MACHINERY LUBRICATION- INDIA SEPTEMBER-OCTOBER 2019 | Page 26
WHAT IF..?
and the oil temperature. The amount of
dispersing additives, the oil’s density
and any impurities also play a role. As
air bubbles arrive at the surface, surface
foam is formed. Therefore, foam
consists of a series of air bubbles, which
are each surrounded by a skin of oil. As
a function of the oil’s surface tension,
this skin of oil can burst more or less
rapidly. The time it takes for the
ascended bubbles to burst and achieve
complete separation from the oil is
mostly dependent on the oil’s viscosity
and temperature, but the content of
polar aging products, impurities and
certain additives also have a bearing.
The oil property that describes how fast
these ascended bubbles burst is called
the foaming behaviour.
Operational Causes of
Foaming
The possible causes of foam formation
24 | September - October 2019 |
in gearbox can be divided into two
groups: transmission and lubricating
oil. If lubricating oil mixes with other
lubricants or contaminants such as
dust or water, foaming can result along
with oil aging, which leads to the
formation of polar oil-aging products,
an increase in viscosity or filtering out
of anti-foam additives by bypass filters.
In practice, you often see an overlap of
several factors. While each factor on its
own would not be a problem, a
combination of these factors can lead
to increased foaming. This makes it
difficult to identify the actual causes.
Flender Foam Test
The
measurement
of
foaming
characteristics according to Flender is
standardized in ISO/DIS 12152. Flender
has developed special test and
standardized. This test delivers much
more reliable results and can improve
www.machinerylubricationindia.com
the reliability of gear oils. The examples
given demonstrate the application of
these test procedures and offer an
overview of foaming problems as well
as their cause. The upper limit of more
than a 15-percent increase in the oil
volume one minute after stopping the
instrument does not equate to an actual
foaming limit for existing gearboxes.
This limit is only valid for the test
instrument and the standardized test
procedure. It is based on the experiences
of Siemens (Flender) in meeting the
requirements of Flender gearboxes.
Some filter manufacturers have even
included the Flender foam test in their
testing procedures to avoid problems
with removed anti-foam agents.
Contact C M Sharma at
[email protected]