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A Guide to
Lubricants
Vehicle lubricants
· A
lubricant is an oil-based mixture containing several types of
additives: anti-oxidants, viscosity enhancers, anti-wear agents
etc.
·
Different types of oil exist: for engines, for gearboxes, for
axles etc.
·
Lubricants are not all the same: their functions vary according
to the base oil used and the additives they incorporate, which
give them specific characteristics and applications (gearbox,
engine etc.)
Gearbox lubricants
Gearbox oil is essentially the same as engine oil. What distinguishes
one from the other is the different mixture of additives each contains
(there are more extreme-pressure additives in gearbox oil, for example)
and their different degrees of viscosity (higher in gearbox oil). Two
types of gearbox oil exist: mechanical gearbox oil and automatic gearbox
oil. They are not interchangeable.
Grease
Grease is a special kind of lubricant - it's solid. Its function,
however, is exactly the same as any other lubricant. Grease is used when
liquid lubricants are unsuitable - for keeping a component firmly in
place, for example. It contains a liquid lubricant, additives and a
thickening agent, usually a metallic soap.
Mixed motor oil
Each type of engine (gasoline/petrol or diesel) has its own specially
developed oil. Nowadays, however, "mixed" oil is increasingly used. It
is especially in demand with mechanics and other vehicle professionals,
who find it useful as an all-purpose lubricant, which saves them from
having to keep many different types of oil in stock. Nevertheless, oils
specifically intended for one fuel type only still perform better than
mixed oils, which must often deal with antinomic constraints.
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The role of the lubricant
Oil has 5 basic functions:
· Oil
reduces friction, improving engine performance and cutting down
on fuel consumption.
· Oil
protects engine parts against wear and corrosion, making engines
more efficient and longer-lasting.
· Oil
helps to eliminate impurities thanks to oil filters and oil
changes to keep engine parts clean.
· Oil
helps to seal engine housings and therefore contributes to an
optimum engine compression ratio for added engine power.
· Oil
absorbs heat to stop engine parts from deforming.
Plus, oil helps save on fuel, and protects the environment (as it
helps reduce emissions of pollutants).
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Designing a lubricant
The 5 stages of designing high quality lubricants
1. Everything begins with the base stock. This may be
mineral, synthetic or a mixture of the two. Depending on the
intended purpose of the new lubricant, researchers will first
determine some basic formulas from which to develop the new
product.
2. After a long series of laboratory tests a shortlist of
suitable formulas is compiled. The next stage is the engine test
bench phase, after which the shortlist is reduced further and
the selected formulas improved upon.
3. Once this series of tests is complete, and if the results
are promising, the oil is brought into compliance with API and
ACEA standards and the specifications of the leading vehicle
manufacturers.
4. The final stage is the fleet test: the new oil is put to
the test in real vehicles, in real driving conditions, over
hundreds of thousand of kilometers.
5. If the new oil is declared fit for service after the fleet
test, it may be approved by the manufacturer of the vehicles on
which it was tested.
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The composition of lubricants
· An oil
can have any of 4 different bases: animal, vegetable, mineral or
synthetic. In the motor industry only mineral and synthetic
bases are used (or a mixture of the two in the case of
semi-synthetic base stocks).
·
Mineral-base oils are extracted from crude oil during refining.
Their physical and chemical characteristics depend on the type
of crude from which they are taken.
·
Synthetic base stocks are chemically produced and consist of
glycols, esters or poly-alphaolefins. Their performances are
superior to that of mineral-based oils, as they exhibit better
heat resistance, higher oxidation resistance and a higher
viscosity index.
·
Additives are chemical products specially developed for their
ability to improve certain characteristics of oils. 7 types of
additives are in general use, though this number can be much
higher for superior-quality lubricants.
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The role of additives
There are many different additives, but 7 in particular are of special
importance:
·
Anti-oxidant additives help prevent the oil from oxidizing over
time, conserving its properties.
·
Anti-foam additives stop the oil from foaming when the engine is
running and prevent the oil pump to fail.
·
Anti-wear additives make the oil more resistant to wear by
reducing friction, helping to prolong engine life.
·
Anti-rust additives help protect the engine against corrosion in
periods when the vehicle is not in use, preventing the premature
ageing of the engine.
·
Viscosity-enhancing additives increase the viscosity of oil in
cold conditions, and also enhance viscosity at high temperatures
to ensure that the engine is correctly lubricated.
·
Detergent additives prevent the accumulation of impurities,
helping the engine to stay clean and perform as designed.
·
Extreme pressure additives increase the film strength of the oil
to protect it against rupture.
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The characteristics of lubricants
The characteristics of a lubricant depend on its base stock and on the
additives it contains - the "mixture".
5 physico-chemical characteristics are especially important in every
motor oil:
· its
resistance to high temperatures
· its
detergent action
· its
ability to prevent wear and corrosion its viscosity.
The technical performance of an oil is measured by the specifications
which it complies with (API, ACEA etc.) and the seal of approval given
to it by vehicle manufacturers.
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Specification of a lubricant
· Three
main types of international specifications guarantee minimum
performance for motor oils: the ACEA,
API and
ILSAC
specifications.
·
Vehicle manufacturers also specify minimum performance levels
for lubricants to ensure the engines they make run safely.
· With
new advances in engine technology, the approvals of the
manufacturer are increasingly important, increasingly detailed,
and increasingly varied.
· One
important point is that some high-quality lubricants can meet
several different specifications and be approved by a number of
different manufacturers.
API, ACEA and ILSAC specifications endorse quality levels recognized
by all manufacturers. However, some of them add their own special
requirements and publish lists of approved products for different
applications (e.g. API SA, API SF, API SG, API SJ, API CE).
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High-quality lubricants
Although they both comply with the same specifications, this does not
necessarily mean that two lubricants are of the same quality.
This is because a specification sets a minimum performance
requirement. High-quality oils often perform far better than the
specification requires.
It's thanks to the work of research laboratories that exceptionally
high performance can be obtained. Nowadays, regulations on pollutant
emissions and fuel consumption in new engines make them more and more
complex and expensive to develop.
That's why manufacturers generally develop their new engines in
association with the manufacturers of motor oils.
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