An investigation has been carried out into the mechanisms of failure of silica bonded investment casting moulds, with the aim of reducing failure rates for larger components. The analysis begins with a detailed microstructural examination of a current commercial mould system using scanning electron microscopy and other allied analysis techniques. The mould structure is shown to be nonuniform and unpredictable, with poor packing of the ceramic constituents leading to a non-uniform porosity network. The structure and distribution of the binder is also established and this indicates that the major load bearing points within the mould consist of thin areas of silica. As such, the overall performance of the mould is directly related to that of the silica itself. This binder is shown to contain impurity elements leached from the ceramic filler at various stages during mould manufacture. These elements alter the phase composition and thermal properties of the binder. Mould temperature profiles for a range of casting sizes have been measured and used to illustrate the relationship between metal weight and maximum temperature attained within the mould section. The profiles are also used to investigate the creep response of silica based binders. It is found that a combination of high temperatures and creep within the silica phase is responsible for the casting defects found with larger components. From these observations, a prediction is made regarding failure mechanisms and suggested remedial action. The thermal properties of several commercial water based binders are evaluated and the suitability of each as an alternative binder is discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:563932 |
| Date | January 1993 |
| Creators | Jones, Samantha |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.bham.ac.uk//id/eprint/788/ |
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