Guest micgrace Posted May 27, 2006 Posted May 27, 2006 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 Posted May 27, 2006 Posted May 27, 2006 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 Posted May 27, 2006 Posted May 27, 2006 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 Posted May 27, 2006 Posted May 27, 2006 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 Posted May 27, 2006 Posted May 27, 2006 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.
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