【作者】 程常桂；

【导师】 邓康； 任忠鸣；

【作者基本信息】 上海大学 ， 钢铁冶金， 2003， 博士

【摘要】 气膜软接触连铸是铝合金加工的一项新型连铸技术，与其它连铸技术相比，生产成本低，操作简单，浇注的铸坯表面光滑，内部组织均匀致密，机械性能好，因此，对于普通挤压铝合金铸坯而言，气膜软接触连铸技术能够取得非常满意的效果，在大断面的硬铝合金、超硬铝合金铸坯浇注中，该技术也具有较强的竞争力。目前，冶金工作者对该技术的研究主要集中在设备构造、气体流量自动控制、浇注合金的种类等方面，取得了一定的结果，但是具体的工艺参数(如拉坯速度、气体流量、冷却水压力、气缝的尺寸等)对铸坯质量影响规律的研究却很少报道，也未曾见过该工艺条件下气膜润滑理论方面的研究工作。因此，本文进行气膜软接触连铸技术的基础研究具有非常重要的现实意义。 采纳铸坯与结晶器内壁“软接触”的设计思想，本文设计出一种新型的气膜软接触连铸结晶器，它具有冷却长度短、传热量低、冷却均匀、润滑性能好等优点，对1080工业纯铝、2024铝合金、6063铝合金进行实验都取得了比较满意的结果。利用气体轴承气膜润滑理论的相关知识，并结合连铸过程中的实际情况，本文建立了气膜软接触连铸工艺条件下的雷诺润滑理论模型，研究了气膜内的压力分布特点及工艺参数对连铸稳定性的影响规律。通过实验，本文研究了气膜软接触连铸稳定进行的必要条件及工艺参数影响铸坯质量的一般性规律。理论计算结果和实验结果非常吻合，得出了一些具有指导意义的结论，这为下一步的工业化试验提供了坚实的理论和实验基础。论文的主要内容如下： 通过传热收缩模型及润滑理论模型的研究，发现在稳定的气膜软接触连铸条件下，气膜内的压力随距结晶器气缝距离的增加单调下降；在非稳定条件下，气膜内的压力则会出现先降后升的“压力阻塞”现象，这不利于连铸的顺利进行。计算结果同时还表明，随拉坯速度的增加、气体流量的降低及环形气缝尺寸的减小，气膜内的压力分布朝非稳定方向发展。合理提高气体流量，有利于保证连铸的稳定性，避免产生“压力阻塞”现象。 通过气缝处金属液的受力分析，本文得出了保证气膜软接触连铸工艺顺利进行的必要条件。当气体背压满足这一条件时，连铸就能稳定进行；低于气体背压条件的下限时，金属液就可能进入环形气缝内，堵塞气缝；反之，气体可能进入会属液内，形成侵入式气孔，降低铸坯质量。 实验结果表明：一定工艺条件下，气体流量对铸坯表面质量的影响存在临界值，高于临界值时，铸坯表面非常光滑；低于临界值时，铸坯表面则存在冷隔、裂纹等缺陷，这主要是其对气膜连续性、周向均匀性和稳定性的影响不同而导致摘要的。影响气膜连续性、均匀性的因素还有拉坯速度、金属液位高度、气缝尺寸等参数，事实上，拉坯速度越大，气膜的连续性、稳定性越差。连铸过程中，气体背压随气体流量的增加而增大，随拉坯速度的增大而减小，因此，合理增大气体流量，可以提高气膜的刚性及其对液态金属的约束能力。 电镜检测及等离子发射光谱分析结果表明:气膜软接触连铸稳定条件下，2024铝合金的皮下反偏析层厚度可降低到100 pm左右，远小于传统 DC连铸工艺条件下的500 pm。由宏观组织检验分析可知，工艺参数合理时，可获得晶粒度为2一3级全等轴晶的铸坯。拉伸力学性能分析则表明，气膜软接触连铸坯的力学性能优于传热条件类似传统DC连铸工艺条件下铸坯的力学性能。这表明通过气膜软接触连铸工艺可以获得高质量的铸坯。 实验研究发现，气体流量、拉坯速度等工艺参数对铸坯的宏观组织、皮下反偏析程度有重要影响。其它工艺参数一定，随着气体流量的降低、拉坯速度的增大，铸坯宏观组织的等轴晶比率降低，一定条件下甚至整个横断面上全为柱状晶;气体流量过低的时候，气膜不能起到软接触作用，此时铸坯的凝固条件与传统DC连铸工艺相似，铸坯宏观组织为典型的三层晶粒结构。铸坯的皮下反偏析程度则随着气体流量的降低、拉坯速度的增大而增加。实验研究还发现，铸坯表面光滑时，铸坯内部质量并不一定好，还需进一步调整气体流量，改善传热条件，才能获得全等轴晶组织的铸坯，这也说明，在气膜软接触连铸条件下，通过调整工艺参数可以获得全等轴晶组织的铸坯，这是非常有意义的。事实上，在合理工艺参数条件下，获取全等轴晶铸坯的实验现象重复性非常好。 实际生产过程中为提高生产率，总是尽可能地提高拉坯速度，但理论分析和实验结果均表明，拉坯速度增大，连铸的稳定性、连铸坯的质量会降低，解决这一问题的有效途径就是提高气体流量。由此可知，对于气体流量和拉坯速度而言，两者对连铸工艺影响的理论分析结果与实验结果是一致的。更多还原

【Abstract】 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更多还原