Abstract
The effect of the mechanical properties of the moisture condensed layer on scabbing were investigated, and the relation of the green and hot properties of the sand to scabbing was also examined. In order to determine the fundamental causes of scabbing, the mechanism of scab formation was theoretically discussed based on experimental data. No distinct relation between the scabbing tendency and the sand properties such as compressive strength, and deformation at room temperature and high temperature, could be found. The thermal expansion and expansion force of the dried sand layer in the mold, assumed to be main factors of scabbing, were estimated based on the mechanism of the scab formation, and the correlations between these values and the scabbing tendency were examined. According to these results, the mold fracture, which causes the scab defect, occures at the moisture condensed layer when the thermal expansion of the dried sand layer exceeds the formation of the moisture condensed layer. The scabbing may be reduced by increasing the deformation of the moisture condensed layer and the modulus of green deformation, and by reducing the shock heat expansion and the modulus of hot deformation.
