Research On Control Of Melt Steel Level, Rolling Force Model And Process Optimization For Twin-Roll Steel Strip Casting

In recent years, twin-roll casting process of steel strip, as a new technology representing the development direction of steel industry, attracts the world-wide attention of the steel researchers. Improvement is still in great need to realize the industrial application. This technology has been investigated for many years in China. However, large gaps are existed between foreign and domestic researches. In the twin-roll casting process, solidification of molten metal is completed rapidly and the process window is in a narrow range. Small variation of the process parameters lead to severe defects of the casting strip, even the stop of work roll and leak of molten steel. Therefore, the measurement and control of process parameters are required to stabilize the casting process, to produce casting strip with good quality and to realize the industrial application. In the present paper, the monitoring system, melt steel level control, rolling force model and processing parameters optimization of twin-roll steel strip casting process are investigated, which provide theoretically and practically basis for establishment of process control system.The measuring methods of process parameters were first analyzed and investigated. The monitoring system of twin-roll strip casting was established by the employment of Siemens IPC and related instruments. The experimental data was analyzed systematically, which provide accurate database for study of twin-roll steel strip casting. Some chief original work and conclusions are as follows.1. The model of controlled device was established based on the analysis of interfering factors and difficulties of melt steel level system. Major and minor loop PID control was investigated and differential first PID control has been employed at minor loop to reduce frequent movement of stopper. In the major loop the fuzzy self-adaptive PID control strategy was proposed. Simulation results indicate the rapid response and robustness of the system.2. According to the experiment results, the relationship between casting speed, location and heat transfer coefficient in different region were established using the inverse method combining the heat balance calculation and simulation. Based on three dimensional finite element coupled analysis theory, a numerical simulation for flow and temperature fields during the solidification of twin-roll steel strip process was conducted. The effects of the pouring temperature, casting speed, liquid surface height in molten pool on the flow field and temperature field have been obtained to provide theoretical basis for the determination of the processing parameters. And a strategy of position of kisspoint was proposed.3. Based on analysis of solidification and deformaion mechanism in the molten pool, twin-roll casting can be divided into two zones by kiss point position. Navier-Stokes equation in fluid mechanics and stream function were introduced to analyze the rheological properities of liquid zone, mushy zone and deduce the analytic equation of average unit compression stress distribution, In the solid zone, the traditional hot rolling model was still used. In calculation of kiss point position, Bayesian regularization was applied to the training of feed forward neural networks to avoid "over-fitting" and improve the generalization ability. The models mentioned above were applied to the calculation of rolling force, which has exhibited high precision.4. In order to improve the flat, gage control precision and surface quality of casting strip, optimization of processing parameters based on kiss point position calculation model, was conducted using the particle swarm optimization method under the condition that the chemical composition and process constraints were set. The result shows that the optimized results were in good agreements with experimental one.