Carbon Fiber

Is the frame still under the original manufacturer's warranty? If so then there might be a basis for a 1-for-1 replacement and the adhesive might be unneccessary. If not then there still might be scope for contacting the manufacturer to receive their advice.

No the bike is already out of warranty.. so replacement would be imposible. It's a generic brand, I'm not sure of the brand. I think its made on taiwan the name is "sjl" i don't know what i means, I try to check on the internet but there were no such manufacturer of brand of its name. Thank you

ok basically what u see is what you get. in the case of epoxy resins the clearer and runnier they are the better, with polyster resins its the opposite to some extent. from memory the best polyester resin that i have used was a very thick and very clear blue, however as with all things the better the product the more it is going to cost. Epoxy is the stroger of the 2 resins however i am unsure as to how well it will go with already fabricated carbon. i know that epoxy does not go well when you lay it up with a fibreglass matt.

as for the repainting of the bike; i am unsure whether you should use a primer i think in this instance if you just sand the bike back a little then you should be fine with applying a gel coat or something similar. however what ever you do DO NOT apply Flowcoat as this is basically a useless substance that is thick horrible to work with and really realy heavy.

Well i hope that helps.

The Stang

Before any action on repair you need to evaluate for signs of corrosion which commonly happens on interface between carbon fibre and aluminium.

While you repair it avoid direct contact of c/fiber with aluminium.

Stang: Thank you for the info advice, I really dont have any idea regarding carbon fiber repair, but your advice elightens me well. As for painting, I am worried that there might be a chemical reaction between the paint I will use and the carbon fiber. I am planning to use acrylic clear coat for automotive or urethane type. Thank you once again.

I repair fiberglass airplane, polyester tends to delaminate so epoxy would be better but better still is vinlyester resin. vinlyester resin is usually about 3 times more bonding power. as far as finishing spray direct with a polyurethane clear such as ppg puts out. sand with 320 or 360 first. Tap plastic in sacramento and sell you the resin or aircraftspruce.com Remember that the uv in sunlight is the enemy of all resin systems.

Do you have a picture of the cracks? Their location and typology may indicate that failure is not far away. Sometimes, strongly repairing a crack can cause more harm than good as it will create lever arms which, in constant cyclical use, can lead to more rapid failure.

A few pictures would help. It may be just cosmetic, in which case bodyfiller might be a simpler solution prior to painting. It is of course impossible to repair the fibre part of the carbon fibre as it is integral in the resin matrix and, as it is associated with a lug, it is in a high stress area by its very nature. So no patching around it will help. May I get shot down in flames by people who know better!

Here is a very useful information on bicycle lugs, especially for carbon fiber with aluminum lugs.

There is a specific comment on repairing cracks for the carbon frame. This is well explained in the second page link below.

Finishing

Any cracks in the assembling areas can be repaired when the frame is glued using the same glue. Take special care during the next sanding step in order to avoid damages to the Carbon elements. After the gluing process, thread and shave the BB Shel.

The glue used is also indicated in the article which is:

Gluing
To prevent deposits of glue in the areas near the assembling points, protect these areas with masking tape. Proceed to glue the parts using a structural adhesive (such as 3M bi-component epoxy Scotch Weld 9323 B/A or VANTICO Araldite 2014).
Spread the adhesive evenly on the surfaces of the composite tube. Repeat the same procedure on the internal surface of the assembling areas.

http://www.bikelugs.com/

http://www.bikelugs.com/PDFs/columbus_mecano.pdf

DO NOT USE Polyester, only Epoxy or better.

Do not sand the carbon fiber, you could reduce the strength, either leave completely alone or just paint, with a proper paint for such surfaces. The problems are probably from inadequate preparation and cleaning of the alu / carbon fiber in the first place, or inadequate design....

Clean everywhere with meths or similar first, then do not touch!! For both glueing & painting.

I'd take it into a good local bike shop and talk to them. They will have experience with that type of repair and might have some kind of kits. I don't have bike experience, but here's a little advice from my various fiberglass/carbon fiber/epoxy/acrylic/aluminum experiences:

Just putting some epoxy on won't help a whole lot - the real strength comes from the combination of the epoxy and fiber. I would recommend wrapping a couple layers of carbon fiber over the tube/lug interface. Look up carbon fiber on www.mcmaster.com and get a small roll (will look like a roll of tape). McMaster will show you what epoxy to use. You can find instructions for fiberglassing many places online. If you have questions, you can send me a message.

For the acrylic coat, I don't believe you'd need a primer, it would mostly be contacting the epoxy that is embedded in the carbon fiber and I doubt there would be an issue with acrylic/carbon. You'll want to go over everything with a fine sandpaper and clean thoroughly before coating, otherwise it will probably flake or peel off down the road.

Out of curiosity, why the clear coat? Seems like that will just add weight to your bike. If you're worried about corrosion, don't be - the carbon/aluminum interface is the only place that might happen and you're already repairing that. If you're worried about looks, I'd buy a new bike :).

I'm not seeing reference as to what type of cracking (the extent/depth) has occurred. As already suggested, in not-so-many-words, the repair approach will be greatly dictated by whether it's superficial surface cracks, or well-through the fibers.

One of the best sources of knowledge I have found for this subject matter is:

http://www.fibreglast.com/

Not only do they carry everything from fiberglass mats and cloths in a variety of weaves/weights, but kevlar, carbon fiber, and specialty materials and fillers as well. Their books (teaching guides) spell out the advantages and disadvantages of one cloth over another (brittleness, abrasion resistance, etc) as well as the differences between polyesters, vinyl esters, and epoxies (which they also sell). Vaccuum molding and bagging gear, and "choppers" also (spray-mat from a gun).

Check them out, and good luck with it ~

There are several precautions required when joining carbon laminates to aluminum. First is to eliminate the galvanic couple due to the materials. If the graphite directly contacts the aluminum, there is a very strong galvanic couple. Any moisture at the joint will cause the aluminum to corrode. The swelling of the resultant aluminum oxide will accelerate the failure. (hint, unless you ride your bike in low earth orbit, there is always moisture present). We typically use a thin fiberglass scrim cloth to separate the carbon from the aluminum. Second is the preparation of the aluminum. Back when I was bonding aliminum to carbon structures, we used a producet called Pasagel to clean and passivate the aluminum on a molecular level. It was basically a phosphoric acid gell that was applied to the aluminum after a fitting was washed with water based detergent, and degreased with MeCl. The passivated surface was only good for bonding for a couple of hours after treatment. At the time I was bonding aerospace components (satellite structures) in a clean room environment. Though there was no moisture in our end use environment, we still used the glass cloth, to protect the joints before the product was put into service. We had to do it right as there was no repair for our products once they were put into service.......

Former Aerospace Composites Process Engineer