重力と膨張圧の有効時期を考慮した球状黒鉛鋳鉄の押湯方案 A Riser System with Advantage of Gravity and Metal Expanding Pressure for Casting of Spheroidal Graphite Cast Iron

  Experiments were conducted to study metal feeding effect in spheroidal graphite cast iron by means of gating system which compensates the shrinkage of liquid metal in a mold cavity. The metal feeding effect is expected when the sprue modulus (half of sprue radius) and runner modulus are larger than 2/3 times of casting modulus, where modulus is defined as ratio of volume to surface area. Discussions are presented on the formation process of shrinkage porocity. And an effective riser system is also proposed according to the hypothesis induced from the above discussions. This is an ideal global-type riser which utilizes expanding pressure of metal during the eutectic solidification process in the riser to eliminate porosities in casting. Modulus ratio of riser to casting varies according to the shape of casting. For instance, the modulus ratio for a ordinary casting is 1.2∼1.35, but that for a wide plate-type casting is 1.5∼1.8.