Online Prediction Model For The Strain Of Continuous Casting Slab

During the process of slab continuous casting, the comprehensive strain at the front of the solidification exceeding the critical strain of slab gives the rise to the internal cracks. Based on a domestic slab caster with the cross section of250mm×1500mm, an online prediction model for the strain of continuous casting slab was established and studied in the dissertation.Firstly, the formula for bulge strain, straightening strain, misalign strain and reduction strain which affect the comprehensive strain were derived by using the simple beam model based on elastic theory and the corresponding estimating formula, modified formula for bulge strain and the estimating formula for thermal stress were also obtained.Secondly, thermal stress and reduction strain of continuous casting slab were simulated. With the help of the finite element software named Marc, a two-dimensional temperature field model for continuous casting slab was established. Based on the former model, the models for thermal stress and reduction strain which are on the basis of the heat-elastic-plastic theory are also built. The thermal stress distribution along the casting line and the reduction strain under different solid phase and reduction amount were obtained through the thermo-mechanical coupling calculation. The corresponding modified formula was derived through the regression analysis of the results, which can be written as follows: where σ is for the thermal stress of solidified shell surface, MPa.0.1959for correction factor of temperature distribution along the direction of slab thickness for Q235steel, Ts for solidus temperature of steel,℃, TB for the surface temperature of solidified shell,℃, and a、E and v for the contraction coefficient, elastic modulus and poisson’s ratio of the slab respectively. where εD is for the reduction strain.0.4217for the correction factor of material properties of Q235slab,0.0816for the correction factor of the factor0.4217, S for shell thickness under the pressure roller, cm, L for the reduction roller distance along the center line of slab thickness, cm, and δa for the roller reduction amount, cm.Finally, the online prediction model for the strain of continuous casting slab which is of great significance to analyzing the reason for internal cracks and prevention was developed, and the model can calculate the real-time stress and strain along the casting line and display the results in the form of chart. Q235steel was simulated under different conditions by using the developed model. It is shown from the results that the bulge strain takes the largest proportion of comprehensive strain and it increases at first and then decreases along the casting line. The misalignment strain, straightening strain and reduction strain were also the important components of comprehensive strain. During the practical continuous casting process, some measures for the prevention of internal cracks can be taken to reduce the comprehensive strain, such as controlling the casting speed to a reasonable extent, reducing the roll distance, taking continuous straightening, improving the accuracy of the arc, reasonably distributing the roller reduction amount, and prevent from taking soft reduction in the straightening zone.The developed model was compiled by VC++6.0. Because of the portability of the program itself, it can be easily transplanted to the online application platform in field to realize the online prediction application of the developed model.