edges of panel under vac

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Sep 6, 2017.

  1. fallguy
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    fallguy Senior Member

    Yes. This is precisely what is happening. I am using a wet bag layup, not infusion, but the problems are exactly as explained. There is air from several sources.

    1. A simple bubble that is trapped in the fabric (22 oz triax), either from a miss with the laminating roller or
    2. A bubble formed when we place the wet corecell over the wet glass or
    3. The other is foaming created by us when we roll out or
    4. Still another is the rebate edges-they are taped down to the table and form a pond and that pond edge is impossible to get bubble free, but I have resolved myself to sander repair there and the veil will support that work (allow some sanding).

    I think if I increase resin and decrease roller work (overworking), we will have less trouble with 1 and 3, but not without other problems.

    If we wet out the corecell just before laying it down that should help as well as the hardener will dry out. A drier spot would cause a disruption to any flow.

    And I am using epoxy compatible veil under the triax for a surface finish, ultra thin csm looking stuff. The veil does not seem to enhance or change the issue. I think I need to turn up the pressure as well, but that is not without problems. The breather fabric is above breather film and it is getting saturated already. So I think I need to turn the pressure up closer to gel or add another layer of breather fabric and anticipate higher resin loss. Also, I am getting a lot of bleed through of resin on the edges that requires trimming. So I was also going to turn on the vacuum before sealing the bag and try to get the part edges sealed, perhaps with some Ziploc bags filled with sand. We are not using a caul plate-the parts are 33' long by about 30" wide.

    I had considered trying to use all my resin for the bottom and the top on the bottom and then trying to scoop excess resin off the part as well. We are definitely overworking the glass. I think if I run at about 200% epoxy to glass ratio, I can cut down on the bubbles from overworking, but there will probably not be a significant amount of epoxy returning to a bucket and I will end up with saturated breather in exchange. So would you guys try to double the breather film and create a trap or double the breather fabric and expect losses or both or neither?

    When I did sample work; the 200% parts came out looking perfect, but my samples were small and had no rebates. And the resin losses on the 200% parts were relatively high. For the part in question, the increase in resin over a 6.5 m^2 part would be 70 ounces, or roughly 6#. I have a feeling that would all end up in the breather fabric. Maybe I should just double up the film and fabric and go for the 200% one time. The film is reusable.

    I ran peelply on both sides this time with similar results as before.

    I do not have enough resin at fabric weight plus 350g/m^2 to be able to use a squeegee. We are using a foam roller to even out the resin prior to laying the glass and then we have a crew of 3 people using 6" aluminum laminating rollers to finish the wetout and remove bubbles. The edges need lots of help with the wetout as the epoxy is in the rebate pond, if you will.

    sorry for rambling-middle of nite, lots to cover to fill you guys in
     
  2. rxcomposite
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    rxcomposite Senior Member

    Infusion, wet bagging, or prepreg the principle is the same. We started with prepreg as we were manufacturing aerospace parts. The prepreg is in "B" stage, partially cured, so when heat (resin turns to liquid) and vac is applied, it is basically wet bagging. The caul plate was just for a good finish bot sides. Peel ply on both sides would also work.

    A client wanted the wet bagging process, so we used the same set up. The same set up, though lower vac. and we use vinyl ester resin.

    Aren't you using resin traps? If not, you can try clamping the vac line on that area. Wet bagging is in principle, is to squeeze out the excess resin. You maybe using too much resin. Try rolling it out more carefully. With us, we just dump the premeasured resin in the center and with a little rolling, we let the vac do its work. Look where you have too much resin squeezing out. That is where your problem could be. Clamp the vac when it starts to overflow.

    I doubt doubling the breather film will work. You will just be sucking more air. There are films with big holes, small holes and yes different spacings.
     
  3. fallguy
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    fallguy Senior Member

    I'll try adding resin and report back.
     
  4. AndrewK
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    AndrewK Senior Member

    I was misunderstanding your resin % ratio, I assumed when you say 150% that you were using 150% of glass weight + the 350g for the core. Which is excessive.
    Better to talk about the ratio of resin to glass in the laminate alone.
    Good to know that a small test panel produced good results although when you say 200% resin I still dont know the % glass:resin in the laminate. As you observed it was too much resin.
    The more excess resin you have the more volume in your breather you require, but its a lot of waste.
    If you take the veil out of the equation, 1:1 by weight resin: glass ratio is enough to wet out and fill the voids between the tows in your stitched glass reinforcement.
    You could actually be floating your glass on resin.
    This is why I suggested that you lay the peel ply and glass first and pour resin over the top. First work with the squeegee at about 60 deg angle to the glass to spread with light pressure. Then lower the angle to ~10 deg with more pressure and you should hear any remaining air popping as you work the laminate, once you can not hear the air popping its done.
    Then wet out one side of the core with the 350g/m2 and press down on to the laminate, when pushing down the core you should observe resin rising up through the perforations in the neighbourhood where the pressure is applied. And resin go back down as you release the pressure.
    Put at least 2" pleats along the edges of the panel plus another pleat every 2 metres.
    To eliminate the bridging at the core edge use a 4" paint scraper and cower with ~ 6 layers of masking tape, use this to push the bag film into the core edge. You have to do this just as the excess air is evacuated from the bag, you will need to open and close the vacuum a number of times at this point before you start forming a vacuum in the bag.
    You can increase the vacuum to 80% if you wish, any higher you can start forming micro voids between the glass filaments especially if you have overworked the laminate with rollers.

    How long have you been leaving the vacuum on for? and what is your working temperature? Note that your resin gel time when in the thin laminate could be many hours, 6++.
    Also pictures please.
    Cheers
    Andrew
     
  5. fallguy
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    fallguy Senior Member

    Well, I found the issue. I am not wetting the core out enough. I made a spreadsheet error. I'm a spreadsheet expert, so very embarrassing. I will send you some pictures of the next part. Thanks.
     
  6. fallguy
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    fallguy Senior Member

    If I wetout the corecell more, or rather adequately, I will have trouble with bleedout, though, I'm sure. Probably will need to turn the pressure down more, perhaps add breather film and double the fabric. My gel time is 120 minutes. I have been leaving the vacuum on a minimum of 8 hours. I had left it on longer earlier, but my pump got super hot, so now I am shutting it off before I go to sleep. My house is massive and a fire out in the boat building area would really get going hard before I knew it. The other thing I could do is avoid turning on any vacuum until 90 minutes after the mix. I don't have the viscosity numbers, but could get them if I worked a bit.

    So, when I redid my numbers, I come up with the following. For a 10.1# piece of 22 oz triax and a .71kg/m^2 corecell wetout rate.
    Fabric wetout at 120% 181 oz
    Corecell wetout 136 oz
    vs what I actually did
    Fabric wetout at 150% or so 216oz, plus 24 oz (from underneath)
    Corecell wetout 44 oz, plus 24 oz (we used more because it seemed too dry (and was))

    For a total of 317 ounces calculated
    308 ounces used.

    However, distinctly different if we wetout the fabric from above and reduce foaming under the glass, and we use lots more resin on the corecell before laying it on.

    For the topside of the laminate, I calculate
    @100% for wetout or 143 oz
    and corecell 136 oz or a total of 279 ounces

    versus used amounts of
    188 ounces.

    I doubt I can even get 279 ounces of resin into the top without making a sloppy mess, but we could for sure go higher than the 188.

    Just real concerned about the excess resin.

    I did not make any allowance in the calcs for peelply and veil..Do you have a resin number for peelply?

    Thanks for your thoughts.. this is a startling revelation.. funny thing is my old friend thought the corecell was drinking resin, he was right

    The other issue is with 120 minute open time resin, when I mix the resin for the bottom, that is the start of my clock. I pour the resin immediately after mixing. Then I have been avoiding mixing the resin for the top of the job until needed. So, for example, if I start at 1pm and it takes us 30 minutes to apply the first coat of resin, then we have 20 minutes for core wetout and application, we'd be at 50 minutes. This is when I would walk over to the prepared resin and hardener and mix for the top. So, let's say for simplicity it takes 50 minutes to do the top and bag. If I turn the vac on at 100 minutes, I will have 70 minutes before the top gels up.

    Do you think I ought to switch to a slow hardener on the top side. That'd mean my topside laminate would gel at about the same time. Is that legit?
     
    Last edited: Oct 7, 2017
  7. rxcomposite
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    rxcomposite Senior Member

    We never had problem with corecell "drinking too much resin" but with the old diab core, it does. If you want, you can "hot coat" the core ahead with resin before laying down the parts. Hot coat means you coat it with resin on all side and let it cure to tacky cure or aggressively tacky.

    Also, it is easier to break down the resin consumption. For hand layup, WR will be about 1:1 ratio (100 oz of resin/100 oz. glass. or 50/50). For veil, it is about 15:1 (you really need to wet out the veil as it is its purpose, resin rich). Add the hot coat of about 12 oz, yard square/per side. Just add all it up (use Excell) and add a fudge factor of about 15% for a start then reduce as you perfect your process. You will be shooting for about 38 to 42% final glass content (WR) so the excess resin will be eaten up by the peel ply and the bleeder cloth.
     
    Last edited: Oct 7, 2017
  8. fallguy
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    fallguy Senior Member

    I missed the Gurit spec wetouts by tons. And I was blaming their marketing department, or at least wondering. I'm sure it is the cause of my imperfections. Given the fact I used a conversion and was running 3-6 ounces per yard instead of 18.5. Or a factor of 5 from spec.

    Here is how I erred. It is really sad.
    .71kg/m^2 convert to pounds = 2.2#/kg = 1.562#/m^2
    or in my case
    .71kg/m^2 convert to pounds (DO NOT USE THIS!!!) = 1#/2.2kg = 0.322#/m^2

    For an error factor of 4.85. Of course, we had trouble with the core getting wetted well at the low number, so I had been making extra batches. The last one I ran double on the error, but was still off in total by about 5# of resin. As an American, I hereby declare my rights to blame the metric system. (not)

    Yes. I did it. And I was a great student at chem and math and would rarely ever make such an error, so it really was just a boneheaded clerical move. Arggh!!

    What about going to slow on the top and xslow on bottom to get the cure rates closer and cutdown on breather getting fully wetted? It will. 70 minutes of vacuum to gel time is what I calculate for the top, 20 minutes for the bottom.

    I think the veil weight is in the order of 1.1 oz per yard, so for 7.3 yards, 8 ounces. So, the 15:1 would mean 120 ounces for the veil? I put it on my digital scale and it actually didn't register, so it might be lighter than that even. The veil doesn't wet out easily. It is so thin it tears rather quickly. I need to actually call the vendor on it because it seems lighter than 1 oz per yard. We could do a partial wetout of the veil, then a top down wetout of the fiberglass, but the veil is too thin to run laminating rollers over without tearing it, and when we ran the foam rollers, they tended to lift it.
     
  9. rxcomposite
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    rxcomposite Senior Member

    You can get 12:1 low on veil on the thick one.
    Wet the surface of the mold first with resin, lay the veil over to tack it then roll with a very wet roller.
    Or you can lay the veil over the mold, tack with resin on several points, then roll with a very wet roller. Keep it wet so there is no friction. Some use 3M adhesive to tack it.

    Try this Textile & Fabric Weight Converter http://www.ginifab.com/feeds/ozyd2_gm2/
     
  10. fallguy
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    fallguy Senior Member

    I will lay the veil and wet it. Then if we are careful we can do a light wetout of it and roll on the glass and wet it from above. I will still have to resolve the excess open time on the top laminate. It won't cure for about 70 minutes of bag time and that is an awfully long time for the vacuum to press on it, don't you think?
     
  11. rxcomposite
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    rxcomposite Senior Member

    Should have been "resin content". Glass content (Gc, the correct way of expressing it) is about 54-60% for wet bagging.

    Prepreg and autoclave has the ideal of about 70% glass.
     
  12. Tungsten
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    Tungsten Senior Member

    So if at 50/50 glass resin could you not wet the table glass 100% and the top glass at 50% knowing 50% of the table glass resin will be passing through the top glass under vacuum?Ive had success with this in small panels not sure how it would work in such large panels.
     
  13. rxcomposite
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    rxcomposite Senior Member

    There are many ways to skin a cat (no pun). My friend works in racing boats and has to do a one shot infusion of the large cat's hull. The outer layer has to be super smooth so they lay the veil cloth first, manually wet lay it up taking time to really lay down a smooth surface. (Veil is very hard to layup. It does not conform to odd surfaces like CSM or loose weave WR). Let it dry tacky, then layup all the rest of material to do a one shot infusion.

    Notice that the process is infusion but the way they lay up the veil is standard wet layup, wait, then then cure.
     
  14. fallguy
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    fallguy Senior Member

    This might help, along with running slow hardener on the top to match cure rates more closely and avoid 70 minutes of vacuum on the inside or top. However, it will be more on the order of say 120% on the table glass and perhaps 80% on the top glass, but I think that is what you mean. We will probably have a fully saturated breather with these rates and the Gurit core wetout numbers. Gurit's spec is 710g/m^2 for core wetout, which is double what Andrew suggested and like 5 times my errant rate. I'd like to follow mfg spec on the next panel.

    My error was in the math, by the way. I had everything written down right, but for some reason divided instead of multiplied. The ONLY reason I discovered the error is Andrew's comment of 350g for the core. I realized that was more than a half pound! Then I realized Gurits spec is over a pound! Darn metric system got me good. The guy in the mirror is an idiot.

    RX - thanks for correcting yourself, I had no idea to what you were referring on the abbreviation.

    I also plan to turn on the vac at 100 minutes, but I expect problems with saturating the fabric. The breather film is reusable or at least it seems porous yet and comes off in one piece, so very tempting to double it and double the fabric. I would end up with a higher resin content and a heavier part, maybe a really nice part even!, but if I do a test run with a bulkhead, I'd get a good idea about how it all works.

    If I saturate the breather fabric, I think I run the risk of losing vacuum on the part to some degree. On the large panels, I run 4 inlets. Even now, there was pretty good saturation in a place we were heavy, and I'm in the neighborhood of adding 5-8 pounds of resin more.

    When I did a minor repair to a destructive test yesterday on BH5 edges, I had a lot of trouble with the wetout of a tiny piece of 22 oz. It is gruesome stuff, especially between that 90 degree section. I realized that bar none, I must wetout both sides of the fabric as well. So my peelply and veil wetout and then another wetout of the glass from beneath and above and a heavier wetout of the corecell is a sound strategy for improvement on my issues. And I do have issues, I have a lot of parts to inject now, so this isn't just a rabbit hole I've taken you all down. Thanks for the continued advice and support.

    Someone told me to use 7g for the peelply, so I think I'll do the same for the veil.
     

  15. AndrewK
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    AndrewK Senior Member

    How much resin are you using for the core? I allow 300g/m2 each face, this is not too different to my interpretation of the Gurit guide 710g m2 both sides ie panel not one surface. I would be shocked if they say 710g each face.

    For thin peel ply that I use I allow 35g m2 for infusion, dont bother for wet bagging as there is excess resin when using 1:1 weight ratio in the laminate.

    Gel time; your 120 minute system is for 100g @ 25'C in a standard size container, in a thin laminate say your 750gsm triax this will be ~8hrs at 25'C. So you need to run the pump for 8hrs at 25'C.
    As a rough guide for every 10'C deviation from the reference temperature you double or half the gel time.
    eg at 35'C 100g in the standard container will be 60 minutes and ~ 4hrs for a thin laminate. And at 15'C this will be 240min and 16 hrs.

    Once again my recommendation is to ditch the veil, it is only complicating things for you. Also making your parts heavier and more expensive for no strength benefit.
    As a guide I found that the very lightweight veil under 100% vac was close to 1:1 weight ratio (if my memory is any good), so a lot different to when it is used in open molding as intended.

    In your post #21 are you saying that to wet out the bottom laminate and core it takes 308 oz, and for the top 188 oz? Surely the veil is not responsible for the difference?
     
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