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Common gearbox failures

Release date:

2022-07-11

The gearbox is a complex system comprising components such as gears, transmission shafts, bearings, and the housing structure. Among these, the housing structure plays a crucial role in providing support and ensuring proper sealing within the entire system; however, it has a relatively low failure rate. As a result, most gearbox failures actually occur in the gears, transmission shafts, and bearings. Statistics show that failures involving gear shafts and rolling bearings account for more than 90% of all gearbox malfunctions. Consequently, in gearbox fault diagnosis, the primary focus is typically on determining whether a fault exists and, if so, pinpointing its exact location. Now, let’s explore the common types of gearbox failures based on the characteristics of vibration signals!

　　 Gearbox It is a complex system that includes components such as gears, transmission shafts, bearings, and housing structures. Among these, the housing structure plays a crucial role in supporting and sealing the entire system, and it has a relatively low failure rate. Gearbox It primarily occurs on gears, drive shafts, and bearings. According to statistics, failures in gear shafts and rolling bearings account for Gearbox More than 90% of failures occur in Gearbox In fault diagnosis, it is usually sufficient to simply indicate whether a fault exists and where the fault has occurred. Based on the characteristics of vibration signals, let's now explore this further together. Gearbox A common malfunction!

　　01 Tooth Profile Error

　　Tooth profile error refers to the deviation of a gear tooth from its ideal profile, encompassing manufacturing errors, installation inaccuracies, and those that arise during service. Here, we’re primarily focusing on tooth profile errors caused by gear usage—such as plastic deformation of the tooth surface, uneven surface wear, and surface fatigue. Additionally, tooth breakage can also lead to tooth profile errors; however, since its vibration signal characteristics are distinctly different from the aforementioned types of errors, it is treated as a separate failure mode for ease of fault diagnosis.

　　02 Gear shows uniform wear

　　Uniform gear wear primarily refers to the material friction damage that occurs during the meshing process after a gear has been in use, and it mainly includes abrasive uniform wear and corrosive uniform wear. When gear teeth experience uniform wear, no significant tooth profile errors typically arise; however, the vibration signal characteristics become noticeably distinct, clearly indicating that these deviations are not attributable to tooth profile issues.

　　03-axis misalignment

　　Misalignment of the shafts primarily refers to a situation where the shafts at both ends of the coupling are parallel but not properly aligned, often due to issues during design, manufacturing, installation, or operation. This misalignment causes distributed-type tooth profile errors in the gears mounted on the shafts. The key difference between vibration signals caused by single gear tooth profile errors and those resulting from shaft misalignment is that, in the latter case, all gears on the shafts will exhibit tooth profile errors simultaneously, leading to signal modulation phenomena.

　　04 Incisor

　　Tooth breakage is a severe gear failure, primarily occurring in two forms: fatigue-induced tooth fractures and overload-induced fractures—though fatigue fractures are far more common. When a tooth breaks, the resulting vibration signal exhibits significantly higher impact energy, distinguishing it clearly from tooth profile errors and uniform gear wear.

　　05 Fuel Tank Resonance

　　Tank resonance refers to excitation caused by impact energy. Gearbox The resonance phenomenon occurring due to the tank's natural frequency. The significant impact vibration energy generated by shell resonance is a very serious malfunction, typically caused by external excitation of the shell.

　　06-axis with mild curvature

　　 Gearbox Failures also occur frequently. If a shaft experiences slight bending, it will cause tooth profile errors in the gears mounted on that shaft. Unlike tooth profile errors caused by a single gear, shaft bending results in significant tooth profile deviations across all gears attached to the same shaft.

　　07-axis severely bent

　　Severe shaft bending is Gearbox A more severe form of failure occurs when the shaft is severely bent, generating significant impact energy and leading to serious consequences. Additionally, the resulting vibration signals differ markedly from those observed in cases of minor bending.

　　08-axis imbalance

　　Axial imbalance is Gearbox Typical failures of the central shaft. Imbalance is caused by eccentricity resulting from deformation during manufacturing, installation, and even after the shaft has been put into use, leading to unbalanced vibrations. If shaft imbalance occurs, gear transmissions may also exhibit tooth profile errors—but this type of failure is distinctly different from simple tooth profile errors.

       09 Axial Clearance

　　Axial play primarily occurs when using helical gears, as two helical gears on the same shaft simultaneously engage with each other. If the axial positioning and locking mechanisms are inadequate, axial play may occasionally develop—typically due to an imbalance in axial forces. This type of axial play severely compromises the transmission accuracy and stability of the gears, and can even lead to impact wear on the gear tooth ends, making it a rather serious malfunction.

　　10 Bearing Fatigue Spalling and Pitting

　　 Gearbox Typical failures in rolling bearings include fatigue spalling and pitting on the inner and outer rings as well as the rolling elements. As the shaft rotates, mechanical impacts occur during the contact between the inner race and the rolling elements, generating force impulses with significant amplitude variations. When a rolling bearing fails, the energy released is much lower than that produced by gear-related vibrations, making diagnosis one of the key challenges.


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