There are chemical substances that are added to the
lubricating oil either to reinforce some of its natural properties or to
provide it with certain new properties that it did not possess originally. Oil
additives are classified according to the properties of the oil which they
reinforce or add. The important additives in current use are:
Oxidation inhibitors – These inhibit the formation of
varnish by preventing the oxidation of the oil at the engine operating
conditions. These consist of paraffines, naphthenes and aromatics.
Corrosion inhibitors – These are also called dispenser
additives. These inhibit the formation of low-temperature sludge binders and
break the sludge particles into finely divided particles, which stay in the oil
in fine suspension and are removed when the engine oil is changed. Thus various
engine parts, for instance, piston rings, main bearings, oil galleries,
connecting rods etc. the detergent additives are polymers and polyphenyl
succinimides.
Viscosity index improves – these are the additives that do
not allow or at least minimize the oil viscosity to decrease with the increase
in temperature.
Anti-foaming additives – the lubricating oils, in general,
have a tendency to foam due to engine vibrations which give rise to churning of
oil in the sump. If allowed to foam, the oil cannot properly lubricate the
engine bearings, apart from loss by over-flowing. Anti-foaming additives are
available that suppress this foaming tendency of oils. Polyorganosiloxanes are
the most common anti-foaming additives.
Extreme pressure
additives – these cater
for more difficult conditions of lubrication, for instance, the one arising
between the highly stressed cams and valve tappets. These prevent metal-to-metal contact by forming a chemical film. Polymeric materials such as
polyisobutene form such additives.
Tags
technology