A Numerical Model of Solidification of a Massive Casting From Malleable Cast-Iron

Abstract

A numerical model of the temperature field associated with solidifying castings aims to achieve two general goals: directed solidification (as the primary condition for a healthy casting), and optimisation of the technology of casting together with the preservation of optimum utility properties of the product. A specific goal of this model is the selection and optimisation of the method of cooling to shorten the solidification time to obtain a spherical graphite structure with good nodular properties, and with a sufficient density of graphite spheres (cells). The speed of cooling during solidification and cooling in the mould is therefore a significant quantity influencing the formation of the structure. The achievement of these goals depends on the ability to analyse and, successively, to control the effect of the main factors which characterise the solidification process or accompany it. The analysis of the quantities is focused on determining the causes of the formation of the heterogenic temperature field during casting, considering the phase and structural changes. It is also focused on the thermokinetics of the formation of shrinkage porosities and cavities and on the prediction of their formation. This leads to the optimisation of the shape and sizes of the risers, the method of insulation, the treatment of the level. The model is applicable to various shapes of castings. The software is capable of analysing the temperature field of the actual casting, as well as the temperature field of the mould and cores, including the dependence of their material. It is also capable of considering non-linearity, i.e. the dependence of the thermophysical properties—namely the material of the casting and mould on the temperature, as well as the dependence of the heat transfer coefficients on the surface and interface temperature. The model is also equipped with an original network generator (pre-processing) as well as graphical output (post-processing).