Epoxy CF products question(s)

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#1

Hey,

Need some opinions, we are trying to reduce our finish time on CF parts we produce, everything we do is epoxy based, when we produce our parts (either VARTM or RTM) we always spend a crap-load of time finishing them off, meaning clear-coat applications. We often get some pin-holes in the parts which we repair prior to clearing but even when pin-holes are not present it just feels like everyting needs 3 hits of clear and 3 blocks in-between which is just getting tiring.

We have tried hitting the moulds with clear-coat and then laying up after they tacked up, better results but still needs to much finish time, did the same with Duratec also, better again, but like the clear in the mould, needed far to much time finishing the part to high gloss.

How do you guys deal with this who also shoot in epoxy? Is there a gel-coat that is epoxy based which will seal the surface in so we just need to process 1 maybe 2 coats of clear to finish the part off?

Recommendations? We are really happy with the resin system we use, no leaks in the bags, we often bag the whole mould to ensure no leaks from the moulds either, there is got to be some product or process that can yield a part which can go for a single hit of clear, no?

Also, what are you guys using to prep the parts for the clear? We usually give it a quick acetone bath and wash down with a desgreaser, then wash again prior to clear.

Opinions please?

#2

I was under the impression RTM produced a class “A” finish. if there are sometimes no pinholes then what is the problem with the finish.

#3

Hi,
We infuse with epoxy daily and spray clear duratec in mould and have no problems straight out of the mould. Parts are typically post cured on the mould before de-bagging. We will get a small amount of print but just rub this out with 1200 or 1500 then buff. We only ever spray clearcoat if the part needs uv resistance. Will post some pics when I work out how to do it.

I always make sure the part is not starved of resin, so once it’s infused I’ll give it another little drink (but not so the laminate is swimming) working on the theory that if there is still vacuum under the bag it could cause vacuum voids , especially when you apply heat. hope that makes sence.

#4

Read the august/september 2011 edition of Professional Boatbuilder. Some hints on avoiding air pockets in there.

Basicly:
-infuse at the highest vacuum level achievable
-beware of moisture. Let it boil off (typically below 20 mbar)
-degass your resin
-bring back vacuum to a moderate level after infusion. (I am not too fond of this, but it can work in certain circumstances. You do need a completely integer bag for that. Otherwise you run into trouble with laminate spring-back)

#5

Thanks for the replies guys, appreciate it, to some of the posts above, we have tried working the vacuum through a high low sequence and QC’ing the part with 3D scanning for surface checks. Basically we scan the part(s) and lay one over a-top of each other digitally in a QC program which measures the surface smooth-ness.

Don’t get me wrong, the duratec has made a big improvement but where we have issues is every single part we build for the automotive side requires clear coat and zero defects. Achieving that with a perfect weave, no bridging or weave voids (resin pockets) we can do but just on the finishing side when the clear goes on we don’t seem to be able to achieve a one hit wonder. At first I thought it must be prep on the part causing the issues before clear but it’s not.

I am wondering if we should soak the part more with resin like mentioned in the above post. Just give it a bit more, we do de-gas the resin prior to infusion, but the parts are quite complex, the mould is actually a 2-piece design due to the part design. This maybe part of the issue as well.

#6

Are the trouble spots near the seam?

#7

Yes we degas the resin too. I assume your resin is solvent free? Are the voids between the in mould coating and the laminate? Also I am careful not to apply too much heat before the resin has gelled as this can cause any voids or air pockets to expand and I don’t directly attach the vacuum source to the laminate as this can drain the laminate.