The aha cf pinhole-free thread

General Composites Discussions Composites Talk
#1

Whew… so many years, and so much effort to discover methods of laying carbon fiber to be pinhole free on the surface.

Apparently West Systems recomends laying down 1/2oz fiberglass into the mold before laying down the carbon fiber. I am assuming ( usually gets me in trouble ) the technician first wets the mold with an even coat of epoxy, then lay down the dry fiberglass 1/2oz cloth ( again i am assuming it is cloth, not mat). Brush down some more epoxy onto the fiberglass and squeegy that, remove excess epoxy that is full of tiny air bubbles. I believe you can use a kitchen sponge to absorb the excess, or perhaps a foam paint brush. Now let that get into the gel state. Now brush down some epoxy, even coat; then lay down your dry carbon fiber, brush in some more epoxy.

Now I have a question… after that first layer of carbon fiber do i concern myself with squeeging and sponging up the excess air bubbled resin for each layer of cf after the first?

Another issue someone stated that can cause air bubbles is pulling too much vacuum? I am guessing the reason may be the boiling point of the resin is lowered by vacuum, and the exotherm of the resin causes it to boil… unleashing gas/air bubbles into the surface finish. Or is it the pressure forced on the lay up does not allow the tiny air bubbles to escape thru the laminate?

This leads to the question… won’t the laminate be resin rich if full vacuum is not pulled right away?

Another reason said for air bubbles it too thick of epoxy. ??

Would over-catalyzing vinyl ester resin and pulling full vac be a serious way to cause gas bubbles in the surface finish, or mixing the epoxy incorrectly?

Please feel free to correct me on anything and add technical help on the subject.

#2

i had a few issues with bubbles in flat surface parts. I spoke to a company and they said to make sure the resins that i used were at 20 deg C or above to work properly and to be working in a room at the same temps. if it was colder, when mixing the resin it will really trap the air in the resin mix, this then transfered to the panels when laying epoxy down.

as for vacuum, i have no idea (yet)

#3

Too thick of resin definitely makes it harder air bubbles to escape. I accidentally bought 20,000 cps resin once and my laminate probably had a 20 percent void content. Comparing that to my 700 cps resin the air bubbles look like the bubbles in soda, rising slowly till they go away, albeit slower.

As for squeegeeing all that resin I think that’s wasteful. For cosmetic or low load parts air bubbles shouldn’t be too much of a concern in terms of strength. So if the first layer is bubble free it won’t matter much if there are some bubbles inside the laminate. If your part is going to be taking a lot of load or excessive fatigue loads then air bubbles could cause structural problems.

#4

one person i was reading quoted as saying he adds a small amount of isopropynol to his epoxy and this solves all of the entrapped air problems in the epoxy mix, and spreading out the resin into the mold.

Isopropynol does indeed get rid of trapped air bubbles, i sometimes spray it onto my overlay coats of epoxy. I just wonder how good/bad it is to directly mix it into the epoxy?

and just so people here know… you can’t buy isopropynol at a store. Composite suppliers sell it. Don’t want anyone thinking rubbing alcohol will work.

#5

Have you tried de-gassing your resin?

#6

The resin supplier I go to recommends spraying a acetone onto overlays to get rid of bubbles. My guess is that the acetone or isopropyl alcohol lowers the surface tension enough to break the bubbles and then quickly evaporates.

#7

Im gonna have to try this soon, be very interesting to see if it works

#8

would the good ole flame method not solve this? taking the flame to it once you have laid down your first layer of carbon?

#9

That is possible i suppose RC51, I think a heat gun would be a better choice. If anyone does use a torch, use a butane torch… other fuel/gases contaminate the epoxy and cause more air bubbles, or fish eyes.

I sure could use a heat gun!:slight_smile: We did try as small butane torch today to pop the bubbles in the epoxy surface coat. However I had a small problem that was worse than bubbles… mold wax was rejecting the epoxy.

Someone had also mentioned a resin less viscous so air bubbles will move more freely.

#10

interesting, didn’t know that.

#11

I am going to contact Resin Services to see what they say about laying up an air bubble free laminate. Their HTR212 with 386 hardener is right around 1200 cps so air always gets into the mix. But let it sit a few minutes and the air rises out slowly. But start to brush the resin around and more air gets into it. frustrating.

Also can you guys recomend a mold wax that won’t bead up the epoxy resin?

Here are the types of wax i have, but have not tried them all.
NC770, TR104, TR regular mold wax, TR liquid mold wax.

#12

Miguires no 16 i find good. Its a little bit paste like. And easy to apply. I generly use that for cf stuff and no8 wax for gf parts.

#13

TR104 should do it.

With NC770 you can forget it. (any semi permanent system, that is)

#14

TR104 i tried and it beeds up the epoxy resin. I have some meguiars… not the #8… my stuff is in a tan/red colored tin.

#15

Ever try Partall paste #2 from Rexco? It’s a PAIN in the @** to buff, but I have good results with it.

#16

That is 87 high temp. Should do the job. Final buffing is the key, with plenty of clean rags.

#17

thank you all so much… this forum is a lifesaver!

I did 3 coats on the mold with regular TR wax. I then brushed down a coat of clear epoxy resin onto the mold surface. Then on a table i wet out a single layer of 6K twill cf, then laid it into the mold. i did not wait for the surface coat of clear epoxy to gel. I then brushed down even more epoxy over that first layer; then i squeegied it lightly, removed the air saturated excess resin. Finally i wet out another layer of 6K twill on the table and then laid that on top of the first cf layer. I worked it in place gently by hand so it went properly into the corners and such. Then i placed a single layer of perforated release ply over the lay up, followed that with a single layer of 10oz bleeder/breather. Finally vacuum bagged it and left it to cure at ambient temp ( 64F degrees). It took past 24 hours to get past gel stage, but once it was sufficiently gelled i removed vacuum. I only did this because i had a vacuum leak anyhow near the vacuum hose on the bag, leak wasn’t near the lay up. And with a bag leak my pump likes to puke oil and smoke. So after 5 hours of being bagged the resin had gelled.

I had better results this time with the cured laminate. Far less tiny trapped air bubbles. There were some tiny voids in between the tows of cf that are visible on the surface. It’s not trapped air… just like the resin didn’t flow in between a few of the tows where they intersect each other.

I did get tons of air filled resin in two corners of the part, but that is just a bridging issue - easy to fix next time around.

My main question now is how do i prevent those tiny dry spots in between the tows? Is that from insufficient vacuum during cure?

#18

LOL yes i have used that cr*p :smiley: like buffing toothpaste. My supplier sold me another can of it a couple months back… i never opened it so i just traded it back to him :cheesy:

Meguiars #8 is a little easier to buff than the Rexal paste wax, still not a dream to buff… but if it’s what you have both will work and do the job. I mean if i absolutely have to i would use them.

#19

The only time I achieved a 100% perfect job was when i infused a carbon laminate, using a quite complicated setup involving Dahltexx from Airtech as a medium to remove air.

Reading what you have done, you could have waited a little, for the epoxy to thicken somewhat. No exact guidelines, however. This is really more art than science. Do you have a pump with exhaust filters? If so, they are gone. Get new ones, and make sure the pump always runs within spec. (no athmospheric pumping). If your pump has no exhaust filter: bad luck, try and place it outside.

#20

What cfm pump do you guys use?