Hey everyone,

This is my first post but I thought it would be a proper time to join since I actually need some specific advice. I just attempted my first resin infusion from a mold I made a few weeks ago and everything was perfect (to me, but I’m anxiously waiting to be corrected haha) until I actually started my resin flow. I just wasted a whole bunch of resin and carbon fiber but not in an overly irresponsible way, I just think I lacked the experience to know what specific materials to use for my application. I think my bagging film is the problem but I’m open to ALL suggestions/burns/comments/laughs, whatever. I want to learn and perfect this, I can take the criticism. I have no idea what I’m doing haha. I’ve read many posts on here and all the write ups and videos about infusion and issues related for days on end before attempting this which I thought I followed closely and I’m sorry if my lack of experience is going to annoy anyone but I didn’t find any posts from anyone with as severe of an issue with bagging film as I just had. Anyway.. Here was my stack up.

-6-8 layers of partall paste 2 wax
-Sprayed 3-4 layers of evercoat mold release PVA
-4 layers of 3K 2X2 twill, about 1mm total dry thickness
-1 layer of green nylon mesh peel ply
-1 layer of Composite Envisions red Flex Flow media
-Stretchlon 200 bagging film. (As you can see the part/mold is deep with several tight radius’s and depth changes, so I wanted to ensure a tight fit with no bridging and I didn’t plan on baking it which is why I chose this film from everything I looked at.. this might have been the death of me)

So long story short I vacuumed down to about 27 in/Hg according to the gauge on my catch pot (my air converter pump thing that I bought is only rated for 26 in/Hg so I figured that was a good start). I valved off the bag setup and much to my surprise for about 50-60 minutes the bag held completely. I mean the analog gauge didn’t move at ALL. I presumably had zero leaks. I was quite proud of myself for a first timer. I for sure thought I was going to have a tornado of air from somewhere finding its way in but nope, held like a champ. That is, dry, at least. Problems started shortly after that when I started the infusion..

After the hour of being under vacuum I slowly re-introduced the pump to the circuit and unclamped the feed line to my freshly mixed/degassed resin cup (let it sit for 10 mins). The flow was decent as it entered the mold. It appeared the resin wanted to flow more in the left right direction but I guess that was because of how I positioned my flow media. (Not sure if there’s a way to get a more omnidirectional flow through the part? That wasn’t my main problem but I’m curious if anyone has any tips on that.) I had the resin flowing about 3/4”-1” a minute.

Here comes trouble.. As soon as about the middle third of the mold was resin saturated, POP.. hole blew open in the bagging film right in one of the round bottom edges, lost almost all vac. Grabbed my tape, sealed it off.. 2 seconds later.. POP.. another hole blew in the bag, other side, completely unrelated.. sealed that one off.. POP... POP.. POP... FML

And that’s how the next hour of my life went. Pops and tape and more pops and more tape. This damn bag blew holes in itself everywhere on the mold. Even in places that had no sharp material like along the smooth edges of the spiral tube up on the flange. Most of the blow through’s were around the radius’s and tight turns, but some just blew open in random flat spots as well. If you were walking near my garage today you would have thought a person with Tourette’s syndrome was making popcorn because there were that many pops and that many obscenities being shouted at the same time. It seemed that as soon as I sealed one off and the vacuum approached 25-26 in/Hg another hole would blow somewhere.

About 30-45 minutes into playing wack a mole and going through more than half a roll of tacky tape I waived the white flag. I couldn’t seal holes fast enough before another blew and then some of the holes I had sealed previously started to leak again. It seemed like the grey tacky tape wasn’t even sticking to the outside of the bagging film that well anymore. Maybe it was just all my sweat pouring off my face from the stress and anxiety as I watched $100 of carbon fiber and resin being thrown into the trash. I hadn’t even been paying attention to the resin flow anymore because I was panicking so much trying to seal the bag.. With about 75%-80% of the part saturated the resin flow had slowed so much because of the constant air leaks I figured at this point I should just save what little tacky tape I had left for the next run. I clamped off the resin, killed the vacuum, and went to go cry in the corner for a few hours.. I’m just kidding. I went to work. I was crying inside though.

So It feels to me like the bagging film just failed. Or I failed and used it improperly. OR I failed by using the wrong bagging film. Now it’s everyone’s turn to roast my methods. I’m hoping someone here can shed light on what caused the bag to blow me. The stretch-o-matic 200 or whatever it’s called is supposed to stretch quite a bit and I didn’t think I overdid it, but maybe I’m wrong. I even left a little extra slack before I sealed it down, but maybe not enough. Who knows. I thought I had everything down solid, but I was wrong.

Someone PLEASE help me decide how to approach this next. I already ordered another gallon of resin and some stretchlon 700 bag film because I read it’s much tougher and a little thicker than the 200, maybe that’s the key? I eagerly await all of your questions and instructions. Thanks in advance for helping me enter the wacky world of composites everyone.

PS I tried to upload an image of my mold but I couldn’t get it to work no matter what size I choose it just hangs on uploading forever. Doea anyone else have issues uploading from their camera roll?

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.

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?

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.