重点研究方坯、矩形坯和工业用圆坯电磁软接触结晶器的软接触特性和传热特性,具有重要的理论意义和实用价值。针对工业用Φ178mm圆坯电磁软接触连铸结晶器,采用数值模拟和实验相结合的方法,研究了结晶器切缝参数对结晶器内部磁场分布的影响规律,并通过低熔点合金热模拟实验,揭示了切缝参数对结晶器内弯月面变形的影响规律。研究结果表明：工业结晶器的上法兰盘对结晶器内的磁场分布具有一定的影响作用。特别是随着电源功率(安匝数)增大到90kW以上时,结晶器上法兰盘对磁场的屏蔽作用逐渐增强；随着圆坯结晶器切缝数目、切缝宽度和切缝长度的增加,结晶器内的磁感应强度和弯月面变形均增大,其中又以切缝数目和切缝长度对软接触效果的影响最主要；当切缝数由24增加到32时,结晶器内最大磁感应强度增加了32%,弯月面高度增加110%；当切缝长度由100 mm增到加130 mm时,结晶器内最大磁感应强度增加了28%,弯月面高度增加了155%。当切缝宽度由0.3 mm增加到0.5 mm时,结晶器内最大磁感应强度增加了15%。这些研究结果为Φ178mm工业用圆坯电磁软接触连铸结晶器的设计提供了重要参数依据。设计并制作了内径尺寸为213mm×85mm的两种非均匀切缝矩形坯电磁软接触连铸结晶器；通过磁场测试和热模拟实验揭示了两种结晶器内磁场分布和弯月面变形的规律。实验结果表明：随电源功率的增大,结晶器内磁感应强度和弯月面高度均增大,且电源功率不改变结晶器内磁场分布特征；结晶器最大磁感应强度所处位置随感应线圈同向移动；液态金属的自由液面应控制在线圈中心附近,此时磁场的利用率最高,软接触效果最好；结晶器内切缝的布置对磁场和金属液变形具有重要的影响作用。研究发现,对于单侧窄面切缝的矩形结晶器,在电源功率一定时,无切缝窄面附近仍然存在磁场；在电源功率达52kW时,无切缝窄面中心的最大磁感应强度是切缝窄面的60%左右；而对于在窄面角部增加切缝的改进型矩形结晶器,其内部磁场分布和弯月面变形都得到较大提高,基本呈现均匀分布,且在数量级上也达到了实现软接触效果的要求；论证了采用较少的非均匀切缝结构,也能够获得矩形坯电磁软接触效果的可行性。设计并制作了内径尺寸为100mm×100mm的非均匀切缝方坯电磁软接触连铸结晶器,并进行了低熔点合金的静态和动态凝固传热实验,揭示了不同电源功率下结晶器内部磁场分布、弯月面变形、凝固坯壳形貌、三相点位置、结晶器壁温度与热流、熔池温度和结晶器冷却水温度的变化规律。实验结果表明：与均匀切缝结晶器相比,其磁场分布和弯月面变形规律变化不大,基本相同；随着电源功率的增大,低熔点合金自由液面的波动加剧,熔池温度升高,初始凝固点下移,形成的凝固坯壳逐渐变薄,直至发生重熔,揭示了高频磁场对结晶器内合金液加热,造成三相点下移的变化规律；随电源功率的增加,合金液和结晶器壁中产生的焦耳热增大,并在切缝处和分瓣体会出现不均匀分布,造成坯壳厚度分布不均,同时结晶器壁温度和热流也升高；连铸结晶器的振动作用促使弯月面区域结晶器壁温度上升；由此,在工业应用电磁软接触连铸技术时,应结合实际连铸工艺合理选择电参数,适当地调节结晶器的冷却水量等工艺参数,这些研究结果对电磁软接触连铸工业实验提供了重要的指导作用。通过以上几种不同型式软接触结晶器的软接触特性研究发现,线圈与结晶器的相对位置、钢液模拟物与结晶器的相对位置以及电源功率三个参数对结晶器内部电磁特性的影响规律并不随结晶器结构型式的变化产生大的变化,基本规律相同。更多还原

【Abstract】 The technology of electromagnetic soft-contanct continuous casting (EMCC) can improve the surface quality of the billets through applying high frequency magntic field to control the process of initial stage of solidification. The distribution of magnetic flux density and the characteristic of meniscus are important aspects to estimate the results of EMCC. The structures of EMCC mold are important not only to the effects of the technology of EMCC, but also to its industrialization. It is the foundation for the technology of EMCC industrialization to know the distribution of magnetic flux density, the characteristic of meniscus, and the characteristic of heat transfer in EMCC mold under the condition different structure patterns (billet, round billet and rectangular billet). The electromagnetic soft-contact and heat transfer characteristics continuous casting mould with different structure patterns have been discussed in this thesis.Regarding toΦ178mm industrial round billet EMCC mold, the distribution of magnetic field in the mold under different slit parameters have been discussed through 3 dimension finite element method (3D FEM) numerical simulation method and experimental method. The effect of slit parameters on the distortion of meniscus has been investigated through the experimental method by using low melting point alloy. The results show that the upper flange of industrial EMCC mold has some effect on the distribution of magnetic flux density. When the input power is over 90kW, the shield effect will come out. The magnetic flux density and the height of meniscus will become larger with the slit number; slit width and siit length increasing. When the slit number was changed from 24 to 32, the maximum value of magnetic flux density increased 32%, the height of meniscus increased 110%. When the slit length was changed from 100mm to 130mm, the maximum value of magnetic flux density increased 28%, the height of meniscus increased 155%. When the width of the slit was changed from 0.3mm to 0.5mm, the maximum value of magnetic flux density increased 15%. All these results can give great support to the design ofΦ178mm industrial round billet EMCC mold.Two kinds of asymmetry slit rectangular soft-contact EMCC mold with the same inner size of 213mm×85mm were developed. The distribution of the magnetic flux density and the characteristics of meniscus in the molds have been discussed through experiments. The results show that:the magnetic flux density and the height of meniscus increase with the input power increasing. But the input power did not change the distribution of the magnetic field. The maximum magnetic flux density will move to the same direction as the induction coil. The free surface of the liquid metal should be controlled near the center of the coil.The positions of the slits in EMCC mold are important to the magnetic field and distortion of the liquid metal. It has been found that in the rectangular EMCC mold which has slits at one narrow side, the magnetic field is not zero at the other narrow side where there are no slits when the input power is not zero. At the input power of 52kW, the maximum magnetic flux density on the narrow side which no slits is about 60% of that on the other side with slits. For the improved structure rectangular mold which is added slits at four conners, the magnetic field and the height of the meniscus in the mold are also enhanced. The magnetic field is also uniformed at the same time. It can be proved that using this kind of asymmetry slit structure EMCC mold can apply the technology of EMCC to the rectangular billet continusou casting.A billet soft-contact EMCC mold with the size of 100 mm×100 mm with non-uniformity segment was developed. By using low melting point alloy, experiments had been done. The results show that compared with symmetry slits EMCC mold the magnetic flux density and the height of meniscus are almost the same with the input power increases. The free surface of the low melting point alloy will fluctuate heavily; the temperature of liquid metel will increases, the initial solidification point moves downwards, and the solidification shell become thinner. The joule heat in the mold will increase at the same time. The temperature and the heat flux of the EMCC mold will increase. The mold oscillation also can increase the temperature of the mold and the selections of electric parameters should be adapted with the technical parameters. The resulets can give great support to the EMCC industical experiment.Through the research of electromangneitic soft-contact characteristics of continuous casting mold with different structure patterns, it has been found the structures of the EMCC mold will not change the electromagnetic soft-contact characteristics which are detemined by the relative positon between the coil and the mold, the relative positon between liquid free surface and the mold, and the input power.更多还原