Lubricants - Constitution

Depending on their physical state, lubricants can be classified into three groups:

• liquid lubricants: of vegetable and animal origin (fatty oils), mineral (petroleum oils) and synthetic;

• Semi-solid or plastic lubricants, which mainly include lubricating greases, but also waxes, kerosenes and petroleum jelly for lubricating applications;

• solid lubricants: lamellar, polymeric, soft metals, salts, oxides, etc.

These different lubricants can be used in the form of dispersions, emulsions or solutions in water, whenever high cooling power (high-speed metalworking) or fire resistance (HF-type hydraulic fluids) is required.

The first two categories of lubricants (oils and greases) contain a variable quantity of additives (up to 25% by mass) depending on the application and severity of service.

To situate the relative importance of each lubricant group, it should be remembered that liquid lubricants account for 96% of the market, greases for 3% and solid lubricants for around 1%.