ferent test conditions: sample at 75° F, sample
at 200° F, and sample at 75° F having been
cooled from the test at 200° F. The foam
volume at the end of the blowing period Is a
measure of the foaming tendency of the oii,
while the foam volume at the end of the settling
period (which is usually zero) is a measure of
the stability of the foam.
Significance: Foaming consists of bubbles that
rise quickly to the surface of the oil, and is to be
distinguished from air entrainment, consisting of
slow-rising bubbles dispersed throughout the oil.
Both these conditions are undesirable, and are
often difficult to distinguish due to high flow
rates and turbulence in the system. These two
phenomena are affected by different factors and
are considered in separate laboratory tests. The
primary causes of foaming are mechanical,
essentially an operating condition that tends to
produce turbulence in the oil in the presence of
air. The current trend in hydraulic oil systems,
turbine oil systems, and industrial oil systems of
every kind Is to decrease reservoir sizes and
Increase flow rates. This trend increases the
tendency for foaming in the oils.
Contamination of the oil with surface-active ma-
terials, such as rust preventives, detergents,
etc., can also cause foaming.
Foaming in an industrial oil is undesirable be-
cause the foam may overflow the reservoir and
create a nuisance, and the foam will decrease
the lubrication efficiency of the oil, which may
lead to mechanical damage.
Antifoaming additives may be used in oils to
decrease foaming tendencies of the oil. How-
ever, many such additives tend to increase the
air entrainment characteristics of an oil, and
their use requires striking a balance between
these two undesirable phenomena.
FOUR-BALL WEAR AND EP TESTS
ASTM D 2266 and ASTM D 2596
Each of the tests described here is designed to
evaluate a different load-carrying characteristic
of lubricating grease or oil. The information
provided by these tests is often used for quality
control and to aid in the selection of lubricants
for industrial applications.
Both tests employ similar equipment and me-
chanical principles. Four 1/2-inch steel balls are
arranged with one ball atop three others, the
three lower balls are clamped together to form a
cradle, upon which the fourth ball rotates on a
General Descriptions of Tests: The 4-Ball
Wear Test (ASTM D 2266) is used to determine
the relative wear-preventing properties of lubri-
cants on sliding metal surfaces operating under
boundary lubrication conditions. The test is
carried out at a specified speed, temperature,
and load, At the end of a specified period, the
average diameter of the wear scars on the three
lower balls is measured and reported.
The 4-Ball EP Test (ASTM D 2596) is designed
to evaluate performance under much higher unit
loads than applied in the 4-Ball Wear Test,
hence the designation EP (extreme pressure).
The 4-Ball EP Tester, of a slightly different de-
sign and construction from the 4-Ball Wear
Tester, is the apparatus used. In this test, the
steel ball is rotated at constant speed against
three other steel balls. Temperature is not con-
trolled. The loading is increased at specified
intervals until the rotating ball seizes and welds
to the other balls. At the end of each interval,
the scar diameters are measured and recorded.
Two values from the EP Test are generally re-
(FIST 2-4 11/90)