Additives used in Lubricating Oils
Modern Lubricants require the use of chemical additives to improve their performance capabilities beyond those of the base
oils used. Base Oil may have some undesirable properties that must be suppressed.
Additives can comprise anywhere from less than 1% to 20% approximately of the composition of a formulated lubricant.
Typical industrial oil may have only 1% additive while automotive engine oil may have more than 20% additive. Generally lubricants
for international combustion will have higher additive %age then for industrial applications. Additives are expensive and can contribute
too much of the final cost of a lubricant.
Additionally, additives are used to enhance the performance of a lubricant. They can also impart undesirable side effects us used in the
wrong concentration. It is important to note that additives will have varying miscibility in different base oils and proper procedures must be
used to insure that they can be completely dissolved into the base oil and not separate out.
There are number of additives which when blended with base oils, change their characteristics significantly. So additives can be used
to maximize the base oils good properties and minimizes its undesirable properties.
The following are general definitions of some major types of additives used in the manufacture of modern lubricating oils.
They promote more rapid break down of foam bubbles by weakening oil films between them. (They break up large surface bubbles and further reduce small air bubbles entrained in the oil).
They prevent the growth of micro organisms and bacteria in oil / water emulsion.
They are added to reduce wear of engine parts operating under boundary lubrication conditions. (They reduce friction and excessive wear
when a full-fluid lubricating film is not present).
They neutralize acidic products obtained from combustion.
They react chemically with the base oil to stabilize its colour.
They protect metal surfaces against chemical attack by water or other contaminants.
They assist the natural ability of the oil to separate rapidly from water. They are also helpful in rust inhibition.
They prevent deposit formation on metal surfaces. Suspend contaminants by reacting with them to form compounds which remain
in suspension (in the oil).
Dispersants absorb onto contaminants, keeping them dispersed in the oil. They create colloidal suspension of particles to prevent formation of sludge, varnish and deposits.
They are surface active chemicals added to base oils to reduce intermolecular forces and permit intimate mixing of very small oil droplets in water. (They promote separation of oil from water).
They prevent seizure of sliding metal surfaces under extreme pressure and temperature conditions.
Act to reduce the friction between the oil molecules and therefore increase the lubricity or slipperiness of the oil.
They form a film over a metal surface to prevent participation of these metals as catalysts in promoting oxidation of the oil.
They prevent or retard oxidation of the oil thereby reducing viscosity (Anti Oxidants) increase and the formation of sludge, varnish and acids.(They promote long service and storage life).
Lower the pour point of paraffinic oils by modifying the form of wax crystallization. (They allow lubricants to flow at colder temperatures).
Prevent metal surfaces especially from rust
Tackiness additives increase the adhesive properties of a lubricant, preventing dripping and splashing during operation. This reduces perational cost and the risk of environmental contamination.
They are high molecular weight polymers added to oils to increase? the viscosity index. (They reduce lubricants tendency to change viscosity with changing temperature).