10 Main Faults of Gearbox

The gearbox system includes gears, transmission shafts, bearings, and box structure, etc. Among them, the box structure plays a supporting and sealing role in the entire system, and its probability of failure is very low. Therefore, in the gearbox, faults mainly occur in the gears, transmission shafts, and bearings. According to statistics, gear, shaft, and rolling bearing failures account for over 90% of gearbox failures.

In the fault diagnosis of gearboxes, it is generally only necessary to provide whether the fault occurred and the location of the fault. According to the characteristics of vibration signals, the common typical forms of faults are:

1 Tooth profile error

Tooth profile error refers to the deviation of gear tooth profile from the ideal tooth profile, including manufacturing error, installation error, and errors generated after service. This mainly refers to the tooth profile error generated after the gear is put into use, including tooth surface plastic deformation, uneven surface wear, and surface fatigue. Tooth breakage can also cause tooth profile errors, but due to the significant differences in the characteristics of its vibration signal from these tooth profile errors, it is classified as a separate fault form for fault diagnosis.

2. Uniform wear of gears

Uniform wear of gears mainly refers to the phenomenon of material friction damage that occurs during the meshing process of gears after they are put into use, mainly including uniform wear of abrasive particles and uniform wear of corrosion. Uniform wear of gear teeth does not cause serious tooth profile errors, and the characteristics of their vibration signals also vary greatly, so they cannot be attributed to tooth profile errors.

3-axis misalignment

Axis misalignment mainly refers to the occurrence of distributed tooth profile errors in the gears on the shaft due to design, manufacturing, installation, or usage issues at both ends of the coupling, causing the shaft system to be parallel but not aligned. The difference between vibration signals and single gear tooth profile errors is that when the shaft is misaligned, all gears on the shaft will produce tooth profile errors, leading to signal modulation.

4 broken teeth

Tooth breakage is a serious fault in gears, mainly in two forms: fatigue breakage and overload breakage, with most of them being fatigue breakage. When a tooth is broken, its vibration signal has a high impact energy, which is different from tooth profile error and uniform gear wear.

5 box resonance

Box resonance is a resonance phenomenon caused by the excitation of the natural frequency of the gearbox box by impact energy. The resonance of the box generates a large amount of impact vibration energy, which is a very serious fault usually caused by external excitation of the box.

6-axis mild bending

The shaft in the gearbox also frequently malfunctions. When the shaft undergoes slight bending, it can also cause tooth profile errors in the gears on that shaft. Unlike a single gear tooth profile error fault, when the shaft is bent, all gears on that shaft will produce significant tooth profile errors.

Severe bending of the 7-axis

Severe bending of the shaft is a more serious form of failure in gearboxes. When the shaft undergoes severe bending, it will generate significant impact energy, causing serious consequences, and its vibration signal is also different from mild bending.

8-axis imbalance

Unbalanced shaft is a typical fault of the shaft in a gearbox. The so-called imbalance refers to the unbalanced vibration of a shaft caused by eccentricity, which can be caused by deformation after manufacturing, installation, and use. When shaft imbalance occurs, it will also lead to tooth profile errors in gear transmission, but this type of fault is significantly different from pure tooth profile errors.

9 axial displacement

Axial displacement mainly occurs when using helical gears. When there are two helical gears engaged simultaneously on the same shaft and there is no good positioning and locking device in the axial direction, sometimes axial displacement occurs, which is mainly caused by the unbalanced axial force. Axial displacement will seriously affect the accuracy and stability of gear transmission, and may also cause impact wear on the gear tooth end face, which is a relatively serious fault.

10. Fatigue peeling and pitting of bearings

The typical faults of rolling bearings in gearboxes are fatigue peeling and pitting of the inner and outer rings and rolling elements. When the shaft rotates, mechanical impact occurs between the inner and outer rings and the rolling element during the contact process, generating a force with a large amplitude of variation called impact pulse. When the rolling bearing in the gearbox malfunctions, its energy is much smaller than the vibration energy generated by the gear, making it one of the diagnostic difficulties.