Clogging in submerged entry nozzles

Casting high quality steel grades requires the use of a submerged entry noz zle (SEN) to prevent oxygen and nitrogen pick-up and to achieve favourable steel flow conditions in the mould. Clogging of the SEN leads to instabilit y of the casting operation as well as to a decrease in slab quality. To und erstand the interactions between liquid steel and the SEN, 156 nozzles from the Sidmar steel plant were investigated with respect to the amount of clo gging. A linear relation between the clogging volume and the clogging weight was o bserved. This indicates that the clogging material's density remains consta nt during the clogging process for the different steel grades. A distinct r elationship was also found between the amount of clogging and the cast stee l weight. No relation between the amount of clogging and the superheating o f the steel nor the steel flow rate was noticed, however. it was also concl uded that for Al killed steels the high Mn (> 3000 ppm) and high C (> 500 p pm) grades causeless clogging than Al killed steel grades with low Mn conte nt (< 3000 ppm) and that Al/Si killed steel grades cause less clogging when compared to Al killed steel grades. When comparing these different steel g rades with respect to their total oxygen concentration in the ladle, it app ears that steel grades, which have a low total oxygen concentration, cause less clogging in the SEN. Based on these observations three combinations SE N/steel grade were selected for further analysis with electron microscopy.