BASIC FUNCTIONS OF LUBRICATIONS.
l Reduce
friction.
l Reduce
wear.
l Reduce
temperature rise.
l Help
cushion or absorb shock
l Minimize
corrosion.
l Avoid
contaminants by sealing out.
l Flush
out the contaminants.
TYPES OF LUBRICATION.
1)
Hydrodynamic Lubrication: In this,
the bearing surfaces are separated by relatively thick layer of the lubricant
to prevent the contact and stability thus achieved can be explained by the laws
of fluid mechanics. This does not require the introduction of lubricant under
pressure to separate the bearing surfaces, although, it is achieved by fluid
dynamics.
2)
Hydrostatic Lubrication: In this, the
lubricant is introduced between the bearing surfaces under pressure, where a
very thick layer of lubricant is desired to minimize the friction to its
lowest. This is done where velocities are very less or zero.
3)
Boundary Lubrication: When the thickness
of the film becomes less due to factors such as drop in viscosity due to increase
in oil temperature, less quantity of lubricating oil, increase of load onto the
bearing, lessening of velocity of moving surfaces etc., a condition occurs
wherein lubrication is bare and surfaces start rubbing with each other
continually. This is called boundary layer lubrication.
However,
when the bearing surfaces are to be operated at slow speed and/or extreme
temperature, solid film lubricants, such as fine graphite powder of molybdenum
disulphide must be utilized because of drawbacks of mineral oil lubricant.
PROPERTIES OF LUBRICANTS.
1)
Viscosity: Viscosity indicates the
relative fluidity of the lubricant. This property of lubricant indicates the
fluidity at the temperature which is varying depending upon the operating
temperature. It is the most important property referring to which manufacturers
recommended the lubricant.
2)
Flash and fire points: Flash point refers
to the temperature at which the vapors emitted from oil due to heating momentarily
ignite in a flash. Fire point refers to the temperature at which vapors of
heated oil catch fire and burn continuously. Fire point is higher than flash
point. These properties are important from point of application of certain
lubricating oils to specific operating temperatures.
3)
Pour point: This refers to the ability of
the lubricant to flow at lower temperature. This is the temperature below which
the lubricant looses its fluidity.
4)
Emulsification: Emulsification is the
property where oil will get easily mixed with water and forms more or less
stable emulsion. This is dangerous to the components as emulsification will
lead to oxidization of oil in the presence of temperature and oxygen/air.
Certain additives are added to break such emulsification of oil.
Demulsification is the property wherein the oil does not get readily mixed up
with water.
5)
Neutralization number: This refers to the
acidity of oil. An increase in this number suggests increase in oxidation of
oil.
6)
Foam: Foam is the property of oil
to have air entrapped and is an undesirable property.
7)
Rust-proofness: Oil has an additional
function of resisting rusting of components it is working with. It is desirable
to have higher rust-proofness of oil.
8)
Corrosion resistance: Apart from avoiding
rust, oil also must not corrode the components itself.
