The Stochastic Dynamics And Optimal Control Strategy Of Aluminum Strip Hot Rolling Tandem Mill

Abstract:The dynamic characteristic of strip hot tandem rolling mill under random and deterministic excitation is the key factor of ensuring its production efficiency, improving product quality and reducing maintenance cost. This paper attempts to investigate the stability, reliability and optimization of the strip rolling mill and the rolling process, including mechanism analysis, model creation, numerical simulation, testing and validation, creating the rolling force random excitation model, building the comprehension targets of stochastic dynamic performance and stochastic dynamic optimal control strategy by combining with the random vibration theory. The Specific studies were carried out on the issues above mentioned, it includes:Investigation of the basic vibration characteristics and mechanism of the aluminum hot strip tandem rolling mill based on field test and signal analysis, the simulation results of the mill inherent characteristics were partly confirmed, it provided the data support for building the rolling force stochastic excitation model combining of the actual production data of hot rolling production line, and its time domain and frequency domain characteristics were investigated. The modeling theory and analysis methods used were also suitable for different rolled materials and rack. The vertical stochastic dynamic characteristics of aluminum hot strip rolling mill were investigated and the mill roll system optimization model were created, it concluded that the random physical and geometrical properties of rolled strip can induced stochastic chatter in rolling process, the oscillation marks on roll and rolled material is proportional to the random rolling force power spectral density, and the variation law of roll gap variance and its power spectral density with the rolling speed were obtained. Taking the natural frequency and damping ratio of roll system as a design variable, and the smallest of vibration acceleration maximum steady value of the roll system as optimization goals, the reliability-based dynamic optimization model of rolling mill roll system were established and the best natural frequency and damping ratio corresponds to the instability probability at the acceleration security threshold were obtained. The stability of the rolling mill and the rolling process were investigated. The single degree of freedom and two degree of freedom vertical vibration model of roll system, the single-modal structure and multi-modal model coupling the torsional vibration and vertical vibration model, and multi-rack vibration model were established. The rolling process parameters on the stability of the rolling process were studied. The two degrees of freedom nonlinear stochastic dynamic model under random excitation for the strip mill roll were established for the first time. The global stochastic stability of roll system were analyzed by using the stochastic averaging method of quasi-non-integrable Hamiltonian systems and the singular boundary theory, and the steady-state probability density function of roll system were obtained by solving the FPK equation of the system. The dynamic reliability of the roll system under different random rolling force ware investigated, the variation of the random vibration response and dynamic reliability of rolling mill roll system were obtained. The stochastic optimal control theory and methods were used for study of vertical vibration suppression of rolling mill roll system; the comprehension targets of roll system were founded. The absolute acceleration and relative displacement mean square response of the roll system on different natural frequency and damping ratio were studied, and their variations of drift coefficient and diffusion coefficient with the total energy of the system for a given rolling speed were obtained, finally the stochastic dynamics optimal control strategy of the roll system was determined. It will be possible to be widely used in design and dynamic analysis for complex mechanical system that the novel vibration analysis and research techniques based on the nonlinear stochastic dynamics, and have important theoretical and practical significance to the methods and theory development and improvement of the mill structure optimization design, chatter mechanism and its suppression.