抄録
The optimum amount of coal dust addition to green sand mixture to prevent pinhole formation in spheroidal graphite iron castings and the mechanism of pinhole prevention were studied using cup-shaped test castings. Green sand was mixed with Simpson's muller. A jolt and squeeze type molding machine was used. The molten iron nodularized by the converter process was poured. Additions of coal dust 3% or more remarkably reduce pinhole formation. Pouring temperature, thickness of specimen and moisture of mold sand have some effects on pinhole formation, but additions of coal dust 3% or more weaken these effects. The volatile matter in the coal dust is greatly responsible for eliminating the pinholes. Pinhole prevention depends not only on the mass but also the kind of gases generated.
