3. LUBRICANT ADDITIVES
Practically all lubricants contain additives to
enhance existing properties, or to impart new
properties. Three general classifications of lu-
bricant additives are surface protective,
performance enhancing, and lubricant protec-
tive.
enhance existing properties, or to impart new
properties. Three general classifications of lu-
bricant additives are surface protective,
performance enhancing, and lubricant protec-
tive.
3.1 Surface Protective Additives
Oiliness Additives. Oiliness, with respect to lu-
bricating oil, is defined as the ability of an oil to
reduce friction between moving surfaces. Oili-
ness additives, usually vegetable or animal fats,
enhance oiliness by tenaciously adhering to the
metal's surface forming an absorbed film of high
lubricating value.
bricating oil, is defined as the ability of an oil to
reduce friction between moving surfaces. Oili-
ness additives, usually vegetable or animal fats,
enhance oiliness by tenaciously adhering to the
metal's surface forming an absorbed film of high
lubricating value.
Antiwear Additives. Antiwear additives work by
coating the metals surface. If light metal to
metal contact is made, the heat from the friction
melts the additives, forming a liquid layer be-
tween the surfaces. This molten additive layer,
being softer than the metal, acts as a lubricant
preventing wear of the metal surfaces.
coating the metals surface. If light metal to
metal contact is made, the heat from the friction
melts the additives, forming a liquid layer be-
tween the surfaces. This molten additive layer,
being softer than the metal, acts as a lubricant
preventing wear of the metal surfaces.
Extreme Pressure Additives. Extreme Pressure
(EP) additives work by reacting with the metal to
form a compound which acts a protective layer
on the metal's surface. As this layer is softer
than the metal itself, under extreme pressure
conditions, the compound layer wears away first,
protecting the metal. As this layer is removed,
the EP additive acts to form another layer. In
contrast to the action of antiwear additives, EP
additives control wear instead of preventing it.
Some EP additives, because of their reactive
nature, can be corrosive to brass or copper
containing alloys. To prevent excessive
corrosion, most EP additives are activated by
the excessive heat created during extreme
pressure conditions but do not react at room
temperature.
(EP) additives work by reacting with the metal to
form a compound which acts a protective layer
on the metal's surface. As this layer is softer
than the metal itself, under extreme pressure
conditions, the compound layer wears away first,
protecting the metal. As this layer is removed,
the EP additive acts to form another layer. In
contrast to the action of antiwear additives, EP
additives control wear instead of preventing it.
Some EP additives, because of their reactive
nature, can be corrosive to brass or copper
containing alloys. To prevent excessive
corrosion, most EP additives are activated by
the excessive heat created during extreme
pressure conditions but do not react at room
temperature.
Tackiness Agent. Tackiness agents act to in-
crease the adhesiveness of an oil or grease.
crease the adhesiveness of an oil or grease.
Corrosion and Rust Inhibitors. Rust Inhibitors
protect ferrous (iron or steel) parts by forming a
film on the part that resists attack by water.
Corrosion inhibitors act in a similar way to pro-
tect nonferrous parts and also act to neutralize
acids with a basic compound such as calcium
carbonate.
protect ferrous (iron or steel) parts by forming a
film on the part that resists attack by water.
Corrosion inhibitors act in a similar way to pro-
tect nonferrous parts and also act to neutralize
acids with a basic compound such as calcium
carbonate.
Detergents and Dispersants. Detergents and
dispersants are used primarily in engine oils to
keep surfaces free of deposits and keep con-
taminants dispersed in the lubricant.
dispersants are used primarily in engine oils to
keep surfaces free of deposits and keep con-
taminants dispersed in the lubricant.
3.2 Performance Enhancing Additives
Viscosity Index Improvers. Viscosity index im-
provers lower the rate of change of viscosity
with temperature. Multi-grade motor oils are the
result of the use of viscosity Index improvers.
provers lower the rate of change of viscosity
with temperature. Multi-grade motor oils are the
result of the use of viscosity Index improvers.
Pour Point Depressant. Pour point depressants
enable lubricants to flow at low temperature.
enable lubricants to flow at low temperature.
Demulsifier. A demulsifier promotes the sepa-
ration of oil and water in lubricants exposed to
water.
ration of oil and water in lubricants exposed to
water.
Emulsifier. An emulsifier promotes the rapid
mixing of oil and water to form a stable emul-
sion. Emulsifiers are sometimes used In motor
oils to allow water, formed by combustion of
fuel, to be kept in emulsion until engine heat can
evaporate it. Emulsifiers are also used in soluble
oils used in some metal working operations and
in some fire resistant hydraulic fluids. Emul-
sification is not a desirable property in most
hydraulic fluids or turbine oils.
mixing of oil and water to form a stable emul-
sion. Emulsifiers are sometimes used In motor
oils to allow water, formed by combustion of
fuel, to be kept in emulsion until engine heat can
evaporate it. Emulsifiers are also used in soluble
oils used in some metal working operations and
in some fire resistant hydraulic fluids. Emul-
sification is not a desirable property in most
hydraulic fluids or turbine oils.
(FIST 2-4 11/90)
6