In the casting process of ductile iron castings, the liquid metal has high viscosity and poor mold filling ability, which is prone to oxidation and secondary slagging, and it is very easy to produce shrinkage porosity and shrinkage defects. The pouring temperature has a great influence on the fluidity of liquid metal.
In addition, graphite will be precipitated during solidification of ductile iron castings, which is easy to cause volume expansion. According to the actual production data of some factories, it is found that about 12% ~ 20% of the defects of ductile iron castings are more or less related to the gating system. Therefore, the correct design of a reasonable gating system is very important to improve the quality and productivity of ductile iron castings. For ductile iron castings gating system, the following functions are required:
① It can control the flow rate of molten iron and prevent the occurrence of cold insulation or insufficient pouring defects;
② In the solidification stage of ductile iron castings, the temperature distribution is controlled, the eutectic expansion pressure is used, and the feeding effect is fully played with the riser;
③ Ensure the stable flow of molten iron, reduce the involvement of gas and avoid the oxidation of molten iron;
④ Filter out inclusions and slag to prevent slag inclusion defects on ductile iron castings when they rush into the mold.