Course: B.Tech.
Subject: Engineering Chemistry
Unit: III(A)
D EFINITION : L UBRICANTS
A lubricant is substance (often liquid)
introduced between two moving surfaces to
reduce the friction between them.
Fluid which is 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.
Gear and
Automotive Oils Transmission oils
Automotive
Grease
C OMPOSITION
Typically contains 90% base
oil(petroleum-mineral oils) and less
than 10% additives
Non liquid lubricants contains Grease,
powder(dry graphite, Molybdenum
disulphite), Teflon tape used in
plumbing etc.
Those non liquid lubricants provide
lubrication at higher temp.(up to 350
°C)
ADDITIVES USED IN
LUBRICANTS
(1) Anti oxidant --- Aromatic
amines,Phenols,Sulphides and phosphates
(2) Corrosion Inhibitor --- Amino salts and salts
of sulphonic acids
(3) Antiwear agents --- Tricresyl phosphate
(4) Foam inhibitors --- Glycerols
Functions of Lubricants
It acts as a thermal barrier and reduces friction
and wear and prevents welded joints
Avoids seizure of moving surfaces
Acts as coolant
Acts as a seal and prevents entry of dust,
moisture, & dirt between moving parts
Some lubricants acts as corrosion inhibitors thus
reduce operational cost .
A good lubricating oil should
have:
• High boiling point
• Adequate Viscosity
• Low freezing point
• High oxidation resist
• Non Corrosive properties
• Good thermal stability
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Types Of
Lubrications
Thick Film
or Thin Film
or Extreme
Fluid Film Pressure
or Boundary Lubrication
hydrodynamic Lubrication
Lubrication
• This is also called Hydrodynamic
or fluid film lubrication.
• Two sliding metal surfaces are
separated from each other by a
o
thick film of fluid ( 1000 A
thick).
• The coefficient of friction in such
cases is as low as 0.001 to 0.03
• Lubricants used : Hydrocarbon
Oils.
• Provided in delicate instruments
such as watches, clocks, light
machines like sewing machines,
scientific instruments etc.
• This lubrication is also called
Boundary Lubrication.
• Its used for high load conditions.
• Very thin film of the lubricant is
adsorbed on the surface by physical
or chemical forces or both.
• The coefficient of friction is 0.05 to
0.15
• Lubricants used for boundary
lubrication should have high viscosity
index, resistance to heat and
oxidation, good oiliness.
• Examples are Organic oils, Vegetable
oils, Graphite and MoS2, Mineral Oils
etc.
• This lubrication is for very high
press/temp/speed sliding surfaces.
• Extreme pressure additives are used
along with the lubricants.
• Chemicals used are compounds of
Cl, S & P.
• These additives form solid surface
films of Cl, S & P.
• High melting point metal
compounds are good lubricants.
• E.g. graphite is used for drawing
wires made up of mild steel.
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Classification of Lubricants
Liquid Semi Solid Synthetic Solid
Lubricants Lubricants Lubricants Lubricants
Eg.Mineral Oil, Eg. Graphite,
Eg. Petroleum
Petroleum Oil, Molybdenum
jellies
Vegetable Oil etc Disulphide etc.
T YPES OF L UBRICANTS
Solid lubricants e.g Wax, Talc, Mica,
Molibdenum disulphide
Semi solid lubricants e.g. Grease and Vaseline
Liquid Lubricants e.g. Mineral oils, Vegetable
oils, Animal oils
Synthetic lubricants e.g. Polyglycols, Silicones,
Organic amines, Imines, Amides.
F EATURES OF L UBRICANTS
Increase efficiency and reduce wear
Dissolving or transporting foreign particles and
distributing heat
Single largest application is in form of Motor
Oil, protecting internal combustion engines in
motor vehicles and powered equipments
Another approach is to use ball bearings, roller
bearing or air bearings which in turn require
internal lubrication themselves
• It’s a measure of a fluid’s resistance to flow.
• Viscosity of the lubricating oil determines its performance
under operating conditions.
• A low viscosity oil is thin and flows easily .
• A high viscosity oil is thick and flows slowly.
• As oil heats up it becomes more
viscous (Becomes thin)
• Too low viscosity of the liquid > Lubricant film cannot be
maintained between the moving surfaces > Excessive wear.
• Too high viscosity of the liquid > Excessive friction.
• Selected Lubricant must be proper viscous.
• Viscosity is usually expressed in centipoise or centistoke.
• Iodine number is the number of Gms equivalent of iodine to
amount of ICl absorbed by 100gm of oil.
• Each oil has its specific Iodine Number.
• So Iodine Number determines the extent of contamination of
oil.
• Low Iodine Number is desirable in oils.
Some oils and their Iodine Numbers are given below :
Iodine Number Oil Example
>150 Drying oil Linseed oil, tung oil
100-150 Semidrying oil Castor oil , Soyabean oil
<100 Non-Drying oil Coconut oil, Olive oil
• Aniline point is the Min temp at which oil is miscible with equal amt of
aniline
• Aniline Point is a measure of aromatic content of the lubricating oil.
• Low Aniline Point oil have high aromatic content which attacks rubber
seals.
• Higher Aniline point means low %age of hydrocarbons (desirable).
• Thus Aniline Point is used as an indication of possible deterioration of
rubber sealing etc.
Determination of Aniline Point :
Aniline + Homogeneous
sample oil Heated in Test tube solution
(equal)
Cooled
Cloudiness
The temperature at which separation of the two phases (Aniline + oil) takes place
is the Aniline Point.
• Emulsification is the property of water 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 demulsification.
• The time in seconds in which a given volume of oil and water
separates out in distinct layers is called steam demulsification
number.
• A good lubricating oil should have lower demulsification number.
• Quicker the oil separates out from the emulsion formed, better is the
lubricating oil.
• In cutting oils the higher the emulsification number, better the oil is.
This is because the emulsion acts as a coolant as well as a lubricant.
• Flash Point is the min temp at which the lubricant vaporizes that ignite for a
moment when tiny flame is brought near.
• Fire Point is the Min temp at which the lubricant’s vapours burn constantly for
5 seconds when tiny flame is brought near.
• If flash point < 140°F = Flammable liquids
And if flash point > 140°F =Combustible liquids.
The flash and fire points are generally determined by using
Pensky-Marten’s apparatus.
•Oil under examination is filled in the oil cup up to the mark
and heated by the air bath by a burner.
•Stirrer is worked b/n tests at a rate of about 1 – 2 rev/sec.
•Heat is applied so as to raise the oil temp by about 5c/min.
•The temp at which distinct flash appeared in side the oil cup
is recorded as flashpoint.
•The heating is continued to record the fire point.
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• Drop Point is the Temperature at
which grease passes from the semi-
solid to the liquid state. So, it
determines the upper temp limit for
the applicability of grease.
Determination :
• Beaker is heated.
• Temperature is raised.
• Grease sample passes from a semi-
solid to a fluid state.
• Temp at which its first drop falls
from the opening is recorded as
drop-point.
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• 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.
• It’s the mgs of KOH required to saponify 1 gm of oil.
• Saponification is hydrolysis of an Easter with KOH to
give alcohol and Na/K salt of acid.
U SES
Other uses are
for cooking,
biomedical applications on human(lubricants for
artificial joints).
A PPLICATIONS
Automotive Industry-Engine oil, Automatic
transmission fluid, Gearbox fluid, Break fluids.
Tractor(One lubricant for all systems)
Other motors(2 stroke engine oil)
Industrial(Hydraulic oils, Air compressor oils,
Gas Compressor oils, Gear oils Bearing and
circulating system oils, Refrigerator compressor
oils)
Aviation
Marine
R EFERENCES
1. www.motosport.com
2. www.umongo.co.za
3. http://www.vidyarthiplus.in/2012/01/engineering-
chemistry1-lubricants.html#
4. www.aimil.com
5. www.machinerylubrication.com
6. A textbook of Engineering Chemistry by Shashi
chawla
