Mechanism of Mold Powder Entrapment Caused by Large Argon Bubble in Continuous Casting Mold
Mechanism of Mold Powder Entrapment Caused by Large Argon Bubble in Continuous Casting Mold
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DOI：
10.2355/isijinternational.41.1529
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发表时间：
2001-12
影响因子：
1.8
通讯作者：
S. Yamashita;M. Iguchi
中科院分区：
文献类型：
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作者：
S. Yamashita;M. Iguchi
众所周知，模具粉末滞留在钢液中会大大降低成品钢的质量。对这个问题进行了大量的调查。图1显示了迄今为止已知的五种模具粉末夹带。最常见的一种是由(1)表示的，它是由从模具的窄面反向流动引起的。覆盖钢水层的模具粉由于作用于模具粉和钢水界面上的强剪切应力而被带入钢水中。(2)是由非定常逆流引起的高剪应力作用引起的。众所周知的开尔文-亥姆霍兹不稳定性是这种夹持的主要原因。第三个(3)是由SEN后面有规律地脱落的卡门涡街引起的夹带。卡门涡街是由SEN端口不均匀的钢水流放电引起的不均匀半月板流产生的。第四个(4)是由SEN端口的大氩泡攻击界面引起的夹带。第五种，(5)，也是由出料流量不均匀引起的。由于SEN后表面压力降低，模具粉末沿SEN外表面下降，并在SEN端口的出钢水流中夹带。在上述五种类型的模具粉末夹带中，第四种类型的机理即使在模型实验中也没有完全了解。这里简要回顾了迄今为止关于这一陷阱的发现。在SEN中提供氩气是为了防止非金属夹杂物（如氧化铝）附着在SEN的内壁上。氩气有时在SEN的端口形成一个大气泡，并在钢液层中上升。这个氩泡穿过钢水和模具粉末层之间的界面，导致模具粉末被困在钢水层中。遗憾的是，模粉的物理性质、模粉层的厚度和氩泡的大小对夹带的影响尚不清楚。因此，本研究的主要目的是澄清这些影响。2. 实验设备及程序
Mold powder entrapment into molten steel is known to lower the quality of finished steel products significantly. A lot of investigations have been carried out on this subject. Figure 1 shows five types of mold powder entrapment known to date. The most popular one is indicated by (1), being caused by a flow reversing from the narrow face of the mold. The mold powder which covers the molten steel layer is carried into the molten steel due to strong shear stress acting on the interface between the mold powder and molten steel. The second one, (2), is caused through the effect of high shear stress induced by unsteady reversing flow. The well-known Kelvin–Helmholtz instability is the main cause of this type of entrapment. The third one, (3), is the entrapment induced by the Karman vortex streets shed regularly behind the SEN. The Karman vortex streets are generated by the uneven meniscus flow which is uniquely related to uneven discharging molten steel flow at the ports of the SEN. The forth one, (4), is the entrapment caused by attack of a large argon bubble coming from the ports of the SEN to the interface. The fifth one, (5), is also caused by the uneven discharging flow. The mold powder descends along the outer surface of the SEN due to pressure decrease on the rear surface of the SEN, and it is entrained in the discharging molten steel flow at the ports of the SEN. Among the five types of mold powder entrapment mentioned above the mechanism of the fourth type is not fully understood yet even in model experiments. The findings obtained so far on this entrapment are briefly reviewed here. Argon gas is supplied in the SEN in order to prevent attachment of nonmetallic inclusions such as alumina to the inner wall of the SEN. The gas sometimes becomes a large bubble at the port of the SEN and rises in the molten steel layer. This argon bubble passes through the interface between the molten steel and mold powder layers and causes entrapment of the mold powder into the molten steel layer. Unfortunately, the effects of the physical properties of mold powder, the thickness of the mold powder layer and the size of the argon bubble on the entrapment are not known. The main objective of this study therefore is to clarify these effects. 2. Experimental Apparatus and Procedure