At present, in the production of nodular iron castings, there are often shrinkage porosity and shrinkage cavity, and there are nearly 24 kinds of shrinkage porosity and shrinkage cavity defects. Shrinkage porosity and shrinkage cavity will seriously affect the mechanical properties of castings, and fracture will occur in serious cases, resulting in heavy losses. Common shrinkage defects:
Exposed shrinkage porosity, shrinkage cavity – shrinkage porosity, shrinkage cavity at gate position, leakage shrinkage porosity, and shrinkage porosity at outlet position.
Internal shrinkage porosity and shrinkage cavity – shrinkage porosity and shrinkage cavity at the corner, shrinkage porosity and shrinkage cavity at the hot joint, shrinkage porosity and shrinkage cavity at the central axis, spongy shrinkage porosity and dispersed micro shrinkage porosity.
Nodular cast iron, like other casting alloys, experiences shrinkage during liquid cooling and solidification, but it is different from other casting alloys.
Ductile iron also experienced an expansion period during solidification, specifically three shrinkage and one expansion. Three shrinkage: liquid shrinkage, solidification shrinkage and solid shrinkage. 1 expansion: graphitization expansion. Therefore, the solidification process of nodular cast iron is the result of dynamic superposition of shrinkage and expansion.