Today, the fault diagnosis of rolling bearings in gearboxes is introduced in detail. The running state of the gearbox often directly affects whether the transmission equipment can work normally. Among the component failures in gearboxes, gears and bearings have the largest proportion of failures, reaching 60% and 19% respectively.

 

The running state of the gearbox often directly affects whether the transmission equipment can work normally. Gearboxes usually include gears, rolling bearings, shafts and other components. According to statistics, among the failure cases of gearboxes, gears and bearings account for the largest proportion of failures, which are 60% and 19%, respectively. Therefore, gearbox failures Diagnostic research focuses on failure mechanisms and diagnostic methods of gears and bearings.

 

As a fault diagnosis of rolling bearings in gearboxes, it has certain skills and particularities. According to field experience, the diagnosis of rolling bearing faults in gearboxes is understood from the diagnosis method of vibration technology.

Understand the internal structure of the gearbox and the characteristics of bearing failure

 

You must know the basic structure of the gearbox, such as what mode the gear is in, how many transmission shafts are there, what bearings are on each shaft, and what types of bearings. Knowing which shafts and gears are high-speed and heavy-duty can help determine the arrangement of measuring points; knowing the speed of the motor, the number of teeth and transmission ratio of each transmission gear can help determine the frequency of each transmission shaft.

 

In addition, the characteristics of bearing failure must be clear. Under normal circumstances, the gear meshing frequency is an integral multiple of the number of gears and rotation frequency, but the characteristic frequency of bearing failure is not an integral multiple of the rotational frequency. Understanding the internal structure of the gearbox and the characteristics of bearing failures is the first prerequisite for the correct analysis of rolling bearing failures in gearboxes.

 

Try to measure vibration from three directions: horizontal, vertical and axial

 

The selection of measuring points should take into account the axial, horizontal and vertical directions, and vibration measurement in three directions may not necessarily be performed at all positions. For a gearbox with a heat sink, the measuring point of the input shaft is not convenient to detect. Even if some bearings are set in the middle of the shaft, vibration in some directions is not convenient to measure. At this time, the direction of the measuring point can be set selectively. However, in important parts, vibration measurement in three directions is generally performed. Pay special attention not to ignore axial vibration measurement, because many faults in the gear box will cause changes in axial vibration energy and frequency. In addition, multiple sets of vibration data at the same measuring point can provide sufficient data for the analysis and determination of the speed of the transmission shaft, and obtain more reference for further diagnosis of which bearing failure is more serious.

 

Consider both high and low frequency vibration

 

The gearbox vibration signal contains components such as natural frequency, rotation frequency of transmission shaft, gear meshing frequency, characteristic frequency of bearing failure, frequency conversion family, etc., and its frequency band is relatively wide. When monitoring and diagnosing this kind of broadband frequency component vibration, it is generally necessary to classify by frequency band, and then select the corresponding measurement range and sensor according to different frequency ranges. For example, low frequency acceleration sensors are generally used in low frequency bands, and standard acceleration sensors can be used in high frequency and high frequency bands.

 

Measure vibration as much as possible on the bearing housing where each drive shaft is located

 

At different positions on the gearbox housing, the response to the same stimulus is different due to the different signal transmission paths. The bearing housing where the gearbox transmission shaft is located is sensitive to the vibration response of the bearing. A monitoring point is set here to better receive the bearing vibration signal, and the upper and middle parts of the housing are closer to the meshing point of the gear, which is convenient for monitoring other gear failures.

 

Focus on sideband frequency analysis

 

For equipment with low speed and high rigidity, when the bearings in the gear box are worn, the vibration amplitude of the characteristic frequency of the bearing failure is often not the same as that, but with the development of bearing wear failure, the harmonics of the characteristic frequency of the bearing failure are harmonic. Will appear in large numbers, and there will be a large number of sidebands around these frequencies. The occurrence of these conditions indicates that the bearing has suffered a serious failure and needs to be replaced in time.

 

When analyzing data, consider both the spectral and time domain plots

 

When the gearbox fails, sometimes the vibration amplitude of each fault feature does not change greatly on the spectrum diagram. It is not possible to judge the severity of the fault or the exact value of the speed of the intermediate drive shaft, but it can be passed in the time domain diagram. Impact frequency to analyze whether the fault is obvious or the speed of the drive shaft is correct. Therefore, to accurately determine the rotational speed of each transmission shaft or the impact frequency of a certain fault, it is necessary to infer both the vibration spectrum diagram and the time domain diagram. In particular, the determination of the frequency of the frequency family of abnormal harmonics is inseparable from the auxiliary analysis of the time domain diagram.

 

It is best to measure vibration under full load of gears

 

Measure the vibration of gearbox under full load, which can capture the fault signal more clearly. Sometimes, at low load, some bearing fault signals will be overwhelmed by other signals in the gearbox, or modulated by other signals and difficult to find. Of course, when the bearing fault is serious, at low load, the fault signal can be clearly captured even through the speed spectrum.