Investigation of Nozzle Clogging during Continuous Billet Casting of LCAK Steel
Abstract
One of the potential causes of nozzle clogging during LCAK-steel continuous casting is reoxidation of metal stream in tundish nozzles and submerged entry shrouds (SESs). The possibility of deposits formation from reoxidation stream products follows from existence of driving force of air leaking; it is negative pressure drop inside nozzles and SESs because of ejector effect of stream, restricted by stopper or slide gate. Experimentally the following was investigated: 1) gas permeability of wall of various tundish nozzles and SESs, and gaskets; 2) composition and form of oxide inclusions in metal samples from tundish and of deposit’s crystals. It was found that ordinary alumina-graphite SESs (without glaze) and fiber gaskets are characterized by high gas permeability. Deposit’s crystals composition and form was absolutely different than ones of oxide inclusions from tundish metal samples. Mainly, crystals have a coral or plate-like shapes and the composition based on Al2O3-CaO-Ti2O3 system. The rate of CaO in different parts of deposit varied from 0.5 to 22 wt. pct. and rate of Ti2O3 from 0.5 to 12 wt. pct. On the contrary, metal samples from tundish consisted of calcium aluminates with titanium impurity (Ti2O3 < 3%). It is shown that the presence of ultra equilibrium titanium in deposits also as coral and plate-like shapes of deposit crystals witnesses reoxidation origin of these phases. It is found that two aspects — 1) low air pressure level inside of nozzles and SESs, 2) high gas permeability of nozzles and SESs without glaze — prove possibility of air leakage, even if nozzle and SES junction are blown by argon. Composition and form differences between deposit crystals and oxide inclusions in metal samples from tundish prove that reoxidation of metal stream in nozzles and SESs is one of the main reasons of nozzle and SES clogging.
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