What are liquid lubricants?

Liquid lubricants are liquids that separate and reduce friction between two moving surfaces and decrease wear and tear.
The properties of good liquid lubricants are as follows

• Properties of oiliness.
• Appropriate viscosity and should not change appreciably with a change in temperature.
• Resistance to oxidation.
• High thermal stability and should be able to dissipate heat quickly.
• High flash and fire points.
• Low acid value and carbon residue.
• High viscosity index adequate viscosity.
• Should not dissolve water, dirt rubber seals etc.
• Should not corrode machinery.