1.
DEFINITIONS
• Lubricant is a substance introduced between
two moving surfaces to reduce the friction
between them.
• Substances which are introduced in between
moving parts in order to reduce the friction,
generated heat & wear and tear of machine
parts are called Lubricants.
• This process of introducing lubricant is called
Lubrication.

2.
Characteristics of good Lubricant
A good lubricating oil should have:
• High boiling point
• Adequate Viscosity
• Low freezing point
• High oxidation resistance
• Non Corrosive properties
• Good thermal stability

3.
Mechanism of Lubrication

4.
Thick Film or Fluid Film or Hydrodynamic Lubrication
It is carried out with the help of liquid lubricants. In this mechanism, two
moving and sliding surfaces are separated by thick film of lubricant fluid
of about 1000A°, applied to prevent direct surface to surface contact
and consequently reduce wearing and tearing of metals. Therefore it is
known as thick film or fluid film lubrication or hydrodynamic (hydro
meaning liquid and dynamic meaning relative motion) lubrication. In
this case fluid is formed by mixing of hydrocarbon oils and anti-oxidants
with long chain polymer so as to maintain viscosity. Fluid film lubrication
is useful in delicate and light machines like watches, clocks, guns,
scientific equipments.

5.
Thin Film or Boundary Lubrication
It is carried out with semi-solid (grease) and solid (graphite
and molybdenum disulphide) lubricants. Boundary lubrication
is a condition in which the lubricant film becomes too thin to
provide total separation. In this type of lubrication a thin film
of lubricant is adsorbed on the surface by weak Vander Waals
forces. Thin film lubrication is operating at relatively low
speed and heavy loading (pressure).

6.
Extreme Pressure Lubrication
In this mechanism, moving or sliding surfaces are under high
pressure and speed, therefore this is known as extreme pressure
lubrication. In such a case high temperatures generated due to
friction, under these condition liquid lubricants are fail to stick and
decompose or vaporize. These problems are minimized by special
additives are added to mineral oils. These additives form durable
films on metal surfaces which can withstand high loads and high
temperatures. Important additives are organic compound having
active groups like chlorine, sulphur, phosphorus etc. They react
with metallic surface to form metallic compound (possess high
melting points and serve as good lubricants under extreme
temperatures and pressures) like chlorides, sulphides, phosphides
as more durable film.

7.
Classification of Lubricants
i) Liquid Lubricants or Lubricating oils:
It includes animal oils, vegetable oils, petroleum oils, synthetic
lubricants.
Animal oils: Lard oil, whale oil etc.
Vegetable oils: castor oil, palm oil etc
good oiliness,hydrolysable,
easy oxidation , costly
Petroleum or mineral oils: lower molecular weight hydrocarbons with about
12-50 carbon atom. They are cheap, available in in abundance, hence widely
used. Their oiliness is low so mostly blended with higher fatty acids or veg. oils
Synthetic lubricants: polyglycol, silicones etc.

8.
ii) Semi-solid Lubricants (Grease):
Semi-solid Lubricants are formed by emulsifying oil and fat
with thickening agents like soap of sodium, calcium, lithium,
aluminum at higher temperature.
Classification :
Soda based: In this case sodium soaps are used as a
thickening agent in mineral or petroleum oil. They are slightly
soluble in water. They can be used up to 175oC.
Lithium based: In this case lithium soaps are emulsifying with
petroleum oil. They are water resistance and used up to 15oC.
Calcium based: In this case calcium soaps are emulsifying
with petroleum oil. They are also water resistant and used up
to 80oC. At higher temperature soap and petroleum oil are
separate from each other.

9.
iii) Solid Lubricants:
Graphite, molybdenum disulphide (MoS2), boron nitride (BN)x are
predominantly used as a solid lubricants. They are used under high
temperature and high load (pressure).

10.
a) Graphite:
It is most widely used as a solid lubricant. Graphite has layer structure;
layers are held together with the help of weak Vander Waals’ forces
which facilitate the easy sliding of one layer on the other layer. It is very
soapy to touch, non-inflammable. It is used at higher temperature
(around 450oC) condition. They are either used as powder form or mixed
with oil or water.
b) Molybdenum disulphide (MoS2):
It is sandwich like structure in which hexagonal layer of
molybdenum (Mo) lies between two hexagonal layers of sulfur (S)
atom. Like graphite each layers are held together with weak Vander
Waals’ forces. It is stable up to 400oC. It is differ from graphite
because it is used in high vacuum unlike graphite (graphite is
mixed with water or oil). It adheres even more strongly to the metal
or other surface.

11.
Properties of Lubricants
Viscosity
• It’s a measure of a fluid’s resistance to flow.
• Viscosity of the lubricating oil determines its performance under
operating conditions.
• Alow viscosity oil is thin and flows easily .
• Ahigh viscosity oil is thick and flows slowly.
• Too low viscosity of the liquid > Lubricant film cannot be
maintained between the moving surfaces > Excessive wear.
• Too high viscosity of the liquid > Jamming of machinery parts >
Excessive friction.
• Selected Lubricant must be of proper viscosity under operating
conditions of machinery part.
• Viscosity is usually expressed in poise or centipoises or
millipoise

12.
Viscosity Index :
• Viscosity of liquids decreases with increasing temperature.
•The rate at which viscosity of a lubricant changes with
temperature is measured by a scale called Viscosity Index.
• If viscosity of lubricating oil falls rapidly as temperature is
have high
raised, it has a low viscosity index.
•Silicones, polyglycol ethers, diesters or triesters
Viscosity Index.
Iodine Number:
•Iodine number is the number of gms equivalent of iodine to amount of
ICl absorbed by 100 g of oil.
• Each oil has its specific Iodine Number.
•It is used to determine the amount of unsaturation in fatty acids.
Higher the unsaturation more C=C bonds are present in fat.
• So Iodine Number determines the extent of contamination of oil.
• Low Iodine Number is desirable in oils.

13.
Aniline point:
•Aniline point is the Minimum temperature at which equal
volume of lubricating oil and aniline form homogenous mixture
and dissolve in each other.
•Aniline Point is a measure of aromatic content of the lubricating
oil.
• Aromatic content attacks rubber seals.
•Higher Aniline point means low %age of hydrocarbons
(desirable).
•Thus Aniline Point is used as an in indication of possible
deterioration of rubber sealing etc.

14.
Emulsification:
•Emulsification is the property of oil to get mixed with water
easily.
• Emulsions can be oil in water emulsion or water in oil emulsion.
•A good lubricating oil should form such an emulsion with water
which breaks easily. This property is called de-emulsification.
•The time in seconds in which a given volume of oil and water
separates out in distinct layers is called steam de-emulsification
number.
•A good lubricating oil should have lower de-emulsification
number.
•Quicker the oil separates out from the emulsion formed, better is
the lubricating oil.

15.
Flash Point & Fire Point
• Flash Point is the min temp at which the lubricant oil gives
off enough vapors that ignite for a moment, when tiny flame
is brought near.
• Fire Point is the Minimum temp. at which the lubricant’s
vapors burn continuously for at least 5 seconds, when tiny
flame is brought near.
• In most cases, the fire points are 5°C to 40 °C higher than the
flash point.
• A good lubricant should have flash point at least above the
temperature at which it is to be used.
• The flash and fire points are generally determined by using
Pensky-Marten’s apparatus.

16.
Cloud Point & Pour Point
• Cloud Point is the temp at which the lubricant
becomes cloudy or hazy when cooled.
• Pour Point is the temp at which the lubricant just
ceases to flow when cooled.
• Both indicates suitability of lubricant in cold
conditions and thus must be low.
• Lubricant oil used in machine working at low
temperature should possess low pour point,
otherwise solidification of lubricant oil will cause
jamming of machines.

17.
Saponification Number
• It’s the mgs of KOH required to saponify 1 gm of oil.
•Saponification is hydrolysis of an ester with KOH to give
alcohol and Na/K salt of acid.
• Mineral oils do not react with KOH and are not saponifiable.
•Vegetable and animal oils have very high saponification
values.
Significance
•Saponification value helps us to ascertain whether the oil
under reference is mineral or vegetable/Animal oil.
• Each oil has its specific Saponification Number.
Deviation from it indicates the extent of adulteration of oil.

18.
Neutralization Point
• Neutralization Point determines Acidity or Alkalinity of oil.
• Acid value/Acid number is mgs of KOH required to
is mgs of acid required to
neutralize acid in 1 gm of oil.
•Base value/Base number
neutralize all bases in 1 gm oil.
Carbon Residue
•Lubricant oils contain compounds rich in carbon and on heating
the oil to high temp. these get deposited as carbon residue.
•Carbon deposits are harmful for machines, particularly in
internal combustion engines and air compressors.
• A good lubricant should have low carbon residue.

19.
Coke Number: % age of Carbon residue is known as coke number.
Coke Number = Wt. of Carbon residue left / Wt. of oil taken x 100

20.
Thank you