DESIRABLE PROPERTIES OF LUBRICATING OILS :

*              Dispersivity or capacity to keep the cold parts of an engine clean.

*              Detergency or capacity to keep the hot parts of an engine clean.

*              Thermal strength or capacity to withstand temperature changes.

*              Anti-oxidant or capacity to resist the action of oxygen.

*              Anti-wear or capacity to contain wear.

*              anti-scuffing or capacity to preserve a film of oil even in the presence of high pressure.

*              Alkalinity  reserve  or  capacity to   neutralise  acids  formed  during  combustion, thereby preventing corrosive wear.

*              Demulsibility or capacity to separate water contaminants.

Resistance to hydrolysis or capacity to withstand the action of water which can affect additives.

Centrifugeability and filterability or capacity to separate insoluble elements.

*     Anti-rust, Anti-corrosive and Anti-foam properties.

  ADDITIVES :

Additives may be defined as chemicals which are added as minor components to lubricating oils to enhance existing natural properties, or in some cases to provide new properties. The amount used may be as low as few parts per million for foam suppressants to more than 20% of special detergent or alkaline additives in marine diesel of special detergent or alkaline additives in marine diesel Cylinder oils.

The type of additives used depends largely upon the service for which the oil is required, but the main types in general use fall into two main groups or classes - (a) those which effect the chemical characteristics and (b) those which effect the physical characteristics.

Chemical characteristics -

1.   Anti-oxidants, sometimes combined with metal-deactivators.

2.                    Anti-corrosion or Anti-rust additives.

3.                    Wear-reducing agents which may be of two types :

a)                    'Oiliness' or 'metal-wetting' agents.

b)                    extreme pressure (E.P.) agents.

4.                    Detergent/Dispersant additives for internal combustion engines.

5.                    High alkalinity additives to combat corrosive wear in diesel engines, specially when burning high sulphur content residual fuel.

6.                    Anti-bacterial additives.

Physical characteristics :

1.   Pour point depressant.

2.                     Anti-foam agents.

3.                     Viscosity Index improvers.

4.                     Adhesive or tackiness agents.

5.                     Solid dispersed additives (e.g. graphite, talc, molybdenum disulphide).

6.                     Emulsifying agents.

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