according so some documentation I found, all resin shrink after gelation between 2% and 5%, polyester is the worst.
This shinkage is due to the thermal expansion occuring when hardening and then cooling later on, once cured it should not shink anymore.
In a mould, the shrinkage is on the side not adhered to the mould surface but you will get a slight inprint which can be polished off

thats the reason big patches of polyester car body filler get stressed by that shrinking on curing and will crack on the smallest bump
Sometimes that shinkage is desired whem using poliester resins on infusion because they come easier out of the mould :-)

Yes. It isn't a lot of shrinkage, you're talking 0.5-1% linear, which is very small. Certainly compared to a polyester or vinyl ester which can shrink anywhere between 6-10% linearly it is very low shrink. So low that it is only affecting the surface finish and not so much the actual dimensions of the component. And yes, doing an elevated temperature cure before demoulding the part will help drastically as this fully cures the part. But there is no such thing as a thermoset resin that fully cures at room temperature. Realistically, they cure enough in 24 hours to build sufficient strength. Then they carry on curing for a long time after that, unless exposed to heat which accelerates the cure. If this happens in the mould in a controlled manner, then you can reach a full cure while the surface is supported and not suffer bad print through (you'll still get a little bit). If the part then ever gets hotter than it was cured, or exceeds its maximum temperature rating, then it will print again.

The issue is more to do with resin content. It is the fibres that print, so the higher the fibre:resin fraction the worse the print-through will be. With a resin rich process like hand lamination, you've got enough resin that it may not become apparent.

Not all 3k's are made equal. 200g's tend to be relatively loosely woven, because that makes it easier to drape - a desired characteristic of a twill. Some 200g's are tighter knit, and handle better. While most 240's are very tightly woven, and are very stable to handle. All of that aside, it is part of the nature of carbon to distort and move as it goes around compound curvature, that is how it works. To keep things neat, you may be better placing a relief cut along the radius rather than trying to do it in one piece. A nice neat seam is usually more aesthetically appealing than distorted fibres.

Yea looking at the specs it seems like a 12K to me too. 19.75 oz or something like that..

Does all epoxy resin shrink that much? I thought after 24 hours at room temp and a 10 hour bake it’s 95% cured or something like that. The hand layup I did with the heavier stuff about a month ago and it’s still like glass (Minus my air pockets from poor saturation with the brush). I did put down an initial layer of resin as a “gel coat” though before I laid the first layer of fabric in.

The 3K doesn’t look terrible, but the 12K definitely looks “neater” and more “factory” around the bends and edges. With the 3K in the tight round pockets and corners up front in the mold I could see the orange tooling coat through the fabric where gaps naturally formed in the weave until I got at least 3-4 layers in there. It wants to tighten up at the top and open up at the bottom sort of, or something like that. The heavier stuff did the same thing but never showed any gaps through the first layer of fabric so from the outside it looks much more uniform and symmetrical. Isn’t 12K more like what would be common for a larger structural part like a carbon hood for a car?

Thanks everyone.

I have never used any of these materials before so I wasn’t sure if that was normal or not. I have a feeling that the stretchlon 200 was so flexible that it sucked down into the flow media and may have caused the unusual flow patterns.

I will look into the MTI hose too. I’ve already ordered the standard red nylon bagging material from CE, waiting for tracking. I want to make sure I get anything else I might need to make sure this next attempt is successful.

I have one more question for you all.. I used 3K 2X2 twill for this layup. 4 layers made the overall thickness about 1mm when I pulled the failed part out of the mold tonight. Each dry layer measures about .25mm thick. The individual sheets of fabric are very thin and the weave is disturbed quite easily when I’m working it into the mold. When I first attempted this mold without resin infusion as a manual layup I was using a yard of carbon fiber that a friend gave me. I just measured some of the scraps from that piece and they measure about .75mm thick without smashing the micrometer down on the fabric too much. Each individual “strand” or bundle of the weave in one direction measures about 2.5mm wide on the thicker stuff, VS about 1.5mm wide on the .25mm stuff that I just used. Does anyone know from those rough measurements what the “weight” model specifications of the thicker carbon I have here is to order?

I’d like to order some more of that heavier stuff for this next go. Even though the infusion failed I can see the finished product well and I didn’t like how the weave looked at all in the bends compared to how the heavier stuff laid in the mold the first time. It was also much easier to work the heavier stuff into this mold than the ultra thin stuff that I accidentally ordered.

I use the tyhe EasyFlow infusion mesh which works fast with epoxy IF2 resin and have a infusion spiral for the resin  and multible vacuum connectors without spiral so I can regulate the where the vacuum is pulled and stop the catch pot filling up.
With the easyflow I did not notice any flow direction no matter how you put that in, it was the vacuum extraction points which helped most.

Thanks, Hanaldo.

I was using this stuff from CE..

https://compositeenvisions.com/flex-flow-stretchable-flow-media-30-wide/

I didn’t think regular flow media should have a bias flow direction either which is why I thought I may have laid it upside down or something. I also thought it may have to do with the stretchlon film I was using filling voids in the flow media that it should be.

I guess I’ll make a nice break zone and try again when my new bagging film comes in this weekend.

Proper/regular flow media shouldn't have a flow direction, that isn't how it works. Knitted flow media and shade cloth (what some people use instead of flow media) can have a bias in one direction because it overlaps itself and so creates a bigger void for resin to flow into. Im not sure if that was you are using, but normally the red flow media is for larger infusions and the green is for smaller. But different brands change it up, just to confuse everyone haha.

Flow direction shouldn't hugely matter for small infusions anyway, you dont need to overthink that. Just have a good 2-3" brake zone at the vacuum end of the layup where you leave the mesh short of the outlet and just use peel ply or breather to continue the air path. This will choke the resin flow so the the rest of the part will wet out before the resin starts to evacuate the chamber. Or get yourself some MTI hose - this is great for learning the ropes and may save you some stuff ups.


As for bagging - pleating is not as hard as you may think. Just make your bag 1.5-2x the foot print of your mould (so use a measuring tape to measure the full LxW of your mould including the deepest sections). Go oversize rather than undersize, trying to skimp on bag will cause leaks. 

Thanks, Torsten.

I was looking at that film as well. I just ordered several yards. I guess I’ll be prepping the mold again soon and pleating the hell out of the extremely oversized bag.

How do you all position/lay your flow media? Is there a wrong way and a right way? Is there an up side and down? I noticed that when I started the resin flow the resin quickly moved left to right but not so much in the forward and back direction which isn’t great in my mold as it’s almost a square shape. I’d like the resin to reach out more uniformly. I had a full circle spiral tube around the mold flange for vacuum so the pull was even. I think it was just due to the direction of the channels in the flow media.

Any suggestions there?

+x

 

N2CFRI - 9/9/2020 2:19:12 PM

Thanks for that information. I hadn’t seen anywhere specifically that the stretchlon films weren’t suited for infusion. It makes perfect sense that the epoxy attacked the bag since I had zero leaks until it was introduced. I was using the infusion resin 4500 system from Fibreglast, but I just ordered a gallon of infusion resin from composite envisions since it’s way cheaper. I originally purchased everything from fibreglast before I found CE. I saw they have several standard bagging films. I think I’m going to call them today and pick their brain about which one to use.Do you have a suggestion for a specific film that I should look into? I also have a package of model 3578-A polyethylene bagging film from fibreglast, I had added it to my original order as a backup. It’s very cheap though and I’m not sure if I should attempt it with that or wait and get some good stuff from CE first.

Hi,
I've done my first 16 foot boat infusion last saturday and is was more or less successful, only messed up on the gelcoat brushing it  :-(
Somewhere here I read to use  nylon bagging film becauswe epoxy does not stick to it and you can save the peel ply
the standard EC nylon (red) bagging film I used was easy to put down with gumtape and the price is very competetive
good luck