Lubrication:

It is the process or technique employed to reduce the friction between the moving parts of a machine.

Lubricants

The substances which is employed in the process of lubrication .Eg: petroleum oil, animal or vegetable oil .

It act as coolant because it reduces the production of heat between the moving parts of the machine in contact.

It avoid the damage of the moving parts of machines by minimizing the production of heat.

It reduces the wear and tear of by keeping the moving parts of machines apart.

It reduces the maintenance and running cost of machine.

It increases the efficiency of machine by reducing the loss of energy.

It can also act as corrosion preventers.

It act as a seal as in piston.

Three types of lubrication are :

Hydrodynamic or Fluid film or Thick film lubrication

Boundary or Thin film lubrication

Extreme pressure lubrication

Also called complete or full flow. Occurs when two surfaces are completely

separated by a fluid film. { Thickness of fluid film is at least 1000 Å } .

In this method ,the lubricant fills the grooves and forms a thick layer in between them so that there is no direct contact between the sliding surfaces.

In this way ,the lubricant reduces the wear and tear by reducing the frictional resistance produced by movement of sliding parts.

It is a semi-solid, consisting of a metallic soap dispersed throughout a liquid lubricating oil . The liquid lubricant maybe petroleum oil or synthetic oil and it may contain additives also.

These are prepared by saponification of fat { fatty acid, vegetable oils } with alkali [like lime,caustic soda ] followed by adding hot lubricating oil while under agitation.

Sodium,calcium,lithium soaps are used as gelling agents.

To improve the heat resistance of grease , inorganic solid thickening gents like finely divided clay,belonite,carbon black etc..

They have high shear or frictional resistance than oils ,can support much heavier loads at lower speeds .

Normally grease can sustain temperature upto 180 degree.

They have a tendency to separate into oils and soaps.

In situations where oil cannot remain in place due to high load,low speed,sudden jerks etc..

I. FOR EXAMPLE :In rail axle boxes; In bearing and gears that work at high T In situations where bearing neeeds to be

sealed against entry of dust,dirt,moisturebecause greases are less liable to contamination by these.

In situations where dripping of oil is undesirable , because unlike oils,greases if used do not splash over articles being prepared by the machine.Foreg:paper,textile industrial machines.

The main function of soap is thickening agent so that grease sticks firmly to the metal surface.

Temperature upto which the grease can be used.

Its consistency.

Its water and oxidation resistance.

CALCIUM BASED GREASES:Emulsion of petroleum oils with calcium

soaps.

Cheapest and most commonly used

Insoluble in water.

Used at low temperature ,because above 80°C oil and soaps begin to separate.

USED for :Tractors, lubricating water pumps.

Thickened by mixing sodium soaps.

Not a water resistant.Since it slightly soluble in water.

However , they can be used upto 175°C .

Used in ball bearings.

Dropping point is very high

It is prepared by the saponification of vegetal oils with lithium hydroxide.

It is thickened by adding adding lithium soaps.

Water resistant

Suitable to use at low temperature [15°C] only.

Used for lubricating engines.

It is prepared by adding lime to resins and fatty oils.Fillers like talc and mica are also added to them.

Water resistant.

Very cheap resin-grease.

Suitable for less delicate equipments working under high load and low speed’

Used where :

1) Operating conditions and load is too high

2) Where contamination of lubricating oil or greases is unacceptable.

3) Combustible lubricants must be avoided

4) Operating condition are such that a lubricating film cannot be secured by use of oils or greases.