The volumetric shrinkage in both grey cast iron and ductile iron is influenced by several factors, including the composition of the iron, the cooling rate during solidification, and the size and shape of the casting. Therefore, it's challenging to provide an exact range that applies universally. However, I can give you a general idea of the volumetric shrinkage range for these two types of iron.
Grey Cast Iron: Volumetric shrinkage for grey cast iron typically falls within the range of 1.0% to 1.5%. This means that the volume of the casting will reduce by approximately 1.0% to 1.5% during solidification and cooling. Grey cast iron has a flake graphite microstructure, which tends to promote the formation of shrinkage cavities during solidification, contributing to its relatively higher shrinkage.
Ductile Iron (Nodular Cast Iron): Ductile iron, also known as nodular cast iron or spheroidal graphite iron, has a more complex microstructure than grey cast iron, with graphite in the form of nodules rather than flakes. As a result, ductile iron exhibits lower volumetric shrinkage compared to grey cast iron. The volumetric shrinkage for ductile iron typically falls within the range of 0.5% to 1.0%.
Keep in mind that these shrinkage values are approximate and can vary based on specific alloy compositions, casting process parameters, and the geometry of the casting. Manufacturers and foundries often conduct testing and simulations to determine the exact shrinkage characteristics for their specific iron formulations and casting methods.
It's important to account for shrinkage during the design and pattern-making phase of casting to ensure that the final product meets the desired dimensions and specifications. The use of feeding systems and risers (to provide additional molten material during solidification) can help mitigate the effects of shrinkage and prevent defects in the castings.