Examination of nozzle clogging in continuous casting

Formation of deposits inside the submerged entry nozzles used in continuous casting of especially low-silicon Al-killed mild steels may often cause nozzle clogging and casting disorder. Technological experience has shown that the application of Ca-treatment before casting usually eliminates this phenomenon. In order to understand deposit formation and the way it can be avoided, we have carried out detailed mineralogical analyses of the deposits formed on the inner and outer surfaces of the nozzles by different techniques. Results obtained from deposits formed during the casting of only Al-killed and subsequently Ca-treated steels show that the results obtained from deposits formed during the casting of only Al-killed and subsequently Ca-treated steels show that the alumina inclusions carried to the wall of the nozzle form the matrix of the dangerous deposits. Application of Ca-treatment resulted in mostly liquid aluminates compounds and almost negligible deposit formation. The outer surface of the nozzles however showed similar deposit formation because of possible reoxidation of dissolved aluminium.