What is lubricant?
Lubricants
In machine, the friction between metal to metal parts arises due to
A lubricant is a substance introduced to reduce friction
between surfaces in mutual contact, which ultimately
reduces the heat generated when surface moves.
moving surfaces and machine experienced a resistance which
retards their movement. Due to friction large amount of energy is
liberated in the form of heat which reduces the efficiency of
It may also have the function of transmitting forces,
transporting foreign particles or heating or cooling the
surface.
machine.
“Substances which apply between two moving and sliding surface to
reduce friction between them are known as Lubricants” and the
process by which friction between sliding surface is reduce, known
as Lubrication
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Lubricants
The property of reducing friction is called lubricity.
USES: Industry, cooking (oils and fats in use in frying pans,
in baking to prevent food sticking), bioapplications on
humans (e.g. lubricants for artificial joints), ultrasound
examination, medical examinations, and the use of
personal lubricant
Properties of a good Lubricant
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High viscosity index
High flash and low pour point.
Total base number
Thermal stability
Hydraulic stability
Demulsibility
Corrosion prevention
High resistance to oxidation
Properties of Lubricants
Properties of Lubricants
a)
Cloud Point: The temperature at which lubricating oil becomes cloudy in
appearance is called cloud point. It indicates the lowest operating temperature.
b) Pour Point: The lowest temperature at which the lubricant oil become semisolid and ceases to flow is called pour point. It indicates the suitability of
lubricants used in cold condition. Good lubricant should possess low pour point.
Below this point the liquid loses its flow characteristics.
c)
Flash point: The flash point of a volatile material is the lowest temperature at
which vapors of the material will ignite for a moment when an ignition source
brought near to it. The lubricating oil should have flash point reasonably above
its working temperature. It is an indicator of volatility. It indicated safe
maximum temperature of operation.
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Properties of Lubricants
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Properties of Lubricants
d) Fire point: The fire point of a fuel is the lowest temperature at which
f) Viscosity Index: The variation of viscosity of a liquid with temperature is
the vapour of that fuel will continue to burn for at least 5 seconds
called viscosity index. A relatively small change in viscosity with
when an ignition source brought near to it. Fire point is around 10 ⁰C
temperature is indicated by high viscosity index whereas, a low viscosity
higher than flash point.
index shows, a relatively large change in viscosity with temperature.
e) Viscosity: Viscosity is the property of a fluid that determines its
resistance to flow. It is an indicator of flow ability of lubricating oil. The
lower viscosity greater will be the flow ability. If temperature increases
viscosity of the lubricating oil decreases and pressure increases
viscosity of lubricating oil increases. In short we can say that good
lubricating oil is that whose viscosity does not change with
temperature
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Viscosity and Viscosity Index
Acid Value
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Total Base Number (TBN)
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Saponification Value
Total Base Number (TBN) is a measurement of basicity that is
expressed in terms of the number of milligrams of potassium
hydroxide per gram of oil sample (mg KOH/g). TBN is an important
measurement in petroleum products, and the value varies depending
on its application. TBN generally ranges from 6–8 mg KOH/g in modern
lubricants, 7–10 mg KOH/g for general internal combustion engine use
and 10–15 mg KOH/g for diesel engine operations. TBN is typically
higher for marine grade lubricants, approximately 15-80 mg KOH/g, as
the higher TBN values are designed to increase the operating period
under harsh operating conditions, before the lubricant requires
replacement.
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Steam Emulsion Number
Classification of Lubricants
Liquid Lubricants: It includes animal oils, vegetable oils, petroleum
oils, synthetic lubricants.
Animal oils: tallow oil, whale oil etc.
Vegetable oils: castor oil, palm oil etc
Petroleum oils: petroleum fractions
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Classification of Lubricants
Synthetic lubricants: polyglycol, silicones etc.
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Classification of Lubricants
b) Semi-solid Lubricants (Grease): Semi-solid Lubricants are formed by
emulsifying oil and fat with thickening agents like soap of sodium, calcium,
c) Solid Lubricants: Graphite, molybdenum disulphide (MoS2), boron nitride
lithium, aluminum at higher temperature.
(BN)x are predominantly used as a solid lubricants. They are used under high
Classification
temperature and high load (pressure).
Soda based: In this case sodium soaps are used as a thickening agent in
i) Graphite: It is most widely used as a solid lubricant. Graphite has layer
mineral or petroleum oil. They are slightly soluble in water. They can be used
structure; layers are held together with the help of weak Vander Waals’
up to 175 C.
forces which facilitate the easy sliding of one layer on the other layer. It is
Lithium based: In this case lithium soaps are emulsifying with petroleum oil.
very soapy to touch, non-inflammable. It is used at higher temperature
They are water resistance and used up to 15 C. Calcium based: In this case
(around 450oC) condition. They are either used as powder form or mixed
calcium soaps are emulsifying with petroleum oil. They are also water
with oil or water
resistant and used up to 80 C. At higher temperature soap and petroleum oil
are separate from each other.
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Classification of Lubricants
CLASSIFCATIONS OF LUBRICANTS
(Based on application)
i) Molybdenum disulphide (MoS2): It is sandwich like structure in which
hexagonal layer of molybdenum (Mo) lies between two hexagonal layers of
❖ Engine oils
❖ Gear oils
❖ Hydraulic oils
❖ Cutting fluids
❖ Compressor oils
❖ Rust protection oils
❖ Transformer oils
❖ Turbine oils
❖ Quenching and heat transfer oils
sulfur (S) atom. Like graphite each layers are held together with weak
Vander Waals’ forces. It is stable up to 400 C. 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.
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❑ Engine oil
❖ Provision of stable oil film between sliding surfaces.
❖ Provision of reliable engine operation in a wide temperature
range.
❖ Rust or corrosion protection of engine parts
❖ Cleaning the engine parts from sludge
❖ Cooling the engine parts.
Gear oil
➢They have proper viscosity
➢Ability to withstand extreme pressure.
➢Thermal and oxidation stability.
➢Corrosion and rust protection.
➢Compatibility with seal materials.
Function of hydraulic oils……
Hydraulic oils : It’s is a fluid lubricant used in
hydraulic system for transmitting power
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Low temperature sensitivity of viscosity.
Thermal and chemical stability.
Low compressibility.
Water emulsifying ability.
Resistance to cavitation.
Rust and oxidation protection property
Compatibility with sealent materials.
Function of cutting oil…..
Cutting oil: It’s is a liquid used in a metal working
operation for reducing friction between the work
piece and tool, and for removal of heat.
▪ Better surface finish.
▪ Longer tool life.
▪ Narrower tolerance of workpiece size.
▪ Lower energy consumption.
▪ Cleaner cutting zone.
▪ Better corrosion protection.
Compressor oil: This fluid is used for
moving metal parts of gas (air)
compressor.
Rust oil: These lubricants provides temporary protection of metal parts
from oxidation caused by moisture, oil contaminants and chemically
active atmosphere.
Function of rust oil……
• It protects materials from damage.
• It has a great industrial use.
• Lengthen the storage period of metals.
Heat transfer oil:
It is formulated to serve as a fluid media in quenching
operation.
Function of heat transfer oil…
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High flash point.
Oxidation stability.
Controlled volatility.
Thermal stability.
Transformer oil: These are di-electric oils used in oiled filled
transformer, some high voltage capacitors and circuit breakers.
Function of transformer oil…
Emulsions
• Prevention of electric discharges between
the coils.
• Removal of heating generated by
transformer.
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Emulsions
Emulsions
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Mechanism of Lubricantion
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Mechanism of Lubricantion
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Mechanism of Lubricantion
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