6 Steps To Equipment Vibration Analysis
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 unstable, what parameters are associated with it, etc. For example: a sudden increase in vibration may be due to a sudden imbalance of the rotor or a sudden decrease in stiffness; whether the unstable amplitude is related to load adjustment, temperature change, start-up and shutdown, etc.
2. Understand the maintenance situation
Whether maintenance has been carried out before and after the vibration starts. If the vibration is not large before the maintenance, then the process of this maintenance and the parts replaced must be very clear. In similar cases, the cause of the fault can often be found from the maintenance process. For example: the vibration is large before the maintenance, and there is no significant change in the vibration after the maintenance, which can also rule out the content that has been repaired.
3. External observation and testing of equipment
Understand the basic parameters of the equipment, such as temperature, sound, pressure, speed, load, oil temperature, vibration, etc., quickly understand the overall operation of the equipment, and roughly determine the type of fault. For some common faults, accurate diagnosis can even be made. Simply relying on signal analysis can easily complicate simple problems.
4. Determine the fault location
Usually, the fault location is at the location with the maximum amplitude. As the distance from the fault source increases, the exciting force will gradually decay. Of course, there are exceptions to this rule. For example: for vertical equipment, due to the relationship between height and stiffness, a fault in the towed part will cause the upper motor to vibrate the most.
5. Simple judgment of the cause of the fault
Some fault causes can be accurately judged according to the relationship between each parameter and vibration, as well as the direction of vibration. For example, the comparison of the vibration amplitude in the horizontal direction and the vertical direction can basically determine the cause of some faults, but before that, the installation structure of the equipment must be clear, that is, the relative stiffness in the horizontal direction and the vertical direction should be intuitively understood. Equipment installed on a solid or rigid support is different from equipment installed on an elastic support. Only equipment with a rigid foundation is discussed here. Assuming that 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 means that the vertical stiffness is less than the horizontal stiffness, which may be caused by looseness or excessive fit clearance. If the vertical vibration of the wheel side bearing is large, it may also be caused by the upper and lower deviation of the centering; while the horizontal vibration close to the impeller side generally indicates rotor imbalance, and the horizontal vibration close to the coupling side is often the coupling misalignment. For axial vibration, it is generally necessary to consider whether misalignment or shaft bending has occurred. Of course, if the axial amplitude is too large, it may also be caused by the imbalance of the extended end rotor. It should be noted that fluid disturbance often causes axial vibration of the rotor, so the load can be adjusted for observation.
6. Combination and comparison of vibration data
If you have instruments and equipment, you should combine them with instrument measurements. If you have previous vibration data, you must compare them to see which frequencies have changed significantly. Faults that cause abnormal vibrations will produce vibrations with certain frequency components, which may be a single frequency, a group of frequencies, or a certain frequency band. Based on 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, focusing on several possible causes of the fault, and then eliminating them one by one in combination with all the characteristics.
