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怎样开浇是双辊薄带连铸过程面临的一个重要问题。在开浇阶段,金属熔池应该逐步地建立以达到最优的熔池液位,而且在两个反向旋转的结晶辊表面形成的凝固金属层必须在引带离开最小辊缝前焊接在一起,以不准确的牵引时间进行不合适的操作,经常导致连铸过程和产品的不稳定以及铸带的中断,这将破坏铸带的成型及随后的卷取。因此,引带恰当的拉速在垂直双辊薄带连铸的开浇阶段起很重要的作用,准确的牵引时间对热分布的变化、流动条件和金属与结晶辊的相互作用都十分敏感。 为了揭示双辊铸造过程基本的传输现象,用一个商品化的PROCAST软件来模拟非稳态的流体流动、热传导和本研究连铸过程初期的凝固特征。一组耦合的质量、动量和能量平衡的控制偏微分方程用有限元方法来求解,用体积流量接近法(VOF)来处理瞬时自由表面问题,热焓法用于处理凝固、相变的问题。这个模型的优点是它处理移动边界问题和流体自由表面问题有很大的能力。用这个数学模型,在本研究中模拟了浇注顺序、流场和对应的温度分布在垂直双辊薄带连铸过程实际铸造条件下金属熔池内的情况。从计算结果可以知道:双辊之间的金属熔池是怎样逐步建立起来的,凝固层在旋转辊上是怎样随时间增厚的都基本揭示出来了。此外,金属熔池的液位、凝固前沿以及最终凝
How to pour pouring is an important issue that double-roll strip casting process faces. During the pouring stage, the metal bath should be progressively established to achieve the optimum bath level and the solidified metal layer formed on the surfaces of the two counter-rotating crystallizing rolls must be welded together before the tape leaves the minimum roll gap , Improper handling with inaccurate traction times often results in instability of the continuous casting process and product as well as the interruption of the strip which will destroy the forming of the strip and subsequent coiling. Therefore, the proper pulling speed of the tape is very important in the pouring stage of vertical twin-roll strip casting. The accurate towing time is very sensitive to the changes of heat distribution, flow conditions and the interaction between the metal and the crystallizing roll. In order to reveal the basic transport phenomena during the twin-roll casting process, a commercially available PROCAST software was used to simulate unsteady fluid flow, heat conduction and the initial solidification characteristics of the continuous casting process. A coupled set of governing partial differential equations of mass, momentum and energy balance is solved by the finite element method. The transient free surface problem is solved by the volume flow approach (VOF) and the enthalpy method is used to deal with the problem of solidification and phase transformation. The advantage of this model is its ability to handle moving boundary problems and fluid free surface problems. Using this mathematical model, we simulated the pouring sequence, the flow field and the corresponding temperature distribution in the molten pool under the actual casting conditions in the vertical twin-roll strip casting process. It can be seen from the calculation results: how the metal pool between the two rolls is gradually established, and how the solidified layer is thickening on the rotating roll basically reveals. In addition, the molten pool metal level, solidification front and final condensation