Research On Eletctromagnetic Continuous Casting Of Hollow Tube

Continuous casting of hollow tube is considered as a profound near net shape technology for pipe production. To produce hollow tubes, which can satisfy the requirements of direct rolling in casting conditions, is the key to realize continuous casting-direct rolling of hollow tubes. The successful application of electromagnetic field in continuous casting and the emergence of novel electromagnetic continuous casting technologies improve the quality of cast tubes and also provide a chance for developing technology, which is aiming to produce hollow tubes with high quality, for electromagnetic continuous casting of hollow tube.Aiming to produce high quality hollow tubes, electromagnetic continuous casting technology of hollow tube was studied by applying electromagnetic process technology. The author fortunately participated in two projects: one is "Basic Research on Electromagnetic Continuous Casting of Hollow Tube" supported by Iron and Steel Cooperation Research Foundation co-sponsored by National Natural Science Foundation and Shanghai Baosteel Group Corporation, and the other is "Research on the Effect of Electromagnetic Field on Cu Tubes During Horizontal Continuous Casting" cooperates with Research Center of Precise Copper Tube of the Chinese Academic of Science. This doctoral dissertation is finished on basis of the above research works. Main research results are as follows:The experimental apparatus was designed for semi-continuous casting of hollow tube. The shaping of hollow tubes was studied by using a lower melting point alloy as experimental material. The effects of technique parameters, cooling cavity structure and conicity of inner-mold on shaping of hollow tubes were discussed. A hollow tube of 60mm-diameterwith the hole being 15mm-diameter was continuous cast successfully by optimizing the structure of inner-mold and setting up of reasonable parameters.According to the solidification features of hollow tubes, numerical simulation computation model of temperature field was established for simulating the heat transfer during continuous casting process. The effects of key technique parameters and the position of second cooling spouting on solidification were analyzed to provide guides for optimizations of technique parameters and structure of inner-mold.The experimental results of continuous casting of hollow tubes showed that there were many problems such as poor surface quality, too many faults, and coarse crystalline grains in solidification structure and poor uniformity of structure in the circumferential direction. In order to obtain hollow tubes with high quality, Electromagnetic continuous casting of hollow tubes with industrial frequency rotating electromagnetic field and middle frequency electromagnetic field outside of outer-molds was developed. The results showed:1) Imposing industrial frequency rotating electromagnetic field could improve the surface quality of hollow tubes, refine macrostructure and accelerate the transition from columnar grains to equiaxed grains, prominently improve the uniformity of macrostructure in circumferential direction. Moreover, distribution of solute element along the radial direction of hollow tubes became more homogeneous than those without industrialAbstractfrequency rotating electromagnetic field.2) Imposing middle frequency rotating electromagnetic field outside of outer-mold with slits could improve the surface quality of hollow tubes, eliminate the surface defects and refine macrostructure of hollow tubes. However, it had little effect on improvement of uniformity of macrostructure in circumferential direction.In order to further improve the quality of hollow tubes under the condition of imposing middle frequency electromagnetic field, hot top electromagnetic continuous casting of hollow tubes was proposed, which was characterized with the combination of hot-top technique and cold crucible technique. Not only the surface quality was remarkably improved and solidification structure was refined, but also the uniformity of structure in circ...