Conventional machinery contains a large number of rotating motion parts, such as all kinds of drive shafts, spindle, motor and turbine rotor, collectively known as the rotary body. In the practical application of various solid of revolution, due to uneven material or casting defects, processing and assembly of error, and even design has a variety of factors such as asymmetric geometry, caused the imbalance of solid of revolution, even though the static balance, when rotation of rotors, the centrifugal force produced by each tiny particles on the cannot cancel each other out, Thus the imbalance of centrifugal force, resulting in dynamic imbalance. What are the characteristics of rotor imbalance?
Random unbalance is generally caused by the loosening of the rotor parts. When there is loosening of the rotor parts, the balance state of the rotor will change, and its vibration characteristics show the characteristics of time and time, and the amplitude (or phase) measured at different times of the rotor is up and down, and the vibration has no specific change law. The characteristics of rotor imbalance are as follows:
(1) Typical characteristics of vibration spectrum: the imbalance problem is usually dominated by high frequency switching vibration, and generally the frequency switching vibration component is greater than or equal to more than 80% of its pass frequency vibration.
(2) the unbalanced force has a certain direction, the centrifugal force in radial basic is uniform, the trajectories of shaft and bearing approximation for a circle, however, because the vertical stiffness of the bearing is greater than the horizontal direction, so the normal movement of the shaft and bearing as the ellipse, which normally horizontal vibration to 1.5 to 2 times larger than the vertical vibration, Beyond this range, there may be other problems, especially resonance problems.
(3) Compared with the axial vibration, when the imbalance is dominant, the radial vibration (horizontal and vertical) is much larger than the axial vibration (except for the cantilever rotor).
(4) The direction of the cantilever rotor imbalance problem, usually, radial and axial vibration are relatively large, it is static imbalance and coupling imbalance exist at the same time, so usually need two plane balance correction.
(5) rotor with unbalanced vibration problem, its vibration phase is stable and repeatable.
(6) The imbalance problem will increase the total amplitude value. If the rotor working speed is close to the resonance point at the natural vibration frequency of the system, a small amount of unbalance vibration will increase by 10 to 50 times.
(7) the phase performance of the rotor imbalance problem, the vertical and horizontal phase difference of the same bearing position is about 90°, and the phase difference of the bearings on both sides in the same direction is equal.
