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There are several methods for applying solid
lubricants.
Powdered solids. The oldest and simplest
methods of applying solid lubricants are noted as follows:
(a) Burnishing: Burnishing is a rubbing
process used to apply a thin film of dry powdered solid
lubricant such as
graphite, MoS2 , etc., to a metal surface. This
process produces a highly polished surface that
is effective where lubrication requirements and wear-life
are not stringent, where clearance requirements
must be maintained, and where wear debris from the lubricant
must be minimized. Surface roughness
of the metal substrate and particle size of the powder are
critical to ensure good application.
(b) Hand rubbing: Hand rubbing is a
procedure for loosely applying a thin coating of solid
lubricant.
(c) Dusting: Powder is applied without any
attempt to evenly spread the lubricant. This method results
in a loose and uneven application that is generally
unsatisfactory.
(d) Tumbling:. Parts to be lubricated are
tumbled in a powdered lubricant. Although adhesion is not
very good, the method
is satisfactory for noncritical parts such as small threaded
fasteners and rivets.
(e) Dispersions: Dispersions are mixtures of
solid lubricant in grease or fluid lubricants. The most common solids used are
graphite, MoS2 , PTFE, and Teflon®. The grease
or fluid provides normal lubrication while the solid
lubricant increases lubricity and provides extreme pressure
protection. Addition of
MoS2 to lubricating oils can increase
load-carrying capacity, reduce wear, and increase life in
roller bearings, and has also been found to reduce wear and
friction in automotive applications. However, caution
must be exercised when using these solids with greases and
lubricating fluids. Grease and oil may prevent
good adhesion of the solid to the protected surface.
Detergent additives in some oils can also inhibit
the wear-reducing ability of MoS2 and graphite,
and some antiwear additives may actually increase wear.
Solid lubricants can also affect the oxidation stability of
oils and greases. Consequently, the concentration
of oxidation inhibitors required must be carefully examined
and controlled. Aerosol sprays are
frequently used to apply solid lubricant in a volatile
carrier or in an air-drying organic resin. However, this
method should be limited to short-term uses or to light- or
moderate-duty applications where thick films are
not necessary. Specifications for solid lubricant
dispersions are not included in this manual. Before
using dispersions, users
should become familiar with their applications and should
obtain information in addition to that provided in this
manual. The information should be based on real-world
experiences with similar or comparable
applications.
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