Lubrication
and Oil Analysis
Most
lubricants used in industry are mineral based and obtained
from petroleum by refining processes and further purification and
blending.
Function
of a Lubricant
Lubricants
have three major functions: limit friction, minimize wear and
dissipate heat.
Limit
Friction
Friction
is defined as the resistance to motion of contracting surfaces. Even
smooth metal surfaces have microscopic rough spots called asperities.
Friction is increased by the presense of asperities on surfaces.
Attempts to overcome the force of friction will increase the
localized heat generated by the contracting surfaces. This heat can
actually create temperatures high enough to weld two surfaces
together.
Lubrication
prevents peaks of asperities from touching each other through what is
called film strength. Molecules of lubricants are naturally
bonded together, often in chains. Any attempt to break the chain
creates an opposite tension that prevents separation.
Minimize
Wear
Wear is
the removal of material from one or more moving surfaces in contact
with each other. The material removed becomes the source of
additional friction and increased wear on the surfaces involved.
A
quality lubricant will fill the valleys of the asperities and
provide an additional film over the peaks of the asperities. The
asperities of the two surfaces are prevented from contracting each
other and wear will be minimized.
Dissipate
Heat
Even
well-lubricated parts will heat up as a result of friction and
external heat. One advantage of liquid lubricants is their
ability to absorb and dissipate point sources of heat.