Roller bearings are one of the sturdiest precision components in industrial motors and other applications, with less than one percent not completing their expected lifecycle. Their very robustness means bearing failure can take maintenance crews by surprise, bringing equipment to sudden and catastrophic halts.

Causes of Bearing Failure

When bearings do fail before the end of their life cycle, the following are the most likely causes:

  • Materials and production flaws (less than 1 percent),
  • Consequential damage (5 percent),
  • Mounting faults (5 percent),
  • Unsuitable bearing choice for application (10 percent),
  • Insufficient lubricant (15 percent),
  • Unsuitable lubricant (20 percent),
  • Contamination by solid objects (20 percent),
  • Aged lubricant (20 percent).

Lubrication Issues

A thin film of oil or grease is needed to cover the rolling and sliding surfaces or bearings and their raceway. Proper lubrication helps:

  • Prevent metal to metal contact,
  • Reduces friction and abrasion damage,
  • Prolongs bearing service life,
  • Prevents rust and corrosion,
  • Keeps rolling elements free from contamination by water or solid objects.

Bearing Mounting and Installation

Mistakes made during mounting and installation can lead to bearing failure. Taking the following steps can reduce failure rates:

  • Use proper tools, including induction heaters and sleeves to press fit entire ring face of the bearing ring,
  • Verify machine shaft and housing tolerances
  • Ensure proper shaft alignment, especially when mounting bearings with separable components,
  • Calculate how lubrication, shaft fit, and temperature affect radial internal clearance.

Operational Stress

When operational stress affects bearings, increased noise and temperature problems are often the most noticeable symptoms. After start-up, bearings usually have temperatures 50 to 104 Fahrenheit higher than the surrounding room temperature and should ideally be lower than 212 Fahrenheit.


A variety of noises can suggest bearing failure, including the following:



Sound

Possible Cause

Hiss

Rough raceway, ball, or roller surface.

Buzzing / Roaring that changes pitch and loudness with speed

Resonance,

Poor fit,

Deformed bearing rings,

Raceway, ball, or roller vibrations.

Crunching heard and felt when bearing rotated by hand

Scoring of raceway surface, balls, or rollers,

Dust or other contamination.

Humming that ends power shut off

Electromagnetic sounds from motor.

Clatter at low speeds, becoming continuous as speed rises

Insufficient lubricant causes bumping in cage pockets

Screeching / howling that changes with speed and temporarily dissipates with lubrication

Poor lubrication,

Large radial clearance.

Irregular squealing

Fitting surfaces may be slipping

Rustling sound that stays the same with speed changes

Dirt,

Rough raceways, ball, or roller surfaces.

Continuous growling at high speeds

Raceway, balls, or roller scoring.

Fizzing or popping

Sound of bubbles bursting in lubricant.

Large sound pressure

Rough raceway, roller, or ball surfaces,

Deformed / worn raceways, rollers or balls,

Large internal clearance caused by wear and tear.

Environmental Issues

Ideally, bearings are sheltered from environmental issues, but industrial and commercial applications rarely occur under perfect conditions. Bearing failure can result from such operating condition factors as:

  • Dust and debris, which can contaminate bearings and lubricant,
  • Water contamination of lubricant,
  • External heat, which can alter radial internal clearance while degrading lubricant,
  • An electrical current passing through bearing elements can generate sparks that cause bearings to pit and flute.

Best Practices for Bearing Inspection

If you suspect bearing failure, take the following steps to isolate the cause:

  1. Visually inspect the Bearing for signs of:
    1. Contamination,
    2. Excessive heat,
    3. Hardened grease,
    4. Blackened grease,
    5. Signs of grease escaping from bearings
  2. If possible, take a sample of lubricant at this stage for additional analysis.
  3. Cut the outer raceway in half using all necessary safety precautions and proper protective gear.
  4. Inspect lubricant and bearing for signs of contamination, including water, debris, and burnt grease due to electrical current. Electrical arcing can also cause small, abrasive metal particles to come loose from bearings.
  5. Clean all components with a manufacturer-approved degreaser or solvent.
  6. Inspect for signs of Electrical Discharge Machining (EDM), which causes microscopic pitting of raceways and bearings.
  7. Inspect for signs of frosting, a grey line around the raceway caused by wear or EDM.
  8. Inspect for fluting, a washboard pattern of damage caused by electrical current. Fluting may be visible to the naked eye or require magnification.

Solutions for Common Bearing Issues


Noise

Symptoms

Possible Causes

Possible Solutions

Loud metallic sounds

Abnormal load,

Incorrect mounting, improper / insufficient lubricant,

Contact between rotating parts.

Improve factors such as fit, preload, housing shoulder position, and internal clearance.

Improve machining accuracy.

Check alignment of shaft and housing,

Modify seals.

Loud regular noises

Corrosion or scratches on runway,

Brinelling,

Flaking.

Replace or clean bearings.

Improve seals.

Replace lubricant.

Irregular Noises

excessive clearance,

foreign particles,

flawed or flaking balls.

Improve preload, clearance, and / or fit.

Replace or clean bearings.

Improve seals.

Change lubricant.

Replace bearings.

Abnormal Temperatures


Possible Causes

Possible Solutions

Excessive lubricant,

Improper / insufficient lubricant,

Abnormal load,

Incorrect mounting,

Excessive seal friction,

Creep on fitted surfaces.

Replenish or reduce lubricant as needed.

Replace lubricant with stiffer grease.

Improve the fit, preload, housing shoulder position, and / or internal clearance.

Check alignment of shaft and housing.

Check mounting accuracy and mounting method.

Vibrations


Possible Causes

Possible Solutions

Brinelling,

Flaking,

Incorrect mounting,

Foreign particles.

Replace or clean bearings.

Correct squareness between shaft and housing shoulder.

Check side of spacer.

Lubrication Issues

Leaking or discolored lubricant can be caused by foreign matter, abrasion chipping, or excessive lubricant. Possible solutions include:


  • Reducing lubricant,
  • Replacing lubricant with stiffer grease,
  • Replacing bearings,
  • Cleaning housing and adjacent parts.

Analyzing bearing failure requires an understanding of both bearings and shaft seal maintenance. Not much can go wrong with bearings, but what can occur has the potential to damage your equipment, create unscheduled downtime, and require expensive repair work.


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