The Basic Study Of Gas Film Soft-contacted Continuous Casting Technology

The gas film soft-contacted continuous casting (GFCC) is a late-model casting technology in the aluminum alloy process, it possesses many advantages compared to other technologies, which include the low yield cost, the simple operation, the slippery slab surface, the even inner structure and the high mechanism performance. Therefore, the GFCC technology receives great satisfying metallurgical purpose for the ordinary extrusion aluminum alloy slab, and has forceful competence in the duralumin and super-duralumin casting also. At present, the metallurgists make researches mainly on the design of equipment configuration, the automatic controlling of gas volume rate and the kinds of casting aluminum alloy, and have obtained some results. However, the influencing regulations of the technology parameters (which include the casting speed, the gas volume rate, the cooling water pressure and the gas slot width) on the slab quality are rarely found in the literature, furthermore, the research of gas film lubricating theory has not still found in the literature. So, it is very interesting to study the GFCC technology.Based on the design idea of soft-contacted for the mold and slab, a new mould has been developed in this paper on substantive experiments, it has some merits such as shorter cooling length, low heat transfer efficiency, even cooling and better lubricating performance, the casting experiments for 1080, 2024 and 6063 aluminum alloy are very successful. It has established the Renault lubricating model under the GFCC technology through modifying of the gas bear lubricating theory in the paper. It has studied the effect of technology parameters on the casting stability and the distributing rule of gas pressure in the gas film. The paper has also studied the general influencing rules of the technology parameters on the slab quality under the GFCC. The mathematic results are coincident with the experiment conclusions, and it also gains some instructional conclusions for the GFCC technology, which give a strong theory and experiment groundwork for the next industrialized experiment. The paper's main contents are showed as follows.Based on the study of the heat transfer modeling and lubricating theory modeling, it finds that the gas pressure decreases with the distant of the calculating location and the gas slot increasing in the GFCC technology, and the gas film can appear the phenomena of pressure backup which the pressure decreases first, then increase underthe instability condition and finally bring disadvantages to the casing. The computational results show that the gas pressure distributing develops forward the instability estate with the casting speed increasing and the gas volume rate and the gas slot width reducing. It is necessary to enhance the gas volume rate logically for avoiding the gas pressure backup.It has gained the essential condition for the GFCC technology by analyzing of the suffering forces of the liquid metal at the gas slot. When the gas backpressure is lower than the lower limit of the essential condition, the liquid metal can enter the gas slot, contrarily, the gas can enter the liquid metal and form incursive air hole which depress the slab quality, when the gas backpressure meet the demand of the essential condition, the casting process is very steady and the slab quality is fine.The experiment results show that there is a critical value on the influence of the gas volume rate on the surface quality of the slab. The surface of the slab is very slipper if the gas volume rate is higher than the critical value, while it is lower, there are some cracks and fold marks on the surface of the slab, that may be induced by the different influence that the gas volume rate on the continuity, the uniformity and the stability of the gas film. The factors effecting the gas film continuity and uniformity also include the casting speed, the liquid metal height in the hot top and the gas slot width, in fact, the faster the casting speed is, the more awfully the continuity and the uniformity of...