型壳制造是熔模铸造的关键工艺环节，直接影响铸件质量。硅溶胶型壳层间干燥时间长，影响供货周期。为了适应熔模铸造生产大型、薄壁、复杂铸件的发展趋势，以及满足市场快速交货的要求，本论文主要围绕减少型壳开裂，缩短制壳周期开展工作。硅溶胶在型壳干燥过程中实现胶凝，常温强度比硅酸乙酯型壳低，在制壳和脱蜡过程中容易造成开裂破坏。论文中结合型壳工艺的具体特点，指出了制壳中干燥收缩受阻是造成破坏的主要原因，同时指出存在两种不同的裂纹自修复机制。脱蜡过程是造成型壳开裂的重要环节，论文对蜡模在脱蜡过程中的温度变化进行了数值计算，分析了熔融蜡的外泄通道，认为必要时可以选择合适位置开设排蜡孔，以降低型壳开裂的危险。作者设计了在生产现场检测高压蒸汽脱蜡釜中模组温度变化的实验方案并进行了实际测量，为分析脱蜡釜中实际热物理过程提供了帮助。在提高硅溶胶型壳质量和缩短制壳周期方面，论文从内因和外因两方面开展研究工作。内因指提高粘结剂性能，研究新型硅溶胶。研究中主要通过对硅溶胶胶体表面进行铝离子改性和填加高聚物PVA来实现硅溶胶快干和增强。为了实际生产的需要，考虑了硅溶胶及所配涂料的保存性。论文研究成果所获得的新型碱性快干硅溶胶能够适应我国耐火材料碱性杂质多的特点。实践证明，新型快干硅溶胶将层间干燥时间从6~12h缩短至1~2h。干燥环境是影响型壳干燥速度和质量的外因。论文对空气相对湿度、空气流动速度、蜡模孔洞的深径比、型壳摆放位置以及通、盲孔特征等诸因素对型壳干燥过程的影响进行了实验研究。实验表明，环境空气流动速度对型壳干燥速度影响很大，风向对深径比大于2的通孔和深径比大于1的盲孔的型壳干燥速度产生明显影响，因此制作型壳背层时要使用4~6m/s的强风，并使用旋转风。为防止面层因干燥过快而收缩开裂，不能用风，并且空气相对湿度应在60%以上。论文中还结合熔模铸造型壳工艺的具体特点对型壳干燥过程进行了三维数值模拟，其结果与实际情况吻合。
Shell building is a crucial process in the investment casting technology, which directly affects the quality of castings. Moreover，the long dipping time of colloidal silica shell is also one of the factors which affects the ability to provide castings in time. In order to improve the capacity of producing large, thin-walled and complicated castings and meet the requirements of quick respondence to the market, this dissertation aims to avoid the crack defects and shorten the cycle time of shell building process.The strength of colloidal silica gel is lower than that of ethyl silicate before firing so that it may crack during shell building and dewaxing. The main reasons of shell crack are analyzed and two kinds of crack self-repair mechanism are pointed out. In the dewaxing process, the temperatures of the wax and the shell in the steam autoclave are calculated and the flow channels of melted wax are analyzed. Based on the above data and analysis, rush holes can be set on appropriate places to reduce the tendency of shell cracking. A set of equipment is designed to measure temperatures of mold trees in the steam autoclave. From the results, the thermal physical process can be described clearly and is helpful for the understanding of the process.The intrinsic and extrinsic factors are discussed to improve the quality of shells and to shorten the cycle of shell building. As the intrinsic factor, a new type of colloidal silica is studied. It owns higher strength with the faster processing property by the addition of Al ion and PVA. The stability of the colloidal silica and the coating are also considered to meet the requirement of validity after a period of storage. The new colloidal silica developed in this dissertation is alkaline and it can adapt to the characters of domestic refractory materials which have more alkaline impurities. Its applications in several investment casting foundries have shown that the time interval between layers can be reduced from 6~12h to 1~2h.The environment condition of shell drying is the extrinsic factor that affects the drying speed and quality. Several factors, such as relative humidity, air flow speed, ratio of depth to diameter of wax pattern, setting place and character of pattern holes, are studied in this dissertation. The experiments show that the speed of air flow is crucial to the efficiency of shell drying. Air flow direction also affects the drying speed of interior shells when ratio of deepness to diameter is greater than 2 for open holes or larger than 1 for blind holes. Therefore the speed of air should be 4~6 m/s and rotating fans should be used in the shell room of back layers. It is also verified that no air should be used during making face layers and the humidity should be more than 60% in order to avoid the cracks caused by too quick drying.The 3D simulation of shell drying is carried out according to the characteristics of shell building and the simulation results are in good agreement with the measured results.
