Base Oils - The building blocks of mineral oil based lubricats.
Info Centre >> Fuel and Lube Oil Technical Manual >> 1. The Basic Building Blocks >> 1.1 Base Oils
The building blocks of lube oils are known as base oils. Generally speaking, base oils are a mixture of various fractions from the crude oil refining process. Additives are then mixed within these base oils to impart additional desirable properties over and above those already present in the base oil. Base oils are refined by solvent extraction (usually with propane at a pressure high enough to keep it in liquid form) and by hydro-treatment (reaction with hydrogen).
These processes eliminate unwanted heavy hydrocarbons and aromatics (benzene-based chemicals) from the oils and make them suitable for use as base oils. The base oils are then mixed in the correct proportions with the additive package to give the correct viscosity grade for the machinery they will lubricate. For engine oils and some gear oils this is quoted as SAE number. Hydraulic, turbine and sometimes gear oil viscosity (non-automotive) are quoted as ISO viscosity grades.