Mathematical And Physical Simulation Of The Fluid Flow Field In Tundish Of Vacuum Induction Furnace For Superalloy Melting

The tundish placed between the melting and pouring chambers in the vacuum induction furnace can distribute and steady the flow of molten metal.And the fluid controlling devices(FCDs)can be designed and placed in the tundish,the flow of the molten superalloy inside can be changed and controlled by the FCDs,the average residence time of the molten metal in the tundish can be effectively prolonged.As a result,the key role to further improve the metal purity can be played by the FCDs during the process of VIM pouring.The flow characteristics of the molten metal are mainly controlled by the,internal structure of the VIM tundish,operating regulations and certain process parameters during the pouring process.Meanwhile,the flow of the molten metal in the tundish is quite complex in the actual production process,and the physical and mathematical simulation can be recommended as the main research methods under the condition of laboratory.In this paper,the physical and mathematical simulation on pouring process of the No.22 vacuum induction furnace with 10 tons capacity for superalloy melting of a domestic special steel plant was researched based on the process characteristics and combined with the site operation regulations and the process parameters during the pouring process.The appropriate level height of the molten metal and the reasonable design of the FCDs were analyzed and confirmed during the steady state pouring process,and the unsteady processes under the pouring starting and ending were researched as well,the influences by different pouring starting regulations and the dam parameters during these processes were verified by the unsteady physical simulation.A physical tundish model scaled for 1/2 was built according to the principle of similarity simulation,and the commercial software FLUENT was used as the solver during the process of mathematical simulation,and the main results are as follows:(1)The steady state flow field of four different level heights under the original tundish structure were researched by physical and mathematical simulation,and their experimental results of comparison coincided quite well,their variation trend were showed by these results.The actual average residence time was longer,and the ratio of the plug flow volume fraction and the dead zone volume fraction was bigger when the model tundish level height was controlled between 80 mm to 90 mm,the prototype was controlled between 160 mm to 180 mm,and the floatation of the nonmetallic inclusions were accelerated obviously in this kind of flow field during the pouring process.The downstream regions of the FCDs were considered as the less active areas of the steady state pouring process.For the convenience of setting and reading of the flow,85 mm was selected as the scheme of water height during the hydraulics experiments of the FCDs' optimization research.(2)The flow of the flow characteristics in the tundish were improved after adjusting and optimizing the slag walls and dams based on the results of the orthogonal experiments:the actual average residence time increased by 9.2%;the ratio of the plug flow zone and the dead zone volume fraction raised from 2.877 to 3.223;the fluid flow speed in the less active region was much faster than the counterpart of original structure tundish,in the other word,the fluid flow condition was more active in those areas after optimization.(3)A reasonable scheme of the pouring starting was confirmed after the experiments of the physical simulation research of the unsteady stage of pouring process:the pouring flow was added to the 1.5 times that of normal pouring flow after the liquid level up to the 1/2 height of the tundish,and kept it until the level reach the normal height of steady state pouring.The transition time and the length of transition ingot became shorter during pouring starting by using the scheme,and not only that,the spiral vortex strength was smaller during this process compared with other schemes.(4)In order to reduce the residual amount of the pouring molten metal left in the tundish,the schemes of designing different holes in slag dams neared to the outlet were explored and,the analyzed results showed that the scheme of a 14 mm×14 mm hole which placed in the left side of the slag dam center was preferable:the slag entrapment amount during pouring starting was small,meanwhile the critical height of the spiral vortex is low during pouring ending.In another word,not only the amount of residual metal could be reduced,but also the purity of the ingot was guaranteed relatively under the unsteady pouring process.To sum up,after adjusting and optimizing the fluid level height and the layout of the FCDs based on the physical and mathematical simulation,the flow characteristics of the steady state fluid field were improved compared with the original structure tundish.By means of the physical simulation of unsteady pouring for the vacuum induction furnace,the reasonable pouring starting schemes and the slag dam parameters were confirmed,and the quality of ingot under the unsteady pouring process was guaranteed relatively,as a result,a theoretical basis for practical production was provided.