Review: The “butterfly effect” in continuous casting

Abstract

The continuous casting (CC) mould may appear very peaceful when viewed from above, but the powder bed hides relentless fluctuations in the following phenomena: metal flow, thermal gradients, chemical reactions and multiple phase transformations. When observed separately, some of these phenomena seem to have a 'simple behaviour', which may appear easy to control through the main casting parameters (e.g. casting speed, pouring temperature and powder type) and associated control systems (e.g. mould level control, automatic powder feeding and mould oscillation). However, when combined, these phenomena exhibit periodic fluctuations in behaviour, which is both difficult to predict and control. For instance, the combination of casting speed, submerged entry nozzle design and slab size can cause the metal flow pattern to shift from double roll to single roll and back, which can cause unstable fluctuations in metal level, standing waves, etc. In this respect, the CC process closely resembles a meteorological system where both variations and local fluctuations in temperature, humidity, pressure, etc., can result in effects that are difficult to predict in the long term. This is equivalent to the famous Lorenz premise: 'Does the flap of a butterfly's wings in Brazil set off a tornado in Texas?' In this paper, we give some examples of the 'butterfly effect' in CC discussed below by using a mathematical model able to predict the slab solidification inside the mould in which various factors affecting the process stability are analysed and the probable sources of fluctuation are identified.

A Novel Investigation of Initial Solidified Shell Thickness of Continuously Cast Slab Based on Solidification Structure

“…Compared with the microstructure in the other positions, the dendrite arms are much coarser near the oscillation marks as shown in Figure c1. Experiment studies concerned about this phenomenon have been carried out to point that the small temperature gradient in the oscillation marks will cause weaker heat transfer, which is good for the coarsening and the development of the dendrite arms …”

Knowledge discovery and predictive accuracy comparison of different classification algorithms for mould level fluctuation phenomenon in thin slab caster

“…Understanding time variant shape of the top surface gives us better insight about the mould level fluctuation phenomenon. Lee et al (2012) compared the metal level fluctuations phenomenon in the continuous casting process with the "butterfly effect", as mould level fluctuations coupled with heat transfer process can cause oscillation marks, cracks, tears or even breakouts. They also emphasis on the limitation of the numerical models due to the inherent chaotic conditions inside the mould.…”

Time-resolved synchrotron tomographic quantification of deformation-induced flow in a semi-solid equiaxed dendritic Al–Cu alloy

“…Understanding liquid migration through a deforming semi-solid medium is critical for a wide range of processes from metal casting [1,2] to volcanology [3][4][5]: during casting, deformation of semi-solid alloys can influence liquid flow, resulting in macrosegregation, which can degrade the mechanical properties of the final product [2,[6][7][8][9][10]; semi-solid magma is deformed by convection and/or tectonic plate spreading, inducing melt migration and segregation [3,4,11].…”