Explanation
Also called lubricant. Any substance that has the property of reducing friction between two friction surfaces and wear or other forms of surface damage. It can be divided into four basic types: gas, liquid, semi solid, and solid. The most commonly used gas lubrication materials is air, such as gas bearings. The most widely used liquid lubrication materials is lubricating oil, including mineral oil, animal and vegetable oil, synthetic oil and various emulsions.
Classification
Metals -> Special purpose metals -> Wear-resistant metals