FED-STD-791D
6.3.4 Connect the fused test cell containing the oil sample and metal specimen to the
vacuum pump. This can be done with vacuum tubing connected through a Kjeldahl connecting
bulb, Ts joint 24/40, and a No. 1 rubber stopper drilled to hold the thermal stability tube.
6.3.5 Mount the test cell, while still connected to the operating vacuum pump, in a water
bath maintained at 80 3C (175 5F). Degas the cell and its contents while shaking gently
for 20 min. A Thomas-Boerner oscillating platform shaking apparatus may be used. Mounting
the tubes about 16 cm above the platform. A manifold can be used to evacuate more than one
cell at a time. If frothing persists, continue the heating and shaking for another 10 min.
NOTE 4:
Certain ester based as well as other type synthetic lubricants are hydrolytically
unstable at the test temperature of 274C (525F). Therefore, the procedure
described in 6.3.5 to remove all water before sealing the cell is necessary. The
pressure in the cell, as measured with a McLeod gauge, or other suitable
measuring device, shall be no more than 10 m before sealing.
6.3.6 While the test cell is still under vacuum it is sealed and drawn off at the capillary
approximately 3 cm above where it joins the cell body. (See Note 3).
6.3.7 Weigh the test cell to the nearest mg.
6.3.8 Insert the glass test cell in the heater [preheated to 274 1C (525 2F)] for
period of 96 hours. If a heating bath is used, insert the test cell in the steel holder and place the
assembly in the bath.
NOTE 5:
Safety shields must always be used as a precaution when placing the test cells in
the heater, removing the cells from the heater, and opening the cells. Tremendous
pressures are generated during the test period.
6.3.9 At the conclusion of the heating period, remove the test cell and allow to cool to
ambient temperature. Wipe down the outside of the cell with suitable solvent.
6.3.10 Visually observe the samples for evidence of insolubles, phase separation,
interactions between metal and oil, or changes in color of the oil. A significant difference in
final color between duplicate tests will necessitate retesting since color differences indicate
improper preparation of one or both of the test cells.
6.3.11 Reweigh the test cell. Any significant loss in weight indicates leakage of the test
cell and the test must be repeated.
6.3.12 As a safety measure the cells must be cooled before cutting them open because of
the pressure which develops in testing. Any convenient cooling method may be used such as dry
ice - acetone, liquid nitrogen, cooling chambers, etc.
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