Types of coolants are :

(a) Gaseous type

(b) Liquid type

1) water

2) fatty oil

3) straight mineral oil

4) cutting fluids

5) soluble oils

(c) synthetic coolants

(a) Gaseous type :

• These type of cutting fluids are applied through a nozzle under pressure.

• e.g. Argon, helium, $co_2$, oil mist, etc.

(b) Liquid type :

1) water :

• plain water and NaOH water, containing alkali are used where cooling and washing away of chips are needed during machining.

• Also water is most freely available, cheapest and best cutting fluid as it conduct very high heat.

2) Fatty oil :

• These oils are used in heavy duty machining work

• These oils are costly

• It give bad smell after some use

• Most popular fatty oil - Lard oil and sperm oil.

3) straight mineral oil :

• These oils are used for light duty operation on non ferrous - metals like Al, brass, mg, etc

• Mostly used in automatic machines.

• This oil can be re circulated and reused.

4) cutting oils :

• These are mineral mixed with sulfur or chlorine and animal fats.

• These are costly.

• Used for special operation like gear cutting, broaching, etc.

5) soluble oils :

• An emulsion is a product which when mixed with water, forms milky dispersion's.

• It is a mineral oil which contains an emulsifier such as soap.

• It has good cooling properties

• Used in operation like turning, miling, drilling etc.

• Disadvantage is it may corrode the machine tool.

(c) Synthetic coolants :

• These are generally non-petroleum products and diluted with water.

• These coolants gives high material removal rate.

• These coolants can not be reused.

• It is mostly used in grinding operation.