MIL-PRF-6085E
(2) Two or more spots of corrosion between 1 and 2 mm maximum diameter.
d. If more than one panel in five fails the protection test as defined above, a retest will be
permitted. Retests shall consist of repeating the protection test using ten additional panels. Reject the
lubricating oil if more than four panels fail the test (adding failures of both test and retest).
4.4.5 Stability at low temperature. A 100-ml sample of the oil shall be maintained at or below -
54°C for 72 hours in a stoppered flask. At the end of that time there shall be no visual evidence of gelling,
separation or crystallization of the oil. Presence of a dense cloud, which does not "settle out" shall not be
cause for rejection.
4.4.6 Corrosivity test
4.4.6.1 Preparation of panels (also see 4.4.4.1).
4.4.6.2 Preparation of steel discs. The following steps shall be performed:
a. Cut three discs 12.5 mm thick from a 25 mm diameter bar stock that conforms to ASTM
A29/A29M, composition E52100.
b. Heat-treat the discs to a hardness of Rockwell C-62. (Rollers that may be obtained from roller
bearings with similar chemical, physical and dimensional properties to the above bar stock after heat
treatment can be substituted for the formation of the discs). In this case, no additional heat treatment is
necessary.
c. Now slowly surface grind on one side to a finish of less than 20 micro-inches rms. If coolant is
used during grinding, slush the discs in absolute methanol. Next, abrade the discs on the surface-ground
side with successive applications of emery polishing paper grades 1/0, 2/0, 3/0, and finally 4/0. Papers
incorporating iron oxide as the polishing medium and wet-dry type papers shall not be used.
d. Wipe the discs clean with sterile absorbent gauze and examine under a 10X magnification for
any signs of corrosion or other defects. Do not use defective specimens. Store the discs in a desiccator
containing silica gel until ready for use.
4.4.6.3 Preparation of brass clips. The following steps shall be performed:
a. Fabricate clips from commercial 0.6 mm brass sheet conforming to ASTM B36/B36M spring
temper. The size and shape of the clips are illustrated in figure 1.
b. Immerse the clips for 20 seconds in the following etching solution:
450 ml water
300 ml conc. sulfuric acid
225 ml conc. nitric acid
8 ml conc. hydrochloric acid
c. After etching, wash the clips in cold running tap water and then in distilled water. Dry with
acetone and store the clips in a desiccator containing silica gel as desiccant until ready for use.
4.4.6.4 Procedure. The following procedures shall be performed:
a. Coat the three discs with the test oil by dipping and stirring the rod in the test oil and allowing
the oil from the rod to drop onto the polished side of the discs.
b. Clamp the brass clips over the coated discs and the assemblies and place them in a test
chamber, which is maintained at 27°C +1°C and 50 percent relative humidity, for a period of 10 days. For
a 50 percent relative humidity, use a sulfuric acid solution with a density of 1.338 at 20°C.
c. After exposure, remove the assemblies and outline the brass clips on the discs using the clips
as templates. Then remove the clips and wipe the test oil from the discs.
d. Examine the discs under 10X magnification for signs of corrosion, pitting or other detrimental
effects. If the test results are questionable, repeat the entire test using new specimens, except extend
the time period to 20 days. In this case, examine the discs as in the previous manner.
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