757 防腐手册 CORROSION PREVENTION MANUAL(31)

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of BMS 10-11, type I primer and a coat of BMS 10-11, type II enamel. The
forward and aft wheel well bulkheads and the keel beam are assembled with
BMS 5-95 fay surface sealant. All non-aluminum fasteners are installed with
wet BMS 5-95 sealant. Interior surfaces of the keel beam from station 900 to
station 1140 receive a coat of BMS 3-23 after assembly and painting. Begin-ning with line number 37, the surface contacted by access doors when in the
closed position is coated with BMS 10-86, type 1 teflon-filled coating.
Beginning at line number 577, for all package freighter airplanes, RR
92018-28 applies corrosion inhibiting compound BMS 3-23 and 3-29 to main
landing gear wheel well (Ref 53-40-03, Fig. 1, sheet 2).

C. Corrosion can occur in the horizontal flange of the tee chord of the keel
beam (Structural Item Interim Advisory 757-28).

D. The surfaces inside the wheel well are exposed to air contaminants and run-way splash and are subject to corrosion.

E. External  drains are either leaf spring or plunger type drain valves, and
they close when the airplane is pressurized. Drain paths through the inter-nal structure go to the external drain valves. Refer to 53-40-02, Fig. 1,
for valve location.

F. A coat of BMS 3-23, type II corrosion preventive compound is applied to
structure within 2 inches of the body skin, and the body skin itself, from
stations 940 to 1040. On airplanes line number 241 and on, per PRR 54133,
this compound extends the full length of Section 44, and also includes the
upper surface of the passenger floor.

G. The corrosion  protective finish for the structure surrounding the No. 1
cargo and No. 2 passenger door opening consists of a chemical conversion
coating (alodine) on clad aluminum parts, anodize surface treatment for
non-clad parts and a coat of BMS 10-11, type I primer. The doubters around
the doors are installed with fay surface sealant. All non-aluminum fasteners
which penetrate the exterior skin are installed with wet sealant. After
assembly, a touchup coat of BMS 10-11, type I primer is applied to bare fas-teners and a coat of BMS 10-11, type II white enamel is applied around the
doors. A coat of BMS 3-23 is applied except on the door assembly and door
opening (Ref 53-40-04, Fig. 1).

Volume 2-757

53-40-01

Page 1
OCT 01/00

CORROSION PREVENTION MANUAL
FUSELAGE -SECTION 44

H. The primary corrosion  area is under the door sill, floor panels, floor beams
and doubters or triplers at door openings.

I. The stringers, frames and skins can get corrosion because of moisture caught
between the skin and insulation blankets. Corrosion starts at broken protec-tive finishes. The lower lobe structure is the same as in Section 43 (Ref
53-30-02, Fig. 1).

J. Insulation blankets  are provided on cabin interiors for passenger comfort
　
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