(1) The following process is recommended for a field repair of bonded rub strips when a heat source is available to provide an adhesive cure temperature within the range 85° to 120°F.
B. Repair Bonded Rub Pads
(1) The rub strip to be repaired shall be reworked per paragraph 2.C. with the following exceptions:
(a)
A new rub strip shall be prefitted on the assembly after the faying surfaces are cleaned and before the adhesive is applied. The rub strip shall be laid flat against the assembly surface without the aid of holding or clamping devices. The gap between the mating surfaces of the prefitted rub strip and the assembly shall be a maximum distance of 1/8 inch. The rub strip may be rolled out flat with a clean roller against a smooth surface to improve the prefit.
(b)
Pro Seal 890 B-2 shall be used as the adhesive.
(c)
The ratio of activator component to the base component shall be 22 (+ 2) parts by weight of activator to 100 parts by weight of activator to 100 parts by weight of base.
(d)
The parts shall be assembled within 25 minutes after adhesive mixing.
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(e) The cure schedule shall consist of the following steps: 1) Warm the assembly to the cure temperature of 90° (+ 5°) F. No less than 1.5 hours shall elapse from the time of adhesive mixing to the time when the cure period shall begin.
2) Cure the assembly for a period of 2 hours, minimum at 85° to 120°F.
NOTE: The temperature sensing device shall be embedded in the adhesive flash next to the bondline.
3) Do not stress the assembly for 20 minutes, minimum, following the cure period.
NOTE: Two heat lamps, 250 watts each, may be used as a heat source. The lamps should be mounted 9 inches apart on a rod, aimed downward 6 inches from the rub strip.
(f) The following method of applying curing pressure shall be optional to the process in paragraph 2.C. 1) During the first two hours after the parts are assembled, smoothing pressure shall be applied to the rub strip at intervals of no more than 15 minutes.
2) The method of smoothing shall be in accordance with that in paragraph 2.C. A continuous bead of extruded adhesive at the bondline is desirable because it indicates proper contact of the faying surfaces. As the adhesive cures in the assembly, increasingly greater smoothing pressure is required to squeeze out any air pockets forming in the bondline.
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TEFLON RUB PADS - APPROVED REPAIRS
1. General
A. This section describes the process to be used for bonding teflon rub pads (TFE plastic) to the airplane structure.
2. Equipment and Materials
A. Teflon Rub Pad (AMS 3651 Polytetrafluoroethylene)
B. Solvent - Final Cleaning of Solvent Resistant Organic Coatings Prior to Non-structural Bonding (Series 90) (Ref AMM/SOPM 20-30-90).
C. Etching solutions
(1)
FluoroBond
(2)
Tetra-Etch
(3)
Sodium ammonia solution
(a)
Anhydrous ammonia
(b)
Sodium metal (technical grade)
D. Containers (polyethylene or stainless steel)
E. Tubing (rubber or Tygon)
F. Rod, glass or polyethylene
G. N-Butyl alcohol (technical grade)
H. Adhesive, RIV-154
I. Masking tape
3. Prepare for Repair
A. Clean airplane faying surface thoroughly with solvent, Series 90 (Ref AMM/SOPM 20-30-90).
B. Clean teflon pad faying surface thoroughly with acetone.
C. Mask opposite side of teflon pad faying surface.
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D. Etch teflon pad faying surface as follows:
(1)
Etching Method I (FluoroBond or Tetra-Etch)
(a)
Immerse the part in the etching solution for a minimum of 30 seconds and a maximum of 60 seconds.
(b)
If the part does not attain a dark brown color in 60 seconds, the etchant has lost effectiveness and the part shall be re-treated with fresh solution.
(c)
The treated part shall be immediately washed with a 3-5% solution by volume of water in n-butyl alcohol to neutralize the excess etchant.
(d)
Wash the part in clean water, remove maskant, follow with acetone wash, and dry with a clean cloth.
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