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Lubrication Basics
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Course Overview
Lubrication Introduction
Types and properties of lubricants
Selecting and using grease
Lubricant systems
The Role of Lubrication 3
• We lubricate to:
– Separate contact surfaces of moving components
– Transfer heat away from contact surfaces
– Protect from corrosion and dirt
• Nearly 50% of all bearing damage is due to inadequate lubrication
– Must choose the right type of lubricant
– Must use the correct amount of lubricant
Lubrication Definition 4
Controlling friction and wear between Race Surface
adjacent surfaces by developing a
lubricant film between them Lubricant Film
Rolling Element Surface
• All machined metal has surface roughness
• Peaks of metal created during finishing processes
are called asperities
– Rough Ground Surface
– Fine Ground Surface
How Bearing Lubrication Works 5
• Lubricant that adheres to the surfaces of the bearing is entrained in
the rolling contact
Where oil starvation,
over-lubrication and
aeration impact bearing
performance
Factors Affecting Lubricant Film 6
These factors all cause a thinner film thickness
• Lower speed
• High temperature
• High load
• Lower viscosity (oil systems)
These factors cause a thicker film thickness
• Low load
• High speed
• High viscosity
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Lubricants
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Lubricant Types
Oil Grease
Selecting the right Lubricant 9
• Factors to consider:
• Bearing size/type
• Applied loads
35 VI (Low)
• Frequency/ability to change
• Speed
• Operating environment (temperature, contamination,
Viscosity
etc.)
110 VI (High)
• Key Characteristics
1. Viscosity Temperature
• Measures flow characteristics
• Varies inversely with temperature
• Expressed in ISO (e.g., ISO VG460) or SAE systems (e.g., 10W-40)
• Must be high enough to support loads, but not so high it generates excessive heat or won’t
flow at temperature
• Viscosity index (VI): measures rate of viscosity change vs. temperature
• High VI/flatter line is generally desirable
2. Flash point
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Temperature at which vapor from a liquid forms a flammable mixture with air
3. Fire point
Temperature at which a liquid forms a vapor that will burn continuously
4. Pour point
Lowest temperature at which lubricant will flow
5. Oxidation stability
Ability to withstand deterioration at elevated temperatures
6. Dropping Point (ASTM D-2265):
Point at which grease liquifies
Oil 11
Liquid at room temperature
May include additives to improve physical properties or performance,
such as viscosity improvers, antioxidants, anti-wear additives, etc.
Petroleum-based (90% of market) Refined from crude oil
Produced through chemical synthesis by chemically
Synthetic (10% of market) altering petroleum-based lubricants
Used in severe temperature environments
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Oil Advantages
Diffuses heat quickly,
Variety of delivery
making it better for Ability to monitor and
systems make it easy
high-speed control flow rates
to use
applications
Easier to keep
Carries away
lubricant clean with
moisture and
filters in circulating
contamination
systems
Oil Viscosity Selection 13
Low Viscosity Oil High Viscosity Oil
Light Heavy
• Choosing the Load Load
correct viscosity
depends on the High Low
application loads, Speed Speed
speeds and
temperatures
Low High
Temp Temp
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Grease
Base oil: Petroleum-based or synthetic
Thickener: Converts the liquid lubricant into a grease (semi-solid)
Additives: Improve specific properties
• Oxidation inhibitors
• Rust / corrosion inhibitors
• Demulsifies: Separate water from grease
• Extreme pressure (EP) additives: Activated by high temperatures, good for gears and
other sliding contact applications
Can be used in applications up to 3,000 RPM
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Grease Advantages
Easier to handle
Simplifies seal design and acts as a sealant
Permits pre-lubrication of sealed or shielded bearings
Generally, requires less frequent lubrication
Other Grease Characteristics 16
• Compatibility
― Mixing the wrong thickener, base
oil or additives may cause
interactions that may adversely
affect the properties of the
grease.
― When re-greasing, need
to ensure that the new grease is
compatible
with grease already in
the bearing
― Check with lubricant supplier
before mixing greases
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Selecting and Using Grease
What’s the Right Grease? How much Should I 18
use?
• Depends on the application requirements
– Is water present?
– Is the environment dirty?
– What is the operating temperature?
– What are the loads?
– How difficult is it to regrease?
– What kind of grease is currently used?
– Etc.
• General rule of thumb: Fill 1/3 to 1/2 of the roller bearings with grease.
Surrounding cavity fill will depend on application conditions.
– Lower speeds should use more grease
– Higher speeds should use less grease
Over-filling/Re-greasing 19
• Over-filling can cause excess churning, resulting in overheating and
excess grease purging
– Overheating occurs because the heat generated cannot dissipate correctly,
continually building until damage occurs
• Under-filling will create grease starvation
• Re-greasing cycle depends on:
– Operating temperature: Each 18ºF temperature rise above 140ºF represents a
50% reduction in grease life
– Sealing efficiency: Poorly sealed bearings need re-greased more often
• Re-greasing rule of thumb, add 1/3 of the initial grease fill
Grease Purge 20
• Properly lubricated bearings will purge a small amount of grease on
start up
– Acts as a barrier seal to help keep out external debris contamination
• Grease sealed bearings carefully
– Applying too much grease too quickly can rupture the seal and
compromise bearing life
– Some bearings are sealed for life, and not designed for re-greasing
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Lubrication Systems
Lubrication Systems 22
• Grease
• Oil Splash
• Circulating oil
• Oil-mist and Air-oil
Lubrication Systems - Grease 23
• Simplest lubrication system
• Ability to keep lubricant where it is desired via the
thickener
o Elevated bearing positions in a gearbox
o Vertical shaft designs
o Lubricating sliding interfaces (roll necks, under bearing
bores)
• Care must be taken not to over-lubricate bearings
Lubrication Systems - Grease 24
• Packing a bearing with
grease
– Must force grease
between rollers and cage
– Pack by hand or with
mechanical packer
Lubrication Systems - Grease 25
Centralized Pumped Automatic Single
Grease System Point Lubricator
Oil Splash 26
• Requires flingers and gear rotation to splash lubrication throughout
a gearbox
– Bearings are subject to dry-start damage after long-term storage where
oil has drained to sump
• Use of baffles and dams improves oil retention at bearing positions
Baffle
Dam
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Circulating Oil
• Improved ability to remove heat for high-speed applications
• Increased flushing of contamination from bearing and gears due to
supply of clean, filtered oil
• With flow alarms and adjustable valves, can provide the right
amount of lubricant to a bearing position and know when lubricant
flow has been compromised
• Ability to keep bearing environment clean to prolong service life
Oil-Mist Lubrication 28
• Atomized at Mist Generator and conveyed to nozzles
• Internal Chock Pressure ~ 0.75 psi
• Venting required for proper distribution of oil
• Oil Viscosity should not exceed 460cSt
• Air and Oil are typically pre-heated
• 10% of oil mist may remain airborne (Stray Mist)
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Air-Oil Lubrication
• Oil transported along inside wall of pipe as a film, not a mist
• Oil distribution cartridges mounted in chock
• Not limited on oil viscosity upper limit if it remains a fluid
• Chock’s internal pressure (3-5psi) helps prevent contaminant ingress
• Oil Consumption is 10-15% of an oil mist system
Air-Oil Lubrication: Delivery 30
METERED OIL SUPPLY
(cc/HOUR)
OIL FILM
AIR-OIL
COMPRESSED AIR STREAM
Air-Oil & Oil Mist Lubrication: Chock Schematic 31
a. Oil entries
b. Combination vent and oil level
c. Oil drainage
d. Combine vent and oil drainage
for inner seal at bottom dead
center
Oil Level for
Startup
