Study On Vertical Vibration Characteristics And Control Of Rolling Mill Under Entry Thickness Fluctuation Of Strip

With the improvement of high precision and high production efficiency of rolling products in modern iron and steel industry,the vibration problem of strip mill is becoming more and more obvious.The fluctuation of strip entry thickness has always been an important factor affecting the vibration of strip mill.Therefore,it is particularly urgent and important to study the influence of entry thickness fluctuation of strip on rolling mill system,and put forward a reasonable vibration suppression method.The main research contents of this thesis are as follows:(1)A dynamic rolling force model with multi-parameter excitations and multi-frequency external excitations is established under the entry thickness fluctuation of strip.Based on the dynamic rolling force model,a single-degree-of-freedom nonlinear vertical vibration model with multi-parameter excitations and multi-frequency external excitations is established.The primary resonance amplitude frequency characteristic equation and superharmonic resonance equation of nonlinear vibration system of strip mill are solved by multi-scale method.Based on the singularity theory,the transition set and topological structure of the global bifurcation of the system are obtained.Finally,the primary resonance characteristics of the nonlinear system under different entry thickness fluctuation,damping and rolling force parameters are analyzed by using the actual rolling parameters.The influence of the amplitude of entry thickness fluctuation and the parameters of excitation terms on the third superharmonic resonance of rolling mill is analyzed,and the conversion relationship between the primary resonance and the third superharmonic resonance is further analyzed.(2)Based on the dynamic rolling force model in chapter 2,a nonlinear two-degree-offreedom vertical vibration model with multi-parameter excitations and multi-frequency external excitations is established.The primary co-amplitude frequency characteristic equation of two-degree-of-freedom nonlinear vibration system of rolling mill is solved by harmonic balance method,and the internal resonance amplitude frequency characteristic equation of two-degree-of-freedom nonlinear vibration system is solved by multi-scale method.Finally,the amplitude of entry thickness fluctuation is analyzed by using the actual parameters of a certain type of strip mill.Effects of damping and rolling force parameters on the characteristics of two-degree-of-freedom nonlinear vibration primary resonance system and internal resonance system.Considering the influence of strip entrance thickness fluctuation,a two-free nonlinear vertical vibration equation of rolling mill with multi-parameter dynamic rolling force is established.The harmonic balance method is used to solve the principal common amplitude frequency characteristic equation of the mill vibration system.In order to further control the primary resonance behavior of the mill,a time-delay feedback control algorithm is introduced and the controlled amplitude-frequency characteristic equation of the system under the control algorithm is obtained.Finally,the effects of entry thickness fluctuation amplitude,system damping and nonlinear parameters of rolling force on the primary resonance characteristics are analyzed by using the actual parameters of the rolling mill,and the influence of the time-delay control parameters on the primary resonance characteristics is further studied.(3)In order to effectively control the two-degree-of-freedom nonlinear vibration system of strip mill,on the basis of the primary resonance amplitude frequency characteristic equation and the internal resonance amplitude frequency characteristic equation solved in chapter 3,the time delay feedback control algorithm is introduced,and the controlled amplitude frequency characteristic equation of the primary resonance system and the controlled amplitude frequency characteristic equation of the internal resonance system under the control algorithm are obtained.Finally,the influence of time-delay control parameters on the characteristics of two-degree-of-freedom nonlinear primary resonance system and internal resonance system is analyzed.Through the research in this thesis,it is found that entry thickness fluctuation will produce a series of complex vibration behaviors,and even cause the phenomenon of jumping.At the same time,the time delay feedback control algorithm is introduced to control the nonlinear vibration of strip mill.