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Bleeding, migration, syneresis: Bleeding
is a condition when the liquid lubricant separates from the
thickener. It is induced by high temperatures and also
occurs during long storage periods. Migration is a form of
bleeding that occurs when oil in a grease migrates out of
the thickener network under certain circumstances. For
example, when grease is pumped though a pipe in a
centralized lubrication system, it may encounter a
resistance to the flow and form a plug. The oil continues to
flow, migrating out of the thickener network. As the oil
separates from the grease, thickener concentration
increases, and plugging gets worse. If two different greases
are in contact, the oils may migrate from one grease to the
other and change the structure of the grease. Therefore, it
is unwise to mix two greases. Syneresis is a special form of
bleeding caused by shrinking or rearrangement of the
structure due to physical or chemical changes in the
thickener.
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