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Rotating machinery axial vibration of 5 big reason and mechanism analysis, expansion of knowledge! - bearing knowledge

by:Waxing     2020-06-01
As everybody knows, in addition to the radial vibration in the operation of rotating machinery, also often occur axial vibration. Radial vibration is occurred in the vibration of the vertical and horizontal directions. Axial vibration is refers to the bearing body including the circle and the circle, the circle between the body and the outer body, or between the ring body and the ring body on installation has a simple structure of rolling body, causing vibration. Compared with the radial vibration and axial vibration processing is more difficult, so we can say this article. So what is the main cause of axial vibration? Excessive vibration force and bearing rigidity is poor. Radial vibration caused by the axial vibration analysis has two situations: a bearing seat is equipped with a bearing and a bearing seat is equipped with two bearings. In a bearing seat is equipped with a bearing bush intuitively, and the axial vibration of the bearing should be caused by rotor axial movement. But in fact, there is a layer of oil film between the rotor and bearing. Rotor axial movement of the oil film is passed on to the bearing shell, it is difficult to cause the axial vibration of the bearing. The axial vibration of unit actually happened is mostly caused by the radial vibration force. From the perspective of the dynamics of radial force and axial vibration is not in the same direction, should not cause the axial vibration. But, after considering elastic bearing supporting, radial force will indirectly stimulate the axial vibration. Now the above graphs, are analyzed. Assumptions on the rotor is a first order of unbalanced force, rotor deflection presents the first mode, as shown in figure ( 一) Shown below. Time t1, on both sides of the rotor bearing bearing center to the outside; T2, on both sides of the rotor bearing bearing center towards inside. Different time, bearing bearing center cyclical change, lead to bearing along the axial runout. First-order flexure, on both sides of the bearing axial swing in the opposite direction. Under the action of second order flexural vibration, as shown in figure ( b) Shown below, on both sides of the bearing axial vibration in phase. If the bearing stiffness is very big, the resulting axial vibration is very small, can be ignored. If the elastic bearing, the radial vibration will indirectly stimulate the axial vibration of the bearing. Within A bearing seat is equipped with two axle bush above, assuming that A and B on both sides of the vertical vibration in phase, if A and B with the same on both sides of the bearing stiffness, radial vibration will not stimulate the axial vibration. If A and B on both sides of the vertical vibration reverse phase, or of A and B on both sides of the vertical vibration in phase, the support stiffness asymmetry, but both sides will result in the two cases and the axial vibration of the bearing. The above two cases of axial vibration, often is accompanied by a large radial vibration. Therefore, when the axial vibration, if the radial vibration is big, the best processing method is first reduce the radial vibration. Engineering practice shows that the radial vibration decrease 10%, axial vibration decrease the percentage may be higher. Such a case, reduce the vibration force is much smaller than the increase of bearing stiffness workload, and the effect is much more obvious. Insufficient bearing stiffness caused by axial vibration analysis sometimes bearing vertical and horizontal vibration eliminated, axial vibration is still larger. This kind of situation is mostly caused by insufficient rigidity of the bearing itself. Bearing seat and bedplate, bedplate and loose coupling between base, combined with the uneven surface contact, secondary grouting looseness, walking at the bottom of the table mat iron, etc are likely to induce axial vibration. This kind of fault processing unit must be combined with maintenance. Other factors caused by the axial vibration analysis of the rotor center deviation is too large rotor, the deflection after coupling bolt connection, journal will appear larger sway degrees, as shown in the above. With the rotation of the shaft, the oil film pressure will change periodically, serious when will lead to the axial vibration of the bearing. As shown in the above loads spherical bearing, spherical bearing for convex spherical outside surface, bearing cover and the bearing of the bearing surface for the concave spherical surface. This kind of bearing has since a function. Trunnion tilt, the bearing can automatically adjust the Angle of the center line of the bearing, the axle bush sharply face and always maintain the axial contact between journal well. However, when the interference between the spherical tile and tile is bigger, the pillow will pin bearing, lose the function, resulting in a larger axial vibration. Resonance caused by axial axial vibration analysis some often arise frequency for two times on the generator bearing axial vibration frequency. Electromagnetic exciting force is the main factor of double frequency induced vibration. Bearing stiffness is normal, and the natural frequency of vibration of the bearing is mostly higher than two times the working speed, the electromagnetic vibration force does not induce twice the frequency of the vibration significantly. However, when the bearing seat and counter or links between bedplate and foundation stiffness is poorer, and the natural frequency of vibration of the bearing could fall into two times near the rotating speed frequency. Under the action of electromagnetic vibration force of the generator, lead to a significant bearing of two axial resonant frequency doubling. Appear this kind of circumstance, need to check the bearing connection stiffness, reducing the rotor of the deviation, check and adjust the rotor of the generator and the uniformity of the air gap between the child and so on.
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