Formation mechanism and prevention and control of main defects in nodular cast iron intake cylinder casting

(1) The elements with high content of C, O, Al, Si and some other alloy elements are found in the defect position of the inlet cylinder casting surface detected by Mt. The results show that the main defect is the primary oxide slag inclusion formed by the aggregation of metal oxides such as SiO2, MgO and Al2O3.

(2) The open bottom return gating system is superior to the closed gap gating system in slag retaining and slag entrapment prevention. The open gating system is preferred for heavy heavy heavy heavy ductile iron castings with large cross-section. On the contrary, closed gating system is more suitable for thin-walled small castings. The application of molten iron filtration technology in the gating system can effectively improve the slag avoiding ability of the gating system.

(3) The scheme of segmented ladder type slag avoidance gating system with reasonable component matching can effectively prevent slag inclusion defects on the surface of intake cylinder casting, and has a good effect on improving the surface quality of nodular cast iron castings.

(4) When the content of C in Heavy Ductile iron is lower than 3.5wt.%, serious shrinkage defects will appear at the top of some castings. The liquid shrinkage can be reduced by increasing the C content. The interference elements such as Ti, Al and P can be controlled by optimizing the melting process, which can also reduce the shrinkage porosity tendency.

(5) In order to realize the dense structure of the casting body, we should not only use the riser for liquid feeding, but also make full use of its own graphitization expansion for self feeding; we should not only feed the castings sequentially from top to bottom, but also realize the balanced solidification of the casting as a whole by using cold iron.

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