(c)
Perform the following fuel or solvent resistance check to verify cure completion. 1) Methyl Ethyl Ketone (MEK) or JP-4 fuel resistance test. a) Saturate a 4-inch square pad of cheesecloth with MEK or JP-4 as
applicable. b) Apply pad to surface to be checked and allow solvent or fuel to flood area. c) Using hard pressure rub the area 100 strokes, counting each movement in
one direction as a stroke. d) Observe whether coating is removed so that metal is exposed (unsatisfactory). If metal is not exposed, cure is satisfactory.
(10) To apply a new fillet seal, do the steps that follows:
(a) BMS 5-26 Type II Class B sealant is used to apply all fillet seals after a precoat of BMS 5-26 Type II Class A-2 sealant.
NOTE: Precoat is not used when you use Pro-Seal 860, B 1/6 sealant. A special primer is used with PR-1826 sealant. Obey the instructions from the manufacturer.
1) To assure selecting correct tools for job to be done, set up a locally fabricated condition to simulate the job. This can usually be done with cardboard or similar material.
(b)
Apply a precoat of properly accelerated Class A-2 sealant to the surface with a stiff bristled brush. Scrub well into crevices and over entire length to be sealed (Fig. 811). Precoat should cover an area 1/2 inch wide on each side of seam. No ridges or voids are allowed.
NOTE: If you let the precoat fully cure, clean with MEK solvennt before you apply the fillet seal. It is not necessary to let the precoat cure unless the precoat and the selant you use for a fillet seal are from different manufacturer product lines. For example, do not use a precoat of BMS 5-26, Type II, Class A-2 with a fillet seal of PR-1826.
(c)
Apply a small fillet of BMS 5-26 Class B sealant, or other approved sealant with an extrusion gun (Fig. 812).
(d)
When a nozzle tip is used it shall point into the seam and shall be maintained nearly perpendicular to the line of travel.
CAUTION: SEALANT MUST BE APPLIED CAREFULLY TO AVOID TRAPPING AIR IN FILLET. OPERATE GUN SO THAT A BEAD OF SEALANT IS CONTINUALLY FORCED AHEAD OF NOZZLE TIP IN THE DIRECTION OF NOZZLE TRAVEL.
502
Feb 01/95 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 28-11-0 Page 815
T52594 T52595 T52596
DeSota (MIL-C-27725) Compound Cure Time 502
28-11-0 as Affected by Temperature and Relative Humidity Nov 15/77
Page 816 Figure 808
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
502 DeSota (MIL-C-27725) Compound Cure Time as Affected
Nov 15/77 by Temperature and Relative Humidity 28-11-0
Figure 809 Page 817
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Products Research (MIL-C-27725) Compound Cure Time 502
28-11-0 as Affected by Temperature and Relative Humidity Nov 15/77
Page 818 Figure 810
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
502 Application of First Fillet
Nov 15/77 Figure 812 28-11-0
Page 819
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(e)
Using a fillet fairing tool press the first fillet firmly into position (Fig. 813). Work the entire beaded section.
NOTE: Fairing tool must be clean. Use no solution or lubricant to make it slide smoothly over sealant. Wipe tool frequently with clean gauze to aid in fairing operation.
(f)
If first fillet has cured but is not clean, then it must be cleaned before application of a second fillet.
(g)
Apply second application of Class B sealant to produce a full bodied fillet (Fig. 814). A larger nozzle will be required than was used for first fillet. If an extruded nozzle head is used, make cuts in nozzle to fit fillet conforming to dimensions in Fig. 815. Use a fairing tool to make sealant conform to full-bodied fillet dimensions if an extruded head nozzle is not used. Remove all air bubbles or re-entrant seal edges. Do not use different sealants for the first fillet and the second fillet.
NOTE: Good sealant application requires patience as well as proper technique. Keep sealing gun nozzle close to prevent air bubbles. If a fillet extrusion head is used, it shall be pressed firmly against the part in such a position that maximum thickness of fillet will be directly over the edge.
(h)
Apply corrosion resistant finish (topcoat) (Ref par. 4.D.(15)) as required.
(11) Repair fastener seals (ref Structural Repair Manual).
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