Nodular cast iron is a kind of cast iron whose graphite is spherical after treating molten iron with spheroidizing agent. Compared with gray cast iron, it significantly improves the plasticity and toughness of cast iron. Its comprehensive properties are close to that of steel, but its economic benefit is significantly higher than that of steel. The so-called “replacing steel with iron” mainly refers to nodular cast iron. The casting material in this paper is nodular cast iron qt500.7. Nodular cast iron is easy to produce dispersed shrinkage porosity due to its paste solidification characteristics. Nodular cast iron has large eutectic expansion force. If the mold stiffness is not enough, it is easy to produce defects of improper size. At the same time, shrinkage porosity is still easy to exist in the casting.
During spheroidizing treatment of nodular cast iron, the temperature of molten iron decreases more in a short time, resulting in poor fluidity of molten iron. In addition, magnesium, rare earth and other elements in the spheroidizing agent are easy to form slag inclusions in the ladle and gating system. If these slag inclusions enter the mold cavity, they are easy to cause defects such as inclusions and pinholes. These defects are the main problems to be solved in the production of nodular cast iron, Based on these characteristics, nodular cast iron has higher requirements for pouring process than gray cast iron.
The gating and riser system in the casting process of nodular cast iron blank is designed, and the tooling of the gating and riser system is modeled. Based on the structural characteristics of castings and the design theory of gating and riser, the gating system and feeding system are preliminarily formulated. This process is the basis of CAD modeling of pouring process tooling, and prepares for subsequent CAE analysis and cam NC machining.