epoxy/aluminium construction ?

[Guest micgrace]

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

 

 

[pylon500]

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.

 

 

[Guest micgrace]

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

 

 

[Guest 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

 

 

[Ultralights]

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.