Using spiral wrap in a traditional vacuum bagged layup...

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#1

has anyone ever tried vacuum bagging using spiral wrap around the entire perimeter of their mold as a means to draw the air out of the bag and to ensure that you have a full deep vacuum drawn over their entire mold?

I have a very large mold, It’s 10 feet long, about 18 inches wide at it’s widest point and 22 inches deep at its deepest point, sort of canoe shaped but for a streamlined human powered vehicle.
I usually work by myself so when It’s time to do a layup I am going fast and furious to get the fabrics saturated and to get the bag around the huge mold.
I have pulled a couple of parts out of it using vacuum valves at fore and aft but I have found out after pulling the parts out that big pockets of resin have been trapped in the middle perhaps from having the resin cutting off the flow of air and it seems that no matter how much breather I put in there I get things like this. I can’t put my valves in the mold itself, they print through and leave distortion on my part, I have to put them on the flange at the nose and tail. I use tons of breather around the inlets and run long pieces down the center of the mold to ensure that the air is not cut off in between.

I’ve thought about going to a fully infused part but I don’t like how I have to change to a very thin epoxy resin. I like using Adtech el-335 but it’s just too thick to infuse. It wets out fine in a standard vacuum bagged layup but it doesn’t like to stay on the almost vertical walls of my mold so I get lots of pinholes around the more vertical surfaces in addition to the pockets of resin in the bottom of it and in the middle.

logic is suggesting to me that having spiral wrap around the entire perimeter will help draw a more even and consistent vacuum over the entire mold. Has anyone tried this?

My pump can pull 29.5 inches so I know I can get the pressure to flatten out these spots, I have even built a 6 port vacuum supply manifold with valves and vacuum gauges so that I could potentially use them to monitor the actual pressure at various spots around the mold.
I have a 75 gallon air tank that acts as a ballast so that I can evacuate the huge 12 foot long bag I need to surround the entire mold quickly after I saturate the fabrics and I use huge .500 ID vacuum lines and It only takes 3 minutes from the moment I seal the bag to the time that it is tight around the mold.
I weigh all the fabrics going into the mold and then add 30% more resin, 8-10% of that winds up in the mixing cups. I have gotten a 55/45 ratio of fabric to resin by weight. The rest of the resin winds up in the breather and peel ply. but I get tons of pinholes along the sides and pockets of resin in the middle.
Maybe some of the resin is kicking early when it pools in the middle and then blocks off the breather but that is just a guess. I usually get a 45-60 minute work time with this resin and the bag is at 20 inches or better an hour after the first batches were mixed.

Am I doing something wrong here?

Any suggestions?

#2

yes its a very common and effective way of getting good vacuum with less ports on large molds

#3

You sure you don’t wanna do a full infusion? Wet lay-up and bagging off something that large is pretty tough…It sounds like you have all the equipment necessary to infuse the part.

You could bag off the entire mould, run a spiral around the perimeter and infuse from the center of the mould. The perimeter spiral should pull the resin evenly all the way up the mould.

You can put a 3 point barb nylon feed with spiral a few inches long on either side of the barb fittings, wrap that in peel ply and fold it up into the bag. It will stay off the part and not print through. You can sip a coffee and watch the whole thing infuse at liesure. Just make sure you have enough resin to keep it fed in case it requires more.

Not suggesting your way is wrong, just another approach perhaps…

#4

Thanks everyone,
I’m starting to warm up to the idea that infusion is really the way to go on this.
I have compiled a big checklist of things not to do and things I should do when it comes to infusion…

  1. use an infusion specific resin that is less than 600cps…check, Adtech marine 820/823 has a 350cps mixed viscosity with good cured specs and is UV stabilized.
  2. Use a flow medium to help the resin flow along the top of and through the fiber stack…I got that.
  3. don’t run the flow medium all the way to the edge of your part, resin will just racetrack to your spiral wrap and won’t penetrate the fiber stack, run it a few inches away…I get that.
  4. Don’t infuse a part too fast otherwise your resin won’t get through the fiber stack. degas your resin…and so on and so on…

So let’s say I got the fiber stack in there, then i got the peel ply, then I got the green mesh tacked on top of the peel ply followed by a long strip of soric running down the middle of the mold so that the resin has a front of about 18 inches to travel to the spiral wrap, perforated release film on top of the green mesh and soric flow media (cut away where the resin enters, I do this to protect the bag from the sometimes sharp edges of the green flow media, it also contours better than the bag material and will resist resin bridging, there could be a pleat in the bag but the resin will never see it because of the release film between it and the bag).

What vacuum level do you have present on your mold before you open up the resin supply?
And what is the advantage of leaving the vacuum as high as possible before opening up the resin supply? Aren’t you compressing the fiber stack so much that the resin won’t penetrate it as easily?
I get that by drawing a deep vacuum you are also removing moisture as well as air but can you overdo that?
And in the event that the resin is moving too quickly do you…
A. reduce the vacuum level at the pump, or…
B. restrict the flow of the resin?

And what do you guys use for brake zone material right before your spiral wrap?

If I’m understanding the infusion process right it seems there are different stages to the infusion. Fist stage is to infuse the laminate stack at the right rate based on the the viscosity of the resin and the gel time. Then you enter the compaction stage when you cut off the resin supply and you crank up the vacuum as high as it will go to compact the whole thing and to draw all the air and moisture out, then you keep the part under vacuum pressure for 12 hours.

I could use my vacuum supply manifold to create zones around the mold where I could help the resin front move along if it’s reached a zone already. I am considering using a tee at the resin supply to use as a secondary vacuum source once i cut off the supply of resin. Then I am ensured a deep consistent vacuum over the entire part.

Am I missing anything here?
Any other suggestions would be appreciated.

#5

Not missing anything ^ you have thought this through…what I can tell you is what we do, often we try to minimize the complexity of shooting the parts, we have done a full spiral perimter, how we would do it is as follows:

After the lay-up schedule…(carbon/glass in the mould)

  1. Lay the peel ply down, we use econostitch red stripe, we run it over where-ever there is glass, single layer.

  2. Flow media, we use Air-tech but the red flow media, not the green. We will take a 3 point barbed nylon fitting, place about a 4" to 6" spiral tube on each side of the barb, wrap it with the econostitch (one layer) and set it aside. We do double up the flow media where the infeed of the resin is to help expel it away from the feedline, since it is the entry point, there is plenty of penetration, this is really a judgement call you can make on whether you feel comfortable or not having it doubled up. If you do decide to do it, a small square is all that is necessary.

  3. We run the flow media within a few inches from the edge of the mould where the part will end.

  4. We bag the mould off at this point, most moulds we will bag the whole thing, not just from the flange with AT-200 but a full wrap around. This ensures you do not have air issues provided the bag is sealed and no leaks.

  5. We connect the feedline(s) and vacuum line up, fold and clamp the resin line and put vacuum to the mould, we pull 28 on the gauge.

  6. We mix the resin (epoxy), take the resin feed line, un-clamp but keep it crimped by hand, drop the end into the resin bucket, un-fold the crimp and let it infuse…

That’s it…we keep 10 hours vacuum on the part via a timer on the system which shuts it off when done. We do not de-gas the resin either, we just mix it reasonably not to cause excess air.

Hope that helps…

#6

You are nearly there.

Some random remarks:

-your current resin seems to be quite low in viscosity, as it sags from vertical walls. Also, with wet bagging, I like the vacuum to be at about 50-70%, not more, to prevent resin starvation. This in combination with P3 or P31 perf film.

Now onto infusion:

place your dry stack, using spray glue when you need it (spray lightly!!!). If you do not need it, so much the better.
if you want a course surface, use peelply. Otherwise, don’t.
then comes the perf film. I have no idea what you have right now, but use a P, P1, P16 or MP22 style, or use Fibertex “Compoflex 150” material. (which is also available in combination with infusion mesh).
A spiral can go in the middle, as a resin feed. You can wrap it in mesh, and manouver it into a pleat of the bag, or use “Enkachannel” or “Resintrak (Airtech) which does not leave an imprint.
the resin feed can be brought in through a hole in the bag, and a special connector, or do not bother, take a T-piece, and a piece of hose, and bring the hose to the side under the bag, leaving the bag in a pleat on the side. (I do not like holes in the middle of bags)
Use a good vacuum film. Normal 50mu nylon film should not be harmed by infusion mesh. 75mu (0,003”) is even sturdier. Make sure you have enough pleats, so you do not have bridging.
As for the vacuum side, keep the infusion mesh some 50 mm short. Install a strip of peelply around the perimeter, and place a spiral on top of that. Or use MTI hose. Both will save you when the resin front is not reaching the side everywhere on the same time.

Pull agood vacuum, and test the integrity of the bag with a drop test. I prefer a vacuum of at least 98%, at which water boils. You might end up boiling off quite some water, especially in humid conditions, and when balsa is used. Sometimes you see the vacuum stall at 98%, for sometimes an hour or more, then suddenly drop further. That is when the water is gone.

Keep in mind Soric needs about 30 minutes to settle and equalise pressure. Foams might have the same issue. You can do a droptest only after that.

I like to infuse at as high a vacuum as possible. Even with polyesters. I tried boiling off styrene, but I did not manage with my 2-stage deep vacuum pump. water was no problem to get boiling, though.
After the infusion I like to bring back the vacuum somewhat, to say 95%, to prevent further water boiling.

Indeed to get a more even laminate, after infusion you can apply vacuum on the resin inlet. Rig a T-piece and 2 valves in the feed line, and connect the T-piece to a resin trap, and vacuum pump. After infusion, close the valve to the resin, open the valve to the resin trap. This works wonders. Expect some 5% of resin to come out. (based on my experiences with a 23 meter boat, and some 2400 kg of resin, of which 130 kgs came out again.

Todo list:
-check perf film (style)
-get the missing stuff
-run a small test (some 30x100cm) to get some experience and test the materials.

Edit: SLS was faster…

Edit 2: And the answer is B. Restrict flow. And use a mesh which is slow. Most hard meshes are way too fast for small products and thin products.

#7

We have done a few large projects such as carbon foam cored boat hulls 28’ with one [vac](javascript:void(0):wink: port and spiral wrap around the edges. It sounds like you are having trouble with the even transfer of your vacuum onto your parts not in direct contact with the bleed and from your description it sounds like you don’t cover the whole part with bleeder, if you did so it should help with [vac](javascript:void(0):wink: distribution you could also try a netting over the top. We make our bleeder a little bigger than the part place the spiral wrap on top then fold back over the bleeder onto itself around the edges making a pocket for it. Stick with masking tape or spray glue. Do you use release film under your bleeder? Pre sticking it to your bleeder can save a bit of time when it come to getting your bag down quick.

#8

Thanks guys, This is all extremely helpful,
In response to Herman, you lay up peel ply over your fiber stack and then perforated film before the flow media? What is the reason for doing so?

Also, you run your resin supply hose under the bag from the side to the middle where you hook a t-fitting to it and go spiral off in both directions? any particular reason you don’t like putting a hole in the center, or am I not seeing this right?

In response to Wightmarine,
“It sounds like you are having trouble with the even transfer of your vacuum onto your parts not in direct contact with the bleed and from your description it sounds like you don’t cover the whole part with bleeder”

I did cover the entire part with bleeder, even over the flange. Everything had peel ply and bleeder and copious amounts of breather everywhere, even under the mold and 3-5 strips of it down the middle of the mold. But the breather would still get filled with resin and then the pockets of resin would be pooling in the middle (lowest point of the mold).

I did a different part (traditional vacuum bagging) that involved putting 1 layer of 18oz hybrid glass/carbon, peel ply then alternating layers of bleeder and breather. I still had lots of pinholes in the final part. I was hoping that the bleeder (finely perforated 1 mil release film) would help keep the resin in the fabric so that the breather would not get cutoff with resin. I don’t think I underestimated how much resin I would need for that heavy fabric but it turned out very badly non the less.

#9

In response to Herman, you lay up peel ply over your fiber stack and then perforated film before the flow media? What is the reason for doing so?

Also, you run your resin supply hose under the bag from the side to the middle where you hook a t-fitting to it and go spiral off in both directions? any particular reason you don’t like putting a hole in the center, or am I not seeing this right?

I usually do larger boat projects, where the peelply needs to stay in the hull, but the rest of the materials have to go out. Therefore I put perf film on top of the peelply. If a peelply finish is not desired, I put the perf film on top of the laminate, or use Fibertex Compoflex 150, which works so much better. (and pulling it out is a cinch)

Why I do not like holes in bags? I usually work with a quite inexperienced crew. Holes in bags are a vacuum integrity issue, they need to be done right. If I can prevent a hole, why not?