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Abstract: The vibration of a frequency spectrum analysis of the composition of the study cited a variety of conditions, a change in frequency components.
Key words: vibration; balance; one octave; spectrum; amplitude
Key words: TB123 Document code: B
 
     According to statistics, 19% of the vibration equipment to automatically imbalance that is one octave, and the resulting imbalance in the action for many reasons. On-site measurements of the spectrum, many the result of a machine with more frequency related, following only one reason for the increased frequency vibration analysis.
     First, a single frequency signal
   Unbalanced rotor vibration time-domain for the sine wave, frequency Rotor frequency, large radial vibration. Figure-frequency spectrum in a stable peak, the harmonic energy to focus on the fundamental frequency, the frequency of other smaller amplitude. When less than the natural frequency of vibration frequency, amplitude frequency increases with speed; when frequency is greater than the natural frequency of vibration, speed toward a smaller increase in the amplitude of the value of stability; when close to the natural frequency of vibration frequency when the machine Resonance, with the largest peak amplitude. As the bearings are usually horizontal stiffness of the small, large amplitude vibration, so that the axis into an oval track. A strong vibration on the extent of the work is very sensitive to changes in speed.
     1. Imbalance in power
Vibration characteristics of the spectrum for close to the sine wave, quasi-circular orbit; radial vibration to the main direction of the general level of magnitude greater than the vertical direction; amplitude and speed is proportional to the square, a frequency multiplier; phase stability, Office close to the phase of the two bearings, bearing the same horizontal and vertical direction of the phase difference of close to 90 degrees.
2. Imbalance in the dual
Vibration characteristics of the spectrum for close to the sine wave, quasi-circular orbit; the two have a greater bearing Department of vibration, a serious imbalance, will have a greater inter-shaft vibration; amplitude and the speed is proportional to the square, Vibration frequency to frequency-based one, sometimes two, the third harmonic components; vibration and stability phase, the phase difference between the two bearings Department 180 degrees.
3. Dynamic imbalance
Vibration characteristics of the spectrum for close to the sine wave, quasi-circular orbit; radial vibration to the main square of the amplitude and speed in direct proportion to the frequency of a frequency-based; vibration and stability phase, phase two bearings close to the Department.
4. External force under the (rotation) have a resonance
Various parts, pieces of the structure under external force generated by the natural resonance for the self-excited vibration, the frequency with a different structure corresponds to that the different stiffness caused by different resonance.
Spectral characteristics of the time domain for the sine wave, the frequency of vibration to a frequency-based.
Second, related to a frequency signal
1. Rotor permanent bending
Vibration similar to the dynamic imbalance and wrong, in order to double the frequency to the main, will have to double the frequency of vibration; vibration with the increase in the speed very quickly; usually amplitude stability, greater axial vibration, the Office for the phase difference between the two 180 Degrees.
2. Rotor exist so that the crack deflection increase
Rotor system appeared on the horizontal axis of fatigue cracks, may lead to broken shaft accident, a great harm. To identify cracks in a timely manner to prevent the sudden rupture of the disastrous accident. Shaft crack commonly used diagnostic method is to monitor the machines through the open stands in the process of "critical speed and a half" of the changes in the amplitude, as well as to monitor the operation of the rotor amplitude and phase changes.
The horizontal axis for the fatigue crack and a half months of the arc-shaped crack, the crack area suffered as a result of the stress state, the horizontal axis shows cracks open, closed, when Zhang closed when three conditions. When the crack shaft of the total area affected by tensile stress, the cracks are open or open with a tendency, no less than the stiffness shaft when the crack stiffness, crack deflection no greater than when the deflection, to a certain speed of the work under the phase and amplitude are Change. When the crack shaft of the total area under pressure stress, the cracks are closed, slightly less than the stiffness of the shaft without cracks, the crack of the rotor vibration does not affect the basic characteristics. When the crack area by alternating pressure on the shaft, the periodic crack open when they closed at on the impact of vibration more complicated.
Horizontal fatigue cracks appear when the stiffness was anisotropic axis, with a non-linear nature of the vibration. And a second harmonic frequency components over time gradually increased, especially in the second harmonic components, with the depth of the crack increase significantly increased.
3. Sliding bearing big gap
Shaft bearings and the gap is too large, similar to the misalignment and mechanical loosening, should pay attention to the distinction. At this point a larger radial vibration, in particular the vertical radial; may have a greater axial vibration, thrust bearings may be higher harmonic components; radial and axial stability for the time-domain waveform of the cycle advantage, Each round of 1 to 3 peak; no greater acceleration of the impact of the phenomenon. If the axial and radial vibration close to the size of the vibration, indicating a serious problem.
4. Gland bearing loose
Vibration frequency to frequency and high harmonics and harmonic score. With a vibration direction and amplitude stability.
5. Coaxiality Shaft poor
Shaft misalignment caused by many reasons, such as installation errors, not enough to adjust, after carrying the deformed-based machines, such as uneven settlement.
Rotor with radial vibration of a frequency multiplier and two main axial vibration in one octave, second and third harmonic frequency-doubling there is stability in the peak, generally up to 50% of radial vibration. With radial vibration of the same size or greater, indicating serious condition.
Third, the other with a frequency-related causes
1. Motor, fan base, such as cracking, and stiffness caused by changes in the resonance easily.
2. Coupling manufacturers to install deviation caused by wear and tear; not supporting the connection nut / bolt defect; coupling nut wear.
3. Rotor temperature gradient effects.
4. Lubricating oil temperature change caused by the instability.
5. Rotor bearings or rigid change.
6. Electromagnetic anomaly.
7. Gearing gear in the cumulative manufacturing error.
 
References:
[1] Wang. Diagnostics simple vibration equipment, industrial machinery Press, 1990.
[2] Shen Qing root. Chemical machinery fault diagnosis technology, 1993.
[3] Beijing Beijing's aircraft, equipment fault diagnosis technology and its application in 1998.