Influence of a rotating electrode on the droplet formation and the refining effect in the electroslag-remelting process

在电渣重熔过程中，使用金属锭作为电极，在渣层中逐渐熔化。通过渣层后，液态金属在水冷铜模内以受控结构凝固。在此过程中，通过化学和物理精炼机制提高了金属的纯度。与铸锭相比，由于液态金属体积较小和感应搅拌的作用，宏观偏析较少。此外，由于局部冷却速度相当低，因此减少了微观偏析。在渣和铜模的交界处，一层1~3毫米厚的渣皮被固化。这一层既减少了铜模的热损失，又降低了金属熔池中的凝固速度。本研究的重点是了解非金属夹杂物去除的基本机理、柱状受控凝固的演变和渣皮的形成。然后，所获得的见解将被应用于使用旋转金属电极的重熔过程，这是一项很有前途的工艺创新，到目前为止几乎没有人进行过研究。由于电极表面的旋转对液态金属的离心力作用，金属液滴的尺寸减小，熔滴比表面积增大，在渣中停留时间增加。通过实验和数值研究，了解熔滴的细化机理和非金属夹杂物的分布。这是通过检查镍基合金718以提高清洁度和以可重复的方式控制凝固来实现的。

During the electroslag remelting process (ESR) a metal ingot is used as an electrode which is gradually molten in a slag layer. After passing through the slag layer, the molten metal solidifies in a controlled structure within a water cooled copper mold. During this process the metals degree of purity is improved by chemical and physical refining mechanisms. Compared to ingot casting less macro segregation can be observed, due to the smaller volume of liquid metal and the inductive stirring. Furthermore micro segregation is reduced, as the local cooling rates are fairly low. At the interface between slag and the copper mold a 1 to 3 mm thick slag skin solidifies. This layer reduces both the heat loss at the copper mold and the solidification rate in the metal pool.The present research project is focused on understanding fundamental mechanisms of removing non­metallic inclusions, the evolution of controlled columnar solidification and the formation of the slag skin. The insights gained will then be applied to a remelting process using a rotating metal electrode, which is a promising process innovation that has barely been investigated so far. Due to the centrifugal force acting on the liquid metal due to the rotation at the electrode surface, the size of metal droplets is reduced while the droplets specific surface and the residence time in the slag are increased.By carrying out experimental and numerical investigations understanding the refining mechanisms and non-metallic inclusion distribution is the objective of this study. This is to be achieved by examining the nickel based Alloy 718 targeting an improved degree of cleanliness and controlled solidification in a reproducible manner.