Bonding aluminium alloy insert with CFRP tube

[carlosgeos]

Hello everyone !

I am in process of repairing a bike frame. The right aluminium dropout is loose. The insert is simply sitting inside the chain stay (see a picture here:

https://imgur.com/a/BSchPnO).

I've seen that some people do what they call "diffusion bonding" where they add a layer of glass tissue in between the two materials. Any opinion on this ? Does it have any advantages over simply applying the epoxy glue without it ?

The bike is a Look KG56 from 1990 and I read that is it made of "60% unidirectional carbon fibre and 40% glass fibre" but I can't be sure.

About the adhesive, which one of these do you think is suitable for the job ?
[ul]
[li]Epibond 420:

https://krayden.com/buy/epibond-420-a-b-50ml-boe00009-ht1821908.html

[/li]
[li]West System Six10:

https://www.westsystem.com/specialty-epoxies/six10-thickened-epoxy-adhesive/

[/li]
[li]3M Scotch Weld 7271:

http://multimedia.3m.com/mws/media/756749O/scotch-weld-7271-epoxy-akryl-lim.pdf

[/li]
[li]JB Weld Original[/li]
[/ul]

Thanks !

 

[blakmax]

Oh dear. You are making all the classic mistakes in adhesive bonding and may even be repeating mistakes that the manufacturer may have made. If you can get the tube and fitting apart, have a look at where the failure occurred. I will bet a good bottle of red wine that the metal has almost no adhesive residue on it. If that is the case, then your problem is not adhesive selection and it has nothing to do with the use or no use of a glass cloth liner (although a glass liner will help with galvanic corrosion, which may be another cause).

The main issue I suspect will be preparation of the metal prior to bonding during the original manufacture. Understand this; adhesive bonding is a CHEMICAL process that relies on chemical bonds formed at the interface between the metal and the adhesive (or primer). Many unknowing manufacturers (and some adhesive salesmen) believe that all that is needed for a good bond is a clean surface. In reality, the surface must be clean, but also must be chemically reactive, so old oxides must be removed. But even that is not enough for long term bond survivability. The most common cause of disbonding is a gradual break-down of the interfacial bonds, and for metals this usually involves hydration of surface oxides. The mechanism is this: the adhesive forms chemical bonds at the time of manufacture. Adhesives absorb moisture from the atmosphere and gradually the oxides on the metal form a hydrated oxide. The classic case is aluminium where the original Al2O3 hydrates to form AL2O3.2H2O. In the process, the original chemical bonds dissociate causing disbonding.

To prevent hydration requires that the clean, chemically active surface is chemically treated to prevent hydration. I suggest that you look at a silane based product such as AC130 or Bogel. (I don't have any commercial interest in these products).

Now if when you dismantle the joint, there is evidence of corrosion, then the recommended treatment will help, and should be coupled with the use of a glass layer as insulation against galvanic corrosion.

Hope this helps.

Regards

Max Davis
Adhesion Associates P/L Australia

 

[carlosgeos]

Indeed, there is no adhesive/residue on the aluminium. It looks as if there wasn't any to begin with !

I'll look into these kind of products for the surface preparation, thanks !