Final Lubricants

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LUBRICANTS



Lubricant

Any substance which is introduced between two moving orsliding surfaces in order to reduce friction and to minimize

wear and tear is known as lubricant, e.g Greases, Mobil oiletc.



Functions of Lubricants

1. It reduces wear and tear by keeping the rubbing surfaces apart.

2. It reduces loss of energy in the form of heat and act as coolant.

3. It increases efficiency of the machine.

4. It avoids machine part loss.

5. It reduces maintenance and running cost of the machine.

6. It acts as a seal.

7. It makes the moving parts of the machine smooth.



Classification of Lubricants

On the basis of their physical appearances

Liquid Lubricants Semi- Solid Lubricants Solid Lubricants

Mineral oilsVegetable oilsAnimal oilsBlended OilsSynthetic oils

GreaseWaxes

GraphiteMolybdenum disulphide



• Mineral oils

These oils are obtained by the fractional distillation of crude oil

under certain conditions and then filtered to remove impuritiessuch as wax by dew axing and acid by acid refining. They are cheapstable and easily available

eg:- different petroleum products.

• Vegetable oils

These oils are obtained from vegetables sources. In earlier timethese were used but now they are replaced by mineral oils. These

oils are mixed in the mineral oils to increase their quality.eg:- Olive oil or sweat oil obtained from fruits of olive tree, golden

yellow in color), Palm oil, Rape seed oil, Castor oil, etc.



• Animal oils

These oils are obtained from animal sources. These can be added to mineral oils to

improve their quality. Examples=Whale oil (pale yellow color, obtained by

distillation of whale fat), Lard oil (obtained from kidney and intestine of and the fatof the pig),Tallow oil (Obtained from the fat of cattle) etc.

• Blended Oils

Mixture of mineral oil with animal oil or vegetable oil is known as blended oil. It actsas a good lubricant. Blending of an oil is done to improve viscosity, oiliness,

oxidation resistance, corrosion resistance and to improve color



• Synthetic oils

These oils are commercially prepared in the laboratories. Where

mineral oils fail to work synthetic oils are used. They are very

effective under severe conditions.eg:- Silicones, Polyglycols, Phosphates, Esters etc

•

Semi- Solid Lubricants Grease are semi- solid lubricants. It is made up of soap dispersed in petroleum oil

or synthetic oils and may contain additives like waxes, fats, petroleum residues.

Based on the nature of soap used greases are of following types.

1. Soda based grease2. Lithium Based grease

3. Axle grease



Solid Lubricants

The two most common solid lubricants are graphite and

molybdenum disulphide. Some organic substances water or oil

are mixed with to use them as lubricants.

Graphite

It is most widely used of all solid lubricants. It is soapy in touch non

inflammable. It can be used up to very high temperatures. When graphite isdispersed in oil it is known as oil dag and in water it is known as aqua dag.

Molybdenum disulphide

It is very fine powder and can be sprinkled on sliding surfaces. It is also used

along with solvents and grease.



Mechanism of lubrication

It is done by three mechanisms:

1. Fluid Film or Thick Film or Hydrodynamic Lubrication

2. Thin Film or Boundary Lubrication

3 Extreme pressure Lubrication



1. Fluid Film or Thick Film or Hydrodynamic Lubrication

This type of lubrication is done by liquid lubricants. In this

mechanism lubricant oil forms a thickness of 1000Å whichprevent the direct contact of the machine parts as a result thefriction is reduced, wear and tear is reduced. In fluid film

lubrication, lubricant should have minimum viscosity underworking conditions and lubricant should remain inside andseparate the surfaces.

This type of lubrication is provided in case of delicate instruments

, lights machines and scientific instruments.



2. Thin Film or Boundary Lubrication

This type of lubrication takes place when a continuous fluid film cannot be

maintained due to low speed, heavy load, low viscosity of the oil and movementof the shaft. In this mechanism the thickness of the film cannot be more thentwo molecular layers. In boundary lubrication lubricating oil should have good

oiliness , long hydrocarbon chain, active polar and functional groups whichpromote wetting and chemical bond formation with the metal surface



3. Extreme pressure lubrication

This mechanism of lubrication is used when the moving surfaces are underhigh pressure and excessive heat is produced, where the normal lubricantsfails to work. These special lubricants are known as extreme pressurelubricants. These are prepared by the addition of organic compounds suchas chlorinated esters and tricresyl phosphates etc



S.NO

Fluid Film or Thick FilmLubrication

Thin Film or BoundaryLubrication

1 In this mechanism lubricant oilforms a film of thickness of 1000

Å .

In this mechanism lubricant oilforms a film of thickness of less

than1000 Å.

2 In fluid film lubrication, lubricantshould have minimum viscosityunder working conditions.

The lubricant should have highoiliness under working conditions.

3 This type of mechanism is usedunder high speed and low loads.

This type of mechanism is usedunder low speed and high loads.

4 The lubricant applied is sufficient

to keep the machine surfacesapart.

The lubricant applied is unable to

keep the machine surfaces apart

5 This mechanism is applied inwatches, clocks, sewingmachines etc

This mechanism is applied intractors, rollers concrete mixersetc



Characteristics of Good lubricants

1 It should neither be very thin nor very thick.2 It should have high oiliness.

3 It should have high boiling point to bear high temperatures.

4 It should not form gum.

5 It should not be squeezed out or stuck to moving parts.6 It should form a continuous layer in the moving parts of the machine underpressure.

7 It should possess corrosion resistance, antifoaming and demulsificationproperties.



Properties 0f lubricants

1. Viscosity2. Acid value or acidity

3. Saponification value

4. Coke number

5. Volatility

6. Oiliness7. Emulsification

8. Flash point

9. Fire point

10. Cloud point

11. Pour point



1. Viscosity

It is measure of flow ability of the lubricant at definite temperatureOr

It is the resistance offered by a liquid towards flow.Units are dynes/cm2 (poise) in c.g.s system and Nsec/m2 in S.I systems.Viscosity decreases with rise in temperature.

2. Viscosity Index

The rate of change of viscosity of the lubricant with temperature is measured by ascale known as viscosity index. It is denoted by V.I

V.I = Vs(o) – Vt x 100

Vs(o) – Vs(100)

Where Vs (o) is the viscosity at 100o

F of the standard oil having V.I=0Vs (100) is the viscosity at 100o F of the standard oil having V.I=100Vt = Is the viscosity at 100o F of the test oil



2. Acid value or acidity

It is defined as the number of milligrams of KOH required to neutralize

the free acid in 1 g of the oil.

The presence of acid in the lubricating oil is harmful to the machineparts as it causes corrosion.

Acid value tells us about the age of the oil as it increases with time dueto the hydrolysis with moisture.

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3. Saponification Value:

It is defined as the number of milligrams of KOH required to saponify the fatty

materials present in 1 g of the oil. Saponification Value is used to distinguishbetween vegetable oil, animal oil and mineral oils etc.

4. Coke Number :

It is the percentage of carbon residue in a known weight of lubricating oil. A good

lubricant has lower number of coke value.

Coke No.= weight of carbon residue left x 100

Weight of oil



5. Volatility

It is tendency of the liquid to vaporize with increase in temperature. A goodlubricant has low volatility.

6. Oiliness It is the property of the lubricant by which it can stick to the surface of the

machine parts operating under high pressure or load. A good lubricant shouldhave high value of oiliness.

7. Emulsification The property of the oil to mix with water to form emulsion which can be eitheroil in water or water in oil emulsion. A good lubricant should have low emulsionformation tendency.

8. Flash Point

It is the minimum temperature at which the lubricating oil gives enoughvapours which can burn for a moment is known as flash point.



9. Fire Point

It is the minimum temperature at which the lubricating oil gives enough vapours

which can burn for at least for five seconds is known as fire point.

A good lubricant oil shouldn’t possess fire point and flash point above theirworking temperatures. These points tell the maximum temperature upto which alubricant can be used.

10. Cloud point

It is the temperature at which the lubricating oil becomes hazy or cloudy isknown as cloud point.

11. Pour point

It is the temperature at which the lubricating oil ceases to flow is known as pour

point.Lubricants should posses low cloud point and pour point otherwise they will solidify

at low temperatures.



Different types of additives

1. Extreme Pressure additives

2. Viscosity index improvers3. Antioxidants

4. Corrosion inhibitors

5. Antifoaming agents

6. Oiliness improvers

7. Pour Point depressants

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1. Extreme Pressure additives

These are additives like chlorinated esters, organic phosphates,

organic chlorinated compounds which increase the capacity of the

lubricant to work under extreme pressure conditions etc.2. Viscosity index improvers

These are additives like polyacetates, polybutenes etc which can be added to the

oil to improve its viscosity index.

3. Antioxidants

These are additives like aromatic phenols or amino compounds which are added

to the oil so that they can be oxidized in preference to the oils.

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4. Corrosion inhibitors

These are additives like compounds of sulphur and phosphorous which prevent

the corrosion of the machine parts. 5. Antifoaming agents

These are additives like glycols, glycerol, silicone etc which prevent foaming and

priming in the lubricating oils.

6. Oiliness improvers

These are additives like fatty acids, fats, vegetable oils which increase the oiliness

of the lubricating oils.

7. Pour Point depressants

These are additives like polymethylacrylates which when added in the oil lowers the

pour point of the oil.

Final Lubricants

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