Abstract
The authors investigated various conditions which produced such foundry defects as scab or rattail; these defects occurred when molten cast iron was poured into a natural sand mould.
The conclusions from this study were as follows :
1. The scab which occurred in the natural sand mould was caused by two factors : the expansion of the foundry sand on the mould surface and the physical load which broke up the mould surface.
2. The scab and rattail were apt to occur as long as the internal stress, which was caused by the thermal expansion of sand, was concentrated on the surface of the sand mould.
3. The more the moisture in mould and the higher the pouring temperature become, the more easily the scab in the natural sand mould forms.
4. It seems that moisture in the sand mould has an influence upon the permiability and the evaporating speed of the moisture upon pouring the molten metal into the mould, and then it has an important effect on the formation of scab.
