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Effect of casting/mould interfacial heat transfer during solidification of aluminium alloys cast in CO2-sand mould

Kulkarni S. N., Radhakrishna D. K.

Materials Science Poland

2011

Vol. 29, No. 2

135--142

The ability of heat to flow across the casting and through the interface from the casting to the mold directly affects the evolution of solidification and plays a notable role in determining the freezing conditions within the casting, mainly in foundry systems of high thermal diffusivity such as chill castings. An experimental procedure has been utilized to measure the formation process of an interfacial gap and metal-mould interfacial movement during solidification of hollow cylindrical castings of Al-4.5 % Cu alloy cast in CO2-sand mould. Heat flow between the casting and the mould during solidification of Al-4.5 % Cu alloy in CO2-sand mould was assessed using an inverse modeling technique. The analysis yielded the interfacial heat flux (q), heat transfer coefficient (h) and the surface temperatures of the casting and the mould during solidification of the casting. The peak heat flux was incorporated as a dimensionless number and modeled as a function of the thermal diffusivities of the casting and the mould materials. Heat flux transients were normalized with respect to the peak heat flux and modeled as a function of time. The heat flux model proposed was to estimate the heat flux transients during solidification of Al-4.5 % Cu alloy cast in CO2-sand moulds.

Evaluation of metal / mould interfacial heat transfer during solidification of aluminium-4.5% copper alloy castings cast in CO2-sand moulds

Kulkarni S.N., Radhakrishna K.

Materials Science Poland

2005

Vol. 23, No. 3

821--838

In this study, two methods were employed to measure the heat transfer coefficient, h, at the metal-mould interface during casting. The first method is to measure the size of gap formed between metal and mould during the casting process and estimate the value, h, based on the gap size. The second method is to measure temperature at certain locations of metal and mould, and by using reverse method, h, at the gap, can be derived. A procedure is also developed to make use of temperature measurement data to obtain the h as the function of casting temperature near the interference. This form of h data is very useful for mathematical modeling of solidification for casting. In the present study, the casting material is Al-4.5% Cu alloy and the mould material is CO2-Sand. The results of the measurements show that the value of h is not a constant, but varies with time/temperature during casting. With the gap size measurement, h is very large in the beginning and keeps dropping afterwards. As the gap is fully developed, h approaches a constant value between 130 and 40W/(m0-2C). By the inverse method, along with the temperature measurement, the value of h increase in the beginning stage and reaches a peak value of approximately 710W/(m0-2C), then h drops rapidly approximately to solidification temperature and rises again until the end of solidification. After that, h keeps dropping until the end of casting.