Research On The Damage Detection Mathod Of Partial Structure Of Vibrating Screen

Self-synchronizing linear vibrating screen not only has big intensity of vibration, simple structure, but also has lower noise, it is applied to coal profession. The screen which working condition is bad, stress is complex, not only receives the vibration load, but also receives the impact load, thus causes the fatigue damage accumulation to produce the crack. The production and expansion of the crack changes the dynamic performance of the system, greatly affects its normal work, it is serious when the consequence which is unable to estimate is created. In order to avoid this kind of phenomenon, once the crack appears, we should accurately examine and diagnose it.Based on modal analysis theory, the thesis researches the crack monitoring method to the partial structure of screen. Regarding the static problem as the special case of the dynamical problem, we can decompose the dynamical problem into static problem under various steps modals and so can unify the static problem and the dynamic problem. Based on the above theory the thesis takes the lower crossbeam as an example, analyzes the damage reason of the partial structure of screen, and forecasts the possible damage spot and the damage character of screen in its working condition.The thesis discusses the screen work mechanism and its basic performance based on the dynamics theory and then introduces the modal analysis theory and the experimental modal method. With MSC Corporation's Patran, Nastran software the author establishes and calculates the finite element model of the lower crossbeam. During the process of calculation the thesis discusses following several issues: the effect of different grid quantity to the computing result; the influence of different grid shape in different location to the computing result. The thesis also calculates the influence of the different position, different depth crack to lower crossbeam natural frequency, and the result, indicates that the crack has the obvious influence to the natural frequency, but has not the obvious influence to the vibration modality. According to the modal analysis theory and the computing result of the finite element the thesis then designs the experimental plan, which estimates the structure damage of lower crossbeam by measuring the change of modal frequency.By the modal parameter measurement experiment, the thesis obtains the screen modal frequency and the vibration modality, and by refering to the finite element analysis result the thesis finds that the crossbeam usually works at the low frequency. In experiment, the thesis finds that there is no obvious distortion occured to the lower crossbeam, therefore there is little possibility that the lower crossbeam appear crack, but there is obvious distortion occured to the band of screen, therefore it is necessary to enhance the rigidity of the band of screen to resist distortion and prolong the service life.According to the vibration modality the thesis designs the installation positions of accelerometers in the lower crossbeam construct damage online measurement experiment. Then by relativity analysis to the measured data the thesis estimates that there is crack in lower crossbeam or not.The experiment result performs that the above estimation is coincident with the actual facts, and it verifies that it is feasible to estimate the lower crossbeam structure damage of screen by measuring the change of modal frequency of the lower crossbeam.