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1) Apply cleaner and allow to soak for a minimum of 10 minutes. Reapply cleaner as necessary to prevent drying of the solution on the skins. After the soak period scrub vigorously with soft bristled brushes. Special attention shall be directed to scrubbing the countersink areas and around rivet heads. Rinse thoroughly with water. Use high-pressure rinse if possible. Check for water breaks. If water breaks are observed repeat cleaning cycle.
NOTE: A water break free surface is defined as a surface which when wetted with rinse water (100°F maximum) either by immersion or spraying, will maintain a continuous film of water for a minimum of 30 seconds. Sharp breaks in the water film or evidence of residue registers failure of the test and an unclean surface.
C. Brush Alodine Treatment
(1) Alodine 1200 or 1200S (interchangeable) treatment shall be applied to all reworked steel fastener heads and the surrounding bare aluminum skin surfaces. Refer to 51-21-31, Alodizing.
D. Fastener Sealant Application
(1)
General
(a) Sealant shall be used to build up reworked areas flush with aluminum skin and under heads of newly installed fasteners. An extremely clean alodized surface is required for adhesion.
(2)
Equipment and Materials
(a)
Solvent - Final Cleaning Prior to General Sealing (Series 92) (Ref AMM/SOPM 20-30-92)
(b)
Clean cloths
(c)
(Deleted)
(d)
Sealant - PR 1422 Class A, Parts A and B
(e)
Sealant - PR 1422 Class B, Parts A and B
(f)
Sealant - PR 1432, Parts A and B
(g)
Extrusion gun or spatula
(h)
Fairing tool, plastic scraper or duckbill nozzle
(i)
Knife made from 2024 sheet with a beveled cutting edge
(j)
Pressure spray equipment - Standard type
(k)
Thinner - Toluene, TT-T-266a
(l)
Fine sandpaper
(m)
Aluminum oxide grit cloth
(n)
Gum rubber buffing wheel
(3)
Apply Fastener Sealant
(a)
Cleaning for sealant adhesion 1) Fasteners a) Remove lubricant from new fasteners prior to installation with solvent, Series 92 (Ref AMM/SOPM 20-30-92) 2) Countersinks and other reworked areas
a) Remove lubricant and other soil from countersinks and other reworked areas by wiping lightly with clean cloths dampened with solvent, Series 92 (Ref AMM/SOPM 20-30-92). Wipe surfaces dry with clean cloths before fastener and sealant installation.
(b)
Sealant application 1) Mixing a) Thoroughly mix the sealants per the manufacturer's instructions. The
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mixing ratios by weight are as follows: PR 1422 Class A - 1 part A (accelerator) to 10 parts B (base) PR 1422 Class B - 1 part A (accelerator) to 7-1/2 parts B (base) PR 1432 - 1 part A (accelerator) to 15 parts B (base)
NOTE: The PR 1422 Class A and Class B can be obtained with a working life of either 1/2 or 2 hours. The PR 1432 has a working life of 1 hour. Mix only the quantity which can be used within the application time of the sealant.
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2) Fastener application a) Apply a small bead of mixed PR 1422, Class B sealant to either the countersink area or underhead side of head of fastener and install the fastener immediately. Remove excess sealant with cloths dampened with solvent, Series 92 (Ref AMM/SOPM 20-30-92).
3) Application to reworked areas a) Apply a brushcoat of mixed PR 1422, Class A sealant to the reworked area. Brush well into the crevice around the fasteners. A continuous coat is required on the reworked surface. b) Apply a mixed PR 1422, Class B sealant over Class A sealant with an extrusion gun or spatula. Fair out the sealant with a fairing tool, plastic scraper or duckbill nozzle so that the surface of the sealant is slightly below the surface of the adjacent wing skin. Use a spatula or fairing tool to work out air bubbles in the sealant.
NOTE: If difficulty is experienced in spreading and fairing out the B type sealant, the following alternate method may be used. Apply the PR 1422, Class B sealant thickly and well above the contour of the wing surface, allow to cure, then pare it off to wing surface with a knife made from 2024 sheet with a beveled cutting edge.
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