Additives
and lubricants
Additives
used in lubricants assume great significance since damages can result
from using the wrong kind of additives, says Vivek Dev
Among the most critical factors that govern the smooth
and trouble free operation of equipment is proper lubrication. A lubricant
acts as a medium of low friction on the surfaces of certain parts of
equipment that are in close proximity to each other and also enables
relative movement between them. But most industrial applications impose
several additional demands on the lubricant.
For instance, in screw compressor applications the lubricating oil must
also carry away the heat developed during air compression. Cylinder
lubrication in an internal combustion engine requires the lubricating
oil to withstand high temperature and pressure conditions in the combustion
chamber. The oil must also be fluid enough to reach cylinder walls and
spread over the surfaces without any delay after start up. Thus, it
can be seen that the lubricating oil is required to perform under varying
conditions of temperature, pressure and other factors, depending upon
the application. Additives (substances added to base oils) help obtain
the performance characteristics required for various applications.
Additives, as mentioned earlier, are substances that are added to a
lubricant to enhance some of its already existing properties or to endow
the lubricant with some new property.
Additives can be categorised into two types according to the properties
that they modify.
Physical property modifiers, as the name suggests, modify only the physical
properties such as viscositytemperature relationship or pour-point resistance
to foaming. Chemical property modifiers, on the other hand, modify the
chemical properties such as resistance to oxidation, corrosion, extreme
pressure, wear, and detergency. The various kinds of modifiers have
been briefly discussed below.
Viscosity Index (VI)
improvers and thickeners VI improvers are widely used in motor
oils, gear oils, transmission fluids, hydraulic oils and various other
applications. Most mineral oils with a VI of over hundred contain a
VI improver. The choice of a VI additive is done on the basis of economics.
If there is no other overriding benefit that can be seen overtly, then
the first thing that needs examination is how the overall formulation
balance is achieved. This process involves the following factors:
>If
there is a need to meet critical physical requirements then the choice
of the additive has to be made carefully. If a VI additive causes considerable
thickening of the oil at low temperatures, it is likely to create problems.
In such cases, a VI additive with equivalent high temperature properties
and lowered low temperature thickening can offer a reduced formulation
cost. Additives
