Classification Of Lubricants

LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

Classification of Lubricants: Lubricants can be broadly classified. On the basis of their physical state, as follows:

I) Lubricating Oils or Liquid Lubricants A good lubricating oil must have-

i)

low vapour pressure (high B.P.)

ii)

adequate

(enough)

viscosity

for

conditions. iii)

low freezing point.

iv)

high oxidation, resistance

v)

heat stability

vi)

non corrosive property

vii) stability at the operating temperatures.

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particular

service

LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

Lubricating oils are further classified as follows: i) Animal & Vegetable oils Before the advent (coming or arrival) of the petroleum industry, they were the most commonly used lubricants. They have good oiliness. However they are costly. Undergo oxidation easily, forming gummy & acedic products & get thickened on coming in contact with air. They have some tendency to hydrolysed when allowed to remain in contact with moist air or aquous medium. So at present they are rarely used as such.

Actually they are used as blending agent with other lubricating oil to produce desired effects.

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LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

e.g. Vegetable oilsa) Olive oils Obtained -

from used for the delicate

olive trees &

apparatus (low press of high speed)

b) Palm

Palm fruits

delicate apparatus.

Castor seeds

delicate

oilsc) Castor oils-

apparatus.

excellent oiliness but insoluble in petroleum.

e) Rape

Colza plant

delicate apparatus.

Hazel nut plant

delicate apparatus.

seedf)

Hazel nut-

e.g. Animal oils a) Whale

Whale fish

used

oil-

for

light

machinery.

b) Neat foot Foot of neat

delicate apparatus.

oilc) Lord oil-

Fats, kidneys & ordinary machines. intestines of pigs

d) Tallow oil-

Cattle

fats. used for machine in

(Bullocks or cow) which high pres & low speed.

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LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

ii) Mineral of Petroleum oils They are obtained by distillation of petroleum. The length of hydrocarbon chain is varies between 12 to 50 Carbon atoms. The shorter chain oils have lower viscosity than the/longer chain oils.

These are most widely used because they are i) cheap ii) available in abundance & iii) quite stable under service conditions.

However they posses comparatively poor oiliness as compared to that of animal & vegetable oils. The oiliness as compared to that of animal & vegetable oils. The oiliness can be increased by addition of high molecular with compound like oleic acid, stearic acid etc.

Impurities in Crude petroleum can be removed by using Dewareing, Acid refining & Solvent refining. 4

LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

iii) Blended Oils No single oil serves as the most satisfactory lubricant for many of the modern machineries. Typical properties of petroleum oils can be improved by using Specific additives. These are also called blended oils. Fatty acids, organic compound Glycols.

It is done to reduce pour point, improve viscosity, increase oiliness, resist oxidation, reduce corrosion & improve color.

iv) Synthetic Lubricating Oils They are chemically prepared compounds. Where mineral oil fail to work, synthetic oils are used. They are very effective in severe (strict) conditions & are used in jet engines, rocket motors, submarines, etc. They are very expensive & sometimes they are used by mixing them with mineral oils.

e.g. Poly alkene glycols & Silicon 5

LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

II) Semi Solid lubricantsThe most important Semi-solid lubricants are greases, vaselines, wares & other compounds of oil & fats. These are called Semi-solid because they are neither solids nor liquid at ordinary temperature.

Greases are prepared by saponification of fat (tallow i.e. hard

fat

or

fatty

acid)

with

alkali

( 𝐶𝑎(𝑂𝐻)2 𝑁𝑎𝑂𝐻, 𝐵𝑎(𝑂𝐻)2 𝐿𝑖𝑂𝐻 ) followed by adding hot lubricating oil while under agitation (Change in condition)

At high temp, the soap dissolve in the oil, where upon the interconnected structure exist & the grease liquefies + it become a shift solid mass. To improve the heat resistance of grease, inorganic solid thickening agents (Linely divided Clay, bentorite, colloidal silica, carbon black, etc.) are added.

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LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

They are usedi)

For high load, low speed, intermittent operation, sudden jerks etc.

ii)

In bearing & gears at high temperature.

iii)

as sealing agents in bearing.

Important greases are i) Calcium – based greases or Cup greases These are emulsion of petroleum oils with calcium soaps.

Calcium hydroxide + hot oil+

𝑈𝑛𝑑𝑒𝑟 𝐴𝑔𝑖𝑡𝑎𝑡𝑖𝑜𝑛

Ca-based grease.

They are cheapest, most commonly used & good water resistance & used upto 800C because above 800C oil & soap beings to separate out.

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LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

ii) Soda-based greases These are petroleum oil thickened by mixing sodium soaps. They are poor water resistance because sodium soap is soluble in water. However they can be used up to 1750C . They are suitable for use in ball bearings.

iii) Lithium based greases These are petroleum oils thickened by mixing lithium soaps. They are water resistance & are suitable for use at low temp (15oC) only.

iv) Axle grease Ca(OH)2 + Fatty Acid (Resin) + Filler (Tale & mica) ---- >> Axle grease. They are water resistance & suitable for less delicate equipment working under high loads & at low speeds.

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LUBRICANTS

III)

CLASSIFICATION OF LUBRICANTS

THEORY

Solid lubricantsSolid lubricants are used in situation such as,

1. When heavy machinery is to be operated at high speed & moderate load or at very high load & low speed. 2. When the machine parts are not easily accessible 3. When the machine is at high working temp & press. & hence under such conditions combustible lubricants are unsuitable.

e.g. graphite & molybdenum disulphide.

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LUBRICANTS

1.

CLASSIFICATION OF LUBRICANTS

THEORY

Graphite – Carbon atom in a network of hexagons

Each C atom bonded by

only

three

covalent bonds.

The distance of fourth carbon

is

almost

double, due to which this

fourth

valency

atom is Hexible & keeps moving about, thereby

weakening

the bonds between different layers.

As a result it is soft & has

a

property.

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lubricating

LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

Ti is non- inflammable, soapy to touch + not oxidized in the presence of air below 375oC. It can be used upto much higher temp in the absence of air. It can be used in powdered forms or as suspension – in oil or water.

i)

The suspension of graphite in oil is known as oil dag & it is used in I.C. Engines.

ii)

The suspension of graphite in water is known as aquaday & it is used in food processing industry.

iii)

Graphite is also mired with greases to form graphite greases which are sued at high temp.

Uses -In air compressors, lathes, railway truck joints, cast iron bearing, etc.

2.

Molybdenum disulphide – Molybdenum disulphide has a sandwich, like structure in which a layer of Mo atoms lies between two layers of S atom. Poor inter-laminar attraction is responsible for low shear strength in a direction Parallel to the layers.

It possesses very low coefficient of friction & is stable in air up to 400 oC. Its fine powder may be sprinkled on 11

LUBRICANTS

CLASSIFICATION OF LUBRICANTS

THEORY

surface sliding at high velocities. When it falls low spots in malal surfaces forming.

It is also used along with colverus & in greases is known

as

molykotes.

used in automotive & truck chassis.

Besides

the

more

important

graphite

&

molybdenum disulphite, the other substances like Teflon, Soapstone, talc, mica, etc, are also used as a solid lubricants.

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