Maximum service temp of carbon fiber bicycles

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#1

I made a repair in a specialized bicycle.
The method i used was to wrap the broken area with prepreg material.
I could also use the wet lay up method but i tend to prefer prepreg use when this is possible.
Before i do anything i checked in specialized site and they claim to use prepreg carbon fiber that cures in 150 celsius .

  1. My thinking is if a prepreg is cured at 150 celsius that means it has at least operating temperature of 100 celcius - this is what i need for my prepreg to cure.

  2. What i did is that i put the frame in the oven and started to elevate the temperature from 70 degrees to 75 then to 80 then 85 90 95 100 ,105,110 and stop . Every time i was letting the temp for 20 min and then ''checking - with my own hands - especially the fork section if i could notice any difference in stiffness or the material softening etc.
    The idea is that if i would feel any difference in the stiffness of the fork that i could inspect easily because there is some play between the legs i would undrestand that i have gone to the thermal transition temperature zone of the material and i would stop immediately.

I didnt notice even the slightest change in the abilities of the material so i cooked with prepreg at 100 celcius fo 2 hours.
Athough i am very happy with the result a person that i respect told me that i shouldnt use prepreg for doing repairs on existing bikes because i may cause serious damage due to damage heat can cause to the frame.

I would really like your input and concerns on the method i used

#2

You can repair the frame with prepreg but you must not put bike in a oven!!!
Wrap damaged area with prepreg reinforcement, make a vacuum bag around the damage area and use a silicone rubber composite curing heating-blankets. This is the only right way.
Use a low temp prepreg, 80 Tg, it is enough.

I use this method to repair Lamborghini, Porsche and other carbonfiber parts of supercar.
Other ways can be compromise the frame.

Anymore it is very difficult to see the damage of a bike frame because you can see just the outer part not the inner part

#3

Ok thank you.
But even on the method that you describe there is a downside - the surounding area of the patch will be affected from the heating blanket … so i may have a failure around the fixed spot.
Anyway i understand that your method seems better …even if there is a slight chance of failure you minimize it . So i need a blanket !!! any advise on where to find it???

#4

Yes,
On damaged area put a patch of prepreg/film release/breather, then make a vacuum bag.
Turn on the pump and after vacuum was done put on a blanket (use Google ti buy it close your area - I have bought my blanket in Italy but is quite expensive)

My method is not better, is just right if you want to use prepreg - it needs vacuum and hot curing. To not compromise all frame is a better way use the hot blanket at 80/90 max degree.

You can use hand lay up but you use a tixotropic resin and after ALWAYS a vacuum bag.

Keep in mind about an internal damaged that you can not see.
In this case you work will be put in trash…

#5

Not sure I agree with star ace. I make my frames with tubes that are manufactured first, mitred, glued then joints wrapped with pre preg, vacuum then heated. It’s the way it is done. Stay below the resin tg and all will be fine IMO. Low temp pre preg is always safer.

#6

I concur ^

I’ve never come across a pre-preg that gets cured at 150 degrees and yet has a Tg lower than 80 or even 100 degrees, it just doesn’t make sense.

#7

[QUOTE=star.ace;60570]Yes,
On damaged area put a patch of prepreg/film release/breather, then make a vacuum bag.

/QUOTE]

Ok …my mistake i always use vacuum bag … what i just did was vacuum bag the spot and put the whole frame inside.
But the idea of heat blanket seems nice … do you have any source of were to buy it

#8

I do not want to be a teacher but I worked for many years as technician for Colnago and Pinarello bikes factory so I know quite well frame building process (bonding tubes and monocoque frames)

But this is not the point
Creator writes the he is not sure of the Tg of your carbon frames.

I have suggested to use low temp prepreg to be safe and not compromise the integrity of the part

There are special prepregs for spot repair some with low Tg (80 c) others with high Tg (up to 200 c)

These are studied to be applied on damage prepreg parts

If your Lamborghini is broken you can not put it again in the autoclave :slight_smile:

Anymore is just my personal suggest, of course everybody can do whatever he wants :wink:

See that:
http://www.compositimagazine.it/automotive-cfrp-repair-or-replace/

#9

Thank you star.
I already checked for lower cure prepregs and of course the spot repair with electric heated silicone is better . - if you have it - i dont…but i will search to have one because in the future i maybe try to make a spot repait in a boat or something and then it will not be better -it will be the only way if i want to use prepreg method… and i really want to stick to to prepreg.
The tsg og specialized i knew it … if it is cured at 150 it cant have tsg lower than 120 … but the main reason i am concerned is that i have 3 CERVELO bikes ready for repair and in a very vital spot at - at the base of the bottom bracket. - And i cant find the temp at witch these bikes have been cured or any tsg spec so i go blind …and i dont know what to do… there is also some concern i have with these bikes in general … the structure is the most elastic i have ever confronted and it makes me insecure …
Thank you hanaldo
Thank you progetto

#10

Can you post a picture of the “problem”?

I may help you with right suggestion

Any more 80 c degree is enough

#11

Of COURSE !!
But i have to go back to my workplace !!
I will go back in the 22nd of August.
Wait to see if i can find anything or if cant i will show you the way i worked with the specialized just for criticism i want to know anything that i could have done better.- (because the criticism of people with Knowledge is what makes you better )

#12

Ok here is the tarmac i already did

1 - The damage
2 - I sanded to reveal Cf , then i trimmed a bit the damage and i want your point of view in 2 things :
a) Do you think i should make a small circular hole (around 2 mm ) at the edges of the cut so 2 holes one at the one edge and another one at the other so that i would stop the tension of the break there . ??? I have seen that being done in the repair of metal. - I did not do it but i want your opinions.

b) I applied a filler/repair paste at the crack so that i would make the hole section strong enough to tolerate the vacuum force of the upcoming step - and it seemed to work. - How would you approach it?

3 - wrapped around 3 layers of uni 330gr cf - 0 first , 45 2nd , 45 3rd and i did not cut the 3 layers the same length - the first was around 8 cm the 2nd 11 the 3rd was 14 the idea was that i wanted the transmition from the old part to the the fixed part which would be a lot stronger and stiff - to be as smooth as possible.

4- Oven 2 hours 100 c

5,6,7 - The looks

#13

As for the cervelo the break that it has is a bit like the red line i draw myself - i just downloaded a similar pic and made it myself

#14

Nice work Creator!

#15

Thank you progetto