The history of lubrication dates back through the ages to when man used animal fats as lubrication.
Things have changed somewhat since those days, although the basic principle remains the same … to reduce the friction between two moving surfaces. Oil serves several functions in a compartment which will vary widely depending on the application. Briefly engine and gear oils are designed to keep the moving parts apart (hydrodynamic lubrication); remove heat (through heat exchanges/radiators); and carry away the contamination (through filtration and oil change) in the case of hydraulic systems. Oil is used to transport power over large distances as well as to lubricate, flush and cool.
Oils generally consist of two parts, the base stock and the additive package.
Most of the oils we are familiar with fall into three base stock groups, although there are others:
Mineral Base which are mined from deep within the earth and are the most commonly used base stocks, the quality of which will vary according to where the oil comes from and the amount of processing of the base stock.
Synthetic Base which are manufactured or man made, they are more thermally stable than mineral bases and are manufactured from a wide range of materials to suit a wide variety of applications. They are generally recognised as better quality than mineral oils but are also more expensive.
Semi-Synthetic Base which are chemically fortified or a modified form of mineral base stocks which give the mineral base stocks specific qualities which may enhance their performance to suit particular applications.
Up to 20% of an oils volume can be represented by the additive package, which are chemicals added to the oil to give it desired characteristics and enhance the properties of the base oil so that it performs differently under different working conditions. Some of the more common additives are as follows:
Detergents are a group of chemicals added to the base which are designed to stop the contaminants generated from settling inside the compartment, forming sludge to keep them in suspension so that they are either carried to the filter or drained during change.
Dispersants stop the contaminations from conglomerating and forming blobs of sludge.
Viscosity Index Improvers maintain viscosity stability over the operating temperature range so that the oil flows at cold start-up and remains viscous at operating temperature.
Friction Modifiers enhance the slipperiness of the oil to keep friction minimised: less friction = less heat = less wear.
Anti-Foam and Anti-Vapour Additives reduce foaming and vaporisation.
Anti-Wear Additives are designed to reduce the wear particularly under load.
Corrosion and Rust Inhibitors reduce rusting and protect surfaces from chemical attack.
Anti-Oxidants reduce oxidation of the base, particularly at elevated temperatures.
Anti foam agents.
Base additives to neutralise acids.