Research And Application Of Hydraulic Tension Control Technology For Cold Rolling Pilot Mill

In recent years, remarkable achievements have been made in the steel industry of China, especially in independent research and development for metallurgical process simulation equipments. However, there are many problems, such as long-term dependence on imports in high technology, the lack of independent intellectual property rights and the core technology subject to developed countries.Cold rolling pilot mill with hydraulic tension is the key equipment for cold rolling experiments and process research. During the working process, the specimen is required to be rolled under constant tension from both left and right sides by hydraulic cylinders. However, the constant tension control during rolling process is very difficult because of the strong coupling between left and right tension, the excess force caused by position disturbance, multi-pass and time-varying process. In order to solve the problems mentioned above, the complex hydraulic design is used in the equipment from abroad and the control algorithms are kept as a black box. The native equipments use conventional control strategy whose control results are not satisfying. In response to these problems, hydraulic control technology for tension control is studied in detail. A new type of hydraulic control platform is designed, based on which the complete mathematical models of synchronous control system are established. Considering the existing problems on site in application process, the corresponding solutions are proposed and used in the scene, and good results are achieved. Some chief original work and conclusions are as follows.(1) From the elastic deformation theory of metallic strip, combined with the theory of plastic deformation and rolling, forward and backward tension of the cold-roll pilot mill with hydraulic tension in work is studied in detail, and the key factors impacting tension control accuracy which are excess power disturbance and the strong coupling between forward and backward tension, are concluded. Conventional hydraulic servo systems are difficult to overcome the above disadvantages.(2) A new set of hydraulic control platform based on servo valves combined with proportional relief valves is designed.Closed-loop tension control and rolling speed tracking are attempted to reach relying on high dynamic response characteristics of servo valve, and the excess power and the strong coupling are attempted to be eliminate relying on good pressure-flow characteristic of proportional pressure relief valves.(3)Based on the characteristics of flow and frequency response of servo valve, the second-order transfer function model of servo valve is founded and the key parameters of the model are obtained. According to compression principle, a set of experimental device for measuring bulk modulus of oil and oil hose is designed, and the experiments are carried out. The exponential model under pressure at room temperature is founded. Based on the flow continuity equation of forward and backward tension cylinders, the force balance condition, and the rolling process technology requirements, the control object model considering variable stiffness, strong coupling, external disturbance, pipe effect, friction, and the nonlinear of servo valve in detail, which provides foundation for the simulation of control strategies and its practical application is built.(4) Considering the control object model, different control strategies are simulated, and the simulation results show that:traditional PID control mode, which can get good static control effect, is not able to get satisfying dynamic performance, and it is likely to cause tension shock. The combined control strategy including speed feedforward and tension feedback is designed, and it can get good static and dynamic load characteristics. However, the control effect gets worse with rolling thinning, tension reducing and rolling speed increasing and other changes in rolling conditions, because the adaptive control strategy can not be completed. On this basis, the control strategy of speed feedforward combined with fuzzy PID tension feedback is quoted. The introduction of fuzzy PID controller can realize adaptive controller parameters adjusted under variable operating conditions, simulation results show that the control strategy can get high response speed, high precision and strong robustness.(5) Based on cold-rolling pilot mill with 100kN hydraulic tension, cold rolling experiments towards typical metallic materials are carried out. The dynamic tension control accuracy is controlled within±1.1kN,when the maximum rolling speed reaches 0.4m/s and the maximum single pass reduction reaches 37%.Therefore, the cold-rolling pilot mill with high-precision hydraulic tension provides reliable technical support for varieties of metal materials in cold-rolling development and research.