Selection of riser position for ductile iron castings

The design of feeding system is the key content of this paper. We discussed the main factors that affect the shrinkage porosity of casting, which are hot metal quality, mold strength and mold technology. The quality of molten iron is greatly affected by the quality of raw materials, the quality of molten iron treatment and smelting process. In actual production, it is unrealistic to control the quality standard of molten iron within a very small process window. Similarly, the process parameters of molding sand are also very complex, and the adjustment of molding sand has hysteresis. In the foundry, the stability of molding sand system is the first priority, and it is generally not targeted Adjust molding sand control for defects of individual products, unless systematic problems (batch defects) are solved.

The most reliable solution in mass production is to design a mold process with strong adaptability. Good mold technology can relax the control range of process parameters of molten iron and mold, reduce the instability in the process and reduce the risk of defective parts.

The riser should be placed at the largest hot spot of the part as far as possible, so as to directly feed the thick part in the liquid shrinkage stage. At the same time, the hot spot of the part can be regarded as the extension of the riser to the inner part of the casting, which shortens the feeding distance to other parts of the part and improves the feeding efficiency of the system.

Some people in the industry also think that the riser can not be set at the largest hot spot of the part, because the riser is connected with the casting through the riser neck. In addition, the heat convection and heat flux effect of the riser neck will form the accumulation of hot spots. The riser not only can not play a role in feeding, but will hinder the self feeding function of the parts in the later stage of solidification, resulting in shrinkage and porosity around the riser neck. However, ZHY casting believes that the above problems can be avoided as long as the size of riser neck is controlled, that is, the time of riser neck closure. The solidification characteristic of ductile iron is “paste solidification”, but the feeding principle should follow the principle of sequential solidification, and the two are not contradictory.

Through the analysis of the hot spot position, it can be determined that the brake caliper needs to set two feeding risers, which are located at the maximum hot spot on both sides.