Inoculation process in gray cast iron and graphite expansion

Abstract

The manufacturing of mill roller shells in gray cast iron demands rigorous control to ensure the integrity of the castings, wherein inoculation emerges as a critical metallurgical step. During solidification, inherent volumetric changes can lead to casting defects, most notably secondary shrinkage porosity. Before the experimental program, the rejection rate due to secondary shrinkage after riser cutting was 8% of the inspected castings; however, these parts were repurposed for other customers who specified a shorter length. This research analyzed the impact of inoculation process variables on graphite expansion during solidification, focusing on the reduction of shrinkage in mill roller shells. The experimental methodology evaluated the formation of primary and secondary shrinkage. After optimizing the conditions (experiment E), the occurrence of this defect was reduced to 0% in the validated mill roller shells (weighing between 3 and 30 tons), while maintaining the mechanical properties within the specification. This successful elimination of defects post-riser removal provides a robust methodology for predicting and controlling the process variables governing their formation.