平面流铸法中气流边界层对熔潭行为影响的数值模拟研究

发布时间：2018-05-22 09:15

本文选题：平面流铸法 + 气流边界层　；参考：《钢铁研究总院》2017年硕士论文

【摘要】：在平面流铸法制备非晶带材过程中,由于冷却辊的高速旋转,在冷却辊辊面会形成一层具有高速度梯度的气流边界层。气流边界层会对非晶熔潭中非晶熔体的流动、传热和凝固行为(简称熔潭行为)产生影响,进而影响非晶带材的厚度、边部质量、表面质量和使用性能。本课题以计算流体力学为理论基础,通过建立数学模型,研究平面流铸法制备非晶带材过程中气流边界层对熔潭行为的影响。在此基础上,分析气体物性参数、环境压力和平面流铸过程工艺参数对气流边界层及熔潭行为的影响,以期阐明气流边界层对熔潭行为及非晶带材质量影响的机理,以期为现场生产过程中控制气流边界层提供理论参考。得出以下结论:(1)在非晶熔潭形成过程中,气流边界层均对熔潭行为产生影响。非晶熔潭尚未形成时,气流边界层会在非晶熔体-气体界面带走非晶熔体的热量。非晶熔潭形成后,气流边界层冲击熔潭上弯月面,会导致气体卷入非晶熔潭,并对非晶熔体的温度分布产生影响。气流边界层会在熔潭边部形成绕流熔潭现象,不利于非晶带材边部质量。(2)采用负压吸气时,吸气位置及吸气压力十分关键。当在熔潭上弯月面侧进行侧部吸气时,较低的吸气负压(5000Pa和8000Pa)对气流边界层的破坏较小。当在熔潭上弯月面侧进行顶部吸气时,吸气负压(5000Pa)能够减弱绕流熔潭现象,从而有利于提高非晶带材边部质量。当吸气负压提高至80000Pa时,在熔潭边部会产生高速逆制带方向气流,不利于非晶带材边部质量。(3)喷吹速度和喷吹方向对喷吹不同气体的效果有很大影响,当逆制带方向喷吹不同气体(Ar、He、CO2)时,喷吹速度的提高有助于破坏气流边界层。当沿制带方向喷吹低密度气体(高温CO2)时,有助于减少气流卷入现象的发生。(4)工艺参数(非晶熔体喷注速度、冷却辊旋转速和喷嘴-冷却辊间距)的调整均会影响熔潭行为。非晶熔体的喷注速度主要影响非晶熔潭与冷却辊辊面的夹角。调整冷却辊旋转速度会改变熔潭内的温度分布。喷嘴-冷却辊间距会改变熔潭上弯月面附近气流边界层速度分布,从而对气体卷入产生影响。增大制带宽度会增大绕流熔潭的最大速度,从而对非晶带材边部质量产生影响。
[Abstract]:In the process of preparing amorphous strip by plane flow casting, due to the high speed rotation of cooling roll, a layer of air flow boundary layer with high velocity gradient will be formed on the surface of cooling roll. The gas flow boundary layer will affect the flow, heat transfer and solidification behavior of amorphous melt, and then affect the thickness, edge mass, surface quality and performance of amorphous strip. On the basis of computational fluid dynamics (CFD), a mathematical model was established to study the effect of gas flow boundary layer on the fluid-pool behavior in the process of preparing amorphous strip by plane flow casting. On this basis, the effects of gas physical parameters, environmental pressure and process parameters of plane flow casting on the behavior of gas flow boundary layer and molten pool are analyzed in order to elucidate the mechanism of the influence of gas flow boundary layer on the fluid-pool behavior and the quality of amorphous strip. In order to provide a theoretical reference for the control of air flow boundary layer in the field production process. The following conclusion is drawn: (1) during the formation of amorphous molten pool, the gas flow boundary layer has an effect on the molten pool behavior. When the amorphous melt pool is not formed, the gas flow boundary layer will take the heat of the amorphous melt at the interface between the amorphous melt and the gas. After the formation of amorphous melt pool, the air flow boundary layer impinges on the meniscus of the molten pool, which results in the gas sucking into the amorphous melt pool and affects the temperature distribution of the amorphous melt. The flow around the pool is formed in the boundary layer of the gas flow, which is unfavorable to the mass of the edge part of the amorphous strip. The suction position and suction pressure are very important when negative pressure is used to inhale the boundary layer. When the lateral suction is carried out on the meniscus side of the pool, the lower suction negative pressure of 5 000 Pa and 8 000 Pa) does little damage to the boundary layer of the gas flow. When the top suction is carried out on the meniscus side of the molten pool, the suction negative pressure of 5 000 Pa) can reduce the flow around the pool and thus improve the quality of the edge part of the amorphous strip. When the suction negative pressure is increased to 80000Pa, a high speed reverse zone flow will occur at the edge of the melt pool, which is unfavorable to the injection speed and the direction of injection on the effect of injection of different gases, which is not conducive to the quality of the edge part of the amorphous strip. When different gases are injected in the reverse direction of the belt, the higher the injection velocity is, the more the boundary layer will be destroyed. When the low density gas (high temperature CO _ 2) is injected along the belt direction, the adjustment of the process parameters such as the injection rate of amorphous melt, the rotation rate of the cooling roll and the distance between the nozzle and the cooling roll will affect the melt behavior. The injection rate of amorphous melt mainly affects the angle between amorphous melt pool and cooling roll surface. Adjusting the rotation speed of the cooling roll will change the temperature distribution in the melt pool. The distance between nozzle and cooling roll will change the velocity distribution of the gas flow boundary layer near the meniscus of the molten pool, which will have an effect on the gas entrainment. The maximum velocity of the flow pool will be increased by increasing the width of the strip, which will have an effect on the quality of the edge of the amorphous strip.
【学位授予单位】：钢铁研究总院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG24

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