Machining Coolants

Coolant are liquids applied to the machining contact surface during the process.  There are a wide range of coolants, such as oils, emulsions, pastes, gels, etc. A coolant is an emulsion of oil suspended in water. 

Coolant liquids are broadly classified into
     Oil based coolants (straight and soluble oils)  and
     Chemical machine coolants (synthetic and semisynthetic)

The functions of the coolant are

To maintain a low temperature. 
The tolerances specified during the machining process may become distorted due to expansion at high temperature.  Hence, the temperature should be maintained at specified range to ensure correct measurement. 

To lubricate the cutting surface
Excessive friction at the cutting surface can cause hardening of the material, making cutting difficult. 

Clean the surface
The coolant keeps the surface by removing material like burrs, dust, etc

Prevent rust
oxidation can occur at the high temperature caused by cutting.  Coolants prevent rust formation by forming a protective surface. 

The coolant is delivered to the desired location by different methods.  Some machines use spraying or flooding.  In some machines, a jet of coolant liquid is focussed on the work area.

The coolant liquid is also a fertile medium for bacterial growth.  This can cause infections over a period of time.  Sometimes, antiseptics are added to prevent bacterial growth.