Optimal control of secondary cooling for medium thickness slab continuous casting

Abstract

A software to simulate the solidification, heat transfer and water flowrate distribution in slab continuous casting was developed by establishing a mathematical model for the heat transfer and solidification in medium thickness slab casting. This model was validated by pin shooting and surface temperature measurement experiments. A reasonable target surface control temperature was found by testing the high temperature mechanical properties of Nb bearing ship plate steel, and then the water flowrate of each loop of the secondary cooling zone was determined by the software. The influence of uneven secondary cooling in the slab width direction on the quality of the slab was also investigated, which provided data for the optimisation of the secondary cooling of the slab caster. On the basis of the above research, an optimisation scheme for a secondary cooling system was proposed. Experimental results showed that the quality of the slab was significantly improved after optimisation. The centreline macrosegregation was reduced, and the ratio of equiaxed grains was increased by 3?18%. In addition, the transverse cracking of the slab was almost eliminated. List of symbolsa, b constant (a is 15?8847, and b is 0?011495) c specific heat capacity of steel, J kg 21 uC 21 c s , c l , c sl specific heats of solid steel, liquid steel and steel in the mushy zone, J kg 21 uC 21 c w specific heat capacity of water, J kg 21 uC 21 E elastic modulus, GPa f s solid phase fraction g gravity constant (9?8 N kg 21 ) h heat transfer coefficient, W m 22 uC 21 h w , h n complex heat transfer coefficients on the broad and narrow surfaces of slab, W m 22 uC 21 H the distance between meniscus and force bearing point, m L f latent heat, J kg 21 L m effective length of mould, m L the distance between meniscus and microunit, m q heat flux, W m 22 -q average surface heat flux, W m 22 Q m water flowrate of mould, kg s 21 S eff effective cooling region of mould, m 2 t temperature, uC t b , t w , t e temperatures of strand surface, cooling water and environment, uC T l , T s liquidus and solidus of steel, uC v casting speed, m min 21 W the flux of cooling water, L m 22 s 21 DP ferrostatic pressure, N m 22 DT w temperature difference between inlet and outlet water of mould, uC Dx, Dy mesh size of slab in its width and length directions (8 and 4 mm in this paper) e radiation coefficient (0?8 in this paper) l thermal conductivity coefficient, W m 21 uC 21 l s , l l , l sl thermal conductivity coefficients of solid steel, liquid steel and steel in the mushy zone, W m 21 uC 21 m Poisson's ratio r density of steel, kg m 23 s Stefan-Boltzmann constant (5?67610 28 W m 22 K 24 ) t time, s

Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet

“…Moreover, the transverse water flux distribution can be used as a method to improve the quality of slab by the collocations of nozzles. Wang et al [14] optimized the water flux distribution along slab width direction through the arrangement of spraying nozzles, and the centerline macro-segregation and transverse cracking were improved significantly. Long et al [15] proposed that a uniform solidified shell in the transverse direction was beneficial to mitigating slab central macro-segregation, thanks to the optimized transverse water flux distribution.…”

GPU-Based Model Predictive Control of Nonlinear Parabolic Partial Differential Equations System and Its Application in Continuous Casting

“…In order to overcome the drawbacks of the parameter control method, the water flow rate should be dynamically adjusted owing to the difference between the measured temperature and the target temperature. It is obvious that the simple form of this method is the PI control algorithm [4]- [6]. The credibility and accuracy of the measured temperature are important for this method.…”

Research on the On‐Line Simulation of a Three‐Dimensional Temperature Field Model of Slab Continuous Casting

“…The slab temperature distribution and its variation in the continuous casting process have a very important influence on the slab quality . The surface max temperature difference was as high as 220 °C in the width direction of the slab and the distance from the first solidified region to the final solidified region was very long (2–3 m) at normal casting speed .…”

“…The slab temperature distribution and its variation in the continuous casting process have a very important influence on the slab quality . The surface max temperature difference was as high as 220 °C in the width direction of the slab and the distance from the first solidified region to the final solidified region was very long (2–3 m) at normal casting speed . Because it cannot meet the requirements of on‐line control in terms of calculation efficiency and cannot be used on‐line to distinguish the differences in cooling conditions in the width direction of the slab continuous casting in the secondary cooling zones, at present, the mostly simulation model of on‐line heat transfer and solidification for providing real‐time temperature field data to the slab continuous casting secondary cooling dynamic water model and dynamic soft‐reduction model is only used for determining the cooling difference in the direction of the casting, ignoring the direction of the slab width .…”