fiberglass viel to remove pinholes on wet layup

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#1

Hey guys,
I was wondering if you could give me more information on using very light woven fiberglass cloth (0.5 - 0.7 oz) as a way to protect against pinholes on a part.

In my application, I’m doing a wet layup in a bag. I’m actually ‘self prepregging’ the material on a flat surface (metered amount of resin per square area of cloth, and distributing it as evenly as possible) and then placing the part in a mold. I’m using breather to wick away excess resin (along with P3 perf ply, if someone could give me a line on where to get anything other than this damn airtech stuff I’d really appreciate it. it seems like that’s all anyone sells in the US), and because of it I’m still getting quite a few pinholes that take a serious amount of spraying and sanding to get rid of.

So, my question is, if I insert a layer of this fiberglass into the part, on the surface layer (between the mold and carbon), will it solve the problem? If it’s 0.5-0.7 oz, is it really “crystal clear”? These parts have a cosmetic application as well. I tried a test run with 3.7 oz cloth and it was terrible, you could definitely see it.

Can you guys break down the application and procedure for me in detail? All of the other threads where it’s mentioned just throw it out there and aren’t elaborated upon

Edit: just for extra detail. I’m using Gurit Sp115 ER and the carbon is 3 to 6 layers of 5.7oz

#2

Just to be clear, this is the effect I’m trying to rid my parts of. This is a pin hole effect, right?

Let me know if these photos don’t load…stupid skydrive -__-

Those large voids, especially in the first one, are what I’m trying to get rid of. That top one was actually made without a breather and the resin was degassed pretty seriously.

I made this thread in reference to this method:

http://www.compositescentral.com/showthread.php?t=4459

#3

the veil will not help too much. Better to infuse the parts, this will give a pinhole free surface

If you must do wetlayup for whatever reason, wet out the material in the mould. Wetting it out before putting it in the mould will trap much more air. Use a different perferated release film and adjust vacuum level

#4

Some are pinholes, the others are voids. To me a pinhole is a miniscule void right in the corner of the threads. About the width of a pin tip. If its large enough to fit a pen tip, its a void.

#5

Yes, wet out in the mould. use a light cloth, until about 160 gram/m2 is becomes clear. 80 gram is fine. I used to work with prepregs which had an 80gram/m2 glass outside layer too. Bus infusion is easier in most cases :slight_smile:

And don’t suck out too much resin if you want cosmetic parts.For vacbagging a p3 release film and 65-60% vacuum is enough. Maybe a bit less vacuum, SP115 is quite thin.

#6

My problem is that I’m using stretchlon so I have to operate under full vacuum which is giving me the resin loss problem.

I’m going to have to try infusing the part, i’ll do it today and try and give you guys an update. really my problem is more of a time issue - I need to make these parts as quickly as possible an wet laying outside of the mold seemed like the best bet

I’m sure I can do an infusing in close to the same time though.
Thanks!

#7

Pre-pregging or prewetting the carbon can be really problematic. I prefer to wet in the mold. I also typically use a light 1.19 ounce glass fabric in the mold first. If the light is just right you can see it in the part. Otherwise it is very difficult to detect.

#8

If you need to use full vacuum, you also need other perf ply. (P31 for example)

However, wet bagging is a very skill-dependant way of making carbon cosmetic parts.

I really suggest reading the MTI hose thread. Using that makes cosmetic parts so much easier. However, you need to switch to infusion.

#9

Thanks guys. I’ve gotten the process down pretty well for wet bagging so it looks like I’m not going to be able to change it at this point - the only issues that i have right now are some minor bridging problems that I think will be pretty easy to solve based on just cutting the consumables in the right manner. Doing an infusion would raise the price by too much based on the consumables as well, although I’ll have to try it with the MTI hose.

Anyways, the fiberglass veil - I tried putting some 3.7 oz on it again last night, and the piece came out pretty decently. You can of course see the fabric since it’s so dense, but the surface finish appears pretty good and there doesn’t appear to be any voids between the glass and the carbon. I’ll have to see how well that translates when I used a light glass. I also will be sanding it tonight to get a better idea of the surface quality.

I purchased the 0.6oz fiberglass chopped strand for soller, and I’m not sure how it’s going to work since i’m using it with epoxy… I spoke to John at soller and he said it’d still be fine (i always thought chopped strand could only be used with PE or VE since the styrene in those resins dissolved the binders in the mat). I’ve also been looking at a 10 yard x 26" roll of .5oz woven eglass from www.cstsales.com. About to order a roll of that (this will probably be what I use in a production scenario).

Herman, I’m trying to get a hold of P6 by airtech but I can only find it in very large quantities right now. Graco supply is sending me a sample though, so hopefully they’ll give me a few yards x 60" which will be enough for quite a few tests runs. edit - also looked up P31, same size pores as P3 and P6, but the spacing is inbetween the two. The p6 that I ordered has the .015" holes every 2", the P31 every 1" (p3 is every 1/4").

Wyowindworks, from that photo I definitely can’t see any glass in there. The fabric I’m aiming to use it actually half as heavy as well. Why do you use 1.2oz instead of a light one?

Thanks guys!

#10

http://thayercraft.com/107-38-20,50%20100%20yd%20rolls.htm

1 ounce fabric is easier to work with in my opinion.

#11

Dang I wish I had seen this yesterday, I ended up purchasing 10 yards of .6 oz eglass from CSTsales.com When it comes in i’ll see how it performs.

So, I tried using the 3.7 oz glass. It accomplished what I wanted and resulted in a reduced pinhole count, but the surface texture of its plain weave is still apparent when you hit is straight with a rattle can clear. A thicker, HVLP application might improve the situation. However I’m hoping that the surface texture from a much lighter weave will be easier to mask. The only issue I can see is that the weave will be so light that imperfections from the carbon layer beneath it might appear through the surface.

I should know by the end of the week!

#12

A key to reducing fabric print-thru is fully cure the part in the mold. If you demold it too soon the print-thru will be more evident. For this reason I heat cure the part while it’s still in the mold to fully cure the resin before demold.

#13

The problem can be resolved without fiberglass veil. Wet your mold out with resin prior to laying down carbon fiber. Wet out that layer of carbon and work it into the fibers with a squeegy or roller… remove any pooled up excess resin with a sponge. You can use stretchlon at half vacuum or any amount of vacuum. Just make pleats in the vac bag. If it’s just a cosmetic part try running the vacuum at 6-10 hg. use release ply with no holes or perf ply with very tiny holes. i use a red perf ply with super tiny holes… not sure of the tech specs on it.

#14

Hi Fastrr, what the idea behind “use release ply with no holes or perf ply with very tiny holes.”

#15

Not sucking the laminate dry, leaving pinholes :wink: