| In recent years,there have been many cases of vibration divergence caused by gradual bending of the rotor of large turbo generator unit,these cases affects the operation of the set seriously.The study of progressive bending and vibration response of rotating machinery rotor is of practical significance to the field fault diagnosis and treatment.First of all,the calculation model of progressive bending of rotor under the action of external force is established,and the influence factors of creep bending are analyzed based on the load short shaft of a gas turbine and the high and medium pressure rotor of a steam turbine.Under the action of external force for a long time,the rotor will superimpose a creep deformation on the elastic deformation.With the development of time,the creep deformation increases and tends to change at a constant rate.The creep deformation is nonlinear to the external force.The longer the action time is,the larger the external force is and the more obvious the creep phenomenon is.The finite element dynamic model is established under the coupling effect of rotor bending and mass unbalance.The vibration response characteristics of a high and medium pressure rotor under pure bending,pure mass unbalance and coupling of bending and mass unbalance are analyzed.Under the coupling action,when the angle between the bending and the mass unbalance is 0°,the two are superposed in a positive direction;when the angle is180°,the bending and the mass unbalance counteract each other,resulting in the "inverted critical" phenomenon and phase fluctuation.Secondly,a rotor test-bed is built to study the creep bending and progressive vibration of the rotor.When there is imbalance in the middle of the shaft,the balance weight on both sides can achieve better results in a short time.After running for a period of time,the vibration during shutdown is obviously greater than that during startup.After measurement,the bending of the rotor is obviously increased after shutdown.The analysis shows that under the joint action of the unbalance in the middle and the counterweight at both ends,the rotor will have irreversible creep deformation,which will lead to the gradual vibration of the rotor.Finally,in view of the progressive vibration phenomenon of the high and medium pressure rotors of a large turbogenerator set,an explanation is given from the point of view of the creep bending of the rotors.After balancing weights at both ends of the rotor,under the action of the bending moment generated by the unbalance amount in the middle and the three forces of the balance weight,the rotor will undergo progressive bending,which can not be recovered,resulting in the continuous climbing of the over critical vibration during the shutdown process,resulting in the phenomenon of progressive vibration.The progressive bending caused by creep takes on a first-order mode shape,and its effect on the vibration is mainly in the region near the critical speed.The field test shows that the counterweight on the unbalance surface can reduce the vibration and restrain the bending development.The dynamic balance test should be carried out on the unbalance surface of the rotor as far as possible. |
