Prediction of Periodic Centerline Porosity and Pulse Marks by CFD and Experimentation for Continuously Cast Copper

For 8 mm OFCu rod, the formation of pulse mark defects on the exterior of the rod and periodic macroporosity (> 1 mm diameter pores) occurring internally along the centerline of the castings have been observed and noted to limit the maximum attainable withdrawal rates (~ 4 m/s). Conversely, the same casting defects have been witnessed for slower rates; therefore, investigations were performed to investigate how the casting motions (withdrawal, dwell, and pushback) formed these defects and could be prevented. Characterization of the physical properties of the cast rods by tensile testing and analysis by optical and computed tomography (CT) imaging revealed correlations to the outer pitch length marks on the rods and confirmed relationships to casting motions and pitch lengths evaluated from metallurgical equations. Computational fluid dynamic modeling using Ansys Fluent v.R1 was applied to quantify the localized formation and dissipation of periodic hotspots internally within the die for the different motions. A mechanism leading to periodic porosity was identified, which was irrespective of the average casting withdrawal rates and enabled prediction of the location, frequency, and magnitude of the macroporosity defect.