Technical data

flashing out suddenly over a large area, it shall be considered
as evidence of impurities on the surface such as free alkali,
residual detergents, etc., and the surface shall also be consid-
ered as failing the cleanliness test. If the water drops coalesce
(go together) into a continuous film of water without a sudden
flash out and form a lens, then the surface shall be considered
as having satisfactorily passed the water break test. Any areas
that fail the test shall be cleaned per TO 1-1-691, and
reinspected.
3.1.11 Evidence of Inadequate Cleaning. During pre-
paint operations of acid-etch and chromate conversion coat-
ings, surfaces should also be monitored for evidence of
undetected soiled areas. When accomplishing the rinse of
etch or conversion coating solution and a rapid flash off or
breaking of the rinse water occurs, this indicates an unsatis-
factorily cleaned area not detected during the random sample
of the water break test. Areas that show evidence of inad-
equate cleaning during rinsing require recleaning and reac-
complishment of prepaint surface preparation.
3.1.12 Corrosion Removal Prepaint Compound, Alu-
minum.
• Exposure of magnesium surfaces to aluminum
prepaint chemicals will initiate corrosion
which will continue even under a new paint
system and ultimately cause severe damage.
• All magnesium surfaces, steel/high strength
steel and cadmium plated surfaces shall be
protected from MIL-C-38334/SAE AMS-1640
solutions.
Masking of all lap joints, hinges, faying surfaces, access
doors, air scoops and other openings that would allow
MIL-C-38334/SAE AMS-1640 to enter or be entrapped is
required prior to beginning the require prepaint process. Also,
masking of unprotected magnesium, steel and cadmium-
plated components shall be done at this time. Masking will be
accomplished per Chapter 2, using masking procedures for
chemical paint removal.
3.1.13 Prepaint Chemical Corrosion Removal Materi-
als. Corrosion removal compound, prepaint specification
MIL-C-38334/SAE AMS-1640, is used for removing oxida-
tion and corrosion products from aluminum alloys which are
not required to be Liquid Oxygen (LOX) compatible. MIL-
C-38334/SAE AMS-1640 is available in two types.
3.1.13.1 Type I, liquid concentrate, which is diluted with
an equal amount of water before use.
3.1.13.2 Type II, powdered concentrate kit, materials will
be dissolved in the volume of water specified on the kit.
3.1.14 Application of MIL-C-38334/SAE AMS-1640
Solution/Not LOX Compatible.
MIL-C-38334/SAE AMS-1640 is moderately
toxic to the skin, eyes and respiratory tract. Eye
and skin protection is required. Good general
ventilation is normally adequate.
Apply solution by flowing, mopping, sponging, brushing or
wiping. The solution is more effective if applied warm (130°
F ±10° F), followed by vigorous agitation with a non-
metallic, acid-resistant brush or aluminum-oxide-abrasive,
nylon mat (A-A-58054, Type I, Grade A). When applying the
solution to large areas, start at the lowest surface working
upward. Applying the solution with a circular motion to
disturb the surface film will assure proper coverage. Allow
the solution to remain on the surface approximately 12
minutes, then rinse away with potable water. Corroded areas
identified for treatment during the prepaint process may
require additional agitation beyond that specified above.
Corroded areas being treated during the prepaint may also
require more than one application and rinse. Examine the
areas being treated witha4to10power magnifying glass to
determine if another application is required. MIL-DTL-5541/
MIL-PRF-81706/MIL-C-81706 chromate conversion coating
shall be applied immediately after the final rinse, and before
the surface dries.
NOTE
When a large area/aircraft is being treated with
MIL-C-38334/SAE AMS-1640 start applying so-
lution to lowest point first and work upward.
3.1.15 Surface Treatment Materials For Aluminum.
There are two specifications which cover formation of Chro-
mate Conversion Coatings with its attendant process appli-
cation and the Chemical Conversion Materials. These two
specifications and their scope are as follows:
NOTE
Chromate Conversion coating specification MIL-
DTL-5541 should be applied after the manufac-
ture of new aluminum alloy repair parts.
3.1.15.1 Chromate Conversion coating specification MIL-
DTL-5541 covers two classes of chemical conversion coat-
ings formed by the reaction of chemical conversion materials
and the surfaces of aluminum and aluminum alloys. It is
designed to provide corrosion protection and better paint
adhesion than uncoated aluminum. It is used on aluminum
alloys as a prepaint treatment for most approved paint
systems; repair of damaged anodic coatings; and treatment of
TO 1-1-8
3-8 Change 3