Corrosion Resistant Finish Mixing Proportions 502
28-11-0 Figure 701 Nov 15/80
Page 708
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
NOTE: Keep containers of mixed corrosion resistant finish compound tightly closed while waiting for application, or contents will gradually thicken and gel.
(2) Apply finish.
(a) By brush (suitable for small areas).
1) Apply thin film (approximately 0.0005 inch) with soft bristle paint brush, brush in one direction as much as practicable. a) Avoid fast scrubbing motions or repeated brushing out of wet compound
which may produce air bubbles, pickups, or voids. 2) Allow to dry for a minimum of 30 minutes. 3) Apply second thin film in same manner as first coat. 4) Ensure that applied finish overlaps any adjacent topcoating previously applied.
(b) By spray (recommended for large areas). 1) Set spray gun to 40 psi air pressure and 5 to 10 psi fluid pressure. 2) Spray finish material on entire surface to be coated in a wet, continuous film. 3) Allow to dry for a minimum of 30 minutes. 4) Apply second coat in same manner as first coat. 5) Ensure that applied finish overlaps any adjacent topcoating previously applied.
(3) Apply zinc rich epoxy primer.
(a) Apply primer by spray or brush (Ref par. (2)).
NOTE: Zinc rich primer must be stirred almost continually during application to prevent zinc settling.
1) Apply 1.5 to 2.0 mils (dry film thickness) to lower surface and to a height sufficient to cover all exposed surfaces of lower stringers.
2) Do not apply to the seal surfaces at tank openings or to O-ring seals.
(b)
Allow zinc rich primer to cure not less than 1 hour before entering tank.
(c)
Within 8 hours overcoat zinc rich primer with 0.0006 to 0.0016 inch thick BMS 10-20.
(4)
Cleanup after corrosion resistant finish application.
(a)
Clean equipment with MEK immediately after use.
(b)
Soak brushes in MEK immediately after use. Discard brushes when bristles become stiff.
(5)
Cure corrosion resistant finish
(a)
Cure BMS 10-20 and MIL-C-27725 finish coatings per Fig. 702
1) Cure time can be shortened by using elevated temperatures and, with some finish compounds, by increasing relative humidity (R.H.) (Fig. 703 thru 706).
(b)
If zinc rich coating is applied, cure for a minimum of 12 hours at 65°F or above prior to fuel exposure.
(c)
Perform the following fuel or solvent resistance check to verify cure completion.
WARNING: SUPPLY PLENTY OF VENTILATION WHEN USING METHYL ETHYL KETONE (MEK), AS THIS SOLVENT IS HIGHLY TOXIC.
502
Nov 15/80 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 28-11-0 Page 709
1) JP-4 fuel resistance test. a) Saturate a 4-inch square pad of cheesecloth with JP-4 as applicable. b) Apply pad to surface to be checked and allow solvent or fuel to flood area. c) Using hard pressure rub the area 100 strokes, counting each movement in
one direction as a stroke. d) Observe whether coating is removed so that metal is exposed (unsatisfactory). If metal is not exposed, cure is satisfactory.
CORROSION RESISTANT FINISH (BY MFGR.) CURE TIME PRIOR TO FUEL EXPOSURE *[1] CURE TIME PRIOR TO TRAFFIC CURE TIME PRIOR TO ASSEMBLY *[1] CURE TIME PRIOR TO SEALING
Bostik West (BMS 12 hours at 65°F or 12 hours at 65° or 12 hours at 65° or Fig. 703
10-20 Type II) above or Fig. 703 above or Fig. 703 above or Fig. 703 *[2]
*[2] *[2] *[2]
DeSoto (MIL-C-27725) Fig. 704 *[2] 24 hours at 65°F or above Fig. 705 or 240 hours at 65°F or above *[2] Not Applicable
Products Research (MIL-C-27725) Fig. 706 24 hours at 65°F or above 240 hours at 75°F and minimum of 30 percent relative humidity Not Applicable
*[1] Verify cure completion by performing fuel resistance check (Ref. Par. 3.D.(5)(c)).
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