I need to bond an aluminum sleeve in a carbon tube.
Is there a specific epoxy that should be used?
How much clearance between the carbon and aluminum would be required for proper bonding?
Do you already know about Galvanic corrosion? It’s really important. You need to have electrical insulation between the carbon and the Aluminium. Seems that the easiest ways are by having a layer of fibreglass, or anodizing the aluminium.
there are a variety of bonding adhesives. The bond gap varies by adhesive. You can check out http://na.henkel-adhesives.com/structural-adhesive-15365.htm
you can add glass beads to an adhesive to ensure proper bond gap.
We had best results with 3M Scotch DP490 when bonding aluminum in CF for wishbones.
I was not aware that Galvanic reactions could occur with carbon. The aluminum sleeve was anodized but very smooth would have preferred some surface texture for better bonding.
Appreciate the information, it’s been very helpful.
It is very bad with aluminum. I have seen pictures of failure in just a couple of years if the aluminum is not protected.
My project involves a mountain bike frame that has an issue with the crank mount (carbon tube), it’s slightly out of spec and standard parts will not work.
One of the fixes done by a local bike shop was bonding 25mm wide aluminum bearing sleeves in the carbon tube with DP490, didn’t work the sleeves
flexed slightly under load and the adhesive failed.
I’ve done a few repairs to damaged carbon bike parts so decided to repair it myself.
I bonded approximately 2.8mm of carbon cloth to the outside of the aluminum sleeve then added some stand-offs to position the aluminum sleeve in the center of the carbon tube. This left about a 1mm void between the sleeve and the carbon tube, I blocked off one end and positioned the tube vertically then injected thin Epoxy resin in 3 stages. The Epoxy resin bonded to carbon shell and the carbon wrapped aluminum sleeve, the question is will the 1mm of Epoxy resin fail under load.
I would imagine 1mm of resin will probably fail as there are a lot of forces acting on that area. I guess you can’t get it out again now? You really need a proper adhesive, not a resin, and a smaller gap (see sammymatiks comment). Are you trying to solve a creaky BB30 bottom bracket issue? If you are, there are specific conversion kits to solve those problems - for example FSA do a kit (search for FSA BB30 Threaded Adapter (B3119)).
I’ve tried a Wheels Manufacturing PF30, then Specialized dealer installed bearing cups that converted it to BB30, they used DP490, cups flexed so bearings moved and the adhesive failed. Tried Wheels Manufacturing BB30 Threaded GXP adapter and FSA BB30 threaded sleeve using Loctite bearing retaining compound, I got crank creak within 5 miles with all attempts. When there’s creak there’s movement and that causes wear on the carbon shell and it will eventually damage the shell.
I can remove the FSA threaded sleeve if the Epoxy fails but it won’t be easy. The frame is junk no matter what the shell is too thin. I have another Specialized BB30 frame and the shell area is twice as thick as this frame and no problems so far.
Manufacturers should have stuck with a threaded aluminum sleeve style shell.
After about 40 miles it started creaking, the bond between the 2.8 mm of carbon cloth and the aluminum sleeve had failed. I was able to remove the sleeve and the 1 mm of epoxy resin, the carbon tube was not damaged.
The reason I used epoxy resin was to be sure there were no voids, didn’t have any experience with fillers but figured they would thicken the resin and might cause voids. During the removal I did not find any voids, it was too soon to know if the resin would have lasted. If the aluminum sleeve had been textured the bond should have been permanent.
I have access to an FSA 46 mm aluminum sleeve that has 3mm thicker walls but since the carbon tube is also 46 mm there is no space for any type of adhesive. The original aluminum sleeve was 42 mm which left space for carbon cloth and adhesive.
A permanent bond between the carbon shell and the aluminum sleeve should make it rigid enough to handle pedaling forces.
How are you prepping the aluminum surface? Sandblasting? Do you fully postcure the adhesive? Photos? How much surface area is being bonded?
Hey! I make carbon bike frames, and we bond in aluminum bottom bracket inserts all the time. I think that your first mistake is using a shell that is wayyy too small- you need to use a 46mm OD shell. (like this one) It should already have a loose interference fit, but once you do your surface prep it may be a slip fit. Speaking of surface preparation, it also sounds like you are having trouble with surface preparation on both the carbon and aluminum. You need to rigorously follow the surface prep guidelines of the adhesive you are using. The adhesive I use is the Henkel Loctite EA E-90FL, it works really well and we have a few frames with 3 year service lives (in Michigan, talk about salt+corrosion here) and no issues with any bonded components.
Good luck!
PS- I meant loose interference fit given that your shell is probably already getting oversized from all the stuff being pushed in/out of it, of course originally a 46mm adapter would be a press fit.
The basic part number for a dipstick tube is 6754. Check eBay occasionally for NOS 6754 to see if one comes up.