Vacuum Bagging (not like hoovers) Carbon construction questions.

[llittrup]

I am building my next frame out of carbon (Gasp!) and have a fully functional vacuum bagging setup built from a fridge compressor and the vacuum advance from a 77 chevy pickup. Pretty high tech right? Anyway I have been getting wrinkles in my practice pieces and would like to not have them.

My process goes like this:

Cut carbon out (5.7oz 2x2 twill for most practice pieces) Mix epoxy with pumps. Wet out on plastic with squeegee. Debulk with top layer of plastic and squeegee the beeejezuss out of the carbon. Remove top layer of plastic. Wrap wetted out cloth onto prepared mandrel (waxed seatpost) trying to maintain tension in cloth while wrapping 4ish times around- and here is where I think there may be an issue, the fabric still 'dents' easily if I press into it with a thumb, maybe a problem? Next wrap with peel ply (econo ply-e from fiberglass supply). The least wrinkly tube I made so far I did a spiral wrap with the peel ply which seemed to help some. Over the peel ply goes the breather. I have been just wrapping the breather material loosely around the mandrel and carbon. I place the prepared part into my vacuum bag (stretchlon 800) flip the switch and pull vacuum.

It seems like every time the vacuum bag material is 'pinching' some of the breather where the two sides of the bag join and this is causing the carbon below to form a ridge or wrinkle. Not just for round pieces but also with the foam core piece that I have tried.

Some questions: Is there something I can practice as far as the bagging goes that will NOT require me to do a carbon layup? e.g. place all dummy head tube/top tube joint in the bag with peel ply and breather on it just to see if I can get it to somehow not pinch the breather? How can I tell if it is going to work or not work?
Help is greatly appreciated,
LL

[Mark Kelly]

You have two problems, one easily soluble, one not.

The easy one is the bags. It's not hard to smooth the wrinkles out as the vacuum pump pulls the pressure down. If find it's best to orient the work with the most critical parts facing the top and bottom, place a sheet of breather cloth below and another above the work then pull the whole lot flat while the vacuum is pumping down. I also make sure I use more release ply than i ever think I'd need and make sure it's tight and smooth over the surface.

The second problem is layup. Any composite with any degree of hoop stiffness must be arranged so there is no radial movement allowed at all. When you think about it this makes sense: what you are building is designed to resist radial stress. If the uncured composite is forced to move, the fibre orientation that resists axial stress will try to do its thing. If you force it to move, the fibres will deform and your design will be compromised.

The easiest cure for this is to do them as single layers and use prepreg or filament winding to maximise fibre volume. I'm in the process of building a filament winder for myself.

[datas_brother]

As Mark said, the easiest way is to do single layers if you really want to vacuum bag. Don't pull a full vacuum at first. Start with just enough for the top and bottom to pull together. That way you can manipulate the bagging materials. Remember, you're reducing the outside diameter through compaction so the thicker you're stack, the more excess you will have.

If you're going over a round mandrel you can also avoid wrinkles by using shrink-wrap tape instead.

If you want to practice with lower cost materials use glass and polyester.

BTW: a fridge compressor isn't the worst setup:

[back40]

I went the pre-preg route right from the start. I found that release coated shrink tape works well when used over tightly wound carbon around a mandrel. I used UHMW for BB and HT layups a while back which made it really easy to slide out afterwards. The tape leaves a spiral line on the surface but it can be sanded out without too much trouble.

back40 bicycleworks: Head Tube Cure and Finish

This is where I got the release coated shrink tape.

Hi-Shrink Tape | ShrinkTape.com

Glen
back40 bicycleworks

[progetto]

I have also switched use to pre preg. I have aluminium mandrels, whack in the freezer after cure and they pull off easy. Have used wet lay in the past, it is a lot harder to make wrinkle free tubes. A couple on tips.
Minimum resin content, once first layer is down, apply next relatively dry and work excess through the fabric.
One layer at a time.
Once layup is done, let it sit until it nears gel, but not to long, use shrink tape ( if relatively round mandrel), use a heat gun to shrink tape, let gel then finish off heat cycle in oven. This process will slightly expand the mandrel making removal much easier. If working to a tolerance you will need to take this into consideration.
You also may want to think about braided sleeve from soller composites which might help the process.

Wet layup can be messy dirty shit but has been around for a long time, you can still make some nice pieces when you get your technique down.
Might also be worth looking at infusion, not sure how it would work on a tube. Pre preg is sooo much easier than anything I've tried. Clean and fun.

I'm hoping Nick will chime in and talk to us about bladder molding. that's where the unlimited possibility open up.


Bill

[Mtblucas]

I am very interested in the carbon fiber techniques, but am pretty fuzzy on all of it. Are you trying to make carbon lugs? I'm thinking a mandrel is just a short piece of tubing that you are using to form the inner contours of carbon lugs. Am I correct? Are you using a regular kitchen oven or do you have an oven in the garage to heat the resin? I am really hoping, yet doubtful, that a kitchen oven will be safe to use without the fear of toxic fumes. I ask because I am working out of a single car garage with way too many bikes in it to have room for an oven.

[llittrup]

The easiest cure for this is to do them as single layers....

As In: layup a layer, cure, add layer, cure etc? That does make sense, less unstable stuff to crunch up and make ridges.

[

I have also switched use to pre preg. I have aluminium mandrels, whack in the freezer after cure and they pull off easy.

YES! This is the difference between whistling a merry tune and cursing up a storm.

I am very interested in the carbon fiber techniques, but am pretty fuzzy on all of it. Are you trying to make carbon lugs? I'm thinking a mandrel is just a short piece of tubing that you are using to form the inner contours of carbon lugs. Am I correct? Are you using a regular kitchen oven or do you have an oven in the garage to heat the resin? I am really hoping, yet doubtful, that a kitchen oven will be safe to use without the fear of toxic fumes. I ask because I am working out of a single car garage with way too many bikes in it to have room for an oven.

For my project I am using a room temp resin system because like you I have no place to put an oven at the moment. The people who have replied to my post and probably most others who are making more that a single frame will probably be using prepreg and heat. I am making a frame by laminating carbon fiber over a foam core that is the frame 'tubes' however I still need 3 round tubes: Seat, Head and BB. Thus the round mandrels (in my case, a seatpost, some 4130 and an as yet un-turned down piece of round stock). No lugs, but I am certain that you could make some. For sure look at the Back 40 blog as well as the carbon building thread in the 'best of frameforum' Solid Gold for tube to tube. (Which is the way my project seems to be headed via the hard way).

Thanks to all for your replies, I really appreciate the help and hope to try out some of these great tips this weekend. Leif.

[Mark Kelly]

As In: layup a layer, cure, add layer, cure etc? That does make sense, less unstable stuff to crunch up and make ridges.

Yep. Slow but since I alternate layers of carbon and wood it's no problem for me.

BTW I'm currently using mandrels made from UHMWPE. Cte is very high so they're easy to remove but you need to externally brace them to keep them straight if you go for 120 degree cure.

I built my own oven using a small industrial PID contoller and scavenged heater elements. Can't fit a whole frame in a domestic oven anyway.

[Mtblucas]

For my project I am using a room temp resin system because like you I have no place to put an oven at the moment. The people who have replied to my post and probably most others who are making more that a single frame will probably be using prepreg and heat. I am making a frame by laminating carbon fiber over a foam core that is the frame 'tubes' however I still need 3 round tubes: Seat, Head and BB. Thus the round mandrels (in my case, a seatpost, some 4130 and an as yet un-turned down piece of round stock). No lugs, but I am certain that you could make some. For sure look at the Back 40 blog as well as the carbon building thread in the 'best of frameforum' Solid Gold for tube to tube. (Which is the way my project seems to be headed via the hard way).

Very cool. I didn't know that you could use the resin that cures at room temp. I'm glad to know you can though. Perhaps I will pick up some carbon supplies and experiment a bit!

[crumpton]

I didn't know that you could use the resin that cures at room temp. I'm glad to know you can though.

dont want to be an ass but is this a joke?

[Mike Mcdermid]

i didnt know they did resin in cans

[llittrup]

This weekend I didn't get as much time to play with composites as I was hoping (My water heater decided it needed to be replaced) but I did tape wrap a layup that came out fairly nice looking. I used a two layers of 11.something oz. 12k unidirectional weave with these weird little plastic 'strings' sandwiching a layer of 5.7oz 2x2 twill. I destructively tested it and it is WEAK. I certainly expected it to be low on hoop strength, and it is. When pieces are stressed in the length wise direction they are still very weak. The tows don't snap clean though, they fold over and look/feel all dry in the middle. It seems like I was unable to completely wet out the large bundles of fiber in this thick fabric. Not going to be using this in my frame. Unless I can figure out how to thoroughly saturate the fibers. Haven't had any issues with the lighter weight twill, I'll probably stick with that.

I also have been experimenting with widening some hub shells. This is one that has a carbon round tube bonded to the alloy hub and several layers of twill on the bias wrapped over everything. This is the 4th prototype that also got subjected to destructive testing... of a chain whip. With the disc mount clamped into a vice and a Surly singe speed cog on the cassette body the irresistible force was applied and the weak link was in fact a link in the chain whip. Seems strong enough to ride.

I am hoping for a bit of help in the peel ply department. The fabric I have is a very tightly woven white fabric (econoply-e from fiberglass supply specifically) and it doesn't seem to easily get 'tight' onto my layups or conform particularly well to curves. How closely does it need to fit to the contours of the layup? Is there a tape that will stick to the peel ply even when wet resin starts to soak into it? I haven't taken any pictures yet because it seems like without an assistant, touching my camera once the resin is all over is a recipe for disaster. Leif.

[Mike Mcdermid]

This weekend I didn't get as much time to play with composites as I was hoping (My water heater decided it needed to be replaced) but I did tape wrap a layup that came out fairly nice looking. I used a two layers of 11.something oz. 12k unidirectional weave with these weird little plastic 'strings' sandwiching a layer of 5.7oz 2x2 twill. I destructively tested it and it is WEAK. I certainly expected it to be low on hoop strength, and it is. When pieces are stressed in the length wise direction they are still very weak. The tows don't snap clean though, they fold over and look/feel all dry in the middle. It seems like I was unable to completely wet out the large bundles of fiber in this thick fabric. Not going to be using this in my frame. Unless I can figure out how to thoroughly saturate the fibers. Haven't had any issues with the lighter weight twill, I'll probably stick with that.

I also have been experimenting with widening some hub shells. This is one that has a carbon round tube bonded to the alloy hub and several layers of twill on the bias wrapped over everything. This is the 4th prototype that also got subjected to destructive testing... of a chain whip. With the disc mount clamped into a vice and a Surly singe speed cog on the cassette body the irresistible force was applied and the weak link was in fact a link in the chain whip. Seems strong enough to ride.

I am hoping for a bit of help in the peel ply department. The fabric I have is a very tightly woven white fabric (econoply-e from fiberglass supply specifically) and it doesn't seem to easily get 'tight' onto my layups or conform particularly well to curves. How closely does it need to fit to the contours of the layup? Is there a tape that will stick to the peel ply even when wet resin starts to soak into it? I haven't taken any pictures yet because it seems like without an assistant, touching my camera once the resin is all over is a recipe for disaster. Leif.

you might want to look at shrink tape and scale down the weave on the fabric to below 6k your going to need more than 14.7psi to wet that out

fyi the little white strands are fibreglass threads that stop the fabric (well they also assist in supporting the fabric as it woven) falling to pieces when heavier (12k) non spread tows are used fyi 2 Peelply is mainly used to apply a rough surface for bonding together its secondary purpose can be to provide an air leak/bridge path (well at least till it becomes resin saturated) in a cacuum bag, it does have other uses but im a bit lost as to what you are using the peel ply for?

[llittrup]

, ... im a bit lost as to what you are using the peel ply for?

Yeah, sorry, I definitely did a poor job of making that clear. The peel ply has nothing to do with the parts I posted pictures of. More for stuff like this: (Yes, I do love breaking things... all for the sake of learning.)

I will be getting some shrink tape, It seems like the way to go for round pieces. Much of the frame isn't going to be round and I am hoping that improving my peel ply application will help me reduce/eliminate wrinkles. Leif.

[Mark Kelly]

Those wrinkles are an example of the hoop problem I wrote about above, that's why they are axially oriented.

You must get rid of them.

Also, think carefully about fibre orientation. 45 / 45 gives best torsional stiffness and strength at the cost of axial and beam stiffness and strength. 0 degrees gives the same result the other way around.

Think about the stress flow in different parts of the frame and make sure your fibre orientation matches. A 10 degree mismatch can cost you more than half the anticipated material properties.

[llittrup]

Those wrinkles are an example of the hoop problem I wrote about above, that's why they are axially oriented.

You must get rid of them.

Also, think carefully about fibre orientation. 45 / 45 gives best torsional stiffness and strength at the cost of axial and beam stiffness and strength. 0 degrees gives the same result the other way around.

Think about the stress flow in different parts of the frame and make sure your fibre orientation matches. A 10 degree mismatch can cost you more than half the anticipated material properties.

I have been thinking a lot about how to orient the layers to make a frame that is stiff and strong. It seems like layup schedules are one of those things that people are keeping pretty close to the chest, or am I just not seeing any? Some of the home-builds I have seen documented look ridiculously underbuilt. I have no desire to push the envelope of light frames; it is to be a fatbike and my riding style is not... um, gentle, but I don't want to outweigh Surlys either.
I have been kicking around the idea of measuring the amount of force it takes to break a production frame and use this data as a baseline for mine. I do have access to 4 aluminum warranty frames (mtb) from a certain big name manufacturer in wisconson and best of all 2 of them are identical and never been ridden (one out of spec bb and another damaged in shipping). As you mentioned the tricky bit is really getting the orientation of the strands correct to be strong in all the required directions. Just because it resists a large torsional force does not mean that it will survive a hard hit head on. I am certainly open to suggestions and wisdom in this department especially. Like so many aspects of this project it is totally different from working with steel.
The Piece in the picture above is just a single layer on the bias, I certainly didn't expect it to be strong, just wanted to see how it draped and I do plan on using a number of plies in this orientation. Seemed like with all the wrinkles on it there was no point in adding more material. Just another learning experience. Leif.