Machinery Lubrication July August 2008

formation of water droplets into a greater mass (as in a
suspension) by creating a chemical bridge between the water
droplets. The next part of the process of demulsification is
coalescence of the water droplets.
When the chemical bridge has been formed, the demulsibility
additive acts to break the emulsion film and replace the emulsified
water molecules to form an unstable film. The demulsifiers
may also penetrate the emulsion to form a path through which
water drains from one droplet to the other.
This mechanism will allow the smaller water
droplets to coalesce into bigger droplets and
migrate to the bottom of an oil tank, where
they may be drained off.
Sulfonates, amines, fatty oils and acids, phosphates and
oxidized wax acids are among the chemicals used as RI. The oil
film formed by RI oils assists in the repulsion of water.
Demulsifiers
Demulsifiers (as discussed previously) act as water
repellants and barriers to water entry (into the lubricant/circulating
oil system).
Effective Lubrication
for Wet Environments
Considering the potentially devastating
effects of water, a lubricant that separates out
water quickly and efficiently must be chosen.
Complementing lubricants that promote good
demulsibility, rust-inhibited oils counteract the
potential rusting of roll necks, journals and
roller bearings mainly through the action of
specially formulated additives.
Important additives that are usually
contained in effective rust-inhibited oils include
oxidation inhibitors (OI), rust inhibitors (RI)
and corrosion inhibitors. These oils are
commonly known as R&O oils. Quality R&O
oils are typically characterized as containing
many, if not all, of the following additives:
Oxidation Inhibitors
Oxidation inhibitors block the formation
of corrosive acids. In addition, OI are used
to prevent oil thickening and the formation
of varnish and sludge due to the oxidation of
the oil. OI terminate oil oxidation reactions
by forming inactive soluble compounds or by
taking up oxygen. Organic compounds
containing sulfur, phosphorus and nitrogen
are commonly used as OI.
Rust Inhibitors
Rust inhibitors are polar materials and
retard rusting by having a stronger affinity
than water for metal surfaces. Polar additives
are attracted to a metal surface in a manner
that iron fillings are attracted to a magnet.
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