Lubricants by shakeer

TOPIC :
LUBRICANTS & MECHANISM OF LUBRICATION
Subject: APPLIED CHEMISTRY-II 2ND
SEM
1
BY :ABDUL SHAKEER
Lecturer in Chemistry
LIET
HIMAYATSAGAR
PUNJAB EDUSAT SOCIETY

LUBRICANTS
The substances which are used to
decrease the force of friction between the
moving parts of machine in contact are
known as Lubricants and the process of
decreasing the force of friction between
the moving parts of machine in contact is
known as Lubrication.

Introduction:
 When on surface of machinery moves
over the another surface, resistance to
relative motion of the surfaces arises.
When we look at the solid surface it
appears smooth to naked eye , but this
smooth surface shows irregularities of
projections and cavities when viewed
under high power microscope.
PUNJAB EDUSAT SOCIETY 3

Projections and cavities in surfaces
When one such surface is placed over
another, its projections fall into the
cavities of the other and get interlocked
.Due to this interlocking , there is
resistance to the relative motion of the
surfaces. This is called the frictional
forces or frictional resistance of friction.
In due course of motion, the old

Friction
 Friction may be defined as the
opposing force that is set up between
the surface of contact, when one body
moves over the surface of another
body.

Friction
The frictional forces oppose the relative
motion between the moving parts of a
machine. Therefore extra energy has to
be spent to overcome the friction , which
increases expenses of energy .The friction
between the moving parts of machines
also produces heat which causes damage
to the machinery. Thus friction causes
wear and tear of the moving parts of
machinery in contact and due to this,the
machines lose their efficiency and
become useless.

Functions of Lubricants
i) Lubricants avoid the damage of the
moving parts of machines by minimizing
the production of heat.
ii) Lubricants reduce the wear and tear of
machinery by keeping the moving parts
of machines apart.
iii) Lubricants reduce the maintenance and
running cost of machine.
iv) Lubricants act as the coolant because it
reduces the production of heat between
the moving parts of machine in contact.

Functions of Lubricants
V. Lubricants increases the efficiency
of machine by reducing the loss of
energy.
VI. By using the lubricants, the relative
motion of the moving parts of
machine becomes smooth and noise
level of running machine reduces.
VII. Lubricants also act as the corrosion
preventers.

VIII.Lubricants also act as a seal as in piston.
Lubricant used between piston and walls of the
container (cylinder) prevents the leakage of hot
gases produced by the internal combustion i.e.it
act as seal.

Mechanism of Lubricants
(TYPES OF LUBRICATION)
 In order to lubricate a machine we have
to keep in mind the conditions under
which the machine is working.
There are 3 types of mechanisms by
which lubrication is done.

 Hydrodynamic or Fluid Film or Thick
Film Lubrication
 Boundary Lubrication or Thin Film
Lubrication
 Extreme Pressure Lubrication
The 3 types are

Hydrodynamic or Fluid Film or
Thick Film Lubrication
 This type of lubrication is done in those
cases where liquid lubricants having
minimum viscosity under working
conditions are used and at the same
time, it should remain in place and
separate the moving or sliding parts of
the machine.

Hydrodynamic or Fluid Film or
Thick Film Lubrication

In the fluid film lubrication, the liquid lubricant fills the
grooves or irregularities of the sliding surfaces, and
forms a thick layer in between them so that there is
no direct contact between the sliding surfaces. In
this way, the lubricant reduce the wear and tear by
reducing the frictional resistance produced by the
movement of sliding parts.

Hydrodynamic or Fluid Film or Thick
Film Lubrication
 The frictional resistance to the movement of
the sliding parts is only due to the internal
resistance between the particles of the
lubricant.

Hydrodynamic Lubrication
The frictional resistance is independent of
the load, But depends upon the area and
relative velocity of the sliding parts and
viscosity, thickness of the lubricants. Due
to this reason, the light machines like
watches, clocks, guns, scientific
instruments etc. and delicate machines
are provided with fluid film lubrications.

Boundary Lubrication or Thin Film
Lubrication
 Where thick film lubrication fails, thin film
lubrication is done .
 Thin film or boundary Lubrication is done for
those cases in which the continuous film of
lubrication cannot persist and direct metal to
metal contact is possible.

Boundary Lubrication

This happens when
i) a Shaft starts moving from rest
ii) the speed is very low
iii) load is very high and iv) viscosity
of lubricating oil is very low.

 In boundary lubrication, the oily
lubricant is filled in between the sliding
or moving metallic surfaces, which is
adsorbed on both the metallic surfaces
by any physical or chemical means and
cannot be removed easily .The
adsorbed lubricant from two thin layers
between the sliding metallic surfaces
and avoid the direct metal to metal
contact. As a result of this ,the frictional
resistance between the sliding metallic
surfaces is reduced

 A thin lubricant should have high
viscosity index, good resistance to heat
and oxidation, good oiliness and low
pour point.
Velocity

 Vegetable and animal oils and their
soaps possess great property of
adsorption and are used for thin film
lubrication.
 Graphite and molybdenum disulphide in
oil are also used for boundary
lubrication. These lubricants form a thin
film on the metallic surfaces, which
reduces the friction and can bear
compression as well as high
temperature.

For the boundary lubrication, the
lubricant molecules should possess
these properties
 They should have long hydrocarbon
chains and the lateral attraction
between the chains.
 They should have the active polar
groups or atoms to promote spreading
and to form the linkage with the
metallic surfaces at high pressure

Extreme Pressure Lubrication
 The fast moving or sliding metallic
surfaces under very high pressure
produce a large amount of heat and
temperature becomes very high. At
high temperature the ordinary liquid
lubricants decompose or even
vapourises at such a high temperature
and fail to stick over the metallic
surfaces .To face such conditions
Extreme pressure Additives are added
to the mineral oils. PUNJAB EDUSAT SOCIETY 24

 The Extreme pressure Additives are
the organic compounds possessing
the active radicals or groups such as
chlorine, sulphur , phosphorus etc.
These compounds react with metallic
surfaces at high temperature to form
metallic chlorides,

 sulphides or phosphides which can
form surface layers on the moving or
sliding metallic surfaces and act as
good lubricants.

Summary
Lubricants –Definition, Introduction
Functions of Lubricant
Mechanism of Lubricant(Types of
Lubrication)
Hydrodynamic or Fluid Film or Thick Film Lubrication
Boundary Lubrication or Thin Film Lubrication
Extreme Pressure Lubrication

Multiple Choice Questions
 A Lubricant is used with the object to
a)increase frictional heat b)increase
resistance
c)decreasing frictional resistances
d)Providing direct contact between rubbing
surfaces
 Boundary lubrication is used for a)watches b)
calculators c) light machines. d) when Load is
very high
c d

MCQ
 Lubricant does not act as a a) seal
b)resistant c)corrosion resistant d)coolant
 Which is not mechanism of lubrication
a)thin film b)thick film c)temperature
lubrication d) extreme pressure lubrication
 Vegetable oils are used for a)thin film
b)thick film c)temperature lubrication d)
extreme pressure lubrication
b c a

MCQ
 For Fast moving machines which produce
large amount of heat, the lubricating
mechanism is a)thin film b)thick film
c)temperature lubrication d) extreme
pressure lubrication
 They should have the active polar groups.
This is true for….......lubrication
a)thin film b)thick film c)Normal d) extreme
pressure
d a

State True or False
 The lubricants for boundary lubricants
should have Long Hydrocarbon chains.
 Lubricant act as a corrosion preventer.
 Lubricant does not act as a seal.
 Lubricants increase the efficiency of
machine.
 Lubricants increase the running cost of
Machine.
 Thick film lubricants have polar groups.

True/False
 Graphite and molybdenum disulphide
in oil are used for boundary
lubrication.
 Vegetable and animal oils possess
great property of adsorption.
 A thick lubricant should have high
viscosity index.
 A thin lubricant should have low pour
point.

Fill in the Blanks
 Boundary lubrication is also called……
Lubrication.
 Thick film lubrication is also called……
Lubrication.
 In Pistons ,Lubricant act as a ………
 Lubricants increase the ……….of
machine.
 Lubricant used for watches is ……….
 At high temperature where normal
lubricant vaporise ……………lubricant is
used.

Thank You

Lubricants by shakeer

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