Lubricants

Lubricants

Sanjeet Kumar NayakGET (Mechanical)

Safety tip…

• Grinding dust from abrasive wheels is made up of extremely fine particles of the metal and the wheel and can be very dangerous to your health.

Avoid inhaling such abrasive particles as much as possible.

Definition• Lubrication is the process, or technique

employed to diminish friction between surfaces in close proximity, and moving relative to each other, by interposing a substance between them.

• The substance interposed is called lubricant.

A bearing surface under the microscope

Even a smooth surface requires lubrication to prevent wear and to reduce friction

Functions of Lubricants

• Reduce Friction & Wear • Cool Moving Parts• Absorb shock• Sealing Agent• Cleans Parts• Prevents Corrosion• Prevents thermal Expansion of parts• Reducing Engine Noise• Minimizes Energy losses

LubricantFilm

Lubricant film thickness 1/100th of a paper sheet

Withstanding pressure of 10 cars on a finger nail

Types (According to physical state)Lubricants

Solid Semi-solid Liquid

e.g. Graphite e.g. Grease e.g. petroleum oil

• It’s a measure of a fluid’s resistance to flow. Viscosity of the lubricating oil determines its performance under operating conditions.

• Too viscosity oil is thin and cannot stop friction.• Too high viscosity oil is thick and has poor flow properties.

Parameters of lubricants1.Viscoity

Viscosity : application :( at 400 C) (indication)

10 – 25 cSt low temp, (very) high speed

70 – 200 cSt standard applications

300 – 1000 cSt (very) heavy load, (very) low speed

VISCOSITY INDEX :• The rate at which viscosity of a lubricant changes with

temperature is measured by a scale called Viscosity Index.• It is the decrease in viscosity of oil per degree rise in temp

between 38 °C & 99°C. • Higher Viscosity Index means less variation of viscosity with

temperature.

Factor affecting Viscosity :• Temperature : Viscosity decreases with increases in temperature.• Load : Viscosity increases with increases in load.• Speed/shear : Viscosity decreases with increases in speed.

Determination of Viscosity Index

Determination of VI (contd.)

• First the viscosity of the oil under test is determined at 38 °C Let it be U• Then viscosity of 100 VI reference oil be H• Then viscosity of 0 VI reference oil be L

• The values of 100 VI & 0VI oils is obtained from ASTM D2270.

• Iodine number is the number of Grams equivalent of iodine absorbed by 100gm of oil.

• Each oil has its specific Iodine Number. • Iodine Number determines the extent of unsaturation present in the oil.

Low Iodine Number is desirable in oils.

2. Iodine number

• Aniline point of an oil is defined as the minimum temperature at which equal volumes of aniline(C6H5NH2) and the oil are miscible to form a single phase upon mixing .

• Aniline Point is a measure of aromatic content of the lubricating oil.• Low Aniline Point oil have high aromatic content which attacks rubber

seals.• Aniline Point is used as an indication of possible deterioration of rubber

sealing etc.

A good Lubricants should have higher Aniline point

3. Aniline point

• Demulsification number defined as the number of seconds required for an oil to separate from water after it has been emulsified under specified conditions.

• A good lubricating oil should form such an emulsion with water which breaks easily. This property is called demulsification.

• Quicker the oil separates out from the emulsion formed, better is the lubricating oil.

A good lubricating oil should have lower demulsification number.

4.Demulsification number

• Flash Point is the min temp at which the lubricant’s vapors' ignite for a moment when tiny flame is brought near.

• Fire Point is the Min temp at which the lubricant’s vapours burn constantly for 5 seconds when tiny flame is brought near.

• Fire point = flashpoint + 5°C to 400 °C • If flash point < 37.8 °C= Flammable liquids

And if flash point >37.8 °C =Combustible liquids.

For ease of storage and transportation lubricants with higher flash point are preferred.

5. Flash point & Fire point

• Drop Point is the Temperature at which grease passes from the semi-solid state to the liquid state.

• It determines the upper temp limit for the applicability of grease.• It is applicable for grease only.

Higher Drop point is preferred in grease

6. Drop point

7.Neutralisation number

• Neutralization number can be either a total acid number (TAN) or total base number (TBN)

• Total Acid Number is a measure of the amount of potassium hydroxide required to neutralize the acid contained in a lubricant.

• TAN indicates age and Oxidation extent in the oil.• Total Base Number is a measure of reserve alkalinity in the oil. It is

measured by mg of KOH per gram of oil.• Alkali is added in the oil as a corrosion inhibitor.TBN indicates corrosion

resistivity of the oil.

Higher TBN or Lower TAN is preferred in an oil.

• Cloud Point is the temp at which the lubricant becomes cloudy or hazy when cooled.

• Lubricating oils used in capillary feed systems should have low cloud points, otherwise impurities will clog the capillary.

• Pour Point is the temp at which the lubricant just ceases to flow when cooled.• Pour point of wax can be lowered by dewaxing , addition of suitable pour

point depressant, by removing the viscous constituent of the oil.

Lower Cloud Point and Pour point is preferred in a Lubricant.

8.Cloud point and Pour point

Desirable properties

• High Chemical stability• High thermal stability• High boiling point• Low freezing point• Non-radioactive• Ease of availability• Economic viability

Additives

• Additives are the substances added to a lubricant to enhance existing properties, suppress undesirable properties or impart new properties so as to increase the range of applicability.

• These are classified along functional capabilities as :» For chemical stability» For viscosity» For contamination control » For lubricity

Additives for chemical stability

Detergents Metallo-Organic compounds of Sodium, Calcium and Magnesium

Chemically react with sludge to neutralize them and keep them soluble

Anti-Oxidants Aromatic Amines, sulfurized phenols

Decompose peroxides,Terminates free-radical reactions

Rust-inhibitors Metal phenolates Provide protective filmNeutralize corrosive acids

Additives for Viscosity

VI improvers Polymers and copolymers of olefins

Polymers expand with increasing temperatures This counteract oil thinning

Pour point depressants

Alkylated naphthalene Modify wax crystal formation to reduce interlocking

Additives for contamination control

Dispersants (anti-coagulants)

Alkylsuccinimide Contaminants are bonded by polar attraction to dispersant molecules.Prevented from agglomeratingKept in suspension due to solubility of dispersant

Anti-foaming agents Organic copolymers Reduce Surface tension to speed collapse of foam

Seal swell agents Aromatic hydro carbons Chemical reaction with gasket to cause slight swell, resulting in tight seal

Additives for Lubricity

Anti Wear Organic Phosphates Chemical reaction with metal surface and forms a film. Prevents metal-to-metal contact

Friction modifiers Organic fatty acids and amides.

Preferential adsorption of surface active materials

Extreme pressure agents

organic sulfur and chlorine compounds

Chemical action to form a surface film

Lubricant Nomenclature

FOR LUBRICATING OIL • According to ISO 3448 standards lubricating oils are named

according to their Viscosity grades.• The Viscosity grade is suffixed

FOR GREASE • Greases are given NLGI number in accordance with ASTM D-

217 test.

NLGI Grades as per ASTM D-217 TEST

Lab Tests - for lubricants

ASTM D 445ASTM D 2250ASTM D 97ASTM D 92 ASTM D 664ASTM D 217

Kinematic viscosityViscosity indexPour PointFlash PointTotal Base Number (TBN)NLGI numbers

Example

SERVOMESH-320• Viscosity :320-350cst(At 40°C)• Viscosity Index : 90• Flash Point : 232 °C• Pour point : -3°C

USES:- Gear boxes

SERVOSYSTEM46

• Viscosity : 43-48cst (At 40 °C) • Viscosity Index : 98• Flash Point :200°C• Pour point : -15°C• Demulsification no : 20mins

USES :-Pumps

Thanks