Rooling bearings operational problems

Bearing - how does it work ?

Bearing - how does it work ?

Bearing - how does it work ?

Classification of damage modes

* Fatigue: subsurface initiated and surface initiated
* Wear: Abrasive, Adhesive
* Corrosion: Moisture, Friction, Pitting - Fretting
* False brinelling
* Electrical errosion: from high current flow and current leakage
* Plastic deformation: Overload deformation, Dirt pits
* Fracture and cracking: Forced breakage, Fatigue fracture/breakeges, Thermal cracking

Subsurface initiated fatigue

* repeated changes of stress


* structural changes to the material
* microcracks under the surface
* crack propagation
* chipping/flaking of the material

Subsurface-initiated fatigue

Structural changes under the raceway surface (highly stressed, well-lubricated small radial ball bearing)

Subsurface-initiated fatigue

Surface-initiated fatigue

* surface irregularities
* limited lubrication regime
* sliding movement
* satin-finishing, surface polishing
* surface microcracks
* micro-scratch surfaces

Surface-initiated fatigue

Surface-initiated fatigue

Initial flaking due to surface fatigue on the inner ring raceway (deep groove ball bearing)

Surface-initiated fatigue

1 Minor roughening or waviness (may even be glossy)

2 Small cracks

3 Local chipping

4 Splinters all over

Abrasive wear

* gradual removal of material
* insufficient lubrication
* penetration of dirt particles (contaminants)
* matt surfaces (mainly)
* degenerative process

Abrasive wear

Light abrasive wear of spherical roller thrust bearing outer ring

Abrasive wear

Advanced abrasive wear of spherical roller bearing outer ring (darkened and dull raceways)

Abrasive wear

Abrasive wear on separator cross bars (cylindrical roller bearing)

Abrasive wear

Polishing wear - shining - (mirror raceway surfaces) on the inside and outside of the spherical roller bearing rings

Abrasive wear

Wear process of the polishing bearing

Adhesive wear

* accelerations in motion
* slipping / rubbing
* material transfer / friction heat
* tempering/re-hardening under stress concentration and consequent cracking or spalling
* placental underloading

Adhesive wear

Adhesive wear

Blurring (streaking) on the raceway of the spherical bearing outer ring (streaking at the entrance to the load zone)

Adhesive wear

Scoring on the roller face spherical thrust bearing

Moisture corrosion

* oxidation / rust (corrosion)
* chemical reactions
* pitting/peeling corrosion
* etching (water/oil mixture or chemicals)

Moisture corrosion

Fretting - pitting corrosion

* micro-movement between mating parts
* oxidation on uneven surfaces
* oxide dust / loss of material
* occurs in load-bearing areas

Fretting - pitting corrosion

Depending on the chemical reaction, corrosion can be :

\- red (haematite, Fe2 O3 )

\- black (magnetite, Fe3 O4 )

Friction corrosion - False brinelling

* contact areas of rolling element / raceway
* micro movements / elastic deformations
* vibrations
* corrosion / wear - shiny or reddish pits
* at standstill: defects in the pitch of rolling elements
* during rotation: parallel grooves

Friction corrosion - False brinelling

Friction corrosion - False brinelling

"Grooves" on the raceway of the roller bearing outer ring

Erosion from high current flow

\- gradual removal of material

\- high current: sparking

\- local heating in very short intervals: melting/welding

\- craters up to 0.5 mm

Erosion from high current flow

Erosion from high current flow

Erosion from current leakage

\- low current

\- shallow craters close together

\- development of recesses on raceways and rollers, parallel to the axis of rotation of the bearing

\- dull discolouration, light to dark grey

Erosion from current leakage

Erosion from current leakage

Overload deformation

\- static or impact loads

\- cavities from plastic deformation in the pitch of rolling elements

\- handling defects

\- localised overload

\- chipping caused by hard/sharp objects

Overload deformation

Plastic deformation of the angular contact ball bearing cage resulting from poor handling

Overload deformation

Cylindrical roller bearing inner ring with chipping caused by mounting

Overload deformation

Pitting on the raceway of a double-row angular contact ball bearing due to incorrect mounting

Dirt pits

\- local overload

\- indentation of particles

\- soft / hardened steel / hard mineral

Dirt pits

Spalling resulting from indentation in the inner ring of a deep groove ball bearing

Extrinsic force breakage

Stress concentration above material strength limit

\- impact / overload

Extrinsic force breakage

Cracked spherical roller bearing inner ring with tapered bore result of excessive seating on the sleeve

Fractures/fatigue cracks

\- exceeding the bending fatigue strength

\- crack initiation / propagation

\- finally forced fracture

\- rings and separators

Fractures/fatigue cracks

Fatigue fracture of spherical roller bearing outer ring

Thermal cracking

\- significant slippage of rolling elements and/or insufficient lubrication

\- high friction heat

\- cracks at right angles to the direction of slip

Thermal cracking

Transverse heat cracks on the lateral surface of the inner ring Tapered roller bearing

Typical symptoms of problems

* Excessive heat generation
* Excessive noise levels
* Excessive vibration levels
* Excessive movement of shaft
* Excessive friction torque counteracting shaft rotation

Excessive heat generation

* Lubrication problem
* Sealing conditions
* Insufficient clearance in operation
* Incorrect bearing load

Lubrication problem

\- Insufficient lubricant - too little grease or too low oil level

\- Excessive amount of lubricant - too much grease without purge ability or too high an oil level

\- Wrong lubricant type - wrong consistency, wrong viscosity, wrong additives

\- Incorrect lubrication system

Sealing conditions

\- Housing seals are too tight or other components Seals

\- Multiple seals in bearing arrangement (housing)

\- Misalignment of external seals (housing)

\- Operating speed too high for contact seals in bearings

\- Seals lubricated incorrectly

\- Seals oriented in the wrong direction

Insufficient clearance in operation

\- Incorrect selection of initial internal bearing clearance

\- Shaft material expanding more than bearing steel (e.g. stainless steel)

\- Large temperature difference between shaft and housing (housing much colder than shaft)

\- Excessive pressure on the taper of the bushing

\- Excessive deviation from cylindricality of the shaft or housing

\- bearing in a deformed housing

\- Excessive tight fit of the shaft / too large shaft diameter

\- Excessive tight fit of housing / wrong housing diameter

Incorrect bearing load

\- Overloaded bearing as a result of changing application parameters

\- Misalignment of two bearing units (units)

\- Angular misalignment of two bearing units

\- Bearing installed reversed / backwards

\- Misalignment

\- Incorrect bearing (size)

\- Excessive thrust loads caused by inverse bearing misalignment

\- Material seizure from insufficient load

\- Excessive preload

Excessive noise levels

* Metal-to-metal contact
* Pollution
* Fits too loose
* Surface damage
* Friction

Metal -to -metal contact

\- Insufficient lubricant

\- Oil film too thin for operating conditions

- Rolling elements sliding (slippage)

Impurities

\- Dents on raceways and/or rolling elements caused by the penetration and movement of solid contaminants

- Particles left in the housing from production or previous bearing failures

\- Liquid contaminants reducing lubricant viscosity

Fits too loose

\- Inner ring creep (turning) on the shaft

\- Creep of the outer ring (turning) in the housing

\- Bearing nut loose on the shaft or on the bearing sleeve

\- Bearing not sufficiently fixed to other components

\- Excessive radial/axial internal clearance of the bearing

Surface damage

* Abrasive wear - ineffective lubrication
* Smearing damage caused by sliding rolling elements
* Impressions on raceways and/or rolling elements caused by rolling away of solid dirt
* Impressions on raceways and/or rolling elements from shock loads
* False brinelling marks on raceways and/or rolling elements caused by static vibrations
* Spalling on raceways and/or rolling elements due to fatigue
* Spalling on raceways and/or rolling elements due to damage initiated on the surface
* Static etching on raceways and/or rolling elements due to chemical or liquid contamination
* (Micro)chipping on raceways and/or rolling elements due to moisture or electric current damage
* Gouging on raceways and/or rolling elements due to flow of damaging electric current

Friction

\- Housing seals not correctly installed

\- Adapter or withdrawal sleeve not correctly installed

\- Spacer rings not correctly mounted

\- Retaining washer leaves bent

Excessive vibration levels

Metal -to -metal contact

Impurities

Fit fit too loose

Surface damage

Metal-to-metal contact

\- Sliding components (sliding instead of turning)

Impurities

* Dents on raceways and/or rolling elements caused by the penetration and movement of solid contaminants


* Particles left in the housing from production or previous bearing failures

Fits too loose

\-Inner ring creep (turning) on the shaft

\- External ring creep (turning) in the housing

Surface damage

\- Wear caused by ineffective lubrication

\- Smearing damage caused by sliding rolling elements

\- Impressions on raceways and/or rolling elements caused by rolling away of solid dirt

\- Impressions on raceways and/or rolling elements from shock loads

\- False brinelling marks on raceways and/or rolling elements caused by static vibrations

\- Spalling on raceways and/or rolling elements due to fatigue

\- Spalling on raceways and/or rolling elements due to damage initiated at the surface

\- Static etching on raceways and/or rolling elements due to chemical or liquid contamination

\- (Micro)chipping on raceways and/or rolling elements due to moisture or electric current damage

\- Gouging on raceways and/or rolling elements due to the flow of damaging electric current

Excessive shaft movement

Loose

Surface damage

Incorrect bearing internal clearance

Loose

\- Inner ring loose on shaft

\- Outer ring too loose in housing

- Bearing incorrectly mounted on shaft or in housing

Surface damage

\- Wear caused by ineffective lubrication

\- Spalling on raceways and/or rolling elements due to fatigue

\- Spalling on raceways and/or rolling elements due to damage caused on the surface

Incorrect bearing internal clearance

\- Bearing with abnormal play

\- Bearing incorrectly mounted on shaft or in housing, excessive face clearance

Excessive frictional torque required to turn the shaft

Bearing preload

Resistance from seals

Surface damage

Design errors

Bearing preload

\- Incorrect clearance selected for replacement bearing

\- Shaft material expands more than bearing steel (e.g. stainless steel)

\- Large temperature difference between shaft and housing

\- Excessive cone seat raise

\- Excessive out of round condition of shaft or housing - compressed bearing

\- Excessive tight fit of shaft and/or housing

\- Excessive preload - incorrect installation (preload)

Resistance from seals

\- Housing seals too tight or other components contaminate the seals

\- Multiple seals in the bearing arrangement (housing)

\- Misalignment of external seals (housing)

\- Seals not properly lubricated

Surface damage

\- Spalling in raceways and/or rolling elements caused by fatigue

\- Spalling on raceways and/or rolling elements due to damage caused by the surface

\- Gouges in raceways and/or rolling elements caused by the flow of harmful electric current

Design errors

\- The faces of the shaft and/or housing are not perpendicular to the bearing seat

\- Shaft protrusion is too large and blocks seals/guards

Insufficient lubricant

insufficient lubricant or insufficient oil leve

Excessive lubricant

too much grease without purge ability or too high an oil level

Housing seals or other components are too tight

Multiple seals in the bearing arrangement (housing)

Misalignment of external seals (binding)

Operating speed too high for contact seals in bearings

Seals lubricated incorrectly

Seals oriented in the wrong direction

Incorrect selection of the initial bearing internal clearance

Shaft material expanding more than bearing steel

Large temperature difference between the shaft and the housing

(housing much cooler than the shaft)

Excessive pressure on the bushing cone

Excessive deviation from shaft or housing cylindricity

bearing in a deformed housing

Excessive tight shaft fit / shaft diameter too large

Excessive fit tight housing / wrong diameter of housing

Overloaded bearings as a result of changing application parameters

Examples:

\- Changing the method of transmission.

\- Increasing the speed of the device.

Misalignment of two bearing units

Displacement linear misalignment

Angular misalignment

Bearing installed in reverse

Unbalanced

Abnormal placenta (size)

Excessive thrust loads caused by crossing bearings

Material blockages

Seizures caused by sliding of insufficiently loaded rolling elements (slippage)

Excessive preload

Dents on the raceways and/or rolling elements

Dents on raceways and/or rolling elements caused by the penetration and movement of solid dirt

Particles left in the enclosure

Particles left in the housing from production or previous bearing failures

Liquid impurities that reduce lubricant viscosity

oil + water

Inner ring creep (rolling) on the shaft

Creep of the outer ring (turning) in the holder