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9/8/98 AC 43.13-1B (4) Small parts may be envelope bagged (i.e., enclosing the entire part in the bag). Larger parts with localized repairs can be bagged by sealing the surface completely around the repair areas with sealing tape and applying the bagging material to the sealing tape. CAUTION: The whole panel must be vacuum bagged to prevent delamina- tion in sandwich skins when using an oven or autoclave. Contoured parts must be restrained with tooling to prevent warpage. b. When the heat for curing the repair is provided by a heat blanket, the blanket can be either inside or outside the vacuum bag. However, the blanket should be covered to minimize heat loss, and the blanket should be separated from direct contact with most bag ging materials by layers of fiberglass cloth. (1) This will prevent localized over heating that could damage the bag. It is some times helpful to place a thin aluminum sheet under the heating blanket to minimize local ized heating. A thin rubber blanket can help smooth the surface of the material being cured. A pressure plate should be used when two or more heat blankets are applied to the same re pair. NOTE: Understanding that various resins behave differently during cure, the choice of bagging arrangements will often vary with the material being cured. (2) The procedure for the bagging ar rangement is as follows: (a) Place a peel ply over the patch material to provide a surface finish for subse quent bonding or painting if not previously ac complished. Place a layer of porous separator cloth over the patch, extending beyond the prepreg and the adhesive. Smooth to avoid wrinkles. (b) With the patch material in place, place the end of the thermocouple wire next to the edge of the prepreg. Tape the wire to the structure inside the bag with heat-resistant tape. The tape should not be in contact with the prepreg or the adhesive. (c) Place bleeder plies as shown, ex tending 2 to 3 inches beyond the patch. The number of bleeder plies needed will vary with the type of resin and the resin content required. (d) Place a layer of nonporous part ing film over the bleeder plies, cut 1 inch smaller than the bleeder plies. This layer is intended to stop resin flow from bleeder plies into breather plies while still providing an air flow path when vacuum is applied. (e) If a pressure plate is used, place it over the previous separator ply. The plate is frequently perforated with small holes to per mit airflow to the breather plies. Bleeder plies may be necessary when using a pressure plate. NOTE: Pressure on the repair will be reduced if the pressure plate does not conform to the repair. (f) Place the heat blanket over the as sembly, making sure it extends 3 to 4 inches beyond the material to be cured. (g) One or more thermocouples should be in contact with the heat blanket to monitor its temperature. Additional thermo couples should be placed near the curing repair to monitor the temperature of the curing resin. (h) When using a heat blanket as the heat source, four to six layers of fiberglass sur face breather or the equivalent should be Par 3-4 Page 3-7PDF Image | AFS-640
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