Enhancing Investment Casting Shells: The Role of Hybrid Fiber Reinforcement in Silica Sol Shells for Precision Casting

As a near net forming technology with high utilization rate, investment casting is the key technology for forming precision and complex thin-walled parts. The silica sol shell has good high temperature strength and surface quality, and is commonly used in investment casting process. However, the strength, air permeability and thermal conductivity of the shell are mutually restricted, which makes the shell used in the field of high-precision complex parts. There are limitations. Fiber is added to the shell as a reinforcing phase, which is expected to improve the air permeability and thermal conductivity while ensuring the strength of the shell. This paper mainly adopts the hybrid fiber reinforced silica sol shell of carbon fiber and nylon 66 to study the influence of fiber content on the properties of silica sol slurry and shell, and explore the best preparation process of fiber reinforced silica sol shell, aiming to prepare High-quality precision casting shells provide theoretical guidance and technical support. The main research results of the thesis are as follows:

When the silica sol slurry is prepared by using the hybrid fiber of carbon fiber and nylon 66 with different content, the fiber content is 4g/L, and the comprehensive performance of the silica sol slurry is the best. When the fiber content is less than 4g/L, the slurry viscosity and coating quality increase at the same time, and the fiber dispersion gradually becomes better. When the fiber content is higher than 4g/L, the Brownian motion of the fibers in the slurry is violent, the Van der Waals force between the fibers increases, the clustered fibers gradually increase, the slurry viscosity and coating quality are too large, and the slurry dispersion becomes worse.

When a single carbon fiber is used to enhance the performance of the silica sol shell, the carbon fiber content is 3g/L, and the comprehensive performance of the silica sol shell is the best. The strength reached the maximum after normal temperature and vacuum baking, respectively 3.97MPa and 4.38MPa, which was significantly improved compared with the traditional shell. When the fiber content is less than 3g/L, the fiber- shaped shell matrix is more uniformly dispersed, the slurry particles and fibers are tightly combined to form a new phase, and the shell strength continues to increase.

When the fiber content is higher than 3g/L, due to the serious flocculation of the fibers in the slurry, the slurry coating performance becomes poor, the shell strength begins to weaken and the high-temperature self-weight deformation of the shell gradually increases.

When the hybrid fiber of carbon fiber and nylon 66 is used to enhance the silica sol shell, the hybrid fiber content is 4g/L, and the comprehensive performance of the silica sol shell is the best. The high-temperature deadweight deformation reaches the minimum 0.49%, and the strength after normal temperature and vacuum roasting reaches the maximum, which are 4.19MPa and 3.58MPa respectively. When the fiber content is lower than 4g/L, there is no obvious agglomeration of the fibers in the slurry, the interweaving state of the fibers and the slurry is more uniform, and the overall performance of the shell gradually becomes better. When the fiber content is higher than 4g/L, the dispersion of fibers in the shell matrix becomes poor, and the bundle fibers gradually increase and appear slightly curved. The splitting effect of fiber bundles is greater than that of the reinforced shell, and the shell strength begins to weaken and breathe The performance and thermal conductivity are enhanced at the same time.