Research Of Cooling Control System And Control Strategy After Rolling Based On UFC For Hot Rolled Strip

Under the background of social advocacy "Green Manufacturing and Manufacturing Green", ultra-fast cooling technology is the core aspect of New Generation Thermal Mechanical Controlled Processing (NG-TMCP); during the application of NG-TMCP in hot rolled strip, it can obtain excellent properties steel products with reduction of component design, realize energy saving, resource conservation and low-costing, tap into high protential of materials, and form a system of green manufacturing process. Based on the significant technology "The equipment and process technology of NG-TMCP for hot rolled strip" of "Green production technology and application demonstration of steel industry" for "12th Five-Year Plan" National Key Technology R&D Program, and focused on the key generic technology of steel industry " The NG-TMCP technology", the multi-objective cooling control system after rolling based on UFC for hot rolled strip was developed, which aiming to speed up to breakthrough the core key technology in iron and steed industry. In this dissertation, the multi-objective temperature calculation model, decoupling control strategy for multi-objective temperature control, method to improve temperature control precision, water precision control strategy and temperature precision control strategy under the condition of accelerating rolling were systematically studied. On this basis, the independent intellectual multi-objective control system of cooling after rolling based on UFC was developed, and the system has been successfully applied in steel production with high accuracy control.(1) In view of field process requirement of ultra-fast cooling, the multi-objective cooling system framework of cooling after rolling was established after considering the actual production condition; then, after analyzing the characteristic for multi-objective system, the seamless and flexible control strategy for ultra-fast cooling and laminar cooling control was studied. Based on the demands of fexible cooling mode of the system, the control structure of multi-objective control system was studied, and the sequential control function of the system was optimally designed, which realized the reasonable division and collaboration in each function.(2) Base on the characteristic of ultra-fast cooling process, the multi-objective temperature control model and self-adptive model of water cooling coefficient were established. First, based on the analysis of the heat exchange of cooling after rolling, the temperature control model was deduced. Secondly, based on the research of factors that affected water heat exchange efficiency, the ultra-fast cooling heat transfer coefficient model and laminar cooling heat transfer coefficient model were obtained by regressive method. Next, in order to eliminate temperature calculation deviation and improve the adaptive ability, the adaptive water cooling heat transfer coefficient model was constructed. It significantly improved the stability and convergence of water cooling calculation, and the temperature control precision was also obviously increased.(3) After adopting expert system PID and Fuzzy-PID control strategies, the decoupling control of water pressure and flow was conducted, and the control strategies have the characteristic of quick response, strong anti-jamming capability and stability during field application. In order to realize the stability of water supply system, the decoupling control strategy between control system of rolling line and pump water supply system was developed. First, in view of the characteristic of cooling water in high pressure mode and low pressure mode, the expert system decoupled PID control strategy was applied to realize high precision control of water pressure. Secondly, after the analysis of water flow change law of different cooling headers, the fuzzy PID parameters self-tuning control strategy was developed to realize precision control of water flux. In the field application, the strong decoupling problems of pressure and water flow control, water system of rolling line and pump station were effectively resolved.(4) Based on the characteristic of process temperature control of different location in cooling after rolling, the control strategies for improving temperature control precision of multi-objective system under UFC were developed. First, after analyzing the characteristic for UFCT and CT control, and the decoupling control strategy and multi-element control calculating mode were developed. Secondly, aiming at the characteristic of ultra-fast cooling, the in-coil self-learning control strategy was developed to realize precision control of UFCT; according to the high cooling rate of ultra-fast cooling, strip temperature distribution in thickness direction during ultra-fast cooling were investigated, respectively. Next, on the basis of multi-objective control system characteristic, the temperature compensation calculating strategy was developed to eliminate the coil temperature control deviation affected by ultra-fast cooling; the PID decoupled hysteresis compensation feedback control strategy was proposed to eliminate the influence caused by hysteresis element. Finally, after the research of strip longitudinal temperature uniformity control,5points learning strategy and the independent self-learning control strategy of UFCT and CT were applied in the system, which effectively improved the temperature uniformity in strip length direction and stability of the system.(5) The strip and micro segment TVD curve calculating algorithm and on-line cyclic modification strategy were proposed based on the research about the irregular strip velocity during rolling to eliminate the temperature deviation affected by velocity fluctuation. First, the change law of strip surface heat transfer coefficient and running time affected by velocity variation were studied. Secondly, in the study of the characteristic of TVD curve for different length of strips, the strip integral TVD curve calculating algorithm, calculating algorithm in running system of stage Sk and calculating strategy for strip segment were developed. Next, the on-line cyclic modification strategy was developed for the irregular variation of strip velocity. The velocity calculating algorithm, calculating strategy and on-line modification strategy above mentioned were successfully applied in field practice, and each strip segment passing each micro cooling section was accurately calculated, which eliminated the temperature deviation influenced by velocity fluctuation.(6) The developed multi-objective control system was successfully applied in strip production with high accuracy control of UFCT and CT. Based on the system, low-cost carbon steel and low-cost pipeline steel were successfully developed, which conserved the key alloy content during production. Besides, the system runs stably with effective control results. With the help of the system, outstanding contributions in quality and efficient of products are made for enterprise, and significant economic benefits are obtained.