Optimization of Oscillation Parameters in Continuous Casting Process of Steel Manufacturing: Genetic Algorithms versus Differential Evolution

Abstract

Continuous casting is a critical step in the steel manufacturing process where molten metal is solidified in the form of slabs of rectangular cross-section. Minor variations in this step can impact the production process widely – from excellent product quality to breakdown in the production chain. In continuous casting the liquid steel from a ladle is first poured into a buffer vessel called a tundish, from where it flows continuously through a bifurcated submerged entry nozzle into a water-cooled copper mould. This mould is about a meter in length; with sectional width about one-and-half meters and thickness about two hundred millimeters. Water is circulated through pipes embedded in the mould walls to extract heat from the liquid steel. Consequently, a thin solidified steel shell develops next to the mould inner walls while inside this shell the steel remains liquid. The shell grows in thickness internally even as it is continuously withdrawn from the mould on rollers and further cooled using water sprays. Finally, the completely solidified slab of requir ed length is cut from the continuously cast ‘strand’. The schematic representation of cont inuous casting is shown in fig 1, see also (World Steel University, 2009). The continuous casting process itself is facilitated by two interlinked sub-processes, namely, mold oscillation and lubricant addition. These essentially seek to neutralize two major and intrinsic problems associated with continuous casting – sticking of the formative steel shell to the internal walls of the mould, and non-uniform development of shell across the strand perimeter due to uneven heat transfer. The mold is made to oscillate along its longitudinal axis with an amplitude less than 10 mm and frequency between 50 and 250 cycles per minute (cpm). The oscillation directly helps in detaching the solidified shell from the mould wall (like a mild AC current ‘disengages’ a human finger coming in touch with a live wire), and indirectly enables the lubricant placed at the meniscus of the strand to penetrate uniformly further down into the small gap between the shell and mould. Lubricant in the form of solid powder is po ured from the top onto the meniscus where it melts in contact with the hot material. The liquid ‘lubricant’ then penetrates into the gap between strand and mould. Both upward and downward movements in the oscillation cycle Open Access Database www.intechweb.org