Types of lubricants
Lubricants oils are classified into many types. Lubricants oils
come from different ways like animal oil and vegetable oil.
Vegetable
oil
These are produced from
seeds, fruit of trees etc. like animal oils; they are also easily oxidized and
become gummy. However, castor oil, which is a vegetable oil once found
extensive use in the automobile industry because of its high viscosity and high
film strength.
Animal
oil
These are obtained from animal fat. They are not
at all suitable for automotive engine lubrication, because they are oxidized
easily and become gummy after some use.
Mineral
oil
Mineral oils derived
from petroleum are perhaps the most widely used in automobiles. The advantages
they possess over the animal or the vegetable oil are:
Greater chemical stability at higher temperatures.
Fewer tendencies to form emulsion with water.
More plentiful and cheaper.
Chiefly the mineral
oils contain hydrocarbons. According to their molecular structures, they may be
further sub-classified into paraffin, naphthalene, aromatic and ole fins. Paraffin
is saturated hydrocarbons with straight or branched chains. Naphthalene are
saturated hydrocarbons with ring structure, aromatic are hydrocarbons with
benzene nucleus and ole fins are unsaturated hydrocarbons with double bonds. In practice, the mineral lubricating oil is a mixture of paraffin, naphthalene and aromatics.
Synthetic
lubricants
Examples of synthetic
lubricants are poly organosilanes or silicon fluids, polyglycerol ether and
aliphatic diester oils. In general, they have superior properties than mineral oils but their high cost limits their use.
Greases
They are suspensions of
metallic soaps dispersed in lubricant oil. Greases find use in automobiles at
places where retention of liquid lubricants is difficult and where high
temperatures are encountered for example axles.
Solid
lubricants
Graphite has been used
as a cylinder lubricant both in powder and colloidal form. It is stable at
high temperatures and has a low coefficient of friction. The special feature of
graphite is that it fills. The pores of the metal make it friction-free.
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