Trejo, Eduardo (2011)
Ph.D. thesis, University of Birmingham.
In centrifugal casting, molten metal is introduced into a mould which is rotated at high speed. The centrifugal force helps to fill thin sections but this benefit may be offset by the effect of the turbulent flow on the casting quality. In this research, the effect of direct and indirect gated mould designs on the quality and reliability of aluminium alloy investment castings made by centrifugal casting was investigated. The scatter in the ultimate bend strength and the modulus of elasticity was analyzed using the Weibull statistical technique, which showed that the Weibull modulus of both properties was significantly improved for the indirect gated cast test bars compared to the direct gated bars.
A detailed microstructural characterization was carried out on the cast test bars, which included grain size, dendrite cell size and porosity. Scanning electron microscopy was used to examine and analyze the presence of defects on the fracture surfaces such as shrinkage pores, entrapped bubbles and oxide films resulting from surface turbulence during mould filling. The results indicated a clear correlation between the mechanical properties and the presence of casting defects.
Water modelling experiments were carried out using purpose-built experimental centrifugal casting equipment and filling sequences recorded using a high speed video camera. The water modelling results showed that the general tendency for the direct and indirect gated mould designs was that the higher the rotational velocity, the lower the filling length and consequently the lower the filling rate. Subsequently, this information was used to validate the computer software ANSYS CFX. An excellent correlation was obtained between the experimental water modelling and simulation results for both direct and indirect gated moulds.
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