Clogging in Continuous Casting Nozzles

Nozzle clogging is a serious productivity and quality problem in continuous casting. This work reviews the causes, effects, and solutions to clogging in continuous casting nozzles. The results of a one-dimensional, steady state analysis of the heat loss from the molten steel stream through the nozzle wall are discussed. The analyses show that steel may freeze within the clog matrix for a relatively small clog buildup. The implication of this result on the mechanism of clog growth and on clogging mitigation techniques is discussed. 1, INTRODUCTION 1.1. Importance of Clogging Clogging in continuous casting nozzles is the buildup of material in the flow passage between the tundish and mold (see Figure 1.). The consequences of clogging include: • Decreased productivity. To compensate for clogging, the flow control device (e.g., slide gate) must be further opened. If the clogging becomes sufficiently severe, the flow control device will no longer be able to compensate and then either a decrease in casting speed or replacement of the nozzle must result. These events reduce the net casting throughput and thereby reduce productivity. • Increased cost. Depending on the casting shop, some portions of the clogged nozzles (e.g. submerged entry nozzle) can be independently replaced during casting. Other clogged portions (e.g., tundish nozzle) can only be replaced by changing tundishes. Several authors report that nozzle clogging, in lieu of tundish lining lifetime, limits the allowable tundish lifetime [1, 2]. For example, Haers et al. reported that clogging reduced the number of heats (290 tons) cast from twelve to six [3]. Therefore nozzle clogging results in additional costs for tundish refurbishment as well as for nozzle replacement