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Basically, there
are two important reasons for changing a lubricating oil:
Contamination
This is the principal cause for changing a lubricant
External contaminants:
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Dirt, paper, rags, threads,
iron filings, dust, earth, damp, steam, water etc.
Other liquids which may
enter the system, corrosive or non-corrosive, such
as refrigerating fluids, cleaning products, acids,
solvents, paint, mixtures of other oils, metallic
particles from machinery, mechanization, decomposition
of sealant, inadequate joins.
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Internal contaminants:
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Internal wear and tear
caused because the lubricant has lost its properties
and no longer works.
Rust, produced because
oxygen enters the system through air or water and
starts a process of corrosion.
Formation of sludge -
all systems are exposed, if only from time to time,
to temperatures and pressures higher than normal,
and this causes the oil to suffer an important thermal
shock - it cracks, forms charcoal and oxidizes, causing
acid formation. The metallic particles act as catalysts
for collateral and parallel reactions, and the effects
are multiplied.
Formation of scum, if
air or detergents have entered the pumps.
Cavities may be formed,
and produce problems in lubrication or refrigeration.
Sometimes the maintenance
teams in companies, with the best intentions, introduce
additives that can cause serious problems if the state
of the lubricant is unknown.
All lubricants should
be perfectly prepared for the function they have to
carry out - they shouldn't be reinforced.
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Consumption
of additives
Many additives are consumed
and/or change their chemical structure due to external effects,
and no longer carry function correctly. At this point we
either top up, or change the oil for new, and thus we have
generated a used oil that must be treated as a very special
waste.
Corrosion inhibitors:
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Corrosion inhibitors
act firstly as neutralizers for acids produced by
oxidizing, and secondly form a protective coating
over metallic surfaces.
When the action of the
inhibitors is reduced, oxygen attack is produced,
and consequently the sludge forms. This changes the
characteristics of the oil, the degree of acidity
progresses, the oil blackens, and performance is reduced.
Corrosion inhibitors
are attracted to metallic surfaces, even to particles
in suspension and to dirt, and consequently are in
part eliminated during filtering. They are also attracted
to contaminating fluids and are removed with them
during purification.
They can also oxidize,
becoming soluble in water and lose efficiency.
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Viscosity:
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The
changes in viscosity that are produced during use are
also a clear indication of the capacity of a lubricant.
If there is an increase this means that there is advanced
oxidization and/or contamination from dirt or water,
and if there is a decrease, it means that there is contamination
from a solvent, another oil with lower viscosity, or
shearing of the oil in use. All these points endanger
the system. |
Anti- wear and tear
additives and E.P.:
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These additives prevent
contact between metallic surfaces in the points where
the contact pressure increases considerably, or if the
temperature rises greatly, as this decreases the viscosity
of the oil, and may cause a rupture in the lubricating
coating, causing the two surfaces to touch and thus
increased and premature wear and tear.
Also,
due to time, presence of contaminants, or severe work
conditions, these additives degrade, hydrolyse, oxidize
and no longer work. |
Dispersing additives:
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The
appearance of dirt, water etc. begins at the moment
the lubricant begins to work. The dispersing additives
make the dirt and other products of oxidization remain
in suspension and dispersed throughout the oil, thus
avoiding their deposit in key points of the system where
they would cause problems.
Logically, these additives
can also degrade or even be inefficient if there is
a high level of oxidation and contamination.
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