Transcript Topic :Lubricants & Mechanism of lubrication

Subject:
APPLIED CHEMISTRY-II
2ND SEM
TOPIC :
LUBRICANTS & MECHANISM OF
LUBRICATION
BY :MANMOHAN KRISHAN
Lecturer in Chemistry
GOVT.POLYTECHNIC COLLEGE
GURU TEG BAHADUR GARH (MOGA)
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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.
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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
projections get broken and deformities arise.
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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.
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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.
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Functions of Lubricants
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.
i)
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Functions of Lubricants
V.
VI.
VII.
Lubricants increases the efficiency of
machine by reducing the loss of energy.
By using the lubricants, the relative
motion of the moving parts of machine
becomes smooth and noise level of
running machine reduces.
Lubricants also act as the corrosion
preventers.
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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.
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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.
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The 3 types are

Hydrodynamic or Fluid Film or Thick
Film Lubrication

Boundary Lubrication or Thin Film
Lubrication

Extreme Pressure Lubrication
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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.
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Hydrodynamic or Fluid Film or
Thick Film Lubrication
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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.
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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.
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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.
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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.
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Boundary Lubrication
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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.
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
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
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
A thin lubricant should have high viscosity
index, good resistance to heat and
oxidation, good oiliness and low pour point.
Velocity
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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.

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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

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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.
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Extreme Pressure Lubrication

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,
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Extreme Pressure Lubrication

sulphides or phosphides which can form
surface layers on the moving or sliding
metallic surfaces and act as good
lubricants.
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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
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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
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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
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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
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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.

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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.

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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.


Thin, fluid film,seal,efficiency Thick film, extm
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Thank You
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