| The important purpose of run-out table cooling is to improve final microstructure state and properties of steel products. Based on the optimization of conventional run-out table cooling (laminar cooling) system and the development of new generation run-out table cooling (ultra fast cooling+laminar cooling) system, theory models such as heat transfer mechanism models, temperature field analytical models and so on, were systematically researched. Characteristics of strip temperature variation under various cooling strategies were analyzed. The effect of rolling speed on run-out table cooling was studied and feedforward control algorithm was designed for non-constant speed rolling. Based on cooling processes, cooling path control strategy was developed and applied to industrial production. In order to improve control precision of run-out table cooling, feedback control based on Smith predictor and long-term self-learning based on CBR (Case-Based Reasoning) were used. On the basis of the above studies, run-out table cooling control system was developed and applied to practical production, and achieved good control effect. The main research contents are as follows:(1) Theoretical models of run-out table cooling were researched deeply. During air cooling, strip dissipates heat to the ambient by radiation and convection. Based on the law of Stephan-Boltzmann, the calculation formula of equivalent heat transfer coefficient of radiation heat transfer (radiation heat transfer coefficient) was derived. The convective heat transfer process during air cooling can be considered as a process that the air sweeps over an isothermal plate, and the calculation formula of convection heat transfer coefficient was obtained based on the boundary layer theory. Based on jet impingement heat transfer theory and boiling heat transfer theory, cooling mechanisms of ultra fast cooling and laminar cooling were analyzed and studied deeply. According to the conduction differential equation, initial and boundary conditions during run-out table cooling, strip temperature field was analyzed by finite difference method. Characteristics of strip temperature variation under laminar cooling, ultra fast cooling, and compound cooling process were studied. The effect of spray header arrangement on the strip temperature variation was analyzed, and characteristics of strip temperature variation under various cooling strategies were obtained.(2) Rolling speed and its effect on run-out table cooling were studied, and high-precision feedforward control algorithm was designed. In order to ensure finishing delivery temperature and increase production, acceleration is usually adopted during rolling, which makes it difficult for run-out table cooling control. In order to guarantee the control accuracy of run-out table cooling, the strip was divided into many segments and precise setup and tracking were done for every segment. According to TVD (Time-Velocity-Distance) curve, running speed and time of every segment under each cooling zone (cooling bank) could be obtained, and dynamic setup was done for the segment which was about to enter the cooling zone, using measured finishing delivery temperature, thickness and so on. If there was a certain deviation between measured speed and predicted speed, TVD curve would be corrected by the measured speed, and then segment speed under every cooling zone would be corrected. Based on the corrected speed, dynamic setup would be done for the segment which was about to enter the cooling zone. Meanwhile, the re-calculation setup would be done for the segments under the cooling zone, using the speed calculated from the corrected TVD curve, which compensated the effect of speed variation on run-out table cooling control.(3) Cooling path control strategy based on ultra fast cooling was developed and applied to practical production. According to cooling process, cooling path control is usually necessary for high additional value products, and finish cooling temperature and cooling rate of every cooling stage are the control targets. Cooling path control strategy was developed and applied to dual phase steel industrial trial, which provides a strong technical means for the development of new steel grades and optimization of cooling processes.(4) Feedback control based on Smith predictor was used in order to improve control precision of run-out table cooling. Run-out table cooling system is a pure delay system, and feedback control based on PID controller is difficult to achieve good effect. The explicit expression of feedback control algorithm based on Smith predictor was derived, and applied to production. When the measured coiling temperature deviated from the target value, it could be adjusted to the required range quickly and steadily by Smith predictor feedback control, which improved the coiling temperature control precision greatly.(5) The determination of long-term self-learning coefficient by CBR technology was studied. Based on large number of production data, and making use of the experience and knowledge effectively, the long-term self-learning coefficient was determined by case construct, case retrieval, case reuse or revise, etc. Application showed that, for specifications with lots of production data, this method could improve temperature setting precision obviously of strip head when specification of rolling product changed.(6) Run-out table cooling control system was established. The structure of control system, functions of basic automation and process automation were introduced. As run-out table cooling report system based on C/S mode was complex to configure, and difficult to maintain and upgrade, a kind of run-out table cooling report system based on B/S three-tier architecture was developed combining with actual needs, and achieved good effect.The results of this study are applied to the conventional run-out table cooling and new generation run-out table cooling successfully. Application shows that the run-out table cooling control system has a high precision, and can be able to meet requirements of different kinds of cooling processes, and significant economic benefits are obtained. |
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