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LUBRICANTSMade by :- Amogh Singhal 1081310109
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What are Lubricants?
Lubricants are the substances that
reduce friction between two surfaces
which move over one other
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Classification of Lubricants.SOLIDS
graphite
talc
chalk
Teflon
SEMI SOLID
grease
Vaseline
LIQUID
vegetable oils
animal oils
mineral oils
blended synthetic
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Solid Lubricants
Solid lubricants are employed in
(1) heavy machinery
(2) situations where semisolid or liquid film of lubricant can't
be maintained
(3) parts to be lubricated are not easily accessible(4) operating temp. and pressure are too high and easily
combustible liquid lubricant can't be used
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Solid lubricants are either used in dry powder form or mixed
with water or oil
Graphite is very soft metal, it is greasy to touch and servesas a lubricant when mixed with petroleum jelly to form a
graphite grease.
Molybdenum Sulphide is stable at high temperature and thus
,it is used in machines which are subjected to high
temperature
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Semi-solid Lubricants
Greases are mixtures of mineral oils and soap
to this mixture we add fillers or chemical additives to give characteristics likeoxidation resistance
rust prevention
extreme pressure attributes
Important Grease
Lime base grease are prepared by treating required amount of fatty oil with calciumhydroxide soln.
It is resistant to water and has a low melting point ,it is not under temperatures exceeding
80o
C
Soda base greases are produced by sodium hydroxide solution. They have high melting
point but are unstable in water
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Properties of Lubricants
1.Viscosity
2.Volatility
3.Acidity and alkalinity
4.Saponification number
5.Oiliness
6.Cloud point and Pour point
7.Flash point and Fire point
8.Aniline point
9.Precipitation point
10.Iodine number
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Viscosity
Viscosity is the property of a liquid or fluid by virtue of which it offers
resistance to its own flow
Viscosity is the measure of the performance of the lubricant
For machine parts moving at slow speeds under high pressure ,a heavy
oil(highly viscous) should be used.
For minimum friction, thinnest(least viscous) oils should be used
EFFECT OF TEMPERATUREAs the temperature is increased, force of cohesion is weakened and thus,
viscosity is decreased
Variation of viscosity with temperature is measured using Viscosity Index.
This scale was introduced by Society of Automotive Engineers(SAE). The
working range of temperature for VI is 38-99oC
VI = 100{(L-U)/(L-H)}
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Volatility
If lubricants containing volatile impurities is
used, the volatile compounds vanishes from
the sample due to volatization and the
quantity of pure compound is reduced and is
left as residue. This may lead to LubricantStarvation.
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Acidity and Alkalinity
Just like pH, acidity and alkalinity are interns of Neutralization Number
Neutralization Number = No. of c.c. of N/10 KOH x 5.6________________________
Weight of Oil taken
Total Acidity/Acid Value/Acid Number
Amount of titrating base ,expressed as mg of KOH required to neutralize all
acidic constituents of 1g of sample
Total Alkalinity/Base Value/Base Number
Amount of titrating acid ,expressed as mg of KOH required to neutralize all basicconstituents of 1g of sample
Significance
If the acid no. of a lubricating oil is more than 0.10,then it is sure to contain an
additive because without additive ,the oil can't have acid number more than 0.10
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Saponification Number
Saponification is the hydrolysis of an ester in presence of NaOH or KOH to give alcohol and
sodium or potassium salt of acid saponification Number is the amount of KOH in mg that isrequired to saponify fatty material present in 1g of the oil
Significance
Vegetable and animal oils undergo saponification but mineral oils do not undergo
saponification.
It is used
1. to distinguish between fatty oil and mineral oil
2. to identify the given fatty oil(for fatty oil, it is a measure of molecular weight)
3. to determine the extent of adulteration in the given oil
4. to determine the extent of compounding fats and oils added to improve oiliness in a
lubricant
Percentage of fatty oil = (C/F) x 100
C = Saponification Number of lubricant
F = Saponification Number of fatty oil
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Oiliness
It is the property of a lubricant to stick on to the surface
under the conditions high speed and heavy load.
An oil with high degree of oiliness will satisfy the above the
conditions
Vegetable oils have more oiliness
Mineral oils have less oiliness
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Cloud Point and Pour Point
Cloud point is the temperature at which the oil becomes cloudy and hazyin appearance
Pour point is the temperature at which the oil ceases to flow or pour
Both these points can be observed if we cool down an oil real slowly
Significance
Lubricants which are used at low temperatures should have low pourpoints otherwise solidification of lubricant will occur and jam the
machine
Aircraft engines require to start and operate at sub zero temperature
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Flash Point and Fire Point
Flash Point is the temperature at which the oil gives sufficient amount of vapours to form an
inflammable mixture with air which catches fire when flame is applied .At this temperature, amomentary flash is observed
Flash point is determined using Cleveland's open-cup (Flash Point below 120oF) and Pensky
Marten's or Abel's closed cup (Flash Point above 120oF)
Fire point is the temperature just like the Flash Point but here the mixture is burned at least for 5
seconds when ignited with flame
Fire point is (5oC to 40oC) higher than the Flash point.
At Fire point the heat from the flash becomes sufficient to evaporate more liquid and maintain
combustion
Significance
A knowledge about flash point and fire point of the lubricants employed will be helpful in
providing safeguards against fire hazard during their storage, handling, transportation and use.
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Aniline Point
Aniline point is the least temperature at which the oil is
completely miscible with an equal volume of freshly distilled
aniline
Significance
It is the measure of the aromatic content. An oil with a
higher aniline point contains more of the paraffinic
hydrocarbons and less of aromatic hydrocarbons
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Precipitation Number
Precipitation Number is the percentage of
asphalt present in the oil
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Iodine Value
The no. of grams of iodine absorbed in 100g of the oil is called iodinevalue
The degree of unsaturation of oils and fats is reported in terms of Iodine
Value
Iodine Value is also used to determine the extent of contamination in a
given oil
Oils are also classified on the basis of their iodine value
Drying oils - Linseed oil, Tung oil etc. (IV>150)
Semi-drying oils - Soya bean oil, dehydrated castor oil (IV = 100 to 150)
Non-drying oils - castor oil, coconut oil (IV
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