Content
In the world of mechanical engineering, bearings are often referred to as the “unseen heroes.” They are the critical interface between stationary and moving parts, designed to reduce friction and support loads. However, despite their robust design, bearings are surprisingly sensitive.
Statistically, only about 10% of bearings actually achieve their calculated design life, known as the life. The remaining 90% fail prematurely. These failures are rarely “random acts of God”; they are the result of specific environmental or operational stressors. When a bearing fails, the ripple effect can be catastrophic, leading to unplanned downtime, damaged shafts, and in extreme cases, total equipment destruction.
This article explores the primary culprits behind bearing failure, providing a roadmap for maintenance professionals to move from a “fail-and-fix” mentality to a “predict-and-prevent” strategy.
If bearings are the heart of a machine, lubricant is its lifeblood. Approximately 36% of premature bearing failures are linked to incorrect lubrication.
Without an adequate oil film, metal-to-metal contact occurs. This leads to increased friction, which generates localized heat. This heat causes the metal to expand, further reducing internal clearance and creating a vicious cycle of “thermal runaway.”
A common misconception is that “more is better.” Over-greasing a bearing causes churning. The rolling elements have to fight through the excess grease, generating immense internal heat. This can actually melt the grease, causing the base oil to separate from the thickener, leaving the bearing with no actual protection.
Using a lubricant with the wrong viscosity is a recipe for disaster. If the viscosity is too low, the oil film won’t be strong enough to separate the surfaces. If it’s too high, the internal friction will cause overheating.
| Failure Type | Physical Symptom | Common Cause |
|---|---|---|
| Insufficient Lubricant | Discolored (blue/brown) raceways | Neglected maintenance intervals |
| Over-Lubrication | Blown seals, grease hardening | Excessive use of grease guns |
| Incompatible Grease | Grease turns to a liquid or “soapy” mess | Mixing lithium-based and polyurea-based greases |
| High Viscosity | Excessive operating temperature | Incorrect oil selection for high speeds |
Contamination accounts for roughly 14% of all bearing failures. Even particles invisible to the naked eye can cause significant damage because the oil film thickness in a bearing is often less than 1 micron.
Dust, sand, or metal chips from other failing components act like sandpaper. They create “bruising” on the raceways. As the rolling elements pass over these bruises, they create stress risers that eventually lead to spalling (the flaking off of metal).
Water is the enemy of steel. Even 1% water in oil can reduce bearing life by over 50%. Moisture causes:
Around 16% of bearings fail because they were never installed correctly in the first place.
Using a hammer and drift to install a bearing is a death sentence. This causes True Brinelling—permanent indentations in the raceways caused by the rolling elements being forced into the metal.
If the shaft is bent or the housing is not square, the load is not distributed evenly across the rolling elements. This creates an uneven wear path that can be seen upon inspection.
Sometimes the failure isn’t the bearing’s fault, but the environment it operates in.
Every bearing has a Dynamic Load Rating (). If a machine is pushed beyond its design specs, the subsurface stresses exceed the material’s limit, leading to rapid fatigue.
In modern industry, Variable Frequency Drives (VFDs) are common. However, they can create stray currents. If these currents find a path to ground through the bearing, they create microscopic sparks (arcing). Over time, this creates a “washboard” pattern known as fluting.
This occurs when a machine is stationary but subjected to external vibrations (e.g., a backup pump sitting next to a running turbine). The rolling elements vibrate against the raceway in one spot, pushing out the lubricant and wearing away the metal.
When a bearing fails, the damaged surfaces tell a story. By examining the wear patterns, we can reverse-engineer the cause.
| Visual Pattern | Likely Root Cause |
|---|---|
| Symmetrical wear path in both rings | Correct operation (Normal fatigue) |
| Wear path shifted to one side of the raceway | Axial thrust or Misalignment |
| Wobbling/Zig-zag wear path | Bent shaft or misaligned housing |
| Circumferential “frosted” or “fluted” lines | Electrical discharge / VFD issues |
| Dull, matte finish on balls/rollers | Abrasive contamination (dust/dirt) |
To achieve the full design life of a bearing, facilities must adopt “Precision Maintenance” standards.
Bearing failure is a symptom, not a disease. Whether it is the grit of contamination, the heat of poor lubrication, or the shock of a heavy hammer, every failure leaves a trace. By shifting focus from replacing bearings to protecting them, companies can save thousands in lost production and repair costs.
Q1: How can I tell if a bearing is failing before it actually stops the machine?
A: Early warning signs include increased noise (grinding, whistling, or chirping), a rise in operating temperature (detectable via infrared thermometers), and increased vibration. Advanced methods like ultrasound can detect friction-related “cries” long before the human ear can hear them.
Q2: Is it better to use oil or grease for lubrication?
A: It depends on the application. Grease is generally used for 80% of applications because it is easier to retain and provides better sealing against contaminants. Oil is preferred for high-speed or high-temperature applications where heat dissipation is critical, or where an oil circulation system is already present.
Q3: Why is electrical “fluting” more common in modern motors?
A: The rise of Variable Frequency Drives (VFDs) is the primary cause. VFDs create high-frequency voltage pulses that can build up on the motor shaft. If the motor isn’t properly grounded or fitted with insulated bearings/brush rings, this electricity “jumps” across the bearing oil film, causing micro-pitting.
Q4: Can a “failed” bearing be refurbished?
A: Large-scale bearings (over 8 inches in diameter) used in heavy industry can often be remanufactured if the damage is caught early (e.g., surface polishing or minor pitting). However, small, high-speed bearings should always be replaced, as the cost of refurbishment exceeds the cost of a new unit.
Q5: What is the most common mistake made during bearing installation?
A: The most common mistake is applying force to the wrong ring. If you are mounting a bearing onto a shaft (interference fit on the inner ring), you must apply pressure only to the inner ring. Applying force to the outer ring transmits the load through the rolling elements, causing “True Brinelling” (instant permanent damage).
Product Categories
Contact Us
+86-510- 88763239
+86-13585028417
#198-601,Minfeng Road, Liangxi District, Wuxi, Jiangsu, China
Ready to Begin?
Get in Touch
Now!
UKL BEARING
English
Español
русский
