High temp epoxy

General Composites Discussions Products Talk
#1

I’ve had a number of requests to repair cf bike rims. I’ve turned them away simply because I can’t find an epoxy that can handle my requirements. During breaking, parts of the rim can easily reach 250°C. Unfortunately they can’t be tempered once they are made because there is always secondary bonding somewhere (spokes glued to rim or hub). During manufacture, this is done after tempering the rim and if you were to re-heat the whole wheel up to 250°C those bonds would come loose. My question:

does anyone know of an epoxy suitable for wet layup that hardens under 80°C but has a Tg > 260°C?

#2

That’s some high temperature,I dont think any wet lay up Epoxy could handle that,even pre preg that the military use is about 180c,is this for pedal bike.

#3

There will be no epoxy that will reach 250° without tempering below 250°. The maximum you can reach at RT is about 100°.

#4

Yes. If you are screaming down a mountain pass at 80 km/h your rims will get that hot during breaking unless you are close to pro level and know how to break at the last second.

Thanks DD for the feedback. I know there are some that offer this service so either they have a secret formula or ignore the risks, which I won’t do.

#5

Go disc brakes!!! leave the heat off the rim :slight_smile:
air brakes?

#6

Riff42, I agree but the UCI and the weight weenies don’t :mad:

#7

That temperature is outside the range of all epoxies ( also for the most advanced formulation…) , then you will never solve your problem until you stay in the field of this type of resins. There exist alternatives but, in my opinion, they are unlikely applicable in your products. I refer to another class of resins , namely phenolic and bismaleimide matrix resins; their cost is prohibitive and the process is very difficult. Thermoplastic resins are another only viable solution, but here things change completely…

If money is not a big problem :smiley: , you could try to make a surface treatment on the rim where brakes work, with the aid of special coatings; this solution is widely used in aerospace and racecar sectors, where is necessary to shield carbon fiber laminate from high temperature sources.

Sure UCI doesn’t permit the use of disk brakes ?

#8

Ciao Wings,

Thanks for the input. When I posted the question, I suspected the answer would be no but I still wanted to try.

What type of coating are you referring to? The only thing I’m aware of is special hardened surface coat that reduces wear. It doesn’t change to heat characteristics, though.

Paragraph 1.3.025 of UCI Technical Regulations for Bicycles specifically allows them only on cyclo-cross bikes. Road bikes must use traditional caliper brakes. Even if they were allowed, nobody would use them since they weigh 3 times as much.

#9

Look at www.zircotec.com

Hope this helps

#10

I am currently thinking of building some carbon fiber clincher rims from some high temperature prepregs that I found. However I can’t figure out a way to mold in the clincher hooks. As I see that you were considering repair wheels were there would have been damage to the clincher hooks. How would you have molded in new hooks?

#11

you will need a relatively complicated mold. 14 pieces total. I did a quick and dirty sketch of what it would look like. Each 1/4 section of the rim would need an internal 3 piece mold (parts 3, 4 and 5 i.e. 12 pieces). The external mold halves are parts 1 and 2 and would be a single piece for each side.

The profile of the rim would be achieved through an internal bladder but the braking surface and clincher flank will be dictated by using the correct amount of carbon for the needed thickness. Pressing parts 1 and 2 together will provide compaction against the internal mold part where the bladder does not go so you need to be very accurate with your thickness calculations.

The mold will need to be made of Al. or steel to get the needed precision.

#12

Now seeing how complicated molding the clinched hooks will be I think I’ll be going with a tubular rim which will also allow me mold spoke holes much easier.

Also if you are still looking for high temperature epoxies, huntsman has a Tris-(hydroxil phenyl) methane-based epoxie with a tg> 300 C that has a retalvity normal cure cycle. Hexcel also has some prepregs with tg around 250C

#13

Here is a company making bike rims! Maybe helps!
http://www.de-tris.com/#!

#14

good for an Ad, but where is the process description?