(2)
There can be holes, nicks, and splits in the seal.
(3)
Splices can be unsatisfactory on the continuous blade seals.
(4)
On the sweeper seal installed on the main entry door, the sweeper seal can make a tear from the end seal attach screws (Fig. 803).
C.
These three types of adhesives are used for repairs to the seals:
(1)
Type I adhesive has two parts and cures in the air. You can handle this adhesive after 8 hours. Do not put force on the adhesive until after 24 hours. It is a silicone-resin type adhesive and is relatively hard and unflexible when cured. General Electric SR-529 adhesive with SR-3900 catalyst is a Type I adhesive.
(2)
Type II adhesives have one part and dry in the air. It is a clear, flexible adhesive that stays flexible when it is cold. You can handle this adhesive after 24 hours. Do not put force on the adhesive until after 48 hours. Use this adhesive for repairs to the blade seals where it is necessary to have flexibility. Dow Corning Silastic 140 RTV or Silastic 731 RTV and General Electric RTV 174 adhesives are Type II adhesives.
(3)
Type III is a two-part, air-cured adhesive (or cured under a plastic film). It is very flexible.
(a)
Use type III adhesive for fast repairs. You can use it in all locations on the seal.
(b)
It is necessary to cure the adhesive for 24 hours before you put a load on it. However, if the fast-repair of the seals is made with the seal in position on the airplane, the airplane can be pressurized after the adhesive has cured for one hour.
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52-09-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
Pressure Seals
Figure 801
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52-09-00
ALL ú ú 01 Page 802 ú Jun 10/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
(c)
Dow Corning 93-076-1/2 or -2 resin and GE RTV 700 are type III adhesives.
(4)
The times to dry the adhesives are correct for temperatures of 75 |5°F with 50 |5% relative humidity. If the temperature or the humidity decreases, the time will increase.
TASK 52-09-00-308-001
2. Repair the Door Seal
____________________
A. General
(1)
The adhesives must be in good condition. These instructions will help keep the adhesives in good condition.
(a)
Keep the adhesives at 40 to 50°F until you use them.
(b)
You can keep small stacks of adhesives (to use in the shop) at room temperature (60 to 80°F) for a maximum of 6 months.
(c)
Always keep the Type II adhesives sealed when you do not use.
(2)
A repair to a seal usually occurs in this sequence.
(a)
Make sure you have easy access to the seal. It will make the repair easier if the seal is not stretched. If it is necessary, remove the seal retainer strips. Disengage the gates to release the tension on the seal.
(b)
Make a decision on the type of repair necessary and the applicable repair procedure. Use fabric when it is possible. Replace the seal if there is too much damage to repair.
(c)
Clean and prepare the surfaces that you will repair.
(d)
Apply the adhesive to the two surfaces to be bonded and hold the parts together in the correct position.
(e)
Obey the pot life limits of the adhesive.
(f)
There are three general repair procedures as follows:
1) Procedure A. This procedure uses only adhesive to repair the damaged seal. a) Apply the adhesive to all of the areas that you will
bond. b) Hold the surfaces together and apply pressure to make sure the parts are fully bonded. c) Let the adhesive dry for the necessary time before the seal is used.
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