Vibration analysis
6 steps
In the field fault analysis, first of all, we should have a macro understanding of the equipment, and get the surface cause according to the external characteristics. Then the mechanism analysis of its main vibration characteristics is carried out to judge the deep-seated reasons.
1, understand the vibration history
When the vibration of the machine increases suddenly or gradually, determine whether the vibration is stable during the period, if it is not stable, which parameters are associated with it, and so on.
For example, the sudden increase of vibration may be the sudden unbalance of the rotor and the sudden weakening of the stiffness.
Whether the amplitude instability is associated with load adjustment, temperature change, start and stop, etc.
2, understand the maintenance situation
If the vibration before and after the start of the maintenance, if the vibration before the maintenance is not large, then the maintenance and replacement of the parts must be very clear, similar to this situation, often from the maintenance process can find the cause of the fault.
If the vibration is large before the overhaul and there is no significant change in the vibration after the overhaul, the content that has been repaired can also be excluded.
3, the external observation and testing of the equipment
Understand the basic parameters of the equipment, such as the temperature, sound, pressure, speed, load, oil temperature, vibration, etc., quickly understand the overall operation of the equipment, roughly determine what type of fault, for some common faults, and even make accurate diagnosis, and simply rely on signal analysis but easy to complicate simple problems.
4. Determine the fault location
Usually, the fault location is at the position with the greatest amplitude. With the increase of the distance from the fault source, the exciting force will gradually decrease.
Of course, there are exceptions to this rule, such as vertical equipment, due to the relationship between height and stiffness, the failure of the towed part will cause the upper motor to vibrate the most.
5. Simple judgment of the cause of the failure
According to the relationship between each parameter and vibration, as well as the direction of vibration, some fault causes can be accurately judged.
For example, the comparison of the horizontal and vertical vibration amplitude can basically determine the cause of some failures, but the installation structure of the equipment must be clear before, that is, there should be a perceptual understanding of the relative stiffness of the horizontal and vertical directions.
The device is installed on a strong or rigid support, which is not the same as being installed on an elastic support, and only equipment with a rigid foundation is discussed here.
If the fan is installed on a rigid concrete foundation, the vertical stiffness of the equipment will be greater than the horizontal stiffness. At this time, for common faults such as mass imbalance, the horizontal amplitude is generally greater than the vertical amplitude.
If the vertical vibration is greater than the horizontal vibration, it indicates that the vertical stiffness is less than the horizontal stiffness, which may be caused by loosening or excessive fit clearance.
If the vibration in the vertical direction of the wheel side bearing is large, it may also be caused by the deviation in the center; The horizontal vibration near the impeller side generally indicates the rotor unbalance, while the horizontal vibration near the coupling side is often the coupling misalignment.
For axial vibration, it is generally necessary to consider whether misalignment or axial bending occurs. Of course, if the axial amplitude may also be due to the overhang end rotor imbalance caused.
It should be noted that the disturbance of the fluid often causes axial vibration of the rotor, so the load can be adjusted for observation.
6. Combination and comparison of vibration data
In the case of instrument equipment, it is finally combined with instrument measurement, and if there is previous vibration data, it must be compared to see which specific frequencies have changed greatly.
A fault that causes an abnormal vibration will produce a vibration of a certain frequency component, which may be a single frequency, a group of frequencies or a certain frequency band.
According to the frequency composition of the vibration signal, the time domain waveform, and the phase relationship of different parts, a number of impossible faults can be quickly eliminated, and attention can be focused on several possible causes of failure, and then all characteristics are eliminated one by one.