T.O. 1-1A-9
½ pint technical hydrofluoric acid (48°HF) (1.15 Sp).
9 gallons of water.
b.
Parts shall be immersed for 3 to 5 minutes in cold acid (50° 105F).
3-259. After removing from the acid, the parts shall be washed in fresh hot or cold running water for a sufficient length of
time to thoroughly remove the acid. Diluted solution of sodium dichromate (Na2 Cr2 07) 12 to 14 ounces per gallon of
water, shall be added to the rinse water as a corrosion inhibitor. The rinsing time depends upon the freshness of the
solution, size of the part and the amount of solution circulated. One half hour or less should be sufficient. Parts shall
then be completely dried by blasting with compressed air or other approved method.
NOTE
The sheet will stain when rinsed with sodium dichromate. The stronger the solution the
darker the stain. A light detectable stain is desired on corroded areas. If the stain is dark
reduce the amount of sodium dichromate added to rinse water.
3-260. Corrosion Removal and Treatment of Aluminum Sheets When Immersion Is Not Practical.
3-261. The surface shall be cleaned with water base cleaner, Specification MIL-C-25769, Type I.
a.
Heavily soiled areas. Dissolve the contents of two 5-pound packages in 10 gallons of water. Stir with a wooden
paddle until fully dissolved.
b.
Lightly soiled areas. Dissolve four 5-pound packages in 50 gallons of water (a 55 gallon drum i
s suitable for this
purpose). Agitate thoroughly with wooden paddle to insure proper mixture.
c.
Application. Apply the solution by spraying, or with a mop, sponge, or brush. Allow to remain on the surface for
several minutes while agitating with a brush. Rinse thoroughly with a spray or stream of water. Do not allow solution to
dry before rinsing as less effective cleaning will result.
3-262. Corrosion Removal. To remove corrosion products use a metal conditioner and brightener, Specification MIL-C-
38334.
CAUTION
Metal conditioner and brightener is for use only on aluminum alloys, and it shall not be used
just for the sake of improving the appearance of material. Material in storage shall not be
treated with this material more than one time.
WARNING
When using acid solution wear approved clothing, acid resistant gloves, aprons/ coveralls,
face shields or respirator. If solution is splashed into eyes, flush thoroughly with water
immediately, and then report to dispensary. For special instructions contact local safety
officer.
a.
Prepare the brightening solution by mixing Specification MIL-C-38334 compound with an equal amount of water,
in a rubber pail.
b.
Apply enough diluted brightener to completely cover the area being treated with a non-metallic bristle brush.
c.
Agitate the brightener by scrubbing with a non-metallic bristle brush. Depending on the ambient temperature and
amount of corrosion deposits pre sent, allow approximately 5 to 10 minutes from application of brightener before rinsing.
When using brightener at high ambient temperature (above 80F) leave brightener on for shorter periods of time. Do not
leave brightener on the surface longer than necessary to dissolve the corrosion.
d.
Rinse the brightener from the surface (using approximately 50 gallons of water per minute. Insure that all traces
of brightener has been removed (shown by no foaming or bubbles while rinsing).
3-263. Chromate Conversion Coating Specification MIL-C-5541, for aluminum alloys. Aluminum alloys which are
treated with Specification MIL-C-38334 shall be treated with Specification MIL-C-5541. Most solutions conforming to
Specification MIL-C-5541 leave a stain. A clear Specification MIL-C-5541 coating is available (reference QPL 5541)
and should be used when a bright metal finish is desired.
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