How do Bearings Fail How do Bearings Fail

How do Bearings Fail?

How do Bearings Fail? Failure mode Classification 1. Causes of Failures have Identifiable characteristics 2. Failure Mechanisms have Identifiable Failure Modes 3. Observed Damage can Identify Failure Cause

Failure mode Classification Fatigue Wear Corrosion Electrical erosion Plastic deformation Fracture

Failure mode Classification Fatigue of Bearing Material This is caused by a fixed load acting on a metallic body at a periodic interval. Starting with development of metallurgical distortion at a depth of 200 – 500 mm below load bearing surface, the final manifestation is Spalling.

Failure mode Classification Fatigue of Bearing Material This is considered as normal end to useful life

Subsurface Fatigue Subsurface fatigue Fatigue Surface initiated fatigue Wear Corrosion Electrical erosion Plastic deformation Fracture – – – Repeated stress changes – Microcracks under the surface Crack propagation – Material structural changes Flaking, spalling and peeling

Subsurface Fatigue Failure mode Classification Spalling

Surface initiated fatigue Fatigue Wear Corrosion Electrical erosion Plastic deformation Fracture Subsurface fatigue Surface initiated fatigue – Surface distress – Reduced lubrication regime – Sliding motion – Burnishing, glazing – Asperity microcracks – Asperity microspalls

Surface initiated fatigue One of the manifestation is Spalling Ø Improper Lubrication Ø Mechanical Damage Ø Heavy load / Extreme Pressure Spalling can also be caused by Material Defect

Surface initiated fatigue Failure mode Classification. Edge Loading

Surface initiated fatigue Failure mode Classification. Improper handling - Impact

Surface initiated fatigue Failure mode Classification. Improper Lubrication

Surface initiated fatigue Failure mode Classification. Improper Lubrication- failure progression

Abrasive Wear Fatigue Wear Corrosion Abrasive wear Adhesive wear Electrical erosion Plastic deformation Fracture – – Progressive Removal of Material Accelerating Process Inadequate Lubrication Ingress of Dirt Particles

Abrasive Wear Contamination Particles

Abrasive Wear due to abrasive particles

Abrasive Wear Flange Wear due to abrasive particles

Abrasive Wear Polish Wear

Abrasive Wear Failure mode Classification. Discolouration due to Inadequate lubrication

Abrasive Wear Failure mode Classification. Inadequate lubrication

Abrasive Wear Failure mode Classification. Inadequate lubrication due to low viscosity oil

Abrasive Wear Failure mode Classification. Lubrication Starvation

Abrasive Wear Failure mode Classification. Lubrication Starvation – cage rubbing on flange

Adhesive Wear Fatigue Wear Corrosion Electrical erosion Plastic deformation Fracture Abrasive wear Adhesive wear – Smearing / skidding / galling – Material transfer / friction heat – Tempering / rehardening with stress concentrations and cracking or flaking – Low loads – Accelerations

Adhesive Wear Skid Smearing

Adhesive Wear Smearing – improper lubrication

Adhesive Wear Smearing – improper mounting

Adhesive Wear Smearing – insufficient load

Corrosion Fatigue Wear Corrosion Moisture corrosion Frictional corrosion Electrical erosion Plastic deformation Fracture – Oxidation / rust – Chemical reaction – Corrosion pits / flaking – Etching (water / oil mixture)

Moisture Corrosion Rust

Moisture Corrosion Ineffective Sealing

Moisture Corrosion Chemical Reaction - Etching

Fretting Corrosion Fatigue Wear Corrosion Moisture corrosion Frictional corrosion Electrical erosion Plastic deformation Fracture – Micro movement of mating parts – Oxidation of asperities – Powdery rust – Loss of material – Occurs in fit interfaces Fretting corrosion False brinelling

Frictional Corrosion Advanced Fretting

Frictional Corrosion Fretting corrosion

Frictional Corrosion Fretting corrosion – Loose Fit

Frictional Corrosion Fretting corrosion – Uneven support

Frictional Corrosion Advanced Fretting

False Brinelling Fatigue Wear Corrosion Moisture corrosion Frictional corrosion Electrical erosion Plastic deformation Fracture – – – Fretting corrosion False brinelling Rolling element / raceway Micro movements / elastic deformations Vibrations Corrosion / wear: shiny or reddish depressions Stationary: Damage at rolling element spacing Rotating: Damage exhibits parallel flutes

Frictional Corrosion False Brinelling

Frictional Corrosion Vibration

Frictional Corrosion Vibration in stationary condition

Frictional Corrosion Cage Damage – Wear of Cage bars Lubrication starvation / contamination

Frictional Corrosion Cage Damage – Wear Rubbing against O/R track – excess speed

Frictional Corrosion Cage Damage – Wear Misalignment

Frictional Corrosion Cage Damage – Wear Misalignment / Insufficient load

Frictional Corrosion Cage Damage – Vibration Broken rivets in a DC Motor bearing

Electrical Erosion – High current = sparking Fatigue – Instant localized heating leads to melting and/or welding Corrosion – Craters up to 100 µm Wear Electrical erosion Plastic deformation Fracture Excessive voltage Current leakage

Electrical Erosion – Excessive Voltage

Electrical Erosion Fatigue Wear Corrosion Electrical erosion Plastic deformation Fracture Excessive voltage Current leakage – Low current intensity – Shallow craters closely positioned – Development of flutes on raceways and rollers, parallel to rolling axis – Dark gray discoloration

Current Leakage

Electric Current Passage Solutions Hybrid deep groove ball bearing Insocoat

Overload Fatigue Wear Corrosion Electrical erosion Plastic deformation Overload Indentation – Static or shock loads – Plastic deformations – Depressions at rolling element spacing – Handling damage

Installation Damage

Indentation Fatigue Wear Corrosion Electrical erosion Plastic deformation Overload Indentation Fracture – Stationary Vibration or shock loads – Depressions at rolling element spacing – Presence of swarf – Soft particulate matter – Abrasive particles

Indentation

Indentation By swarf

Fracture Fatigue Wear Corrosion Electrical erosion Plastic deformation Fracture – Wrong handling – Hammer blows Handling Installation Secondary failure

Fracture Due to wrong handling

Fracture Due to hammer blows

Fatigue Fracture Wear Corrosion Electrical erosion Plastic deformation Fracture Handling Installation Secondary failure – Excessive drive up / preload – Inadequate support

Fracture Excessive drive up

Fracture Inadequate support

Fracture Cage Damage – Wrong mounting Mounting force on cage

Fatigue Fracture Wear Corrosion Electrical erosion Plastic deformation Fracture Handling Installation Secondary failure – Advanced smearing – Heavy fretting corrosion

Fracture Advanced smearing

Fracture Heavy fretting corrosion