The main task of instrument oils is to reduce shear forces and maintain a thin oil film without forming breaks on the surface of the rubbing parts of instruments. By viscosity, instrument oils are classified as highly viscous, medium-viscosity, and low-viscosity. Instrument oils are held on smooth parts of precision mechanisms in the form of droplets and in clearances - by surface tension forces.
Oils used for lubricating instruments and apparatus are conventionally divided into four subgroups:
- general-purpose oils;
- oils based on mixed (mineral and synthetic) foundation;
- special-purpose oils based on mineral and synthetic foundation;
- lock oils.