Study On Vibration Coupling Characteristic Of Secondary Failure Due To Rub Contact Under Working Speed Of Big Rotor System

It is necessary in petrochemical manufacture plant to decrease clearance between the rotor and stator, such as shaft seal clearance, in order to decrease leaking energy loss and improve the performance and efficiency of rotating equipment. When there is deterioration fault or big vibration with the rotor, which would cause contacting rub. The fault of rub is usually caused by other faults that cause rotor response out of acceptance region clearance, that is to say, the rub contact fault are normally going with other faults, which coupling together to activize composing vibration. Vibration is calculated from force divide rotor dynamic stiffness, when there is rub in the rotor train that would suffer two kinds of force, the first force is the impact force that is caused by rotor and stator contact, which would cause transient vibration and force of partial deformation and rebound; the second force is friction tangent force and radial friction force, which cause coercionary vibration; At the same time, the dynamic stiffness is changed by rub contacting, furthermore, which change the critical frequency or speed. The stiffness and force change caused by friction let the rotor dynamic response become very complex. So it is necessary for us to research the friction that affect the rotor train response by using the plots of spectrum and phase curve. But if there is sub synchronous vibration frequency, the rotor must reach to certain rotating speed, this kind of finding is the function that help us to diagnose the rotating equipment at working rotating speed.Rub is normal secondary fault in rotor train, which is potentially caused by unbalance, Looseness or oil whip etc. Unbalance is avoidless in every rotor train, therefore, we researched the theory in practice of full annular rub under balance response, input the factor that cause the unsteady rotor, we find out critical qualification that cause the forward precession rub and reverse precession rub under unbalance force, we give the evidence to avoid reverse precession, at the same time, we prove it is impossible for the rotor train to response reverse procession vibration under lubrication. In order to research the rotor train rub caused by oil whip and rotor looseness under normal operation condition, we set up the rotor dynamic model that is used to study the coupling model of unbalance-fluid whip-rub and the coupling model of unbalance-looseness-rub. We got the theory of coupling vibration by researching theory and data in experiment, separate the defection vibration characteristic of oil whip and looseness under rub condition by using orbit, spectrum and waveform etc, highlight rotor characteristic that cause the signal different.We get the result by study theory and do experiment in practice, which it is possible that the rub can decrease the affect of oil whip and looseness. That is to say, vibration has no certain direction under the coupling of oil whip and rub, however, the vibration has certain direction, furthermore, the rub grade increases and synchronous vibration appears when speed increased, the sub synchronous vibration appear only at certain speed, it is seldom to appear for the super synchonous vibration, whose amplitude is much lower than synchronous vibration.It is difficult to diagnose the rotor rub and contact because the rub is stochastic and instantaneous by using FFT, so it is usual to use wavelet method, but it is difficult to calculate big data when we use the wavelet to separate and diagnose the defection signal of vibration. Therefore, we use FFT to diagnose at first, and then use wavelet to identify fault of rub, we save the time and decrease the quantity of calculation for the work.