Research on Critical Rolling Speed of Self-excited Vibration in the Tandem Rolling Process of Thin Strip

Abstract

*Abstract：Rolling mills are typically complicated dynamic systems due to the coupling of structure and technique. Under the feedback excitation of inner sources, self-excited vibration is triggered when driving energy is transformed into vibration energy in structures under certain circumstances. The rolling speed is a direct index for measuring productivity, and also a key factor in triggering instability of rolling machines, therefore a research on the critical rolling speed possesses major significance in the forecast and control of self-excited vibration. Taking into consideration the equivalent elastic-plastic stiffness, an 8-DOF structurally asymmetrical model of a certain 6-roller rolling mill for thin strip is set up. A model of rolling process is established based on the plane strain hypothesis and the SLAB theory, and effectively verified by comparing the calculation value and the actual measurement of the rolling force, furthermore the increment model of rolling parameters is attained by TALOR expanded formula, thus a dynamic model with the coupling of structure and technique is presented. The LAPLACE transform is executed to get the characteristic equation in the S-domain, the instability condition of the system and the rolling speed threshold of the self-excited vibration is obtained by the application of ROUTH stability criterion. The influences of technical parameters are analyzed, and then the ways to the optimization of technical schedules are correspondingly proposed. By combing calculation conclusions with the actual producing problems, the typical vibration phenomenon and the vibration suppressing strategies are simulated during the increasing-speed stage and the steady-speed process respectively, and these problems are demonstrated and explained through the relations between the critical rolling speed and instable self-excited vibration. These results show that as a major index for the evaluation of the vibration and stability of rolling mills, the critical rolling speed can be improved through the optimization of the technical conditions and the distribution of the reduction schedules, thus a high-speed stable rolling process is achieved in the tandem rolling mill of thin strip.

Stability Analysis of a Nonlinear Coupled Vibration Model in a Tandem Cold Rolling Mill

“…Damping coefficients of the intermediate and backup rolls are calibrated by a simulation program [31,32]. First, Shock and Vibration the dynamic differential equation of the system is regularized to obtain the equivalent damping matrix.…”

Vibration Characteristics of Rolling Mill System under Constraints of the Nonlinear Spring Force and Friction Force from Hydraulic Cylinder

“…e coefficient of friction between the cylinder and the piston will change due to the periodic change of the vibration velocity of the hydraulic cylinder, and the friction exhibits nonlinear. In the running process of the hydraulic cylinder system, under the action of the oil source pressure and the load pressure, the dynamic hydraulic spring can be formed due to the compressibility of the oil [15]. e nonlinearity of the spring force makes the natural frequency of the system unstable, and the stability of the response area becomes complicated [16].…”

Dynamic Model of the Hot Strip Rolling Mill Vibration Resulting from Entry Thickness Deviation and Its Dynamic Characteristics

“…Liu et al [5] studied the vertical vibration of the strip mill using the piecewise nonlinear constraint arising from hydraulic cylinder. Gao et al [6] simplified the rolling mill structure into an eight-degree-offreedom (8-dof) spring mass model and analyzed the critical rolling speed using the stability criterion. The second method analyzes the rolling deformation zone to obtain its dynamic characteristics based on the Kalman equation or the Orowan equation.…”