Carbon Fiber Finishing

My building partner and I have been doing a lot of experimental vacuum bagging with carbon fiber and have gotten the proceedure down but the finish is always dull. I'm curious what the best method for getting the deep gloss wet look that so many professionaly built carbon fiber parts have? We have experimented with putting a resin/hardner coat over the finihsed product which give this look initially but it doesn't level correctly so the finish is wavy. We have also tried clearcoat but it doesn't seem to give the depth. So, what is the best way to get the look we are trying to achieve?

Hi Mike,
I have vacuum bagged (on a flat table covered with drafting mylar) some flat panels out of kevlar/foam/kevlar for my floorboards, plus demo'ed the method at EAA a couple of times. I can take a stab at a little speculation on the question.

I suspect the professional stuff is done in female molds with a good polish and the layup is done with a resin rich layer against the mold on top of the release agent. No bleeder or absorber on the mold side.

I get good gloss on my "mold surface" of the sheet of mylar. The opposite side is not glossy but that is because I use peel ply as the bleeder cloth. Removal of the peel ply automatically causes a matte surface of course.

What Bill said, I Fabricated my carbon fiber instrument panel with the same plan plus I had use of an autoclave.

Bill,

I was in Ashville last week at the Biltmore. The fall colors in the mountains were spectacular.

Pat Stewart said:

I had use of an autoclave.

Click to expand...

ENVY..

Pat Stewart said:

Bill,

I was in Ashville last week at the Biltmore. The fall colors in the mountains were spectacular.

Click to expand...

Glad you enjoyed it! I think you lucked into the exact right weekend. Last weekend was the kickoff and the leaves will be down very soon.

If you're making flat pieces of carbon fiber try a piece of glass as your mold. Do a wet carbon layup then put a second sheet of glass over and put this entire thing in the vacuum bag. Also make sure you're using a good epoxy and not polyester resin.

Bill

Suffice it to say that the finish part mold surface will only be as glossy as the original mold was to start with. The resin reproduces the mold finish rather well, including the level of gloss.

Do you have a mold?

Are you using vacuum resin infusion or layup and then evacuation?

If you do layup, peel ply, then soaker, then pull to -30 - it will suck ALL the resin out of your part. Fantastic for strength, but not pretty.

I am making some plenum covers using a mold and resin infusion.

#1 the vacuum bag can have zero leaks. If pulled to -30, it needs to stay there for a day.

#2 The resin viscosity and temperature must be compatible.

#3 The infusion rate must be controlled during the process - slow to ensure the reinforcement is wetted fully as the resin wave progresses.

#4 Resin dams (areas where it is hard for resin to flow) are required to impede the resin flow (at the end edge) and allow the reinforcement to saturate behind it.

#5 When the resin reaches the end. Cut off the resin, and cut off the suction side.

#0 - Begin by evacuating the resin and harder (separately) for 30 min prior to mixing and beginning.

Hard expensive lessons learned. Beautiful part. At 99.5% perfect part now, and still learning to reach a 100% part.

Answer the questions above and lets see what you are doing.

Older picture, but I demolded one yesterday that looks like/better.

Glossy Carbon Parts

If you want glossy finish carbon parts, I'll echo what has been said:
1: start with a mold that is clean and finished to a high gloss.
2: wax the mold well, then spray with PVA.
3: paint the mold with resin before laying in the carbon.
4: vacuum bag it, but don't pull more than 24-25"
5: after the part is de-molded and cleaned, shoot it with clear coat pretty heavily
6: color-sand the clear coat to 1500-2000 grit,

Other than looks, it is not worth it from a weight point of view. You can make lighter parts faster in good but not perfect molds, filled, sanded, and painted like other composite parts.

Polish the mould, or use a sheet of glass - or a flat tailgate window from an SUV
Needs to be resin rich to get a deep finish, so put plenty in before the cloth and don't squeegee or stipple too much - make sure the corners are not starved.
Don't vac bag - will suck all the resin out.
Too much resin un-supported by cloth will crack up in service.

Pete

Without a mold

I think he asking about how to get a good finish without a mold. It is not that difficult.

I made some custom pieces for my 7. They were laid up with 2 layers of glass cloth and 2 layers of carbon fiber. After wetting out I applied Peel ply. When cured I sanded to get a uniform surface. If this is not a structural part and probably isn't on an RV, don't worry if you get into the carbon a little when sanding. This will be taken care of later.

Another wet coat of epoxy was added. Sanded to a nice finish with reducing grits of paper. Once I got the finish I wanted I resanded with 320 grit wet to get a rougher surface for the clear coat. The parts were then clear coated with several coats. I wet sanded all the way to 2000 grit. The finish looks every bit as great as a molded piece.

With the piece I made I wasn't going to go to the trouble of making a mold for 1 left and 1 right part. Carbon for RV's is mostly bling anyway.

One little cool tip..... Naw saving that one

We call that "aesthetic carbon." We don't do much of it; we're mostly a structural carbon shop.

It is rather difficult to get a pinhole-free surface with epoxy unless you are using advanced techniques and materials. Epoxy beads up on a waxed surface, and it is hard to get all the beads to hold hands even with the best of technique.

Two tricks we have used to get reasonable aesthetic carbon parts:

* Paint the mold with polyester resin, let cure, and then do an epoxy layup on top of that. The polyester wets the waxed mold OK, and the epoxy wets the polyester OK.

* Make an epoxy/carbon part, cure, and demold. Clean and acetone the molded surface, varnish with polyester resin, and then spritz with acetone to smooth out the varnish.

In my experience, the black carbon fiber surface will probably have a limited aesthetic life when used where it will get direct sunlight. Unless you're using a high-temp process like pre-preg, the high temps and temperature cycling will cause the surface coat to go either yellow or chalky pretty quickly.

Thanks, Bob K.

So, if it's just looks you're after, try finishing the piece as normal and then sending it out to be hydro-dipped. The finished part will be shiny and you can choose from many different weave patterns. I finished my white NACA vents that way and people have thought they were carbon fiber even while handling them, until told the truth.

You might consider coating your carbon fiber parts with thhttp://www.duratec1.com/pdf/904-061%20FLYER%20WEB.pdfis.

Shiny finish with UV protection.


Warren
Plymouth, MN
RV-7

I have had good results with spraying two to three coats of clearcoat into a well waxed mold; letting it cure and then abrading with a maroon Scotch-brite. Dont use air pressure to blow out the mold as you will lift the clearcoat from the waxed mold. Rinse and let dry before doing the layup using your favorite method.

Personal opinion only: don't use PVA; just obsessively wax the mold with Johnson's pure carnuba paste floor wax. The same wax you used on the floor in Basic Training. You can also spray the mold with epoxy primer to pre-prime your parts. This really works best if you are vacuum bagging your parts and select your bleeder layer to leave the part slightly resin rich.

Although these are good shortcuts, the tried and true method will always be sanding, more sanding, and wet sanding; then re-coat and repeat the sanding process.

There are a ton of techniques using sanding blocks and other tools to get a flat surface, but its really tough to avoid the manual labor. Make sure you use a resin that is UV protective, and you can use an automotive clear spray on that final coat.