Macroscopic Mechanistic Modeling for the Prediction of Mold Slag Exposure in a Continuous Casting Mold

Abstract

Argon gas injection into a continuous casting mold facilitates many factors related to smooth and long casting sequences by reducing nozzle clogging, improvements in steel cleanliness by inclusion floatation, etc. However, an unoptimized gas flow rate may deteriorate the cast slab quality through mold slag exposure, slag entrapment into the solidifying shell, etc. Formation of mold slag open eyes (MSOE) removes the protective slag layer to invite the issue of liquid steel reoxidation. Different MSOE formations were observed at varying flow conditions through physical modeling experiments. Total MSOE area helps in determining the extent of reoxidation. This study aims to predict the dimensionless MSOE area by developing a macroscopic mechanistic model which results in a model equation in terms of a “densimetric Froude number (Fr_D,m)” and two unknown arbitrary constants. To close this equation, Fr_D,m is obtained by evaluating its unknown characteristic, i.e., mold plume velocity (U_mp). It was calculated at different gas flow rates (Q_g) using shadow-imaging technique applied on a 1:7 scale water model. Average velocity of bubbles (approximated as U_mp) in plume was estimated by individual bubble tracking using an ImageJ macro validated against the manually calculated U_mp. Then, Fr_D,m was calculated using both manual and automatic U_mp values. In separate water modeling experiments, total MSOE areas at same Q_g values were obtained. Then, dimensionless MSOE area was calculated by dividing this total MSOE area by total plume area. Dimensionless area was correlated with manual and automatic Fr_D,m. This correlation is compared with the model equation, and arbitrary constants were obtained to close the model equation. Finally, a zone-wise mean bubble size analysis was introduced to strengthen the assumption regarding the probable location of MSOE.

Appendix

ImageJ macro code for automatic measurement of bubble velocity

filepath=File.openDialog("Select a File");

dir=File.getParent(filepath);

open(filepath);

name = File.nameWithoutExtension;

run("8-bit");

setAutoThreshold("IsoData");

//run("Threshold...");

setThreshold(0, 139);

//setThreshold(0, 139);

setOption("BlackBackground", false);

run("Convert to Mask", "method=IsoData background=Light");

run("Fill Holes", "stack");

run("Watershed", "stack");

trackpara = "minimum=50 maximum=50000 maximum_=100 minimum_=1 save display show show_0 show_1 save=" + dir + File.separator + name+".csv";

run("MTrack2 ", trackpara);