Topics
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Introduction
Types of Lubricants
Viscosity
Viscosity Ratings
Terminology
Types of Lubricant Additives
Types of Lubricating Oils
Types of Greases
• Note: Please refer to chapter 4 Lubrication in the text.
1
Introduction
• Purpose of lubrication:
1. To reduce friction
2. To cool down moving parts
3. To prevent corrosion (component wear from chemical reaction
with the air and moist)
4. To prevent contamination
Note: The cost saving achieved from selecting and applying the proper
lubricant is far greater than the saving from using an inferior lubricant.
• Lubricants function by forming a thin film that acts as a barrier
between the moving parts.
• The low coefficient of friction that greases and oils have reduces the
friction between the machine components.
• Example 1: (Refer to figure 3-1 on page 38) what is the coefficient
of static friction between two components made of hard steel in the
case when there is no lubricant present (dry) and when there is a
lubricant?
Answer: 0.78 when dry, drops to 0.11-0.23 when lubricated
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Forms of Lubricants
• Lubricants may be:
- Liquid lubricants such as automotive engine oils
- Semisolid lubricants such as greases.
- Solid (dry) lubricants: such as graphite powder
and molybdenum disulfide. They can function at
very extreme temperatures as high as 2000 oF and
as low as -395 oF. They also can withstand very
high loads (more than 25,000 psi)
- Gas lubricants: such as a stream of pressurized
nitrogen gas.
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Viscosity
• Viscosity: A measure of the fluid’s resistance to
flow.
• The best lubricant is that which has the lowest
viscosity possible to maintain a film that
separates the metal parts.
• Viscosity Index (VI): a measure of the change in
viscosity with temperature. As VI increases, the
less is the change of the lubricant’s viscosity with
temperature.
• Kinematic viscosity: is the measure of inertial
force to viscous force.
• Units of kinematic viscosity are:
• m2/s (the SI unit)
• the Stoke (1 m2/s = 10,000 stokes )
• Saybolt Universal Seconds (SUS)
Source: Wikimedia
Commons.
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Viscosity Measurement
• Viscosity of a liquid may be approximated using a
Viscometer in units of Saybolt Seconds, accuracy is 90-95%
• Use the viscometer to approximate the viscosity of some
Oils.
• In this instrument the viscosity of a liquid is compared to
the viscosity of an oil.
• What is the viscosity of the oil inside the viscometer?
200 SUS
5
Viscosity Ratings
• SAE viscosity rating: Society of Automotive Engineers
established a rating for engine oils
• Other lubricant grade standards are those by the International
Standards Organization (ISO), American Gear Manufacturers
Association (AGMA).
Example: What is the viscosity in SUS of a SAE 30 weight oil
(Refer to Figure 4-1 on page 60 of the text)?
Answer: About 500 SUS.
A SAE 5W-30 oil acts like a 5 weight oil in cold temperatures
(100 oF and less) and a 30 weight oil in high temperatures
(around 210 oF).
A multi-grade oil
A single-grade oil
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• There are 11 viscosity grades used by SAE:
0W, 5W, 10W, 15W, 20W, 25W, 30, 40, 50, 60
• Example: Arrange the automotive engine oils shown
below by thickness from high to low at high temperatures.
Then arrange them by thickness from high to low in cold
temperatures.
• Answer: at high temperature: d, then a and b, then c
at cold temperatures: b, then a and d, then c
(a)
(b)
(c)
(d)
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Terminology
• Flash point: the lowest temperature at which vapor combines with
oxygen and produce a flash when an ignition source is applied.
• Fire point: The lowest temperature at which a flame ignites the lubricant
vapor. Note that at the flash point, ignition stops when the igniting source
is removed but continues at the fire point.
• Pour Point: The lowest temperature at which the lubricant will flow by
the effect of gravity and still be used.
• Color: the color of the lubricant changes due to oxidation and presence of
contaminants.
• Demulsability: The ability of oil to separate from water.
• Consistency: (for greases only) the degree to which grease resists
deformation. Classified and tested by penetration depth procedure set by
the National Lubricating Grease Institute (NLGI).
• Dropping Point: a term used for greases only, it is the maximum
temperature before the grease falls through an orifice.
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Types of Lubricant Additives
1.
Oxidation inhibitors: prevent reaction between lubricant and oxygen
from occurring. Oxidation results in oil breakdown and formation of
acids.
2. Extreme Pressure (EP) additives: these additives are used to increase
the ability of the lubricant to carry high loads, such as in gear lubricants
and bearings carrying heavy loads.
3. Defoamants: additives that facilitate the breakup of foam bubbles.
4. Film strengtheners: form films that are attached to the metal surfaces.
5. Detergent Dispersants: they are added to hold dirt particles
6. Anti-rust additives
7. Viscosity index improvers: most commonly used in making engine
oils, they increase the viscosity at high temperatures without changing
the viscosity at low temperatures.
8. Pour Point Depressants: to decrease the pour point temperature in cold
environments.
9. Demulsifier additives: added to repel water
10. Solid additives
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Types of Lubricating Oils
• There are three types of lubricating oils:
1. Animal/Vegetable Oils: rarely used as
additives
2. Mineral/Petroleum Oils: extracted from
petroleum
3. Synthetic Oils: synthesized from pure carbon
and hydrogen gases in a controlled process.
Their viscosity changes very little with
temperature.
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Types of Lubricating Greases
• Greases are composed of oils and thickening agents in
about 9 to 1 ratio of oil to thickening agent.
• There are several types of lubricating greases:
1. Lithium Soap
2. Calcium Soap: water resistant grease
3. Sodium Soap: can be washed away with water
4. Complex Soap
5. Synthetic Greases: fire resistant and can be used over a
wide temperature range (-60 to 450 oF)
6. Mineral/Petroleum Oils: extracted from petroleum
7. Synthetic Oils: synthesized from pure carbon and
hydrogen gases in a controlled process. Their viscosity
changes very little with temperature.
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Methods of Lubricant Delivery
• There are five main methods of applying lubricants:
1. Manual methods: such as using a manual grease gun (see
figure 4-7 page 76 in text)
2. Drip Methods: use gravity to supply oil drops.
3. Automatic Grease Lubricators: a reservoir is used to
supply grease. The grease is put under pressure by the
action of a spring to supply grease at a precalculated
amount.
4. Bath method: such as in lubricating chains.
5. Splash and submersion methods: such as in gearboxes,
where splashing is performed by the rotating gears.
6. Pressurized lubrication systems: such as in automotive
engines.
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Review Questions
1. The main purpose of lubricants is to reduce
_______
friction between contacting solids.
2. What are the four forms of lubricants?
Liquid, semisolid, solid, and gas lubricants.
3. Name some units for measuring kinematic
viscosity:
Stoke
m2/s
Saybolt Universal Seconds (SUS)
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Review Questions
4. The picture below shows a lubricant case, what
type of thickening agent is used in the grease?
A complex agent containing lithium soap
5. What does dropping point mean?
Dropping point is the
maximum temperature
that the grease can
withstand before it falls
through an orifice.
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Review Questions
6. What are synthetic lubricants?
Lubricants that are synthesized from purified
carbon and hydrogen gases.
7. Which form of lubricants is grease?
Semisolid form
8. The picture below shows a lubricant case, what does
NLGI stand for?
NLGI stands for National
Lubricating Grease Institute,
which classifies greases into
grades by their penetration
index.
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Exercise
1. Refer to the table in figure 4-1 p. 60 in the
book, What is the viscosity range for each
of the automotive oils shown in the pictures
in room temperature?
SAE 10W: 165 to 240 SUS
SAE 30: 400 to 580 SUS
2. You are assigned the task of verifying that
the viscosities of engine oils fall within the
range for each grade at cold temperatures.
You will be handed samples of some
automotive oils, find their viscosities using
the viscometer, then compare your
measurements to the range shown in figure
4-1 on page 60.
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