28-11-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
(c) Mix the sealant compounds as shown in the manufacturer's instructions.
NOTE: Always use the curing compound with the base compound
____ from the same repair kit. Do not mix the contents of one repair kit with that of a different kit. Do not mix the sealant too much or the time you can apply the sealant will decrease.
CAUTION: MAKE SURE NO AIR BUBBLES ARE IN THE SEALANT WHEN YOU MIX
_______ IT. IF THERE ARE AIR BUBBLES IN THE SEALANT, IT WILL NOT BOND CORRECTLY.
(d)
Mix the curing compound and base compound until the sealant is of a constant, equal color. 1) If a mixing machine is not available, use a clean spatula.
(e)
Put the sealant in a container cleaned with methyl ethyl ketone (MEK).
CAUTION:_______DO NOT FREEZE MIXED SEALANT AFTER YOU THAW IT. THE SEALANT IS NOT USABLE IF IT IS FROZEN MORE THAN ONCE.
(f)
If you do not use the mixed BMS 5-26 Type II or BMS 5-45 sealant immediately, you can keep the sealant for a longer time if it is refrigerated. 1) Put the sealant in a sealed container. 2) Write the date you mix sealant, sealant type, class,
supplier, and date when the sealant cannot be used. 3) Discard all sealant kept more than 21 days at -40°F (-40°C). 4) Discard all sealant kept more than 7 days at -20°F (-28.9°C).
S 398-244
(4)
Sealant application time (Fig. 804):
(a)
The time in which you can apply the mixed BMS 5-45 Class B-1/2 sealant is 1/2 hour at 77°F (25°C) and 50% relative humidity.
(b)
The time in which you can apply the mixed BMS 5-45 Class B-2 sealant is 2 hours at 77°F (25°C) and 50% relative humidity.
(c)
The time in which you can apply the mixed Pro-Seal 860 B 1/6 sealant, MIL-S-83318, is 10 minutes at 77°F (25°C) and 50% relative humidity.
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(5)
BMS 5-26 Type II and BMS 5-45 sealant squeeze-out life:
(a)
Squeeze-out life is the length of time you can use the sealant for structure assembly when you apply faying surface seals.
(b)
The time, shown in (Fig. 804), is the maximum time between when you start to thaw the sealant or mix sealant that is not frozen and the final attachment of mating surfaces.
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28-11-00
ALL ú ú 01 Page 827 ú Oct 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
S 398-246
(6)
Sealant curing:
(a)
You must let the BMS 5-26 Type II or BMS 5-45 sealant cure for the minimum time (Fig. 804) before you continue maintenance operations in the fuel tank or refuel the fuel tank.
(b)
Pro-Seal 860, B 1/6 sealant can touch fuel after 2 hours and has a cure time of 4 hours.
WARNING: DO NOT START OR STOP THE BLOWER EQUIPMENT WITH THE AIR
_______ HOSE IN THE FUEL TANK. OBEY ALL SAFETY PRECAUTIONS WHEN YOU USE WARM AIR. FAILURE TO OBEY THE SAFETY PRECAUTIONS COULD CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
CAUTION: DO NOT APPLY SEALANT WHEN THE STRUCTURE TEMPERATURE IS
_______ LESS THAN 50°F (10°C) OR MORE THAN 140°F (60°C). THE SEALANT WILL NOT CURE CORRECTLY IF THE STRUCTURE TEMPERATURE IS OUT OF RANGE.
(c) The best conditions to cure the sealant are at an ambient temperature of 77°F (25°C) and a relative humidity of 50 |5 percent, with a good flow of air in the area. 1) Relative humidity is an important factor in the cure time
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