Vibration Analysis And Dynamic Characteristics Study On The Decanter Centrifuge

The horizontal decanter centrifuge is a kind of centrifugal settling and separation equipment which is used in extensive areas. As a kind of rotary machine with dual-rotors, the inner rotor is the screw and the outer rotor is the bowl. The vibration problem is always an obstacle that baffles the development of decanter centrifuge. For a certain type of decanter centrifuge, comprehensive vibration tests as well as numerical analysis are conducted to study the main vibration faults and vibration characteristics of the decanter centrifuge which have certain significance for the structure design of the decanter centrifuge.Vibration tests under no-load conditions on the characteristics of the decanter centrifuge are carried, the conclusion of the machine resonates by two-times frequency at a low rotating speed because of the asymmetrical screw rotor is get by amplitude-frequency drawings and amplitude spectrum analysis. Under the influence of two-times frequency, the decanter resonances at a low rotating speed which can lead to severe vibration. Therefore, the symmetry of the screw rotor should be improved when designing the decanter centrifuge. The vibrations of the system under load and synchronous conditions are tested respectively, and the results show that the vibration is much more serious and the resonance region is widen under load condition; the vibration intensity of the system under synchronous condition is the same as that of asynchronous condition, but the asynchronous condition is more dangerous because of beat vibration.Based on the nonlinear transient dynamics analysis of ANSYS and simulating the rotation by rotary displacement constraint, the finite element model of asymmetric rotor is build and vibration characteristics of asymmetric rotor under gravity and unbalanced force are simulated. The result indicates the rotor resonates at a low speed by two-times frequency(2×f) and the vibrations in different direction are identical. About the unbalance response characteristic, amplitude and phase response are of great difference for the unbalanced mass at the same axial but different phase location. Based on this characteristic, two improved methods applicable to the dynamic balance of asymmetric rotor are proposed.In view of statically indeterminate structure of the decanter centrifuge, an iteration calculation model of nonlinear bearing stiffness is built. Considering gear meshing stiffness, material and lubricant film damping, using solid elements, coupled dual-rotors vibration model of screw-differential mechanism-bowl is build. Applying ANSYS modal analysis, critical speeds along with vibration modes of dual-rotors and single-rotor are simulated, and the impacts of the differential mechanism and single-rotor modal on dual-rotors modal are obtained. Based on the model, further researches about the impacts of bearing stiffness and rotor wall thickness on the modes of the system are conducted. Using harmonic response analysis, the dynamic responses of the centrifuge under single rotor unbalance excitation are calculated, the results indicate that the system responses differently for the different rotors. Applying transient structural analysis, beat vibration characteristic of dual-rotors system with little rotation speed difference is obtained, and a conclusion of the system responses separately for the unbalance mass of different rotors at a low rotating speed is get.The results of the study have certain significance for the structure design, high speed dynamic balance and vibration diagnosis of the decanter centrifuge.