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CAUTION : DO NOT FREEZE PR WITH 1/2 HOUR APPLICATION TIME. Mixed and frozen sealants which have thawed shall not be refrozen.
Pre-assembly operations such as fitting, filing, drilling, countersinking, dimpling and deburring shall be completed before cleaning and sealant application.
Surfaces must be clean and dry, free from dust, lint, grease, chips, oil condensation or other moisture and all other contaminants before the application of sealant.
Sealants may be applied to primed or unprimed surfaces. Epoxy primers shall have good adhesion to the substrate material and shall have been heat cured or shall have aged for at least 48 hours prior to sealant application.
AAAA
Validity : S / N 1 - 9999 20-00-09Page 202
(BA) OCT 97
Sealants shall not be applied when the temperature of either the sealant or the structure is below 16°C (61°F).
Fay sealed joints must be closed and securely fastened before expiration of the work life. Excess sealant must squeeze out of a fay sealed joint when attachment is made. Drilling and reaming of holes through a fay sealed joint are permissible only if the joint is secured by a minimum of approximately one-half of the fasteners required for final installation. However, manufacturing and changes performed after sealing are not recommended and shall be held to a minimum.
After application, sealants shall be free of entrapped air bubbles and shall not exhibit poor adhesion. All fillets shall be smoothed down with a filleting tool before the sealant application time has expired.
Sealant extruded through a hole by a rivet shall be wiped from the end of the rivet before bucking. Threaded fasteners which have been shank or underhead sealed shall not be retorqued after the expiration of the application time of the sealant. In torquing, turn the nut rather than the bolt, if possible.
After sealant is applied, joints shall not be flexed until sealant is tack-free.
5. SEALANT PROPERTIES
Application time is the period during which the sealant can be satisfactorily applied. After this time, the material does not "wet" the surface properly and may fail in adhesion. Class B compounds sometimes exhibit lack of wetting by rolling up ahead of the sealing gun or drawing up behind the gun. Sealant which does not wet properly or which is difficult to extrude from the sealing gun shall be discarded.
Tack-free time is a stage, during the cure of the sealant, after which the sealant is no longer tacky. When the sealant is pressed firmly with the fingers tightly closed in but no longer adheres to the knuckles, the sealant is tack-free. If any drilling chips and dirt touch the sealant before it becomes tack-free, the sealant will become contaminated. All assembly operations and moving of the structure before the sealant is tack-free shall be avoided, except for faying surface seals.
Curing rate is a stage, during the cure of the sealant, after which the sealant is sufficiently firm.
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TB20 MAINTENANCE MANUAL 20 STANDARD PRACTICES AIRFRAME TB20飞机维护手册 20 标准施工机体(48)
