In this Master's thesis titled “Characterization of dimensional and mechanical properties of ceramic investment casting shells” we briefly present investment casting, from the design of the pattern itself, the production of a wax pattern, the production of the ceramic shell and the casting itself. We discuss the issue of sintering the ceramic shell and how the sintering parameters affect the final mechanical properties. At the same time, we also checked the changes in geometry throughout the entire process from the master pattern to the final casting. The methods used to produce the necessary components and experiments are also described. The focus was on XRD and DSC analysis, sintering of ceramic shells and comparison of the master pattern with the wax pattern and the final casting using 3D scanning and 3-point flexural test.
We found out that sintering ceramic shells at temperatures above 1000 °C leads to phase transformations from the amorphous silica to the β-cristobalite phase and thus maximum mechanical properties are achieved at temperatures close to, but below 1000 °C. XRD and DSC analyses clearly showed the transformation from amorphous to the β-cristobalite phase and presence of α-cristobalite. The 3-point flexural test confirmed that the presence of α-cristobalite leads to faster critical failure and lower mechanical properties. We also found out that with longer times, the mechanical properties start to decrease due to growth of crystal grains and the optimal sintering time is around 1 hour. Both the wax pattern and later the final casting shrank during solidification and lead to 2 % linear shrinkage each or a total of 4 % linear shrinkage in length and width.
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