Infusion Frustration

General Composites Discussions Composites Talk
#1

I decided to update the infusion tutorials so earlier today I set started a simple infusion, just a flat square. I let it sit dry under a vacuum for a hour and there was no notable drop so I went ahead and infused. I come back 4 hours later and the right side is full of bubbles. Turns out I left ONE thread of peel ply sticking out from under the tacky tape and the air leaked in from there.

In a last act of desperation I mixed up some more resin hoping to reinfuse the part but no dice, the first run gelled already.
Sigh well I’ll try again tomorrow, hopefully with better results

#2

even a 1/8 hg drop is too much in 15 minutes. One good thing to always do is do a close up inspection at the side level of the sealant tape. You will suprised how many potential leaks you can find.

#3

I’ll definitely be doing that from now on. I’ll also have to get sharper scissor to cut my peel ply and not use the same ones for cutting fiber. The dulled edges ripped the peel ply apart leaving loose threads everywhere

#4

thats why a large flange always good for infused parts, you dont need your fabrics so close to your sealant. It also gives you plenty of time to stop you resin. Did you turn your vacuum line off to see if you had a drop? I am suprised you didnt notice a slight drop from the peel ply strand.

#5

Yea I did, My typical infusion goes like this
1.Seal parts
2.pull vacuum
3.Wait X amount of time and check vacuum
4. Repeat 2 and 3 until no leaks are noticed
5.Infuse

I guess this time the combination of a slow leak and me only waiting 30 minutes was enough for me to miss it. Another thing is that I’m using a Harbor Freight Vacuum gauge and it’s difficult to read much more than half a centimeter of mercury.

#6

you can get some half decent gauges from mcmaster-carr for decent prices. accurate enough to notice a tiny leak. I think we pay $20/ea for ours. Havent had a problem with them.

#7

I’m going to do that right now. Those digital ones sure look nice but damn they’re expensive. I think I’ll get a large dry gauge.

#8

here is the part number, 38545K161

#9

you should buy a pair of EC electric scissors. They work really well for just about everything you would want to cut. A good investment in my opinion.

#10

Thanks for the tips Hojo. As I get more serious about my work the little things are starting to matter much more. Now let’s see if I can get these purchases past my professor!

#11

No problem, good luck! Cheers!

#12

Do you have a leak detector? Although I inspect my bags manually, the leak detector still finds a couple of leaks that I overlooked.

Also, a large (in diameter) vacuum gauge helps. more movement. There is also gauges which are logarithmic, so more vacuum, and they get more accurate, these are really nice, but dramatically expensive.

I get digital vacuum gauges for a decent price, these are nice too. Also some companies have digital vacuum switches with a display. I have one lying around, but did not set it up yet. to control the vacuum pump it needs more then just the switch (power convertor, relay switch, housing). It is actually the housing that lacks at this moment…

#13

I got a bigger vacuum gauge and I use an engine stethoscope as a leak detector. At the moment all the composite parts I make are for research so they’re really simple small pieces. Once I start making larger more complicated pieces though I definitely am going to buy, or at least borrow a leak detector. I saw one being used on an aerospace part and it picked up leaks I could have never found.

#14

I didn’t realize even a tiny air leak caused by a peel ply thread could cause such a problem. I believe you though. I plan on buying a larger dia. vac gauge and a leak detector asap.

I was wondering why the surface of my infused part was so dry now i know it’s from the carbon fiber strands that were trapped under the bag sealant tape and not having a perfectly sealed bag. I will also double tape all my infused parts from now on with two rows of sealant tape spaced a 1/4" apart. I just wish the yellow AT-200 bag tape wasn’t twice as costly as the black AT-199 because the yellow seals so much better. I guess I should look at it as being worth the extra couple dollars if it produces a higher quality part.

Is anyone infusing with the black AT199 sealant tape? Which sealant tape do you generally use for infusion guys? I came on the forum today to hopefully find an answer to end my infusion troubles… looks like this is a big step in the right direction.

#15

The yellow tape is twice as expensive because it’s twice as thick! I use the yellow tape for pain free infusions, the large width and extra thickness make it easy to push all the creases of the bag right into it. The black tape works as well but it’s less forgiving. If I have a piece I need well made I use the black in the inside, yellow on the outside and black to seal leaks I find. If I was ever to make a critical expensive part I would use yellow twice.

#16

The yellow has a higher operating temperature so is good for autoclaves. The black has a lower temp so can’t be used in autoclaves.

#17

I also use the yellow and wont use the grey or black anymore. I would have leaks or the tape just wouldn’t stick if you touched it by accident. The Yellow you can lay the bag down, lift it back off and re-position it then lay it back down and have no worries. Plus if you tape it twice with the black your using twice as much material, and you said the yellow costs twice as much. So aren’t you really spending the same amount of money and doing more work? I pick up a case of yellow and it can last me 6 months and they have a shelf life of 1 year at 72 degrees F.

Oh and that stethoscope that Canyon talked about, those are a great investment if you can’t get one of those ridiculously over priced composite leak detectors. The automotive leak detectors Canyon was talking about can be bought for under $100bucks. And if you find the right one, they do the same thing. The just doesn’t say composite on the package so they can’t screw you over on price.

#18

The stethoscope I bought was just basically a doctors one with a rod instead of a flat disk at the end. It cost me approximately 4 bucks. Rotorage is right though you can picked up automotive ones for cheap.

#19

About Airtech AT200Y and AT199, and sealing in general:

So far, with the aid of a leak detector, I never have been able to not seal a bag properly, whichever tape used. I use Terostat 81, Ce-Sense Sealant tape (our own product) or Airseal 2 by Airtech, and they all do the job. I have even been able to seal a bag properly using a 10x1mm sealant tape (roughly 2/3 the with and 1/3 the thickness of what is normally used).

What is critical is fiber pollution. Always clean the flange with a rag before putting tape down. Perhaps even twice. And use the leak detector. (whichever type). I will see if I can offer a good deal on them. Lot of companies make a lot of money on them. Leak detectors sometimes even surprise me for finding leaks I could not imagine were there.

If you find a fiber protruding from the tape, fold back the vacuum film, stick another piece of tape over the edge, remove the backing, and fold back the vacuum film again. This usually does the job.

If you like double seams, make sure you apply a piece of permeable material between the 2 tapes. This could be anything, a piece of rope, a strip of bleeder, or some tube mesh, which we sell specifically for that purpose. Then apply a higher vacuum on the so created double seam. If a leak occurs, it will get solved by the high vacuum between the tapes. The same principle is sometimes used when bagging for a 100% void free carbon mould, where not only the tape seam is double, but the whole bag, with strips of bleeder every 30cm between the double bag. It is a lot of work to setup, but it assures a perfect airtight bag.

#20

This is a great idea. Ensures you get no leaks on the part even if you do have leaks in the bag. It is complicated but when you’re making difficult and expensive parts I’m sure it’s worth the trouble