Prediction of Shrinkage Defects in Iron Castings Using a Microporosity Model

A numerical model for prediction of shrinkage defects in iron castings has been developed. The model is based on gas pores evolution during solidification. It describes the evolution of gas concentration using mass conservation, and the change in melt pressure due to solidification contraction using Darcy’s equation, with mixture continuity assumption in the liquid and the mushy zone. Gas pores nucleation has been calculated using the partial pressure of gas obtained from Sievert’s law. The growth of porosity has been estimated using an equation based upon the total melt pressure on the pore, concentration and temperature of the gas. The porosity model was calibrated against literature data for microporosity, and then applied to the prediction of shrinkage defects in a ductile iron casting. Comparison between the model predictions and experimental measurements indicated that the porosity model can be applied not only to the prediction of micro-shrinkage but also to that of macro-shrinkage. Existing shrinkage prediction models based upon thermal models, such as Niyama criterion and the modulus of retained melt in mushy regions cannot predict correctly both micro- and macro-shrinkage.

Effects of Changing Size-Weight Parameters on the Temperature Dependent Exothermic Riser Sleeve Properties

Exothermic riser (feeder) sleeves are used to retain the heat in risers and to increase solidification duration. A riser should be enough hot to become the last solidified part in a mould cavity. Thus, risers can feed the other parts to result in sound casting products without cavity like defects. They are particularly preferred for steel and ductile iron casting operations which have high pouring temperatures. Exothermic riser sleeves are a mixture of metallothermic-based exothermic and insulating materials (Al, Fe2O3 and SiO2 etc.) that are manufactured in different sizes and shapes. In the present study, performances of some selected commercial sleeves were evaluated in terms of reaction duration, flammability and temperature change etc. Some thermochemical modelling studies were performed to understand the effect of reactant composition on sleeve performance prior to the performance tests.