Lubricants

Lubricants

Introduction
In all type of machines, the moving surfaces rub against each other. Due to this rubbing a resistance is offered to their movement. This resistance is known as Friction. This friction will cause a lot of wear and tear of surfaces of moving parts. Due to the friction large amount of energy is dissipated in the from of heat therby the efficiency of machine gets reduced.

Definitions
Lubricant
Lubricant is a substance used in between two moving surfaces to reduce the friction.

Lubrication
Lubrication is a process of reducing friction and wear between two moving surfaces by adding lubricant in between them.

Functions of a lubricant

1. It prevents the contact between the moving surfaces and reduces wear tear and surface deformation of the concerned parts.
2. It reduces the energy so that efficiency of the machine is enhanced.
3. It reduces the frictional heat and prevent the expansion of metals.
4. It acts as a coolant by removing the frictional heat generated due to the rubbing of surfaces.
5. At sometime it acts as a seal preventing the entry of dust and leakage of gases at high pressure.
6. It reduces the maintenance and running cost of the machine.
7. It minimizes corrosion.

Requirements (or) Characteristics of a lubricant

1. A good lubricant should not undergo any decomposition, oxidation, reduction at high temperature.
2. A good lubricant should have higher flash and fire point than the operating temperature.
3. A good lubricant should have high oiliness, viscosity index aniline point.
4. A good lubricant should not corrode machine parts.

Classification of lubricants
Lubricants are classified on the basis of their physical state as follows.

1. Liquid lubricants
(a) Vegetable oils – Palm oil, castor oil, etc.
(b) Animal oils - Whale oil, tallow oil, etc.
(c ) Mineral oils – Petroleum fractions.
(d) Synthetic lubricant – Silicones, polyglycol ethers, etc.
(e) Blended oils (or) Compounded – Mineral oils with various additives

2. Semi- solid lubricants
Greases, vaselines, etc.

3. Solid lubricants
Graphite, molybdenum-disulphide, etc.

4. Emulsions
(a) Oil in water type – Cutting emulsions.
(b) Water in oil type – Cooling liquids.