ANALYSIS OF INTERMIXING DURING LADLE CHANGEOVER IN CONTINUOUS CASTING PROCESS

Abstract

The dominance of the continuous casting method over conventional casting in primary metal production has been recognized for over a century. The advantages which include a substantial increase in yield, better quality, more uniform production, energy saving and higher productivity made the metallurgical industry, and the entire world of the metal users explore methods to optimize the processes parameters involved in continuous casting. Ladle change over in continuous casting steelmaking process leads to change in grade of the steel coming out through the tundish. The main function of tundish has been as a distributor or buffer vessel in continuous casting process. More recently it has been found that apart from serving as a buffer between ladle and mold, quality of steel is greatly governed by the tundish owing to its metallurgical capabilities in terms of mixing, inclusion removal, stratification etc. The intermixing phenomenon takes place when new composition (grade) of steel is made to flow in tundish from the new ladle after the old ladle (carrying old grade steel) is emptied into it. The intermixed composition of steel has less market value as compared to specified grade specification. The introduction of the appropriate size and precise location of the flow control devices help to modify the flow pattern and minimization of intermixed grade. An experimental set up has been fabricated using Perspex glass. Two different shapes of tundishes have been fabricated. The experiments were conducted for bare tundish as well as tundish with flow modifiers. Numerical investigation of grade change in two strand slab caster tundish during ladle changeover in continuous casting steelmaking process has been carried out using educational version of CFD software PHOENICS. Navier stokes equation were solved with the use of standard k-c model to find the steady state velocity field inside the tundish. Further tracer dispersion study was carried out (step input) to find the F-curve from which the intermixed amount were calculated. Intermixed amount was first found out for bare tundish. Further, Flow modifiers were introduced to see its effect on the intermixed amount as compared to that from bare tundish. Further different positions and height of dams are considered in order to investigate its influence on the intermixed grade. The effect of different shape of tundishes on intermixing length was evaluated for different grade specifications.