I’ve seen some people who do carbon overlay with light fiberglass on top of carbon,what’s the advantage of that? and vis versa (other than it cost more for the materials)
Tighter and finer weave, no pinholes in the surface. And a bit sandable before you hit the carbon and destroy the weave.
Often Carbon and kevlar finished kayaks and canoes will have a light glass cloth on the outside of the carbon face for the reasons mentioned above; it also adds a little depth of shine to the finish. The cloth when wetted out becomes transparent.
I have some 3.7oz cloth will that be too heavy of cloth to use for this type of application? what’s the typical process of doing this?
I usually use a tight weave 2 ounce glass. If I remember right it’s 56x56. I think the 3.7 once will make the carbon look hazy and isn’t really fine enough to avoid small pinholes.
how drapeable is that? I had some tight weaves before but they feels like peel ply and does not form into shapes.
It’s conforms as well as any other reinforcement. You can move to 1 ounce Style 6060 or 1280 if you need more conforming ability.
Better impact resistance - protects the carbon. Also added stiffness without extra cost of carbon. If what you’re talking about is structural of course.
The stiffness of a light glass on top isn’t much. But I’ve used similar wheight of glass, 2 layers between CF for a stiffer (non structural) product. Works great, and makes tha part a bit less brittle.
I’ve used it like the above mentioned and also at times when I’m building a part with a splice seam that requires a little extra resin to level out the surface for the asthetics. I don’t want any cracking in the clear. Some of these parts are automotive. Here in Florida, our interior surface temps easily cycle to 150 deg F plus up around the dashboard during the summer as measured out in my parking lot so stability is a must. I was using 1.3 oz and switched up to a fine .7 oz because I was seeing localized areas where the fabric was showing in the clear.
yea you guys were right 3.7oz seen to be a little too thick, and does make the part look a little hazy.
wow 150 deg F?? won’t those carbon delaminate from the part? what’s the count for the 1.3 and .7 oz fabric you are using?
Delamination can be a problem. I always try to push parts from the mold and avoid sticker type overlays when possible. Not so much on composites stuff but plastics and things are a concern. There are many ways to skin that cat though.
The .7 is 56x56. not sure on the 1.3
Update 03/03/12 I had some parts on the dashboard this week and measured 160F. We aren’t into the 90F range yet.
Problems with print are mostly solved with a higher Tg epoxy, and sufficiënt postcure.
…and not demolding too soon. Most of the resin shrinkage happens in the later part of cure. If you demold the part before most of the cure has happen the molecules on the surface of part are more mobile and will rearrange themselves to continue to link. This will cause the fabric to print-thru. Adding heat after demolding will enable even more molecular mobility to complete the cure and the print-thru is worse. Add enough heat so you exceed the Tg of the resin and the resin will try to find it’s most relaxed position and you will get print-thru.
If you leave the part in the mold and post-cure, the molecules against the mold surface will stay “stuck” there and the crosslink network will build itself around the surface molecules. This will greatly reduce if not eliminate print-thru. If the resin is cured too quickly it can have more internal tension. If the temps then get close to the Tg then the resin can be soft enough to allow the molecules to move around and find a position with less stress. Wammo, you’ve got print-thru in an older part because of internal stress.
So to reduce print-thru:
- Strive to establish a near complete cure before demolding.
- Cure the part in a fashion so there is the least amount of internal tension in the part.
- Use a resin with a Tg that above the survice temp.
- Use fine and tight weave fabrics on the face of the part.
So when you guys cover another layer of fiberglass, do you wait until the first layer of carbon to cure first then cover with fiberglass or you wet out both at the same time when doing overlay? won’t it trap air bubbles under fiberglass cloth?
I want to try this method but rather hear some input before I try it out so any input would be appreciated
You would want to do it at the same time. This way you will get a chemical bond between the layers. You won’t trap any more bubbles than you would doing anything else.
Hi there,
Be carefull when you ad glass on carbon parts.
If it’s a structural part you have to know glass and carbon have not the same reaction under high temp (ex: californian sun etc…) By the way on painted carbon parts I use a 30 gr mat as a barrier coat to avoid structural effect in the paint. That means this kind of fiber do not affect the machanical performance of CF… If you want and carbon clear part, Use 2 coats of Vinylester or PUR clear gel coat that you’ll can sand and buff after curing… Good luck!
Steph
I’m assuming that this also helps minimize print through in the clear coat.
Yes, exactly. But don’t dream, after month and thermic shocks, a light print could appare on glossy coat but realy less than a part using a single coat or without finish viel 30gr…
Take care, you could find two type of finishing viel: a glass mat easy to cut by hand and an other one that require cutter… Take the first one.
Steph