I am making my 1st mold. I will be making it out of carbon fiber and resin, using a preexisting part as a template.
The mold will be used in an autoclave.
Can someone recommend a specific carbon fiber fabric and specific resin that will not shrink, melt, or deform when used to mold items in an autoclave?
Thank you.
Any resin that’s high temp would be fine. I take it you’ll be doing a wet layup? You can find resins through various vendors online. I prefer to use PTM&W and BJB resins.
I’ve used BJB 1607 http://www.bjbenterprises.com/epoxy/laminating-resin/tc-1607-a-b-1/
It’s got good wet out and has service temp of 350 and is 95D hardness. We did room temp cure then you need a post cure. We’d also make slurry for filling any sharp corners and for an over coat after the surface coat. Only bad thing is it’s a bit harsh and tends to give me a rash. We were making big parts and doing messy wetlay ups.
As for cloth. Depending on what your’e making. You can use chop strand matte or use 10z glass. It’s also nice to have woven roving for quick thick buildups and a strong mold. Also if it’s a bigger part or awkward shape, it’s nice to put some sort of egg crate structure behind the glass for support and rigidity. You can some compressed board or even cardboard or metal if it’s a large part.
This is good information. I guess I need to study the range of materials.
I’d like to make a vocabulary list of terms I should understand.
You mention hardness, service temp, slurry, chop strand matte…
I think I will try to assemble a complete list of terms that anyone getting started (and seasoned pros) could have as a reference. Here are a few I see on this thread and a couple others I can think of.
Resin (Service Temp, post cure, hardness)
Carbon Fiber (pre-preg, uni, woven, modulus)
Fiber Glass (10z is a measurement of what?
Slurry
Chop Strand Matte
Feel free to add terms and definitions or other good information on each term if you’d like, I will try to do a complete write up of everything I have documented in MS Word so far when I have some spare time.
Many terms and concepts to understand… just gotta keep using them and
repeating them and they become innate.
THere’s a few books that might be worth reading. I have handouts some where with a glossry of terms from my classes, I’ll try to find it and save you the trouble of having to figure all the terms out.
As for the previous posts question:
carbon fiber: much much on this topic… too much for a quick overview in this post.
Fiber Glass (10z is a measurement of what? - a measurement of ounces per square yard usually, can also be in grams per square meter, or other measurements.
Slurry - I mean a mix of resin and some filler. Fillers vary widely and have different properties. some examples: microbaloons, fumed silica (cabosil), talc, milled fibers, cotton flox, etc.
Chop Strand Matt - or CSM is a non woven reinforcement, glass/carbon, made from chopped fibers that are held together with a binder. You can also get CSM that is stitched (aka stiched matt) for infusion. It’s weaker and cheaper than wovens, bulks up quickly, helps to avoid print through if uses as first ply, and tends to soak resin.
what temperature you curing at? What will your part made from, carbon, fiberglass, kevlar, other?
How hot can I go before I need Nitrogen?
I think it’s how much pressure can I go, not heat. When you pressurize air, the o2 levels get too high and the mixture becomes self combustible… something along those line. I’m not sue but I think it’s something lik 25psi… Anyone else know the exact pressure max on air?
I’m assuming you’re talking about autoclave?
Well if N2 isn’t necessary for oven cures then that’s good to know.
Nitrogen is for autoclave.
Oven cure is just vacuum or else some other pressure intensifier.
yah would suck to have to use N2 for ovens…
I saw an oven that has N2 system.
interesting. What did it use N2 for?
Ahh, it looks like it was for some purpose other than curing composites. Something to do with coatings.
I was confused because I was searching for composite curing ovens and ended up looking at some ovens designed for curing some other things.
I see, must be to prevent oxidation of the paint… so many different kinds of ovens.
I’m not an expert in the slightest when it comes to composites but I am one in compressed air. Air that has been pressurize does have more O2 per cubic Whatever but it also still has it’s N2 so the proportions are still no different than normal air. For example you can take air to 3500 psi and it will not explode if lit. (And I have tried that)
interesting. Well I’m not sure the exact physics of it, since I"m no compressed air expert, but I know that autoclaves that go to higher pressure always use N2. Not sure what the exact reasoning is. Maybe the o2 is more reactive at high pressure/temp and degrades the metals?
Either way, any autoclave I’ve seen/worked with uses N2 for higher pressures.
Maybe some one knows the full explanation behind it?
I kind of suspect that it isn’t the air that one might worry about igniting, but the resin or it’s fumes. Having any kind of ignition inside a pressurized metal vessel doesn’t sound like an optimal situation. The pressure might also lower the ignition temperature for the resin’s fumes, I am not sure.
Based on discussions I’ve have with mechanical engineering professors the go to reason I’ve been told has to do with safety. Compressed oxygen becomes much more ignitable. Adding heat to an already exothermic reaction with combustible materials just makes everything more dangerous.
Additionally nearly all pressure vessels include rupture disks or other pressure fail safes, meant to fail in the event of an overpressure, but it’s my understanding that overpressure due to a fire is extremely hard to control as the pressure buildup is faster than the relief.
I was told by a couple autoclave manufacturers that you can go to 250F safely with compressed air, but you intend to cure higher, like 350F+ than you should use nitrogen otherwise theres a big risk of fire
It’s actually because nitrogen is more stable with temperate. That’s why they fill tires with it in cars. It will not change temp or pressure like air will.
and the nitrogen doesn’t migrate through the rubber as much, hence you have more constant pressure. It’s more of a race car thing.