Study On Dynamic Design Of The Large Vibrating Screen With Hyperstatic Net-Beam Structure

The vibrating screen with high processing capacity is urgently needed in coal industry with the increasing demand of coal energy sources. Meanwhile, the maximization of screening machines can reduce the needed number of vibrating screenings and low the cost of equipments and thus brings a good economic benefit. But the maximization of vibrating screens will lead to the deficiency of structural stiffness and strength and affect service life. Now the traditional design methods, concerning static strength and kinematics analysis, are still in use and most of the products are designed through adopting empirical data and safety factor to calculate design parameters. This method can not reveal dynamic stress state of internal structure and make the design reasonable which affects service performance and life of products. Thus it is an important research subject to design large vibrating screenings, raise the design level and improve working reliability and service life of vibrating screenings.A new designed large vibrating screen with hyperstatic net-beam structure was studied in this dissertation. The author applied finite element method (FEM) and advanced vibration test method to design the large vibrating screen. The result shows that the reliability of the vibrating screen is increased.Three new types vibrating screens with high screening efficiency were proposed based on the principle of screening process with constant bed thickness. Accurate vibration mechanical models of two screens were built according to their structural features, using dynamics principle of mechanical system. With vibration theory of multi-freedom system applied, the author analyzed motion characteristic of the vibrating screens. Screening technological parameters including amplitude, velocity, throwing index of some specific points on the screen surface were calculated and their screening characteristic were studied.Structure features and screening characteristic of banana vibrating screen and their applicability were analyzed.The features of hyperstatic structure and the feasibility of the structure which was applied in the design of large vibrating screen were analyzed. A large vibrating screen was designed based on the banana structure, adopting hyperstatic net-beam structure which is composed of static plates, exciting beams and crossbeams. Main technical parameters, critical components and the dynamic parameters of the vibrating screen were established.The dynamic characteristic of banana vibrating screen was analyzed and the structural strength and reliability was studied. The method of improving calculation accuracy of the finite element model was given. A proper finite element model of the vibrating screen was set up and an adaptive method was showed for the simplification of the bolts. The FEM was used to solve natural characteristic of local important structure and integral structure of the vibrating screen. The results offer a basis for the dynamic modification of the structure and provide a reference for the test points'arrangement of the modal experiment. The author made a dynamic response analysis of the vibrating screen, applying the FEM. The dynamic stress and strain of the integral and local structure at the working frequency were obtained. The results show a better performance of the hyperstatic net-beam structure and find out structure defect of the vibrating screen.The vibration test on the vibrating screen's prototype was accomplished, applying advanced test experimental technology. The modal parameters of the vibrating screen were gained by means of the modal experiment test. The results reveal the effectiveness of the finite element analysis and point out the weakness part of the vibrating screen.The sensitivity analysis method was used to modify the structure of vibrating screen.The paper used experimental modal frenquency and vibration modes to construct goal function according to the lagrangian multiplier method. The mass update matrix and stiffness update matrix which is applicable to the finite element model were given. The sensitivity analysis method was applied to modify local structural parametres of the vibrating screen based on the results of FEM and experimental modal analysis which made the dynamic parameters more reasonable and improved the structural stiffness and stability of the large vibrating screen.In order to solve the problem of high dynamic stress which led to the damage of the large vibrating screen, the author made a structural optimization of the vibrating screen. The size of reinforcing ribs and the mass of the side plate were optimized based on several frequency constraints. An applicable optimization criterion was given and the algorithmic method of analytical sensitivity was embedded in the program. The author complied a program with high convergence rapidity and solving accuracy, applying augumented lagrangian multiplier method, to confirm the best position of reinforcing ribs on the side plate and obtain lower dynamic stress with the least number of reinforcing ribs. The optimal results show that the structural stiffness of the side plate is improved and the deformation is decreased and thus the structural reliability is enchanced. The vibrating screen was stable and reliable when it was used in production. The test results of no-load running experiment show that the performance of the vibrating screen accord with the design requirements well.