51-20
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EFFECTIVITY:
C I R R U S
A I R P L A N E M A I N T E N A N C E M A N U A L
M O D E L S R 2 0
15 Dec 2014
(6)
Foam Core Replacement
Foam core must be replaced prior to laminate repair if significant damage to the core exists due
to penetration of the composite sandwich structure.
MGS L418 and L285, and Epon 862-based filler paste may be used for foam core replacement.
When using MGS L418 and L285 based filler paste, no cure is required prior to the lamination
process because the filler paste uses the same base resin as the structural adhesive. Epon 862-
based filler paste should be considered when replacing foam core in complex shaped areas as
the total time required for the necessary cure, surface preparation, and lay-up will be shorter.
(a)
Acquire necessary tools, equipment, and supplies.
(b)
Using rotary tool, utility knife, and putty knife, cut material as required to remove entire
damaged core. Ensure extents of material removal are perpendicular to the toolside sur-
face. Maintain a minimum 1.0 inch (2.5 cm) radius on core removal.
CAUTION:
Do not damage bagside (interior) laminate during core removal.
Note:
It may be necessary to install a backing plate to the reverse side of the inner
laminate to support this process.
(c)
Sand off residual core from the surface of the inner laminate. Be careful not to cause sep-
aration between core and inner laminate during this operation.
(d)
Inspect for separation of the inner laminate from the core. Continue to sand back until all
separated laminate is removed.
(e)
Fabricate core replacement to fit repair area with a maximum gap of 0.10 inch (0.25 cm)
and thickness to match core area to be repaired.
(f)
Prepare bond surface by sanding inner laminate with 80 to 120 grade paper.
(g)
Remove all dust and debris with clean oil free compressed air and a vacuum.
(h)
Solvent clean repair area.
(i)
Mix filler paste.
(j)
Apply filler paste to edges and underside of core and a thin layer to the inner laminate sur-
face.
Note:
On contoured surfaces it will be necessary to apply enough pressure to
maintain contact between core and inner laminate. Small weights may be
used to apply sufficient pressure.
(k)
Insert core into damaged area and lightly clamp core into place.
(l)
Cure repair.
Description
P/N or Spec.
Supplier
Purpose
Utility Knife
-
Any Source
Core removal.
Putty Knife
-
Any Source
Core removal.
Rotary Tool
-
Any Source
Core removal.
Aluminum Oxide Paper
80 to 120 grade Any Source
Abrasion.
Sandwich Core Material
(Refer to 51-30) (Refer to 51-30)
Core replacement.
Wooden or Plastic Spatula
-
Any Source
Apply filler paste.
Filler Paste
Core replacement.