Harmonic analysis of the elastic grate - card element of the dynamically active sieving surface of the vibrating screen

Abstract

Sieve surface vibrating screens should provide fairly complex movement of the bulk material particles sifting. In order to ensure the necessary conditions for the work of screening surfaces, it is proposed to use the new design dynamic elastic surface- active screening sieves self-cleaning grate - card. Composite elastic grate-card elements without preliminary deformation, installed in the box vibrating screen. Console horizontal shelves grate card elements under the influence of vibration strength data makes sophisticated vibration-spatial movement. Since the formation URCC aperture is "active" cantilevered horizontal shelves, it becomes necessary to study their motion trajectories in view of the design parameters of the sieve and forced vibrations vibrator box.
Purpose of the study: The method of determination of natural frequencies and mode shapes of the elastic (rubber) member forming fabric sieve vibrator, which will reach the greatest amplitude oscillations during operation of the vibrating screen. The research problem: develop a model grate-card element sieve URCC for harmonic analysis with the finite element method. Since the grate-card element has a complex shape, it is proposed for the solution of using the method of finite elements.
Harmonic analysis procedure consists of four main steps: model building; definition of the type of analysis, the job options, impacts the application and obtain a decision, "of expansion" mode, analysis of the results. The properties of the material should be linear and isotropic or orthotropic, constant or temperature-dependent. The nonlinear properties (nonlinear elasticity, plasticity, creep) are ignored. Due to simplify and reduce the time calcgthat considered half-card grate element, which kalozheny appropriate limits.
As the base member will take-card grate element experimental vibrating screen model developed by the authors at the Department IMMTA National Metallurgical Academy of Ukraine. In the tires used in 2959 with the following characteristics as the material: density elastic moduli Poisson's ratio Changing the frequency of the disturbing forces 0 ... 120 Hz, at an operating frequency of 25 Hz screen. The figures show the amplitude-frequency and phase-frequency characteristics for different points. On the chart, there are two clearly defined natural frequencies for horizontal vibrations and vertical -
When replacement of an element of constant beam of rectangular cross section, we obtain the values of natural frequencies and . As can be seen, for horizontal oscillation frequencies are in good agreement. Eigenfrequency depends on the geometric dimensions and physical and mechanical rubber properties (density, elastic modulus and Poisson's ratio).
In practice, the most easily varied mechanical properties of rubber, as mold value that specifies the geometric dimensions, is quite high. Graphs show the amplitude-frequency characteristics of the oscillation of points with different values of the modulus of rubber elasticity. With increase of the modulus of elasticity increases the natural frequency and the amplitude are reduced. In practice, in the manufacture of card-grate element, it is possible to select the desired modulus follows. If the sorted bulk material contains a large amount of undersize product, it is necessary to intensively act on the material quality of segregation, i.e. vertical components of oscillation should be maximized. If a lot of "hard grains" in the starting material, it is necessary to improve the self-cleaning screens, and therefore increase the grate fluctuation in the horizontal plane.
When the range of variation of the modulus of elasticity horizontal oscillation eigenfrequencies changed within 17 ... 34 Hz, and the vertical - 37 ... 72 Hz. For more substantial frequency range necessary to change the shape and dimensions of the card-grate elements.