Lubricants required to operate under
boundary lubrication conditions must possess an added
quality referred to as “oiliness” or “lubricity” to
lower the coefficient of friction of the oil between the
rubbing surfaces. Oiliness is an oil enhancement property
provided through the use of chemical additives known as
antiwear (AW) agents. AW agents have a polarizing property
that enables them to behave in a manner similar to a magnet.
Like a magnet, the opposite sides of the oil film have
different polarities. When an AW oil adheres to the metal
wear surfaces, the sides of the oil film not in contact with
the metal surface have identical polarities and tend to
repel each other and form a plane of slippage. Most oils
intended for use in heavier machine applications contain AW
agents.
Examples of equipment that rely exclusively
on boundary lubrication include reciprocating equipment such
as engine and compressor pistons, and slow-moving equipment
such as turbine wicket gates. Gear teeth also rely on
boundary lubrication to a great extent.
