This presentation contains Properties of a good Lubricant in details along with most important property Viscosity Index.

1. Lubricant Properties
Engr. Tarique Ahmed Memon
Lecturer @ Department of Mechanical Engineering
Quaid-e-Awam University of Engineering, Science &
Technology (QUEST) Campus Larkano, Sindh, Pakistan.

2. CHARACTERISTICS OF GOOD LUBRICANT:-
1. LOW VAPOUR PRESSURE.
2. HIGH BOILING POINT.
3. NON CORROSIVE NATURE.
4. GOOD THERMAL CONDUCTIVITY.
5. ADEQUATE VISCOSITY.
6. HIGH FLASH & FIRE POINT.
7. HIGH OILINESS.
8. LOW VOLATILITY.
9. LOW FREEZING POINT.
10. DOES NOT FORM EMULSION.

3. Properties of Lubricants
•
1. Viscosity
• Viscosity Index
• 2. Flash point
3. Fire point
• 4. Cloud point
5. Pour point
• 6. Oiliness
7. Corrosion
• 8. Emulsification
9. Physical stability
• 10. Chemical stability
11. Neutralization number
• 12. Adhesiveness
13. Film strength
14. Specific gravity
• 15. Volatility

4. Viscosity
• Viscosity is the most important characteristic of
lubricating oil.
• Viscosity refers to the tendency of oil to resist
flowing.
• Viscosity changes with temperature, since
increasing temperature causes oil to thin and
have a lower viscosity, while decreasing
temperature causes oil to thicken and have a
higher viscosity.

5. Viscosity
• The viscosity of lubricating oil is considered the best single index of
the use for which the oil is to be recommended.
• The viscosity determines the friction loss, heat generation,
mechanical efficiency, load carrying capacity, film thickness,
lubricant flow, and wear.
• Viscosity is truly a measure of the physical ability of a fluid to
maintain lubrication under specified conditions of operating speed,
temperature, and pressure.
• Viscosity is thought of as that physical property of a fluid which
offer resistance to relative motion of its parts.
• This corresponds to an internal fluid friction produced by the
molecules of a lubricant as they flow past one another.
• The greater this relative motion, the greater is the internal
resistance that the lubricant offers.

6. Viscosity of Liquids

8. 1. Viscosity
if a surface to be lubricated is normally at high temperature it
should be supplied with oil of
a higher viscosity.
Low viscosity fluids flow easily (water, alcohol);
High viscosity fluids pour slowly (molasses, cold honey, etc.)
• The higher the intermolecular friction (longer molecular
chains), the higher the viscosity.
• Viscosity determines film thickness and film strength in
machines. It also influences other important factors such as
those in the table below.

10. • Any object will sink faster in fluid of low viscosity such as water,
and will sink much slower in a high viscosity fluid such as glycerin.
• Viscosity of a fluid can thus be "measured" by the time it takes for
object, such as a steel ball bearing, fall through a test tube with
oil, for example.
Steel Ball fall speed is inversely proportional to Oil
Viscosity Faster through less viscous oil; Slower through
more viscous oil

13. viscosity index
• The viscosity index is a characteristic used to indicate variations in the
viscosity of lubricating oils with changes in temperature. The higher the
level of the viscosity index, the lower the variation in viscosity at
temperature changes.
• In other words, how much viscosity changes as temperature changes.
• The viscosity index, or VI, of a lubricant describes how the oil’s viscosity
changes as its temperature changes.
• As temperatures increase, viscosities decrease, and vice versa.
• For example, a piece of machinery that operates over a wide range of
temperatures will require a lubricant with a high VI, meaning that the oil
will retain its lubricating characteristics whether it is starting up cold or
running at full speed and peak temperature.
• It is the rate of change of viscosity between two temperatures.
• The lower the VI, the more the drop in viscosity as the oil warms up.
• The higher the VI value, the less the drop in viscosity as the oil warms up.

14. Viscosity index diagram
The slope of the lubricant with a high VI is more horizontal: the viscosity remains more stable
across a wider temperature range.
This means a lubricant with a higher viscosity index is more desirable, because it provides a
more stable lubricating film over a wider temperature range.
The lower the VI, the more the viscosity is affected by changes in temperature. The higher the
VI, the more stable the viscosity remains over temperature fluctuations.

15. 2. Flash point
• It is defined, as the lowest temperature at which the lubricating oil
will flash when a small flame is passed across its surface.
• The flash point of the oil should be sufficiently high so as to avoid,
flashing of oil vapors at the temperatures occurring in common
use.
• The flash point is the temperature at which the oil sparks, but a
flame is not sustained.

16. 3. Fire point
• It is the lowest temperature at which the oil burns continuously.
• The fire point also must be high in a lubricating oil, so that oil does
not burn in service.
• The fire point is the temperature at which the oil sparks and the
flame is sustained.
Flash point explains the lowest temperature for ignition, but the ignition may not be
sustained;
whereas fire point explains the lowest temperature where ignition is achieved and
the ignition sustained for some time. The fire point is always slightly higher than the flash
point

18. 4. Cloud point
• When subject to low temperatures the oil changes from liquid
state to a plastic or solid state.
• In some cases the oil starts solidifying which makes it to appear
cloudy.
• The temperature at which this takes place is called the cloud
point.
• Petroleum-based lube oils contain dissolved wax.
• At a low enough temperature, referred to as the cloud point, this
wax will separate from the oil and form wax crystals.
• These crystals can clog filters and small openings, deposit on
surfaces such as heat exchangers, and increase the viscosity of
the oil.

19. 5. Pour point
• The lowest temperature at which a lubricant will flow or pour like a liquid.
• It is an indication of its ability to move at low temperatures.
• This property must be considered because of its effect on starting an
engine in cold weather and on free circulation of oil through exterior feed
pipes when pressure is not applied.
• The pour point refers to the minimum temperature at which a lubricant
continues to flow.
• Below the pour point, the oil tends to thicken and to cease to flow freely.
• Pour Point is therefore measured typically with lubricants, wherein Pour
Point is the lowest (coldest) temperature that a fluid will still flow, though
at a low flowability rate.

20. 6. Oiliness
• This is the property which enables oil to spread
over and adhere to the surface of
the bearing. It is most important in boundary
lubrication.
• It is an important properties of a lubricant, it
shows
the capacity of a lubricants to stick on the surface
of
machine parts under high pressure and load

21. 7. Corrosion Stability
• It is properties of lubricant which represents
its resistance toward the metals.
• A lubricant should not corrode the working
parts and it must retain its properties even in
the presence of foreign matter and additives.

22. 8. Emulsification
• A lubricating oil, when mixed with water is
emulsified and loses its lubricating property .
• The emulsification number is on index of the
tendency of on oil to emulsify with water.
• It is the property of a lubricant due to which the
lubricating oil mixed with water to form an
emulsion.
• A good lubricant should have low emulsion
number.

23. 9. Physical Stability
• A lubricating oil must be stable physically at
the lowest and highest temperatures between
which the oil is to be used.
• At the lowest temperature there should not
be any separation of solids, and at the highest
temperature it should not vaporize beyond a
certain limit.

24. 10. Chemical Stability
• A lubricating oil should also be stable
chemically.
• There should not be any tendency for oxide
formation.

25. 11. Neutralization Number
• An indication of the acidity or basicity (alkalinity)
of an oil.
• The neutralization number is expressed in
milligrams of potassium hydroxide or
hydrochloric acid needed to neutralize any acid or
base in one gram of oil.
• The Acid Number (AN) test uses potassium
hydroxide as the neutralizing agent, and the Base
Number (BN) test uses hydrochloric acid as the
neutralizing agent.

26. 12. Adhesiveness
• It is the property of lubricating oil due to
which the oil particles stick with the metal
surfaces.

27. 13. Film strength
• It is the property of a lubricating oil due to which the
oil retains a thin film between the two surfaces even at
high speed and load.
• The film does not break and the two surfaces do not
come in direct contact.
• Adhesiveness and film strength cause the lubricant to
enter the metal pores and cling to the surfaces of the
bearings and journals keeping them wet when the
journals are at rest and presenting metal to metal
contact until the film of lubricant is built up.

28. 14. Specific Gravity
• It is a measure of density of an oil.
• It is an indication regarding the grade of
lubricant by comparing one lubricant with
other.
• It is determined by a hydrometer which floats
in the oil, and the gravity is read on the scale
of the hydrometer at the surface of the oil.

29. 15. Volatility
• It shows the evaporation behavior of lubricant
at high temperature.
• A good lubricant should have low volatility

30. THE END