Introducing myself

General Composites Discussions Composites Talk
#1

Hi everyone,
I just found this site today by accident. I’ve done some car pieces in the past with fiberglass, never liked the look of carbon fiber on street cars but making tubes and valve covers looks like something I’d like to do. My eyes hurt from reading almost every post here!

But first off, I’d like to learn what I can do decrease my working time as well as decrease any secondary work I have to do after a part is made. I need to get to know the terms used in order to communicate with you guys here too.

Currently, I use a one inch brush and batches of 6-8oz poly resin in a disposable paint tray liner from Home Depot. I soak the mat in the tray (is this pre-preg?)and lay it up onto the plug (overlay?). I guess what akes the most time is getting everything properly soaked with resin and properly adhered to the surface.

I suppose a bigger container would help, but mixing the resin and catalyst is a pain. I’ve never used epoxy resin.

Then when I’m done, I usually end up having to sand a lot, even though I tried to make the plug or the mold as smooth as possible.
I guess I’m not using enough gelcoat or something…actually I just use a layer of resin, let dry til tacky and then start lay up. Is this the right way?

Here’s some pix of my hood and door panels. I have an air dam in the works right now followed by a bumper and rear diffuser.
All before April 24th (with paint and everything). So as you can see, I need to get my ass in gear!

http://www.v8zcar.com/s30z/sm%20zcca-04-06-19-0055.jpg
http://www.v8zcar.com/s30z/sm%20zcca-04-06-19-0036.jpg
http://www.v8zcar.com/s30z/smy-v8z-doors%2004-03-28-04.JPG

Thanks!
Owen

#2

Where do I start.
Welcome!
No that is not pre preg. pre preg is a term used to describe a usually carbon fiber material pre impregnated with a specialty resin that is usually shelflifed at a 6 month to 1 year term. it is usually kept refrigerated or frozen, and it is somewhat gooey or a slight bit tack. it is placed in a mold and laid out against the mold surface then bagged using a typical vac bagging procedure. peel ply perforated peel ply, breether or bleeder cloth, and a vacuum bag sealed along the edges
Then it is pulled free of air, and placed in an autoclave to add heat and more pressure while it cures.
That is Pre Preg.
You are doing some good old fashioned down and dirty chopped mat layup for the sounds of it.

Overlay is when you take a carbon fiber sheet of fabric and directly bond it to a part by using a resin. This is overlaying

No, you aren’t using enough gelcoat…You admit to just using the laminating resin. Gel coat is a specialty blend of the same family of materials, however it is meant to be the face of the part. If your mold is smooth and looks like what you want it to, your part will be as smooth by using gelcoat.
I often pull my parts, trim them and ship them. Not always, but often.
Nice work so far. keep it up. By the way. You don’t have to wet out the resin in the tray. it can be done on the plug. you can place your mat on the waxd and released plug. Then just dip your brush into the resin and tamp it onto the mat. it takes a while for the binder to saturate. if you keep doing this, it will lie flat and you can add layers a little at a time.

#3

Great post again Dougie…

Try making small test panels to see how the resin wets out the glass, work time before gelling or “B” staging, cut it with a metal box knife while “B” staged and how long to fully cure too.

Use PE (polyetyene=PE) sheeting as you don’t need mold releasing or use glass and wax to practice mold releasing.

JM

#4

also good suggestions, Jim
especially the polyethylene. I use it for a lot of my flat stock.

#5

Thanks doogie48084, dirty wet layup are the exact terms I would use! The reason I soak the mat in the tray first is that it takes forever to do it the way you described, which is how I first started out.

I also can work faster this way. I just lay a portion of the mat in, soak it, move it to another area of the tray and flip it over, fold a dry portion over, and then tamp the mat. Before, doing a 8 x 4 inch piece would seem to take forever…

GGROP, can you explain the PE sheeting to me? I just use car wax with carnuba, I prefer the paste in a tube. Never used PVA, or the proper tools. I’ve used WD40, PAM, etc. but the paste wax gives me the best results.

Thanks again!
Owen

#6

Another question, should the mold or plug surface be hard? I know it should be smooth but should it be hard as if were clearcoated?

I’ve read some stuff on Duratec on this site, some kind of clear hardner mixed with gelcoat.

Owen

#7

Owen, As oppsed to soft as in What?
I guess I will say that it should be hard enough to wax and buff to a good shine.
I use the duratec (thin, sprayable Gelcoat) to give my parts a good hard shell, and to give my carbon fiber a good topcoat. In most instances I don’t even spray with a urethane clear coat.

#8

Sorry, say as opposed to bondo or some other filler, maybe even a polyester primer like PCLs or PPGs DP90. I’m wondering if my pinholes come from there, shrinkage, etc.?
Owen

#9

pin holes are just air that is in the bondo

#10

I have often used primer to seal my bondo patches and if i’m in a hurry, I will go and wax and polish, then pva (greenseal) and I am ready to gelcoat.

#11

I use a 4:1 epoxy primer as the final coat in many of my applications, whether it be plastic that i repaired to make a plug or a fiberglass plug. I just watch for pin holes, and i fill those with a laquer putty if need be. otherwise I’ll take a little time and sand out the mold of it needs a little bit.

#12

Typing about pinholes, I was talking with Cosby at Bondline the other week and he tells me that he gets a lot of high $ areospace composites molds / tooling that won’t hold vacuum. It is thru the laminate. They have came up with a system to ID it and then to seal it. www.bondlineproducts.com

#13

I used to use drafting paper The old fashioned kind that was sensitve to amonia. i would vacuum bag it and then spray the back of the tool with amonia and the paper inside the bag would show up blue where there were leaks. I need more paper, but that is how we did it.
yes the tools can be leaking. we found that to be a problem with most of our customer supplied tools.with

#14

Dougie, you nailed it…hammer on!

#15

that is a great idea, I was wondering how I would check leaks

#16

you can get leaks thru 1/4" thick fibreglass molds??? :shock:

#17

Yes…

#18

I had a mold supplied to me for a hood. It was almost 3/4 inch thick and had leaks all over. We had to completely wetout the back of the mold with epoxy laminate resin two times in order to get all the leaks.

#19

Cosby at Bondline would show me pictures of areospace molds like 50’ long and maybe 1" thick with welded steel bracing that his company would have to seal, but they use a special silicone while the mold surface is under vacuum to seal those molds.

#20

You’d be surprised by how many leaks the mold can still have no matter how thick it is. Sometimes the leak is from a crack in the gel coat where there’s a void between it and the first layer of reinforcement. This void, although small, can travel from the crack all the way to the outter edge of the mold. So in this case you’ll have leaks no matter how thick your mold is.