Study On The Structural Dynamics And Dynamic Design Of The Large Varied-line-trajectory Equal-thickness Vibrating Screen

Coal is the main energy in China. Coal preparation is the most effective and economic method for coal production of environment-friendly and high-efficiency. As key process of coal preparation, screening operation is widely used for coal classification, medium-draining, dewatering and desliming. With a constantly increasing coal consumption, large vibrating screens with large capacity and high efficiency are in great demand. Though the traditional equal-thickness vibrating screen generally performs well, it still faces with some disadvantages such as dynamic stress concentration, low structural strength and difficult manufacturing. Thus, how to ensure and improve the structural strength and rigidity of the large vibrating screen is the primary problem for designing large-sized and high-efficient vibrating screen.This dissertation mainly aimed at developing a new type of large equal-thickness screen named the large BGJ3660 varied-line-trajectory equal-thickness vibrating screen. Main points focus on the virtual screening, the dynamic characteristics of the screen surface, the mechanical design, dynamic analysis, vibration measurement and screening experiment of BGJ3660. Main work and conclusions are as follows:Discrete element model of an equal-thickness screen was established based on the 3D discrete element method. Virtual experiments were performed on the difficult-screening particles with 0.8 times of the diameter of the screen aperture, and particles distributions under the state of particles stratification and penetration were obtained. Effects of the equal-thickness screen inclination angle, vibrating angle and vibrating intensity on the screening effect were also discussed. Results show that with the vibrating intensity increases, the screening efficiency and screening completion time decrease. Best screening effect can be obtained when a vibrating screen with screen inclination angle of 0.5°, vibrating angle of 45° and vibrating intensity of 3.5.Dynamic model for the vibrating screen with elastic-structure classification screen surface of the BGJ3660 was established, followed by the deriving oscillatory differential equation based on the Lagrange’s equation. In order to obtain the theoretical response, equivalent stiffness of the elastic structure was calculated. Numerical example and experimental test showed that the elastic-structure could lead to the screen surface having larger vibratory intensity than that of the corresponding position on the screen structure. Additionally, dynamic characteristics of the medium-draining screen surface with modularized polyurethane screen plate of the BGJ3660 were analyzed, which presents a feasible way to improve the reliability and processing efficiency of large vibrating screen.Exciting apparatus of BGJ3660 was established. With the operating principle illuminated, dynamic analysis of BGJ3660 was conducted and verified by the steady-state solution and Newmark-β numerical method, which verified the feasibility of the oscillating along variable straight line. Methods to ascertain key parameters and components of BGJ3660 were presented, followed by developing the experimental prototype. Then, dynamic characteristics of the whole equipment and the key components were obtained by the model analysis and the harmonic response. Under the working frequency of 16.67 Hz, the maximum dynamic stress of the screen structure didn’t exceed 24.50 MPa, the largest lateral oscillation of the screen box didn’t exceed 0.45 mm, which this is in accordance with national standards. So, the design of the BGJ3660 is advisable and the structure construction is reasonable.With experimental BGJ3660 manufactured, tests on the vibration parameters such as kinematic parameters, lateral oscillation, dynamic stress of the screen structure and screening processing parameters such as the screening capacity, flow velocity of the materials were conducted. Results show that track of the measured points are all approximate line segments from the feed-in end to the feed-out end, and the corresponding vibration intensity decrease as well. This is consistent with thetheoretical analysis and result of simulation. Amplitude of measured points are within design value, the vibrational frequency is close to excitation frequency, the natural frequency is consistent with design value. Lateral oscillation of the vibration screen can meet national standards of vibration screen’s steady operation.The stress of every point coming from experiments is less then allowable stress,the vibration screen is within allowable limits. The magnitude of the screen noisy is relatively low, less than 90 d B. Flow velocity of materials is diminishingly from the feed-in end to the feed-out end, the capacity and screening efficiency can meet requirement. Test results of the BGJ3660 show that it accords well with the design demands and has a good screening effect.