Technical data

NOTE
• PreKote SP may be applied by pressure
sprayer, spray bottle or fluid feed attached to
sander.
• The first coat of PreKote SP may be hand or
pneumatic scrubbed using 180-grit scrub pads.
• All coats of PreKote SP may be removed
using a clean, lint-free cotton rag moistened
with isopropyl or denatured alcohol, instead of
rinse with water.
e. Follow procedures outlined in application of PreKote
SP, Paragraph
3.1.20.
3.1.23 Corrosion Removal Solution For Magne-
sium.
• Do not allow rags, brushes, abrasive mats, or
any other item soaked with A-A-55827 chro-
mic acid or the chromic acid pickle solution
prepared with it to come in contact with any
organic solvent (MEK, acetone, paint thinner,
A-A-59601/MIL-PRF-680 dry cleaning sol-
vent, etc.); fire will result.
• A-A-55827 chromic acid and the chromic acid
pickle solution prepared with it are highly
toxic to the skin, eyes, and respiratory tract.
Chemical splash proof goggles and/or face
shield, chemical resistant rubber gloves and
apron are required. Good general ventilation is
usually adequate. Assure this operation has
been reviewed by local Bioenvironmental En-
gineer. In case of eye or skin contact, flush
with water immediately and report to the base
medical facility.
Chromic acid pickle solution which is a mixture of A-A-
55827 chromic acid in water may be used to remove surface
oxidation and light corrosion from magnesium alloy surfaces.
It is not adequate for removal of deep pitting, heavy corro-
sion, sand or other blast media residue, or the effects of
blasting which will require use of one of the mechanical
methods described in this chapter. If properly used, this
chemical method removes much less metal causing much less
reduction of sectional thickness than mechanical methods,
but it shall not be used on parts containing copper or steel
inserts unless they are completely masked off. Do not allow
excessive amounts of anions such as chlorides, sulfates, or
fluorides to build up in the solution; they tend to coat or etch
the metal surface rather than removing corrosion products.
Do not reuse old solutions; prepare fresh solutions for each
separate removal operation.
a. Mix 24 ounces of A-A-55827 chromium trioxide in
enough water to make one gallon for each gallon of
solution being prepared in a container fabricated from
lead lined steel (any alloy), stainless steel (any CRES
alloy), or 1100 aluminum alloy. For depot level opera-
tions only, a removable part that is being treated can be
completely immersed in the solution with an immersion
time ranging from one to 15 minutes at an operating
temperature ranging from 190° F to 202° F (88° C to 94°
C). For hand application with the solution at room
temperature, the dwell time for the solution on the
surface is 15 minutes minimum to 30 minutes maxi-
mum. Paragraph 3.1.21 step b through Paragraph 3.1.21
step d are for hand application. Paragraph 3.1.21 step e
through Paragraph 3.1.21 step f apply to both the
immersion and hand application methods.
b. Mask off the surrounding areas, in particular to include
all nearby operating mechanisms, joints, crevices, cop-
per and/or steel inserts, and plated steel to keep the
solution from attacking them.
c. Apply the chromic acid pickle solution carefully to the
corroded area with an A-A-289 acid brush.
d. Allow the solution to remain on the surface for approxi-
mately 15 minutes for a solution at room temperature.
Agitate the area with an A-A-289 acid brush having half
the bristle length cut off or a A-A-58054, Type I, Grade
B or C abrasive mat.
e. Thoroughly rinse the solution from the surface with
plenty of fresh tap water.
f. Repeat the preceding sequence as necessary until all
corrosion products have been removed and the metal is
a bright metallic color.
3.1.24 Surface Treatment Process For Magne-
sium.
Chromic acid solution is highly toxic to the skin,
eyes and respiratory tract. Avoid all contact. Skin
and eye protection and vapor controls are re-
quired. Assure this operation has been reviewed
by local Bioenvironmental Engineer.
Chemical pretreatment solution provides a passive surface
layer with an inhibitive characteristic that resists corrosive
attack and also provides a bond for subsequent coatings. The
solution consists of the following materials and must be
mixed in the ratio specified:
TO 1-1-8
Change 3 3-15