3. Bearing Failure

BEARING FAILURES

Most common failure reasons in Pumps

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Poor lubrication Contamination/ Ingress of media Poor fitting/handling Operating Conditions

20% 20% 20% 40%

The percentage values are based on discussions with maintenance people around the world and no statistics. Electrical erosion (passage of electrical current) is common.

Typical bearing failure Vibration level Prewarning time

Detection by SKF condition monitoring

Detection by lubrication analysis

Damage starts

Bearing failure

Detection by listen and feel

Detection by traditional low frequency vibration monitoring Time

Failure mode classification ISO

1. Fatigue 2. Wear 3. Corrosion

4. Electrical Erosion 5. Plastic Deformation

1.1 Subsurface fatigue 1.2 Surface initiated fatigue 2.1 Abrasive wear 2.2 Adhesive wear 3.1 Moisture corrosion 3.2 Frictional corrosion 4.1 Excessive voltage 4.2 Current leakage 5.1 Overload 5.2 Indentation 6.1 Forced fracture

6. Fracture

3.2.1 Fretting corrosion 3.2.2 False brinelling

6.2 Fatigue fracture 6.3 Thermal cracking

5.2.1 Indents from debris 5.2.2 Indentation by handling

Root cause failure analysis Failure Operating conditions - Load - Speed - Lubrication

Failure analysis - Wear pattern - Type of failure Development of the failure

Primary damage reason

 Actions

Documentation

Load path pattern

Stationary radial load Inner ring rotation

Stationary combined radial and axial load Rotating inner ring

Typically pattern of a bearing at the non-locating position of a pump

Typically pattern of a bearing at the locating position of a pump

application.

application.

Obvious faults

Poor fitting or bearing final variants selection Too much excessive internal clearance

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Variation in contact angle causes skidding and/or cage failure •

The cage of a dismounted bearing after 4500 h in operation,

The ball of a dismounted bearing after 48 h in operation, smearing marks

Sufficient axial load

Insufficient axial load at high speed

Similar contact angles inner and outer ring

Variation in contact angles inner and outer ring

Poor lubrication causing polishing wear  Appearance: Flat mirror-like surface due to polishing and plastic deformation of the surface asperities

Influence on service life: Normally not so dangerous in paper machine applications.(Bearing service life can be 20 years or more)

 Actions: When using a lubricant giving adequate lubrication there is no polishing wear. However, normally no need of any actions.

Wear because of lubricant starvation  Appearance: Yellow/brown bands because of high surface temperature

Influence on service life: Great influence

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Check that the lubricant reaches the bearing More frequent lubrication

Poor lubrication giving surface distress Influence on service life: Great negative influence on the service life

 Actions: Increase the oil film thickness if possible • Check the water content (should be max. 200 ppm) •

Insufficient lubrication factors

Lubrication Factors  –

Incorrect selection grease or oil for the application (at install, esp. at relubrication)  –  –  –

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Insufficient grease or oil quality ● ● ●

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Wrong viscosity, too low or high Wrong Consistency, too low or high Grease bleed rate too low

Lack of Lubricant / Excess of Lubricant Grease deterioration Oil level too low or high

Impurities ● ● ●

Mechanical seal wear, Nilos rings Oil line contamination Water

Pass of electrical current Pulse width modulated (PWM) frequency converters

Hard and discolored grease

High frequency shaft grounding currents. Grounding path through driven machinery.

Grey and bright surfaces

Motor with circulating HF current

Capacitive discharge currents

Washboard in raceways

Failure caused by poor fitting Mounting pressure applied to the wrong ring

 At rolling element distance there are indentations giving spalling.

Failure caused by poor fitting

Indent caused by a roller during assembly

Failure caused by poor fitting

Corrosion Stand still corrosion.

Etching marks on ball space distance of on angular contact ball bearing outer ring

Etching marks on ball space distance of on angular contact ball bearing inner ring

Corrosion / Deep seated rust Water concentration in a stationary bearing •

The water is heavier than the oil and will sink until it comes to a suitable gap between roller and raceway •

roller

water

water outer ring

Free water will accumulate at the bottom of the bearing •

Deep seated rust on the outer ring

Plastic Deformation  – Debris Indentation

Load concentration on the raised rims

Debris indention of an inner ring

Spalling starts as a crack beneath the surface

Indentations caused by foreign particles

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Hard ones: Metal pieces Soft ones: Paper, cotton waste

Indentations in the raceway of a Cylindrical

Failure caused by poor fitting, misalignment

Misaligned outer ring  – rotating inner ring and stationary outer ring

Otter ring of a deep grove ball bearing that have been misaligned in relation to the shaft

Inner ring of a cylindrical roller bearing that have been misaligned.

Failure caused by vibrations

Inner ring of Spherical roller bearing

Inner ring of Spherical roller bearing

Failure caused by fretting corrosion

Fretting corrosion on the OD of a Spherical roller bearing outer ring

Fretting corrosion on the ID of a Cylindrical roller bearing inner ring