Abstract
Nozzle clogging of low carbon micro-alloyed Al killed steel is a crucial castability problem at steelmaking shop. The nozzle clogging index (NCI) was earlier developed by R&D and implemented in the control room of the caster. This parameter gives the clogging status of submerged entry nozzle. In the present work, the root cause for higher NCI was identified by developing a correlation with the upstream parameters. A correction parameter was applied to avoid some misleading NCI values (encountered during the process). Primarily wide variations in bath killing practices by Al bar addition and higher lime addition at TAP were found to have significant impact on NCI during casting. Subsequently, higher Al wire injection at on line purging station and relatively lower lime addition at ladle furnace were also found to have higher NCI. Based on the statistical analysis, the optimum ranges of the upstream parameters were suggested to conduct a plant trial for getting lower NCI. Overall the NCI was reduced from an average value of 0.66 (bad heats) to 0.26 (good heats) for a complete trial casting sequence.
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