As shown in the figure, the shrinkage casting defects produced by automobile steering knuckle during actual production are mostly distributed on the main hot joint. Shrinkage porosity not only affects the mechanical properties of ductile iron castings, but also affects product costs, including process yield and production efficiency. The feeding effect of ductile iron castings is directly related to the material and structure of ductile iron castings. The commonly used methods to eliminate or reduce shrinkage casting defects generally include riser feeding, chill quenching, local accelerated cooling of core sand and smelting and pouring process adjustment and control. Because there are many hot spots in the steering knuckle of the automobile and the shape is complex, if the riser is used for feeding, the mold design is more difficult and the temperature field calculation is complex; If the cold iron is used, it will increase the difficulty of modeling, and if the cold iron is used alone, it often makes the shrinkage loose and moving position, which cannot be completely eliminated.
Therefore, if there is only small shrinkage porosity or micro shrinkage porosity in ductile iron castings, it can be solved by adjusting and controlling the melting and pouring process. The adjustment and control of smelting and pouring process generally includes two aspects: control of chemical composition and strengthening of inoculation.