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Why a Single Bearing Failure Triggers Total Gearbox Collapse: Industry Insights
In the practical application of traction gearboxes for rail transit, a common phenomenon emerges during disassembly and inspection: while one bearing shows obvious damage, other components such as gears, adjacent bearings, seals, and even the gearbox housing also exhibit abnormalities to varying degrees. On the surface, it seems like an unfortunate chain of events, but from an engineering perspective, this is a typical characteristic of gearbox systems—bearings in gearboxes never operate as independent components, but as a strongly coupled system. Once a key node in the system deviates from its normal state, the failure of other components is merely a matter of time.
Bearings: The "Force Network" at the Core of Gearboxes
Bearings in traction gearboxes do far more than just "support the shaft." Collectively, they perform four critical functions:
- Constraining the spatial position of the shaft
- Balancing radial and axial forces generated by gear meshing
- Controlling shafting stiffness to maintain the meshing center distance
- Providing stable geometric relationships for gears
These functions form an intricate "force network" within the gearbox. Any change in the operating state of one bearing will rewrite the force distribution path—explaining why bearing issues often manifest in gear performance ultimately.
Clearance Anomaly: The First Domino to Fall
In numerous gearbox maintenance cases, a highly frequent starting point of failure is the abnormal axial clearance of one bearing. This anomaly can stem from three main causes:
- Deviations in clearance adjustment during assembly
- Wear-induced changes after long-term operation
- Effective clearance "consumed" by temperature rise
Initially, such changes rarely trigger immediate alarms, but they quietly alter the force balance of the entire shafting system.
Shaft Position Drift: A Fatal "Minor Change"
When a bearing's clearance is either too small or too large, the direct consequence is shaft position drift. Unlike visible large displacements, this drift typically manifests as:
- Minute axial position changes
- Slight tilting of the shaft axis
- Redistribution of loads among bearings
For high-precision gear meshing systems, however, these "minor changes" are sufficiently catastrophic.
Gear Meshing: The Hidden Danger of Uneven Loading
Ideally, gear design aims for uniform load distribution across the tooth width and contact areas within the designed meshing zone. But when the shaft deviates due to bearing issues, the meshing state deteriorates progressively:
- Localized stress concentration on tooth surfaces
- Significant wear on one side of the tooth width
- Contact patches shifting toward the tooth tip or root
This uneven loading drastically increases local contact stress and directly drives up system temperature.
Abnormal Temperature Rise: A Sign of System "Rescue Failure"
As gear meshing deteriorates, the system enters a dangerous cycle:
Uneven meshing → Increased friction power → Rising temperature → Further changes in bearing clearance → Worsened meshing conditions
At this stage, the gearbox exhibits telltale signs such as abnormal local bearing temperatures, significant temperature differences across the housing, and changes in oil color or odor. Yet the root cause remains the initial neglected bearing anomaly.
Why "Undamaged" Bearings Fail Too
When one bearing fails prematurely, others cannot escape the consequences. Three key factors contribute to this:
- Forced redistribution of loads: Bearings previously operating within safe load limits are forced into overload conditions.
- Significantly increased shafting vibration: Elevated vibration accelerates wear on all moving parts.
- Deteriorated overall lubrication environment: Abnormal temperatures and vibration compromise oil performance, reducing lubrication effectiveness.
This explains why disassembled gearboxes often show "minor issues" in every bearing.
From "Single-Point Failure" to "Systematic Collapse: The Complete Evolution Path
A typical failure progression follows a clear sequence:
- Initial stage: Abnormal clearance in a single bearing
- Intermediate stage: Changes in shafting positioning
- Development stage: Uneven gear meshing
- Amplification stage: Abnormal temperature rise and vibration
- Outcome: Synchronous damage to multiple components
This is not an accident but an inevitable result in system engineering.
Beyond "Fixing What's Broken": A System-Centric Approach to Gearbox Maintenance
Pub Time : 2026-01-07 10:05:52
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Hangzhou Ocean Industry Co.,Ltd
Contact Person: Mrs. Lily Mao
Tel: 008613588811830
Fax: 86-571-88844378