Study On Dynamic Characteristics And Non-steady State Vibration Mechanism Of Vertical Roller Mill

Vertical roller mill is the key equipment of cement production line. In the production process, the most frequent failure of vertical roller mill is non-steady-state vibration. The vibrations can cause mechanical damage, seriously affecting productivity, become the difficult problem urgent need to solve in the cement production. This dissertation, based on the work of research and analyze the force and load compressive stress distribution between roller and the material, analyze the dynamics of the mill hydraulic loading system and the transmission, try to reveals the mechanism of non-steady-state vibrations generated in vertical roller mill, in order to reduce the early destruction of parts caused by vibrations and reduce equipment failure rates, to do some valuable work for promoting the application of this highly efficient grinding technology in China. In this paper, the major work accomplished and the main conclusions are as follows:(1) Grinding mechanism of vertical roller mill is studied according to a single particle breakage and the material layer breakage two aspects. For single material grinding parameters - largest clamp angle and the ratio of roller diameter to particle diameter are calculated. The influence of materials particle size and the friction between the roller and the material layers on clamp angle are analyzed. Combining roller movement curve measured at the site, three stages of material layer breakage are analyzed. The reasons lead to lateral wear of roller and the "plow zoned" wear are studied, and the cause of the instability of layers movement, the physical properties of materials and material layers and the tangential velocity difference between roller and millstone as well as the relationship between roller wear and the mill vibration are revealed and analyzed.(2) Research on distribution of compressive stress are carried out respectively from the circle view direction of roller, the width direction and three-dimensional rolling regional; present the three-parameter Weibull distribution curve model to describe the stress from circle view direction of roller; establish mathematical model of the stress distribution in the circle view direction of roller, the width direction and in three-dimensional rolling regional as well as the mathematical expression of positive pressure act on roller, the vertical and horizontal component of positive pressure; Three-dimensional stress distribution graph in the rolling regional is obtained by calculating and simulation.(3) The hydraulic loading system simulation model are established, using the roller displacement signal obtained at the site as input of hydraulic simulation system, to investigate the dynamic characteristics of hydraulic loading simulation system. The system pressure got by simulation is very consistent with the system pressure by measurement, to verify the correctness of the simulation system of hydraulic loading. The simulation results revealed the relationship of instability of the movement of layers and the physical characteristics of layers with system pressure and mill vibration. Created hydraulic simulation system have guiding significance for the dynamic design of hydraulic loading system, there are strong prospects for practical application.(4) The dissertation conducted a dynamic analysis for inner impact of the planetary gear reducer caused by time-varying mesh stiffness and comprehensive error, research shows that: In the dynamic load factor and gear backlash, the low-speed and overload planetary gear system occur abnormal acceleration waveforms, indicating that there is an impact loading act on the meshing tooth surface. Test results prove the accuracy of this conclusion. Using the measured data of the hydraulic system force as load of the reducer transmission system, the dissertation simulate dynamically for the of transmission system. From the simulation results, fluctuations phenomenon exist in the reducer meshing force and in the axis torque, due to changes in the hydraulic system loading, resulting in the torsion vibration formation inside the reducer.(5) Vibration test methods are used to conduct a multi-point vibration tests on reducer. Through analysis and study of test results, it is found that the frequency components of reducer frequency domain vibration signal is very rich, mainly including the rotation frequency of shaft, gear tooth meshing frequency, cyclical passage frequency of bearing rolling body through the bearing zone, sliding bearings self-excited vibration frequency, the motor vibration frequency excited by effects of electromagnetic, self-excitation frequency of equipment related to the structure, the vibration frequency excited by variable load, as well as the relative frequency of the harmonic and the modulation frequency.