Hi Zekewarg, I think I'll try your idea, thanks. I'm not sure if it'll be quite the same but it's worth a try.

I am worried about the prepreg curing before I can use it. I'll have to buy a freezer specifically for it as I'm not sure how safe it'll be next to the frozen peas and carrots. Mmmmm carbon flavoured epoxicles.

I did see that video before and he even claims that it's better that the bought stuff, so it's definitely worth a try.

On a side note, how cool is that plane that he makes? A full carbon, pressurised, LS1 powered plane.

Yup I know this video... their airplane looks awesome. Anyway...

Yup, some people do their own prepregs. They store it in freezer.

It reminds me that Paul or Matt from EC staff said in a previous post they would not use their resin if it had freeze, at least not before doing a small test part. But maybe its not concerning catalyzed resin?

If EC resins dont work with freezing, then which resin could we use? Is it more a matter of resin itself or catalyst chemistry?

The guys from Algie Aircraft use their prepregs, and they do super cool stuff with it (I'm in love with the propeller). But what is their goal? 100% pinholes free panels or the less resin as possible (and well, pinholes can be filled before clearcoat, right? ). And, they use an autoclave, which helps greatly compared to ourselves, DIY'ers.

But then why do aeronautic and formula one people use commercial (but high end) prepregs? it would save them TONS of money doing it themsleves but they dont do it. So another question would be, for me at least : what is the major difference for a same resin, between a man making his prepreg and a machine doing prepregs? Is it just vanity of saying "i used high end prepreg and you cant afford it, lil guy" ?

So, I bet EC guys will have to come and give their input on that.

 



 


    A $1000 electronic device will always protect a 10 cents fuse

I just tried it with my home made prepreg. I'll know in about 8 hours as it's 19 celcius here today. I'll let you guys know how it went but I'm betting it'll have air bubbles or voids. Fingers crossed though.

I agree with both Joe and Steenfeldt, I´m awaiting judgement fråm EC. On the other hand, it is not (for me) an absolute necesstity  to be able to freeze it, just to get it as malleable as it was in the F1-video would be great. Is that possible with the standard resins?

Hi Guys,

Homemade Prepreg by definition is easily possible to produce, by its very name it simply refers to the reinforcement fibre being impregnated (soaked) in resin prior to it being placed into the mould. However the type of prepreg that can be ‘home-brewed’ really cannot be compared to commercial materials.

Normally when the term prepreg is used it refers to a cloth impregnated accurately and consistently with epoxy resin that is at it’s ‘B’ stage of cure, to do this the specialist resins are heated to a liquid and the cloth is passed through the resin ‘bath’ and then a series of rollers all under perfect tension, heat and time control. This is then rolled with separation film sealed and stored frozen until use. The ‘out-life’ (time the material remains usable after being taken out of the freezer) varies from around 6hrs – 3months, 2-6weeks is typical for most common prepregs.

The resin in the prepreg is slightly ‘tacky’ but not wet when it is in it’s workable state at room temperature, the material can be temporarily softened with heat from a heat gun to aid working it into complicated contours. The layup procedure for prepreg requires accurate placement and particular attention to bridging and mould intimacy, These materials are then vacuum bagged and cured under heat (typically between 80 – 140 deg C) either in an oven or an autoclave (a pressurised oven). When the prepreg is heated the resin becomes liquid allowing it to flow and conform to the mould surface. After the curing cycle which is typically between 1.5 – 8hrs the part is complete and can be released.

In answer to your questions on freezing, I’m sure that the standard laminating resins can be frozen as long as they are fully sealed and are allowed to come up to room temperature before being removed from there sealed environment, if they are exposed to air while they are frozen the moisture from the air will condense on the resin and become absorbed which will cause issues with the cure.



Here are the potential problems with a homemade prepreg:

Resin Distribution and impregnation; Evenly applying the resin at the correct ratio (typically 60/40) and ensuring that it has fully penetrated the cores of the fibre tows can be tricky.

Getting to ‘B’ stage; the window where this material would be usable even with slow hardeners is small… you would be lucky to have more that 1 hour.

Sealing the material; actually getting a non-stick material to apply it to, so it can be sealed and frozen is trickier than you would think.

Working with the material; Having a tight time-frame and variable levels of tack the layup process can be made much more difficult.

Final finish; unless you have (like me!) the privilege of an autoclave which cost many tens of thousands of pounds, your surface finish is likely to be plagued with voids and pinholes.




The one method I had moderate success with:

In developing and testing the oven only pinhole free easy-preg system I did get one home-made method to work reasonably well, here’s what I did:

1.    Evenly saturate 1 ply of 200g twill with 160gsm of coating resin (double normal ratio) on a sheet of waxed paper.
2.    B-stage this for 12mins at 75 deg C, allow to cool and apply a second ply of dry cloth to this tacky surface.
3.    Seal into a poly-bag and freeze
4.    Remove from freezer allow to thaw and use in a chilled workshop (12deg C)
5.    Bag and cure laminate at 80deg C for 2hrs

This system produces virtually pin-hole free surfaces due to the dry plies of cloth acting as a core breather; a refined single ply version of this technology is used in the easy-preg with huge out-life and consistency advantages.

The impracticality, labour intensity, unreliability and wastage meant that we never even came close to implementing this system for any form of production, but for those experimenters out there feel free to give it a go!

In summary resin infusion will yeild much much better cosmetic and structural components than a home-made prepreg will.

I feel a prepreg video coming on!... Within the next month or so I will show you exactly how to use the easy-preg to get completely pinhole free, perfect prepreg components without an autoclave; it took us years to refine and I’m sure even the most experienced composites engineers will be impressed with what it can do!

And keeping on-topic – Yes you can use a domestic oven for curing, be-careful, never leave them alone, and verify all set temperatures with a thermometer. Other that that for small components they can be really useful.

Paul Statham
Easy Composites / Carbon Mods - Technical

Wow thanks Paul, that's a great answer. Thanks for the time you put into that.

I'm going to demould my homemade prepreg effort tomorrow morning (in about 8 hours) as it's been cold here today, I want to give it more time. I think if it works then I'm going to get some easy preg.

Update... I got impatient and just demoulded it. I got a very straight weave on most of my product but there were voids and pin holes in the tight corners. I don't think I can make homemade prepreg work for me.

Paul, I'm making a cover for my iPhone 4. I've used RTV2 silicone for the moulds, both plug and female. I've done it this way because I need a perfect finish on both the inside and the outside. I couldn't get vacuum bagging to work with the tight corners either. Do you think your easy preg system would work in a situation like this? I plan to put two layers in the mould and press the plug in and throw it in the oven.

Here are the voids I ended up with...



Also... do you think the easy preg will fix the way that weave spreads out like that?

I just realised that I'm getting confused between "Easy-Preg" and "Vari-Preg". Sorry about that. It's the vari preg that is in my price range. Do you think vari preg will help with the spreading out of the weave and the voids?

Thanks to both Paul and Adam!

I´m probably going to (at first) just try to cut my fabric, the preg it and let it get tacky, then mould it.

To me at least, the most intising enticing prospect is to get as close to the fabric in the video as possible in the form of ease of use, to get it to almost directly stick into any corner and thus easily securing complex shapes.

Q: Is high quality professional prepreg with bagging and autoclave stronger than infusion in oven?

PS: I could just see in front of me how Paul and Matt turned on the computer in the morning and with increasing amounts of dread went through last nights posts. "Come oooon guys, why can´t you just infuse like everybody else?"

Hi Adam.

Haha I no only too well about the impatient de-mould! those results don't look bad to me at all, however your life will be much easier with the vari-preg for that part if you get your processing sorted, somthing that I only recently heard about but seems perfect for a prepreg iphone case is capitalising on the thermal expansion of the silicone.

To do this you must first make a rigid tool for your female mould, the prepreg should then be laid into this, you will layup the prepreg with snips in the corner so the weave does not have to distort. You then need to insert your silicone male tool into this and press it into the tool by clamping a flat rigid plate to the back of the silicone. When you place this into the oven the silicone will expand more than the tool, thus pressing the prepreg onto the surface with great force, the theory is that this can, if done correctly, exert autoclave pressure without the complexity cost and risk associated with compressed air. 

If you wanted to give this I go I would be very interested in seeing how you get on, we have in the past made runs of ipad cases using prepreg with a press moulding method, it would be great to see how utilising the differential in the CTE (Coefficient of Thermal Expansion) of the materials works!

Infusion is by no means the only processing method we recomend, however if done correctly the performance is rivalling that of prepreg, and cost can be much lower, but prepreg processing and matched tooled methods will always have their place, In our production we are about 50/50 prepreg/infusion, although going back 3 years and we were more like 90% prepreg, so infusion is working it's way in! Prepreg is really tough to beat for small intricate parts.

Paul Statham
Easy Composites / Carbon Mods - Technical

@ Adam: Do you have any info on the silicon mould making? Pics of the mould etc?

PS: Just got to large boxes from EC, sweeet (although the stuff got stopped in customs, TWICE).