【作者】 王聪聪；

【导师】 应富强；

【作者基本信息】 浙江工业大学 ， 机械设计及理论， 2009， 硕士

【摘要】 镁及镁合金以其低密度、高比强度、高比刚度等优异的性能被广泛地应用于航空航天、汽车制造等领域。由于镁合金易于氧化燃烧,使得镁合金气体保护技术成为镁合金应用的关键技术之一。纵观镁合金保护气体的研究现状,大部分集中在保护机理方面,而关于保护气体在镁合金熔炉内的流场特性及在此基础上的装置研究还很不成熟。本文研究了镁合金熔炉内保护气体的流场特性,并针对熔炼工艺设计了保护气体的控制系统,研究内容具有重要的理论价值和实际意义。论文分析了保护气体在镁合金熔炉内的流动过程,建立了镁合金熔炉内保护气体湍流流动的数学模型,应用FLUENT流体计算软件进行了数值模拟。使用有限容积法对控制方程进行离散,然后用SIMPLE算法求解,进而分析了工艺参数(入口速度、入口浓度)和工况(镁液温度、镁液高度)对保护气体流场的影响。使用TECPLOT软件将数值模拟得到的计算结果用图像表述出来,从而更为直观地表现出保护气体在熔炉内的流场及分布状况,实现计算结果的可视化。模拟结果表明:保护气体的入口流速应该控制在一定范围内,若流速太小,保护气体受热浮力作用发生上浮现象,若流速太大,会造成保护气体在镁液上方分布不均。调节保护气体的入口浓度能够有效调节保护气体的有效成分在镁液上方的含量。当工况发生变化时,改变工艺参数能够获得很好的保护效果。针对保护气体在镁液上方分布不均的现象,提出了利用多孔分流器来优化保护气体流场。采用理论分析和计算流体动力学分析相结合的方法,得出了多孔分流器各孔口流量分配规律,为多孔分流器的改进打下了基础。研究表明:通过增大多孔分流器主管直径,有效降低了保护气体在分流器内的压降,从而提高了多孔分流器孔口出流的均匀性。为了确保保护气体流量的稳定性及良好的系统性能,设计了以PLC为核心控制单元、触摸屏为人机交流平台的保护气体自控整体方案。以质量流量控制器为测控器件,实现了对保护气体流量及浓度的精确控制。更多还原

【Abstract】 Magnesium and magnesium alloys have been widely used in spaceflight and automobile making for its excellent properties such as low density, high specific strength and high specific rigidity. Due to their chemical active nature, Mg alloys are prone to oxidation and ignition. Therefore, the technique of gas protected melting become part of the key techniques in Mg production and application. In terms of the present developing and research conditions of shielding gas for magnesium alloys, most of the focus is concentrated on protective mechanism. Whereas, it is not very mature in terms of the characteristics on flow field of shielding gas in magnesium alloy melting furnace and the apparatus for the shielding gas. This work is involved in the characteristics on flow field of shielding gas in magnesium alloy melting furnace and the control system apparatus is design base on the melting process.In this work, shielding gas flow process in magnesium alloy melting furnace is analyzed. With the aid of the software—FLUENT, the mathematical model of turbulent flow in the magnesium alloy melting furnace is established. The governing equations are solved with SIMPLE algorithm in finite volume way. According to the simulation result, the factors affecting the component of flow field are discussed such as process parameters (e.g. inlet velocity, concentration ratio) and working condition (e.g. the temperature of molten magnesium alloy, the liquid height). The results are displayed by TECPLOT, so the flow fields and gas distribution are showed directly to realize the visualization of the calculations. The results of numerical simulation indicate that inlet velocity should be controlled within certain range, the rising phenomenon will occurred due to the buoyancy force if the inlet velocity was too small and the phenomenon of uneven distribution above the magnesium alloy molten surface will occurred when the inlet velocity was too high. The concentration of the effective component above the magnesium alloy molten surface can change along with the inlet concentration. Good protective effect can be obtained by changing the process parameters when the working condition is changed.Aiming at the phenomenon of uneven distribution above the magnesium alloy molten surface, the apparatus of multihole diverter is put forward. It adoptes theoretical model and finite element numerical simulation to achieve the distribution of multihole diverter and the premises for uniform distribution of flow. Research shows that the pressure drop of the shielding gas in the multihole can be reduced by increasing the diameter of multihole main pipe, and the outflow uniformity is improved effectively.The steady of gas flow and good system performance are very important during the magnesium alloys melting process. A reasonable scheme is designed by using PLC and Touch-screen as the core of control unit. The accurate control of flow is achieved by adopting Mass flow controller.更多还原