Gluing Carbon fiber

[crazyjr]

How can you bond CF sheets? I have been thinking of making a chassis for my T4 and need some structural pieces, especially where the rear bulk and shock tower are attached. I also want to do a battery box, But may settle with stand-offs if necessary. I know the best way is to form the chassis, before bonding the sheets. But i only have some 3mm sheets, Is there a glue or epoxy that will bond sufficiently and be durable?

[pinkpanda3310]

Other people probably know better than me but I've glued cf before. When I asked around I was told this -

You can use regular 2 part epoxy/aroldite. Lightly rub back the cf on both peices to expose the fibres. Mix the aroldite and apply then clamp the peices together. Because it is 2 part epoxy it is a chemical reaction that to some degree relies on heat to go hard. Normally it would produce enough heat from the reaction to help this process. When it is compressed between the cf sheets it is obviously very thin so if you can apply some kind of heat to aid it that would help. The scenario I was advised was to place it in a car in the sun for an hour or so immediately after clamping. I think for most aroldites 40-50 degrees celcius is the sweet spot to aid hardening. 60-70C is I think when glues start to deteriorate.

I got that info from a fella at a cf manufacturing co. I thought it was good info so he got my business. Might be an idea to try the same, ring a cf company.

Good luck

[PBO]

You want a 6mm laminated sheet? That's going to be incredibly stiff

I work with CF & a basic few tips;
-you want an epoxy glue with 60min curing time
-the faster curing time, the more brittle the resin will be
-you should allow the sheets to cure in 20-25 (celcius) ambient temp
-give the faces to be glued a good scratch with say 120p paper
-mix the resin & let it sit for a few minutes before you pour it out
-spread it out evenly with a plastic spatula
-put a little weight on the sheets once glued to ensure the top sheet has even pressure which will encourage the resin into the scratched surface

You need very little resin to make a very strong lamination & too much between the sheets will allow delamination to occur in a crash (for example)

In contrast to the advice panda was given, I wouldn't accelerate the cure with heat...heat is normally used in pre-preg not resin gluing, heat with resin can cause exotherms & you don't want that

[crazyjr]

Originally Posted by PBO

You want a 6mm laminated sheet? That's going to be incredibly stiff

I work with CF & a basic few tips;
-you want an epoxy glue with 60min curing time
-the faster curing time, the more brittle the resin will be
-you should allow the sheets to cure in 20-25 (celcius) ambient temp
-give the faces to be glued a good scratch with say 120p paper
-mix the resin & let it sit for a few minutes before you pour it out
-spread it out evenly with a plastic spatula
-put a little weight on the sheets once glued to ensure the top sheet has even pressure which will encourage the resin into the scratched surface

You need very little resin to make a very strong lamination & too much between the sheets will allow delamination to occur in a crash (for example)

In contrast to the advice panda was given, I wouldn't accelerate the cure with heat...heat is normally used in pre-preg not resin gluing, heat with resin can cause exotherms & you don't want that

I'm not gluing two sheets together, 3mm is plenty of thickness for the 1/10 truck. My plan is to build up the rear and the battery box, to support the shock tower. The stock chassis has a raised place to mount the shock tower, I am trying to mimic the setup. I always wanted an old school cf plate chassis and decided to do this for the T4. My plan also includes using a GT2 front suspension to avoid having to try to bend the front.

thanks for the advice from both of you, it will be used and followed

[PBO]

I'm not familiar with T4 CF chassis although I'm guessing it's the carbon variation rather than the carbon fibre...??

It might also mean you're considering gluing cut pieces 'end on' to the sheet? this isn't the strongest way of completing a join but if you take a few cues from boat guys & drill a series of small holes along the bottom edge for the resin to run through it should provide additional strength

[pinkpanda3310]

Originally Posted by PBO

heat with resin can cause exotherms & you don't want that

What's an exotherm PBO? I just breifly googled it and a heap of stuff came up relating to plants.

[PBO]

From one of our suppliers website


http://www.gurit.com/exothermic-reactions.aspx

An exotherm is an uncontrollable reaction between a solvent-free resin and hardener, which happens when the heat generated by the resin-hardener reaction cannot escape readily.
The trapped heat accelerates the reaction, which in turn generates more heat and further accelerates the reaction until it becomes uncontrollable. This normally happens only in bulk mixes, as mixed resin applied to a job is usually in a thin film (e.g. coating, glue line, laminate layer, filler layer, etc) from which heat readily escapes.
Care should be taken to control excessive exotherms, which can result in overheating of the product and possible thermal decomposition.
There are several factors that can affect the degree of exotherm produced:

• The volume and configuration of the mixed mass as this can determine the degree of exotherm.
• The temperature of the mix, as this can increase the reaction rate.
• Not using the mixed materials quickly enough, particularly if it is a ‘fast’ resin / hardener system (gel time 5- 20 mins).
• The reactivity of the epoxy resin and the curing agent

The process should be carefully reviewed to determine the possibility of an exothermic reaction occurring before commencing operations. The potential for an excessive exothermic condition is related to batch size; and the larger the batch mix the greater the potential, even with relatively low reactivity curing agents.
As the heat of reaction builds up it causes a faster reaction rate, which can result in still greater heat generation and a runaway situation can quickly result.
For every 10ºC rise in temperature the reaction rate doubles. To reduce the risk of exothermic reactions reduce the batch size.

[crazyjr]

Originally Posted by PBO

I'm not familiar with T4 CF chassis although I'm guessing it's the carbon variation rather than the carbon fibre...??
The only available T4 CF chassis is the factory team molded one

It might also mean you're considering gluing cut pieces 'end on' to the sheet? this isn't the strongest way of completing a join but if you take a few cues from boat guys & drill a series of small holes along the bottom edge for the resin to run through it should provide additional strength basically what i am planning to do, I may even go with alumnium standoffs If gluing the CF isn't strong enough

Comments in red in quote

[pinkpanda3310]

Whilst exotherm is a valid point and something I didn't know about, I don't think we need worry about it in rc applications. The link you gave us is for more industrial applications. I can't see a 2-3mm bead of epoxy heating itself to the point of decomposition.

Was interesting to learn about though

[KaztheMinotaur]

The cheap Hobby King epoxy will do that if it too thick.

[PBO]

Originally Posted by pinkpanda3310

Whilst exotherm is a valid point and something I didn't know about, I don't think we need worry about it in rc applications. The link you gave us is for more industrial applications. I can't see a 2-3mm bead of epoxy heating itself to the point of decomposition.

Was interesting to learn about though

Epoxy is epoxy it doesn't discriminate between RC & other applications

The melodramatic Gurit summary aside, what exotherm means is a compromised bond, how much depends on a few factors. If you think cooking your Araldite in your Kingswood at 40-50 celcius is a good idea, then who am I to stand in the way of backyard theories!! I sense that crazyjr probably doesn't want his gluing to come 'unstuck' if he can avoid it though & slower, moderate temps gives better results

[KaztheMinotaur]

Where is a good place to buy CF at?

[pinkpanda3310]

Originally Posted by PBO

Epoxy is epoxy it doesn't discriminate between RC & other applications

The melodramatic Gurit summary aside, what exotherm means is a compromised bond, how much depends on a few factors. If you think cooking your Araldite in your Kingswood at 40-50 celcius is a good idea, then who am I to stand in the way of backyard theories!! I sense that crazyjr probably doesn't want his gluing to come 'unstuck' if he can avoid it though & slower, moderate temps gives better results

I was referring more to the volume/mass of epoxy being used ie- a smaller quantity spread more thinly would dissapate heat better. When I did my stuff the glue might have been 1/10mm thick between the cf sheets?? The excess was wiped so that might have been 1/2mm.

IDK maybe I've been lucky it hasn't caused me any problems

[crazyjr]

Originally Posted by KaztheMinotaur

Where is a good place to buy CF at?

not sure right now, I got mine from graphite-girl on Ebay about three years ago

[PBO]

Originally Posted by pinkpanda3310

I was referring more to the volume/mass of epoxy being used ie- a smaller quantity spread more thinly would dissapate heat better. When I did my stuff the glue might have been 1/10mm thick between the cf sheets?? The excess was wiped so that might have been 1/2mm.

IDK maybe I've been lucky it hasn't caused me any problems

You're right about heat dissapation but generally speaking epoxy resins don't like being heated - it reduces the strength of the resin

The ideal temp window (generally speaking) is between 10 - 35 celcius...this is for ambient, resin & substrate equally

When you go above or below the resin looses strength