Study On Controlling Phase Interface Technology In Producing Hollow Ingot Continuously By Non-sleeve Method

Hollow ingot was named comparatively to normal ingot. It is an important raw material for the large-scale tube, pressure-enduring products and water engine axletree. Hollow ingots could greatly save the raw materials, reduce the cost and improve the quality of the products as well. But the production of hollow ingot is still at its infant stage in China. Thus we generally use normal ingots and have to import hollow ingot for special-used devices. With the rapid growing economy, the demand for hollow ingot is increasing, which puts high pressure on the research of hollow technology in our country. There are two major techniques in producing hollow ingot, one is called inner sleeve method, and the other is called non-sleeve method. The scientific research on the first one started earlier and its application in manufacture was much more mature than the later. However, it cannot produce the ingot continuously because of the basic mechanism of the technique itself. Whereas the non-sleeve method, as a completely new technology patented by the Japanese Kawasaki steel CO. LTD. cannot do. However non-sleeve method requires a rigorous high heat environment. This paper used thermodynamic methods combined with numerical simulation to investigate the non-sleeve technique, and conducted the research on the influence of the thermal environment upon the shape of the surface of the condensation phase and its development. The paper started with a brief introduction on the production of hollow ingot both at home and abroad, the analysis on different mechanisms of these techniques, and the description about the numerical simulation method. The key technique of non-sleeve method is to control the solidification direction, in accordance to the theory of directed solidification. The paper still listed the numerical simulation method commonly used in solidification process and most popular numerical techniques. Solidification is a complex heat transfer process accompanying with phase change, so the thermal environment plays a crucial role of the direction of the phase interface and the microstructure of ingots during solidification process. The paper used the control volume method in simulation and also established the mathematical model and solving methods. The paper deals with a six tons normal ingot solidification for convenience. The computed solidification curve was well agreed with the experimental results by Weingart in 1975. The simulation results also indicate that the natural convection has important influence on the shape of interface and its forward process. Finally it was discovered that there exists local circuit flow in the big circuit in the liquid phase during the earlier solidification. In Chapter 3, the author made the mathematical model based on the physics one got the two heat transfer coefficient curves that is suitable for non-sleeve technology, investigated the impact of ingot structure on solidification, and concluded that the mould structure with proportion of 3:1 is best for non-sleeve technique. At the end, the paper posted the problems which needed to be solved in non-sleeve technique, and also provided suggestions in selecting the solidification materials and designing mould.