DIY Prepreg

After watching and reading about making your own prepreg carbon from Woodward Aerospace, I decided that it looks like an easy enough process. The only question I couldn't find an answer to was what are some recommended resin systems for this purpose.

I emailed Woodward for clarification on their preferred epoxy, but got no reply. So, what are some places to find epoxy that is suitable for making your own pregpregs, specifically for out of autoclave?

 

What are the advantages of pre preg vs wet preg vs infusion? It seems to me that for a quality pre preg you would need an impregnator, in which case you may as well impregnate as you need it (wet preg) in which case just about any epoxy will do. The only advantage I see for pre preg is if you want to store it for some reason. Personally i think infusion achieves a similar end result with a lower up front cost. jmho. I don't know where you can find a suitable resin system for pre preg, perhaps contact proset, they are very helpful and if they don't have a suitable product they can probably lead you in the right direction.

Steve.

 

No special equipment required, you have better control over resin to fiber ratio and more time to perfect the layup and vacuum bag, also less mess and waste compared to infusion and wet layup.
Plus, if you want to take full advantage of epoxy strength, you want a post-cure anyway.

 

Your question implies you dont really understand what is happening here.

If your looking for something to use "out of autoclave" then you can use ANY wet laminating resin... yes, ANYTHING.

But if you do so, this is a completely pointless process because you dont have the time to setup everything you would if doing an autoclave bagging process. With high temp cure resins suitable for autoclave, you can take your time setting up the layup and only once it goes in the oven, will it begin to cure. This is what they are doing in the video. The completed pre-preg can be stored in the freezer for a long time before using it.

The closest thing you would be able to manage without a high temp cure resin, would be to use a very long open time epoxy. You can buy epoxy with pot life of several hours or more. Consult the data sheets of the epoxy systems on the market to find a suitable resin. This may give you enough time to make the pre-preg, setup your laminate, and then vacuum bag it before the resin starts to gel. Of course it depends on the complexity of the layup and part geometry if you have enough time to do it.

At the end of the day, wetting it out on a piece of plastic is no different to wetting it out on the part your making. Thus this process is pointless unless your using an oven and other normal pre-preg practices.

I wetout every peice of fibreglass tape - used to joins sandwich panels together - on a peice of plastic before rolling them out on the job. This is pre-preg without an autoclave too, but its no different to wetting it out on the job, i just find it easier and less mess to do it this way...

 

I am looking for high temp cure epoxy resin suitable for vacuum bagging in an oven. Out-of-autoclave simply means I would not be using a pressurized oven.

Here is a link to a product that is probably what I am looking for http://www.ambercomposites.com/tencate-e525-sp-and-e525 But I was just making this thread to see if there was a go to resin system for this type of construction(like the West Systems of the prepreg world).

 

This is not really pre preg, just wet lam on plastic with a resin appropriate for long term storage and oven cure. This is only one of the goals of pre preg, the other, perhaps more important goal of true pre preg is control of your fiber fraction, i think typically in the region of 65-70% fiber, this can not be achieved by spreading your resin around with a squeegee. Now if this is going to be used in an autoclave you have the opportunity to squeeze some of the excess resin out into your bleeder, just the same as vacuum bagging at atmospheric pressure except you have more pressure available. This is different to how pre preg works, with pre preg your fabric is impregnated with the correct amount of resin through the use of an impregnating machine before being stored in the freezer, so when it is bagged and autoclaved the plies are simply compacted together under heat and pressure, you are not squeezing out excess resin, there isn't any. What you end up with is a very predictable laminate unattainable by any other method. A closer method to pre preg than the method shown in the video is wet preg where you wet out your fabric with an impregnating machine and place it straight on the job and bag it, you are getting the advantages of pre preg without the extra refrigeration equipment required to store it. Btw, you still end up with just as much in the way of consumables as infusion and all of the same equipment requirements. There is nothing to stop one from post curing any laminate produced by any method for improved properties.

Steve.

 

Well the same resins used for normal pre preg are your only option... the pressure doesn't make it cure, the heat does.

So you need to search out pre preg resin manufacturers...

 

Sicomin (france) produces and sells resin for DIY prepregging.

 

How do the results from wet preg compare to vacuum infusion?

 

Susho, thanks for the lead. Unfortunately, Core Composites(US supplier for Sicomin) doesn't carry the SR121/KTA31x. They said they could order some on their next order, but it's probably uneconomical to import a small quantity for a diyer.

 

Not. comparable to wet layup, but easier to cut and lay, without the tows falling out of caron weaves.

 

There is some interesting analysis here:

http://www.gurit.com/files/documents/6_cost_study_infusion_vs_prepreg.pdf

 

That is for factory manufactured prepregs, with the right resin ratio already in or on the fibre. DIY prepreg is vacbagging with some extra time, because the resin doesn't harden further than a b-stage. Both infusion and OoA prepregs provide better quality, probably for less costs (in bigger projects than some home tinkering)
In my opinion DIY prepreg has a limited range in where it is effective and efficient to use, mostly where infusion isn't possible due to the building process, and you don't have enough time for vacbagging.
OoA prepregs usually have better characteristics for air evacuation too, which I haven't seen (yet?) is DIY prepregs. Void content and surface quality are possible problems therefore.

 

If you do some digging in the archives (back issues) of "Professional Boatbuilder" magazine, you'll find a good bit of helpful info on home/small shop resin impregnators. And also how to get up to speed on running them, common issues/snafu's etc.
I'm up WAY past my bedtime, so my memory's a touch shoddy, but they may even cover how one or two shops made their own machines.

I'm thinking that mostly what was covered was for making your own wet preg, but once the guys got the glitches worked out they were VERY happy with the results. Both resin to fiber ratios, & consistency of wet out were far better than by hand, & after a while, given that they were using less resin, they found that the hardware & cost of the learning curve, more than paid for themselves. In addition to a better end quality product.

Just an allegorical "think".

PS: One nice thing about pre-pregs is that (knock on wood) they're sticky enough to stay in place where you lay them. So critical fiber alignment is maintained. But they aren't messy like wet preg, or hand rolling resin in place (both of which can be, at times, prone to sliding out of alignment, or off of steeply curved surfaces).

 

I built my own hand cranked resin impregnator years ago when i used to manufacture snowboards, it was a small one at 16" wide using 3" hydraulic cylinder rod for the rollers and you set it up with a feeler gauge. I am now using resin infusion and find it a great system.

Steve.