(2)
BMS 5-81, a two-part epoxy material used for overcoating the entire center wing section upper panel and front spar areas including fillet seals and protruding structural and fuel fittings.
C. Equipment and Materials
(1)
Clean cheesecloth, gauze, new or laundered rags, tissue paper, or other absorbent material with less than 0.75% soluble content trichloroethylene or carbon tetrachloride, 1% acetone or water. There shall be no silicone grease or oil content
(2)
Cleaning Solvent - BMS 10-7 (Ref 20-30-11)
(3)
Primer - BMS 10-11, Type I (yellow) (Ref 20-30-41)
(4)
Sealant - BMS 5-81, Type II (preferred) or BMS 5-81, Type I (optional) (Ref 20-30-11)
(5)
Abrasive paper - 180 grit or finer
(6)
Flat, bristle brush
(7)
Sealant - BMS 5-79, Class B (Ref 20-30-11)
(8)
B01013 Solvent – Final Cleaning Prior to Fuel Tank Sealing (Series 93) (Ref AMM/50PM 20-30-93)
(9)
Thinner - TL-29 (Ref 20-30-41)
(10)
Brush-On Stripper - Turco 5351 (supersedes Turco 5292B) (Ref 20-30-41)
D. Repair Fuel Barrier Sealant
(1)
If a large area of BMS 5-81 barrier sealant and primer has been damaged or destroyed, proceed as follows:
(a)
Remove coating from damaged area and from small portion of undamaged coating immediately adjacent to the damaged area using brush-on stripper.
(b)
Remove softened material with hardwood Teflon or polyethylene scrapers. Rinse area clean with sponge and water.
(2)
Strip damaged fillet seal.
(3)
Smooth and feather the damaged area by lightly sanding with 180 grit or finer abrasive paper. Avoid abrading to bare metal if possible.
(4)
Remove any contamination with a clean cloth saturated with B01013 solvent, Series 93 (Ref AMM/SOPM 20-30-93).
(5)
Wipe dry with a clean, dry cloth.
(6)
When bare metal is exposed, refinish (Ref Chapter 51, Prepaint Cleaning and Pretreatment - CP; and Decorative Paint System - CP).
(7)
Apply BMS 10-11 primer, feathering the coating as it overlaps the adjacent, undamaged area. Allow to dry for 30 minutes to 4 hours (Ref Chapter 51, Decorative Paint System - CP).
(8)
Apply fillet seal of BMS 5-79, Class B sealant where fillet is missing. Cover any exposed nuts, bolt heads, rivet butts with same sealant.
(9)
Prepare BMS 5-81, fuel barrier sealant for application.
(a)
The base resin and catalyst shall each be homogeneous, free from lumps or gelled particles.
(b)
Prior to measuring out the required amounts, mix each component in its container to ensure homogeneity.
CAUTION: BE CAREFUL DURING BOTH MIXING AND BLENDING TO MINIMIZE AIR BUBBLES.
(c)
Carefully blend the base resin and accelerator in the ratio of 100 parts base resin to
506
28-11-0 Page 838 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/98
538 Secondary Fuel Barrier Sealant Repair
Nov 15/77 Figure 827 28-11-0
Page 839
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
7.1 parts accelerator by weight by slowly stirring the accelerator into the base resin.
WARNING: AVOID BREATHING VAPORS. USE ONLY UNDER APPROVED VENTILATION. KEEP AWAY FROM OPEN FLAME.
NOTE: Blending ratio on a volume/weight basis is 1 gallon of base to 9.9 ounces of accelerator (0.62 pounds).
(d) To aid application, the blended BMS 5-81 may be thinned with B01013 solvent, Series 93 (Ref AMM/SOPM 20-30-93) TL-29 thinner up to a maximum of 15 percent by volume of blended sealant.
(10) Apply two coats of BMS 5-81, fuel barrier sealant with a flat, bristle brush to a dry film thickness of 10 to 20 mils (sag areas shall not exceed 25 mils).
CAUTION: DO NOT APPLY BMS 5-81 WHEN THE AIR TEMPERATURE IS BELOW 500F (100C) OR WHEN THE RELATIVE HUMIDITY EXCEEDS 95%.
NOTE: For optimum results, cure temperatures (coating surface temperatures) above 800F (26.70C) are required.
(a)
Extend coats of sealant to overlap undamaged area surrounding fitting.
(b)
Allow a minimum of 1/2-hour drying time between coats for horizontal surfaces or 2 hours, minimum, for vertical surfaces.
(c)
Keep tank out of service and protect from temperature extremes until sealant is fully cured (Fig. 828).
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