Abstract
Eutectic solidification is accompanied by an increase in volume due to graphite crystallization. The swell or the increase of mold cavity due to its expansion is often observed in ductile iron castings. To investigate the relation between the value of iron expansion and the external restraining forces in effect, cylidrical test castings, 60 mmφ × 120 mm in size with 5 mm thickness, were poured in various rigid molds. Increasing the rigidity of the mold decreases the amount of expansion during eutectic solidification, but it was difficult to supress the amount defined in this test casting to 0.4% even with the most rigid mold in general use. The movement of the external wall of mold during eutectic solidification is very small, therefore adding the external restraining forces to the external wall of mold dose not cause a considerable decrease in the amount of expansion. The expanding iron exerts pressure on the surrounding mold and reaction forces from the mold determine the expansion of the cast iron. The expansion rate of the cast iron varied between 0.4% and 0.8%, and the expansion pressure varied between 2.5 kg/cm2 and 0.5 kg/cm2 in the usual molds.
