A Lubricant can be anything, which controls the friction forces between two surfaces. A lubricant, depending upon the necessity and design can, either reduce or increase or control the friction. It is also used as a sealing medium, cooling medium and cleansing medium, depending upon applications and design.

A lubricant can be liquid, semi- liquid or solid. Grease falls under the semi-liquid category. Solid lubricants can be made mostly of plastics, especially PVC and Teflon. Normally, a lubricant means liquid lubricant.

A lubricant is made in a blending plant. In a blending plant, the base oils (which may constitute up to 99% of the lubricant, by volume) are mixed with specially selected additives. Before blending, the base oils are mixed etc. Blending is normally done in Kettles, where the oil is heated up to 60o C and heavily agitated.

Either mechanical or pneumatic agitation can be used. Additives are then added and the whole mixture homogenised by thorough mixing - technically called blending. This is not a process whereby the chemical characteristics change - there is molecular change. After blending, the product is filtered and then packed. In special cases - like Transformer Oil - the product is degassed and thoroughly filtered.

The newer form of blending- especially used in large blending plants, is in-line blending, where the different components mix while flowing inside a pipeline.

The two main constituents of a lubricant are base oils and additives. Base oils can be more than one (depending upon the final product viscosity needed) and additives can either be a mixture (called an additive package) or components.

Base Oil is the name given to basic building block of a lubricant. It is sometimes also called base stocks . Base stocks are mineral (or petroleum) or synthetic origin, although vegetable stocks may be used for specialised applications. The base stock provides the basic lubricating requirements of a lubricant.

However, unless it is supported with additives, base oil will degrade and deteriorate very rapidly in some operating conditions. Depending upon the base stock, petroleum, synthetic or others, different additive chemistries need to be used for making different kinds of lubricant.

Base oils are made and supplied by refineries. A refinery is a plant where the crude oil is distilled into various fractions. Normally the last but one portion of the heaviest stocks is the lubricant base stock. The main base oil producers are the big oil companies.

Base oils can be classified according to their basic chemical nature as to paraffinic, naphthenic or aromatic. According to viscosity, they can be classified into various neutrals - 150 SN, 500 SN. SN stands for Solvent neutral (see below) and the number stands for the viscosity of the oil is SUS (Saybolt Universal Seconds - see below - ) at 40o C.

Base oils can also be classified by the kind of treatment they get during refining. If they are made by being selectively treated with different solvents, then the base oil is called solvent neutrals. If they are made by hydro-finish process they are called hydro-finished base stocks. If they are made by the cracking of heavier molecules, they are called hydro-cracked base stocks.

Base oils are also classified to their viscosity index (see below) to whether they are Low Viscosity Index (LVIs) or Medium Viscosity Index (MVIs), High Viscosity Index (HVIs) or extra High Viscosity Index (XHVIs).

Base oils are made in the refinery by a number of processes - basically distillation. Distillation under atmospheric pressure removes the gasoline and distillate fuel components, leaving a "long residue" containing the lube oil and the ashpalt. Further distillation under vaccum yields " neutral distillates" overhead and an ashpalt residue. Simple treatment with sulphuric acid, line and clay turns the distillate into acceptable LVI stocks.

For HVI and MVI stocks, some form of solvent extraction is necessary to remove coloured, unstable and low VI components. Finally, wax is removed by dissolving the oil into methyl-ethyl ketone (MEK) and chilling and filtering to yield oils with pour points in the -10 to -20o C range. At the refiner's option, the oils may be "finished" with hydrogen to remove sulphur, nitrogen and colour bodies. The process is shown below.

Base oils, as discussed earlier, are classified, and traded mainly according to their viscosities. The main base oils that are commonly used in the lubricating oil industry are 70N, 150N, 500N, and 150 Bright Stock. These oils vary in colour and viscosity - the colour getting darker and the viscosity increasing as we gon from 70N to 150BS.

As shown above, the number of all neutrals indicates the viscosity of the product at 40oC in the old unit of Saybolt Universal Seconds. For Bright stock, the number indicates the SSU viscosity at 100o C.

Napthenic base oils are used when the final lubricant is expected to work at moderately lower temperatures. Paraffinic base oils are used when the Viscosity Index requirement is high and the temperatures are not that much lower. These are the largest kind of lubricating base stocks used. Aromatic base oils are seldom used - and find their main application as processing oil.

Extra Solvent treated paraffinic and naphthenic base oils are used to make turbine oils. XHVI base oils, with very low volatility, are used to make thinner oil s for the extreme cold whether. Synthetic base oils are used in applications where the temperature is either too high or too low.

Base oils called mineral base oils because they are obtained from the mineral-deteriorated-crude oil. This is to differentiate them from the "synthetic" base stocks.