21
Des-Case Confidential THE IMPACT OF CONTAMINATION ON ROLLING ELEMENT BEARING LIFE
Des-Case Confidential
THE IMPACT OF CONTAMINATION ON ROLLING
ELEMENT BEARING LIFE
Des-Case Confidential
2
Des-Case Confidential
2
70% of loss of machine life is due
to loss of surface material
Loss of UsefulnessRef: MIT, E. Rabinowicz
What Causes Machines to Fail?
Des-Case Confidential
3
Des-Case Confidential
3
Ref: MIT, E. Rabinowicz
Slide 0035
Surface Degradation
What Causes Surface Degradation?
Des-Case Confidential
4
Des-Case Confidential
4
Slide 0040
Ref: NRCC, STLE
What Causes Machines to Wear?
82% of mechanical
wear is caused by
particle contamination
*
*
Most common lubrication related failure modes for rolling element bearings*
Des-Case Confidential
5
Des-Case Confidential
5
Des-Case Confidential
5
Des-Case Confidential
5
Contact Fatigue
Where it occurs: Particle-induced fatigue pitting can occur anytime clearance sized particle exist between surfaces in rolling contact (EHD films).
How to stop it: Particle-induced fatigue wear can be reduced or eliminated by removing clearance-sized particles from the oil or increasing the oil’s film thickness beyond the size of the particles.
Des-Case Confidential
6
Des-Case Confidential
6
Des-Case Confidential
6
Des-Case Confidential
6
Three-body Abrasion
Plastic Flow Cutting
Where it occurs: Three-body abrasion occurs any time clearance-sized particles are present in the oil between two surfaces in sliding contact.
How to stop it: Three body abrasion can be reduced or eliminated by removing clearance-sized particles from the oil or increasing the oil’s film thickness beyond the size of the particles.
Des-Case Confidential
7
Des-Case Confidential
7
What Causes Bearings to Fail?
• Specific to rolling element
bearings, it has be estimated
that over 50% of bearing
failure are induced by
contamination
• According to SKF “bearings
can theoretically have an
infinite life, provided particles
the same size as the lubricant
film are removed”
Des-Case Confidential
8
Des-Case Confidential
8
How Big is a Micron? How Big is the Oil Film?
Dynamic clearance = 0.1-10 microns
In most rolling element bearings the dynamic clearance between the rollers and raceways under load/speed is the same size as pollen, soot or red blood cells
Des-Case Confidential
9
Des-Case Confidential
9
Oil and Water do Mix
Dissolved Water
Can effect oil life by increasing oxidation rates and degrading additives.
Emulsified Water
Causes machine wear via corrosion, cavitation and loss of film strength. Shortens oil life by increasing oxidation, additive degradation and water washing.
Free Water
Serves to indicate that the oil has reached saturation for dissolved and emulsified water
Factors that affect demulsibility
➢Viscosity➢Contaminants➢Loss of additives
➢Oil type➢Oxidation➢Temperature
States of Coexistence
Des-Case Confidential
10
Des-Case Confidential
10
Effects of Contamination on Bearing Life
Damage Caused by Contaminant Type
Direct Machine Wear
Damage to Lubricant
Indirect Damage
Particle Contamination
• Abrasion• Fatigue
• Oxidation• Particle Scrubbing• Viscosity Increase
• Varnish / Deposits• Corrosive attack• Increased aeration
Moisture Contamination
• Corrosion (rust, fretting corrosion etc.)• Cavitation erosion
(journal bearings)
• Oxidation• Hydrolysis• Water Washing• Viscosity Increase
• Varnish / Deposits• Corrosive attack• Increase Aeration• Exacerbates all wear
mechanisms due to loss of film strength
Des-Case Confidential
11
Des-Case Confidential
11
Effects of Particle Contamination on Bearing Life
3x Life Extension!
Des-Case Confidential
12
Des-Case Confidential
12
Effects of Water Contamination on Bearing Life
Oil appears “hazy”
Oil appears clear
Des-Case Confidential
13
Des-Case Confidential
13
Beware of Cycling Temperatures
0
50
100
150
200
250
300
350
400
450
0 50 100 150
Wat
er c
on
ten
t/p
pm
Oil Temperature/ F
Typical saturation curve for ISO VG 68 AW Fluid
100% saturation
65% saturation
50% saturation
30% saturation
• When a machine shuts down and the oil cools, the relative humidity within the oil rapidly increase until the oil hits the dew point, resulting in free and emulsified water
Des-Case Confidential
14
Des-Case Confidential
14
Des-Case Confidential
14
Des-Case Confidential
14
Sources of Moisture & Particle Ingression
breather/vent during
normal aspiration
Through the dipstick
port or other open vent
Through the shaft seal
due to wash down or
normal ambient
humidity
Des-Case Confidential
15
Des-Case Confidential
15
Des-Case Confidential
15
Des-Case Confidential
15
Headspace Management – the Key to Contamination Control
Strategies for headspace management
➢Desiccant breathers➢Hybrid breather➢Nitrogen purge➢Conditioned air purge➢Expansion chambers
"At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.“
Henry’s Law 1803
Des-Case Confidential
16
Des-Case Confidential
16
Des-Case Confidential
16
Des-Case Confidential
16
OEM Vent Port vs Desiccant Breathers
Upgrading basic vents or OEM fill ports to desiccant breathers helps
control contamination
Des-Case Confidential
17
Des-Case Confidential
17
Des-Case Confidential
17
Des-Case Confidential
17
Controlling Headspace Cleanliness and Humidity
inhale exhale
Des-Case
Confidential
18
Des-Case
Confidential
18Des-Case
Confidential
18
Des-Case
Confidential
18
Desiccant Breathers Help to Maintain a Low Headspace Humidity
0
10
20
30
40
50
60
70
80
90
100
0 1000 2000 3000 4000 5000
Re
lati
ve H
um
idit
y
rH % DC-3 Test 1
Des-Case Confidential
19
Des-Case Confidential
19
Additional Strategies for Controlling Contaminants
Des-Case Confidential
• Top off oil • Check oil level • Take oil sample • Drain/fill oil • Kidney loop oil
Des-Case Confidential
20
Des-Case Confidential
20
• Over than 50% of bearing failures are due to water or particle ingression
• Particles the same size as a red blood cell (3 microns) can reduce bearing life by as much as 66%
• The best way to control oil cleanliness and dryness is to control the headspace cleanliness and humidity
• All lubrication tasks including oil changes and top-offs, sampling, levels etc. should be done without exposing the oil to the ambient environment
Summary
Des-Case Confidential
THANK YOU FOR YOUR
PARTICIPATION
![Rolling Bearing Failure Analysis 2010[1]](https://static.documents.pub/doc/80x56/577cc4781a28aba7119968bb/rolling-bearing-failure-analysis-20101.jpg)
