epoxy/aluminium construction ?

Hi, probably a question for Ian

Do you have any recomendations

or advice on bonding aluminium together with epoxy? i.e. CASA

viewpoint, material and practice acceptable.

Micgrace

As a former RAAF 'Aerostructures' repairer with a bit of

background in bonded structures, be prepared to pay lots of money for

not only the exotic epoxies, but the infrastructure that goes with them;Freezers,Vac bag systems,Autoclaving systems,Cleansuits,Etch chemicals.That's not to say it's impossible, but a purely bonded Primary structure means you have to be real sure that it all sticks together.The main problem with bonding aluminum (or any metal)

is that you need to create some form of textured surface for the

adhesive to hang onto, many think that bonding is like that trick where

you can hold two polished surfaces together with a drop of water.Unfortunately this has no shear load ability, and this is the most typical load requirement in aerostructures.Many of the repairs I do, stem from the use of slightly acidic (or alcalinic) epoxies to help etch at the bond site.This

can work for a while, but eventually heat and flexing movement will

allow moisture to enter the join and combine with acid residues to

attack at the bond surface.In a recent example a Cessna 182 of about the 70's era (that's a later one!!) turned up with bulging at the ribs on the leading edges.The early (50's & 60's)

Cessnas' had rivetted ribs in the leading edges, the later ones are

bonded for a quicker and better finish, but this one had de-bonded most

of the ribs and started to corrode the leading edge skins.Remember, I'm talking here about primary structures, you really need to say where you want to go bonding stuff....There are lots of discussions about this sort of thing on a really good homebuilders site in the US;goto http://www.homebuiltairplanes.com/forums/Arthur.

Thanks Arthur,

I was not going to use the bonding purely on

it's on, or as a substitute, and not on primary structure, and then

only with rivet backup (mainly to eliminate squeaks i.e. for those that know, not the audible kind). This is for a 95.10, so some info on a suitable (uncertified) method is appreciated.

Micgrace

Thanks again.

From the site you mentioned, this appears to be

the holy grail of aviation, a simple expoxy compound that reliably bond

aluminium without the extensive procedures you have used.

Apparently some of the Hysol products are used in homebuilts (namely 956)with useage of fasteners to prevent peel and to add thier own measure of strength.

I might do some experiments to see for myself what could be used.

Micgrace

i have worked with HYSOL products for many years, namly on Boeing

aircraft, the 747 and 767. 956 was used to bond aluminium and

composites together as well as bonding alluminium to other metals., (other

hysol resins boeing approved are Hysol 956, 3130, K230 and 304, there

are otehrs but require temps of approx 3 or 400 deg to cure) the

alloy surface was lightly scuffed with scotchbrite to give the resin a

key surface, then lightly primed with a bonding primer, i cant remember

the name but it was a very pale yellow colour, and applied very thinly,

dipping a rag into the primer, then drying the rag onto a clean rag,

then using the almost dry rag to apply the primer..

heat was applied as well as vacumn, heat can be provided by heat lamps, (similar to automotive panel beaters use)

or heated blankets controlled by a computer or in an autoclave. in the

field as many of our repairs were, vacumn can be provided by a air

operated ventury, or vacumn cleaner, thermocouples placed on the bonded

area and connected to a multimeter to read the temperature, and

manually move the heat lamps as the temperature is reached at the bond

area.

though most Hysol resins will also allow room temperature curing,

though this usually takes a few days at 21 deg C and vacumn can be

maintained for the time of a cure.. vacumn and heat are not essential

but preferred. vacumn can be replaced by clamps and weights depending

on the job being bonded.