Lubricants and its properties

5/27/2018 Lubricants and its properties

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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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Lubricants and its properties