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September - October 2017
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7
the Group V PAG lubricant. These are the
typical contamination levels observed during
a lubricant exchange.
Visual Compatibility
Visual compatibility was the first phase of
the compatibility testing. The lubricants were
observed after they were blended and stored
for three to five days. ASTM D7155 describes
how to study samples and provides an appear
-
ance guide for rating compatibility. Are the
lubricants
clear and bright or do they appear
cloudy? To meet the compatibility criteria,
the blended lubricants must be "absolutely
bright." As seen in the photos on the right,
the studied lubricants all passed the visual
compatibility tests.
If the two lubricants do not have good
compatibility, three interactions are affected:
liquid-air, measured by the lubricant's foaming
proper ties (A S TM D892); liquid-solid,
measured by the formation of insoluble solids
(ASTM D7843); and liquid-liquid, measured
by the lubricant's demulsibility (ASTM D1401).
Foam
The change in the liquid-air interaction is
measured using the ASTM D892 foam test. This
measurement looks for a negative change in
performance after the lubricants are blended.
The test reports three values: the amount of
foam at the end of the 5-minute blowing period
(foaming tendency), the amount of foam at the
end of the settling time (foam stability), and
the settling time. Most new lubricants have a
foaming tendency ranging from 10-60 millili-
ters and a foam
stability of 0 milliliters.
Results of the visual compatibility tests
90% PAG/10%
Mineral Oil 1
90% PAG/10%
Mineral Oil 2
BLENDED
LUBRICANTS
FOAMING
TENDENCY FOAM STABILITY SETTLING TIME
90% PAG/10%
Mineral Oil 1
60 mL 0 mL 39 minutes
90% PAG/10%
Mineral Oil 2
50 mL 0 mL 33 minutes
Foam test results
