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concerns regarding moisture- seeing as how it needs to be stored in a cooled environment do you not get condensation on the surface of the prepreg when you take it out of the freezer? is this not detrimental to the resin?
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is an autoclave necessary for prepreg use? I know its ideal but can the process also work using atmospheric pressure(ie vacuum pump) and an oven to provide cure temps?
An autoclave isn’t necessary. You can get better results with an autoclave but it depends on what kind of prepreg you are using. I shouldn’t wory to much about moisture.
Just store in a sealed plastic bag and let it sit at room temperature before you use it. Most manufactures have a handling and storage recommendations in the datasheet.
Also, google Out of Autoclave Prepreg.
Full roll will take about 6 hours to get to room temp. I usually get them out of the freezer when I go home for he night, and cut what I need for several products, which I repackage in smaller bags. The out time at roomp temp. is limited.
And you don’t need an autoclave. Like mentioned above, try to get out of autoclave (ooa)prepregs.
Exactly what susho said. Keep the roll sealed and airtight in the bag. let it thaw COMPLETELY to RT before removing from bag. Then, cut what you need, or more…seal back up, and throw it back in the freezer. Helps to have a desiccant pack inside the roll. if that goes bad, recharge, or get new packs.
As for autoclave, it depends highly on the prepreg itself. Some are made FOR the autoclave, some for out.
As for autoclave:
Most out of autoclave prepregs have lower viscosity resins, and a higher flow rate. They also mostly have higher resin contents. This can make it a bit harder to get a void free laminate, especially if the user is in a hurry.
Moisture: most has been said. Keep in bag until at room temperature, then cut what you need (or if you make several similar parts, cut “fiber packs” for these parts and package these in sealed bags).
Check the datasheet for outlife. This can be several months at room temperature. In general hotmelt prepregs have longer outlife than solvent based prepregs.
thanks guys great info.
Any recommendations for out-of-clave prepregs?
would anyone say that it is possible or a good idea to have a ooa prepreg as the first cosmetic layer in a stack and dry fabric for the remaining and then follow with infusion and cure the whole thing together? My question stems from a pain in the butt that laying dry fabric into a complex mold can be…
http://www.easycomposites.co.uk/products/carbon-fibre/pre-preg/easy-preg-surface-layer.aspx
Thats pretty much what you have to work with as far are as OOA prepreg in small quantities are concerned.
And no, in my opinion you should do one or the other…Go with a surface layer of the Easy-preg and then add some heavier backing layers for added stiffness. Prepreg is nice to use on complex molds.
There is nothing wrong with curing a surface layer and later infusing. But you would be wasting tons of bagging materials
it sounded to me like all at the same time
Yea I got that part but… I’ve never tried. I would think different resins mixing would be problematic.
Seems pretty impossible to find any OOA prepregs in North America. Europe seems to have a LOT of selection…
Any suggestions? I contacted TenCate/ambercomposites but they want nothing to do with me in Canada lol…
That is not quite true!
Moisture is a sure fire way to a poor void content.
You should be sure the prepreg has thawed correctly and remove any residual moisture from the sealed bag before opening.
You “should” also laminate in a temperature and humidity controlled environment and regulate the humidity.
If you do not respect the prepreg or choose to laminate in poor conditions you will get a poorer result than if you used a clean room
70% is the upper threshold for laminating.
The ideal temperature for laminating is one that the prepreg has a very low tack. This helps when removing the air which gets trapped between the plies.
Let me explain why moisture is important to avoid:
This air will have moisture in it, so the lower the humidity, then the lower the amount of humidity trapped within the plies. This air expands when you heat the part to cure it and not all of it will escape. If the air trapped within the plies has high humidity, it will expand more for a given volume than air with a low humidity content = bigger voids ( remember @ 100C the moisture will boil too)
Autoclaves don’t necessarily remove more or all the air from the part, the added external pressure compresses the air so it becomes much, much smaller! @ 6 Bar the void can technically be 6 times smaller. When using a lab to test samples from an autoclave I have yielded void contents less than 0.1%. The “normal” acceptable upper limit for atmospheric cure is 1-2%.
There is quite a big difference in void content between an autoclaved parts and atmospheric parts.
By using NDT tools you can detect if a prepreg job has not been processed correctly - high humidity trapped within a cured sample will scatter a signal from a 5MHz probe. In samples sent to the lab, you will see the void content is higher and quite often visible to the naked eye.
If your going to the added expense of using prepreg, believing that it will automatically give you a better job, then that isn’t the case if you don’t process the material correctly to release it’s ultimate properties.
The reality is that it is important to follow a tried and tested procedure to give you the best results from prepreg, but if your not chasing the best from your materials - which you are charging at a premium to your customer - then why use the best in the first place?
Try Newport adhesives and composites… Very good and I can recommend!
Contact Cytec, they bought out ACG. ACG stuff is really good, but expensive. Also, Gurit has OOA prepreg thats pretty good too, its available in N.A.
Thanks for the info guys!
I can’t recommend Gurit…
The spa-preg system was a PITA and contained needle voids… A lot!
It would exotherm wildly if you got the ramp rate/dwells wrong, and it’s supposed to be a system to cure 85-100mm in a single shot, but struggled with 30-40mm
Do you mean Sparpreg? This material was designed to make Wind blade spar caps. For the type of parts people are doing here, it would be best to use Gurit Sprint prepreg which works fairly well
OOA prepreg, I have used the Gurit SC 110system recently with excellent results.
It was selected as the parts we were building had large UD planks within the structure and the parts were 30 metres long, not anything to do with wind turbines!
The issue related to the breather plies (dry XC305) which was added to the stack at intervals and became infused with the resin from the UD whilst curing. The principle was akin to Sprint.
My question is: has anyone checked and verified the void content of their ooa laminates after processing in real world conditions?