Process Simulation And Optimization For Secondary Cooling In Continuous Slab Casting

Secondary cooling control technology is the key factor for stabilizing and enhancing slab quality in continuous casting process. Accurate description of heat transfer/solidification process and real-time and reasonable control of secondary cooling are the basic requirements for high efficient continuous casting. Therefore, the researches aiming at more accurate understanding the process such as methodologies of numerical calculation about slab secondary cooling, technology optimization and process detection have momentous theoretical significances and practical values.Firstly, taking continuous casting slab as research object, the paper establishes slab heat transfer/solidification calculation model and develops the secondary cooling numerical simulation and visualization system for continuous casting slab using OpenGL based on the characters of slab heat transfer and solidification. By simulating the slab solidification process under different technological parameters, the slab cooling process is presented directly and clearly to gain detailed information on slab heat transfer/solidification state. The development and application of numerical simulation system provide reliable approach for control and optimization of secondary cooling water volume.Secondly, according to the target temperature of steel and metallurgy criterion, the secondary cooling technology is designed based on roller configuration and distribution of the heavy plate caster in a domestic steel plant. On the ground of the development of secondary cooling numerical simulation and visualization system, the simulation analysis of slab solidification process is conducted, and the rationality of technology system is validated. The response characteristics of solidification process influenced by technological parameters are discussed, and the solidification and heat transfer behaviors of three typical steel grades is compared and investigated.Thirdly, considering the importance of boundary conditions for slab solidification and heat transfer calculation, and basing on the inverse problem optimization theory, the secondary cooling heat transfer coefficients calculation model by means of inverse problem with temperature measurement is developed. According to the measured data of slab surface temperature, nonlinear estimation method is utilized to inverse calculate the heat transfer coefficients of secondary cooling zones, and slab surface temperature detection and pin-shooting experiment are applied to verify the accuracy of the developed model.Further, by aiming at overall consideration of metallurgy criterion, secondary cooling water volume and slab surface temperature, the paper proposed a secondary cooling technology optimization method based on modified Particle Swarm Optimization (PSO) algorithm by introducing the mutation operator. In the algorithm, the cost function is designed by co-considering the metallurgy criterions of target temperature, temperature restrictions, temperature increasing/decreasing rate, bulging control and water volume. Selecting the heavy plate of alloy medium carbon steel as research object, three approaches including PSO, CFPSO and MOPSO algorithm are used to analyze and discuss the optimized secondary cooling water volume, slab surface temperature and algorithm efficiency.Finally, the paper researches the online detection method of slab solidification process, and a new method named vibration method for detecting slab solid fraction and solidification process is presented. Its principle is by imposing a periodical forced vibration with certain frequency and amplitude on slab surface, the solidification process could be detected real-timely according to the discrepancy patterns of the feedback signals of exciting force and forced vibration displacement due to the different damping attenuation of vibration in liquid and solid phase transfer process. Therefore, the purpose of accurate prediction of slab liquid-solid fraction and the final solidifying end position could be accomplished accordingly. On the ground of theoretical derivation, the paper establishes the model for online detecting solid fraction. The physical simulating experiments, finite element calculation model of liquid-solid coupling forced vibration are developed in order to simulate and verify the results of dynamic response. And the suggestion for applying the method to a plant is proposed. The results of this research provide theoretical foundation for the detection method of online direct measurement of slab solidification process.