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Posted for "John Barrett" <2thman@olympus.net>:
Ted makes some excellent points here. We recommend riveting or screwing our
hinges at each end where the loads are high (landing gear doors, cowl attach
etc) to avoid the peel risk he speaks of. We also advise using a high peel
strength adhesive - Hysol 9339 is the material many of us know about
because it came with our Lancair kits. However there are many more choices
and brands that result in a peel strength of 50 lbs per sq inch. or greater
(our recommended minimum for Carbinge.)
Keep in mind that an adhesive bond with aluminum is NOT as secure as a bond
with composite materials like our hinge. This could be the result of direct
differences in bond strength between the materials or it could result from
differences in coefficient of expansion. (Aluminum changes shape with
temperature change at a greater rate than composite - so the joint will work
back and forth microscopically as temperature changes.)
Also remember that you WILL have oxidation and corosion in the aluminum
hinge between the pin and the loops of the hinge. This will result in play
developing over time and in black streaks around the hinge as the oxidized
aluminum powder washes out of the hinge. Carbinge uses a nylon bearing that
has been shown to resist wear of this type (Carbinge doesn't develop slop
over time) and does not corrode at all.
If you do use aluminum, an etch just prior to bonding will definitely
improve bond strength. It's purpose is identical to sanding the surface of
composites just prior to bonding. In both cases it provides greater surface
area and it also "activates" suface molecules for a few minutes allowing a
modest chemical bond that adds to the mechanical bond. A good way to do
this for aluminum is with a micro etcher - It's an air abrasion system that
uses aluminum oxide particles that are very small (I can't recall the
diameter but .005" or 5 microns comes to mind). I don't know if chemical
etching is as effective as sandblasting. Ted, does your reference material
compare the two?
Best regards,
John Barrett, CEO
www.carbinge.com
rivet at each end to reduce the chance of peel failure
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