This test is used to determine
the deterioration of lubricants, particularly EP gear oils, under severe
oxidation conditions. The sample is placed in a gear case in which a spur
gear set and a test bearing
operate under load while heat
is applied and air is
bubbled through the oil. The
temperature of the lubricant is maintained at
325 degree F during the test.
The above apparatus and
method were developed at the Ordnance Fuels and Lubricants Research Laboratory, Southwest Research
Institute, and a report by
Meckel^10 summarizes the contents as follows: “A description is given of the apparatus
recommended and a list of
Purchase Materials, Instructions for Cleaning, Assembling and Disassembling the Gearcase. Also Test Procedure and Detail
Drawings of the Assembly are included.”
Variations in test conditions and their effect
on oxidation of gear lubricants, using this spur gear thermal
oxidation apparatus, were reported by
Meckel and Quillian^9 and should be
consulted if a program
of tests on the
subject are to be made. The test in question is particularly
valuable for use in
developing oil additive
combinations which will
retard oxidation in service.
During this test, viscosity of
the oil are determined at
intervals of 10 hours and
the test is concluded
when the increase
in viscosity reaches
a point called for in the specifications.
Specification MIL-L-2105B
calls for a test time of 50
hours, at which time
the increase in
viscosity shall be a
maximum of 100 per cent. Also, at
the end
of this period, the n-pentane
insolubles must not be
more than 3 per cent
by weight and the
benzene insolubles not more than 2
per cent by weight. Further, the test
method requires inspection of the various
parts, that is gears, bearings and
catalyst, for the amount
and type of
deposits. The gear teeth are
inspected and any abnormalities of the surfaces
noted. After all deposits are removed from the
catalyst, this is weighed to
determine the copper activity of the
lubricant. The test bearing wear is also determined
with a special fixture and
dial indicator.
An analysis of traditional glasses techniques for identifying the thermal-oxidation balance of equipment lubrication exposed a lack of connection with area service results.
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