(Prime 20 LV infusion Epoxy) foaming under vacuum

Discussion in 'Materials' started by otseg, Jul 16, 2009.

  1. otseg
    Joined: Jan 2007
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    otseg Junior Member

    We have been unable to solve the problem of the epoxy foaming under vacuum when it hits the feed lines under the bag. The foamy epoxy goes into the top laminate stack and stays there. We get a 6' to 16" wide white streak under the feed lines and the laminate compressive properties are compromised. We degas the first 10 gallons of resin. After the feed lines fill we don't de gas all of the resin, as we have found that once the feed lines fill its not a problem.

    Anybody have a silver bullet to this problem? I'm ready for a lead one for my head.
     
  2. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    I was going to suggest degassing the resin before you start the infusion but you got that. How long do you keep a full vac on the layup before you start the resin flowing? Are you using a flow media? I've had similar results on much smaller parts. I let the resin lines fill to the point where it's just about to enter the stack and stop it for a few mins. This'll bring the layup back down to full vac before I let the resin loose into the layup. I've used heavier (Aerotech red) flow media that seems to trap a lot of the foaming resin and keep it there.
     
  3. otseg
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    otseg Junior Member

    I was going to suggest degassing the resin before you start the infusion but you got that. How long do you keep a full vac on the layup before you start the resin flowing?

    2 hrs for a small part, over night for a large one.

    Are you using a flow media?

    We are now, it helps soften but not eliminate the problem. it simply spreads the foamy resin out over a larger area.

    I've had similar results on much smaller parts. I let the resin lines fill to the point where it's just about to enter the stack and stop it for a few mins. This'll bring the layup back down to full vac before I let the resin loose into the layup.

    Thats excellent. We found out the same through trial and error. We call it burping the lines.

    I've used heavier (Aerotech red) flow media that seems to trap a lot of the foaming resin and keep it there.

    We tried both, and as far as minimizing the foam, you still have the foam. We use the green because it flows faster. This is a shot of infusion that utilizes the grooved core, no flow media. If it had been with flow media, then the white would have been softer/wider.
     

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  4. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    Is that a wood core or foam?

    Most wood is porous and will leak. Try enclosing the entire part in a bag for a perfect vacuum.

    Once you "burp" the resin lines try releasing it slowly to start and once it gets moving then open them up full.

    Are your feed lines spiral wrap? If so try putting a piece of peel ply under them and on top of your layup. The peel ply will let the resin through to the glass and maybe stop the foamy stuff from hitting your layup. Just a though.

    Have you got any pictures of your layup before you start the infusion? Maybe re-routing the vacuum & feed lines would help.

    How exactly are you de-gassing your resin?
     
  5. otseg
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    otseg Junior Member

    Is that a wood core or foam?

    Its H-80 Divynicell

    Most wood is porous and will leak. Try enclosing the entire part in a bag for a perfect vacuum.

    We use a precision Vacuum guage and our drop tests are close to perfect.

    Once you "burp" the resin lines try releasing it slowly to start and once it gets moving then open them up full.

    Substantially we do, however a small part is 10' long, a large part might be 50'

    Are your feed lines spiral wrap? If so try putting a piece of peel ply under them and on top of your layup. The peel ply will let the resin through to the glass and maybe stop the foamy stuff from hitting your layup. Just a though.

    They were Omega flow extrusions, then we switched to spiral wrap and now we have a product we make ourselves. We have tried all types of laminate stacks under the feed line. Works like a couple layers of Kevlar would stop a 9 mm. We have also laid the feed line on a 100 oz of fiberglass laid on a perf. Helps a little.

    Have you got any pictures of your layup before you start the infusion? Maybe re-routing the vacuum & feed lines would help.

    see below

    How exactly are you de-gassing your resin?

    4 gal at a time in a big chamber full vacuum for 10 minutes. The resin and hardner are dispensed through a static mixer. We are not introducing air through mixing.
     

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  6. Stumble
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    Stumble Senior Member

    Otseg,

    It sounds to me like you are experencing the effect of being to good at your quality control. :p

    I know it sounds weird, but by mixing the resin in a way that prevents bubbles from being introduced you effectively eliminate the ability of the resin batch to actually be degassed. The problem is that there are two types of gass molocules in a batch of resin, the first is the small bubbles usually caused by mixing air into the batch these are easily removed by exposing the batch to a vacume and it sounds like you are doing this. The problem is the second state of molecules in a batch.

    This is the gass molocules that are actually disolved into the liquid, and these will not be removed by simple exposure to a vacume. It requires a nucleation site for these molocules to be pulled out of solution not just a vacume. In a simple vacume degassing process the mixed in bubbles act as nucleation sites and help pull the disolved molocules out, but you are being careful to NOT create bubbles preventing this from occuring. So your quality control here is actually hurting the finshed product since the lack of bubbles reduces the ability of the disolved molocules to be evacuated. This of course leaves you with a supersaturated batch of resin with molocules of gasses just begging to be released, add in a little turbulence from being forced through the infusion process and the resin foams.

    The trick then is to try and get this supersaturated resin to give up the molocules it is storing, and that can be done in a number of ways. Either purposefully indice lots of small bubbles to act as a nucleation sight, through a process called sparging, or add a filter that is good at causing nucleation to pull the molocules out of solution.


    For a technical paper on exacally this problem see http://www.lightweight-structures.com/index.php?option=com_content&task=view&id=34
     
  7. otseg
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    otseg Junior Member

    The scotch pad as a bubble initiator I heard about earlier today for the first time. Initially I built a vacuum chamber to hold a bucket with the chamber top that had a gland into which the static mixing nozzle supplying the resin fit. Resin pissed through the vacuum on its way to fill the bucket. It was probably effective, however in another test I also watched a full bucket of mixed resin bubble so vigorously on its own, I concluded that the dispensing chamber was unnecessary.

    I could easily insert a bubble maker with air injection as a component to the static mixer, but the supplier was adamant that the resin should not be aerated.

    Yes we are all about QA procedure as we achieved our DNV approval, are working on our ABS composite certification which I formally had for my previous facility and are seeking to achieve an ISO 9002 registration at year's end.

    Functionally we solved the problem by building sacrificial laminate discrete from the real part. That got us though the parts we needed to make. Sometimes I would get cocky thinking I had the problem licked with some new procedure and then get a totally unexpected comeuppance. I need to study the link you provided in detail. I really had hoped that this was not my problem to solve.

    My guts tell me that solvent based diluents are used to reduce the epoxies viscosity for infusion, but the supplier swears it's not. I was prepared to build 1000 Kg capacity resin and hardener vacuum storage containers to pre degas the components, but was warned that needed components would be bled off.
     
  8. AndrewK
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    AndrewK Senior Member

    Otseg,

    I have experienced the same but not to the extent of degrading the laminate as shown in your picture as it is being trapped in the shade cloth used as the flow media.
    In my case I think that it is the vapor pressure of the hardener that is the problem. The reason why I say this is that the problem is much worse if I blend fast hardener with the slow. With the slow I only notice it if the temperature is >35'C.

    I placed small clear glass jars containing the fast, slow hardener and resin into a large clear jar and pulled a vacuum on this.
    After the initial release of dissolved gas the slow hardener and the resin had a gas bubble form say every 30 sec, the fast hardener every couple of seconds, clear difference.
    Vapor pressure is temperature and pressure related, if you can not resole it by other means you could try reducing the vacuum say 90% after the infusion is complete.
     
  9. otseg
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    otseg Junior Member

    I was keeping my molds and resin at a constant 82 F, winter and summer. A fellow I met found that he could endlessly make the resin outgas again after degassing by raising the temperature in 10 degree intervals. Higher temp, more gassing. Maybe it would help to keep the resin cooler.

    I did a part and infused it at 600 millibars. It seemed to not gas. then I cranked the vacuum to 20 millibars and like magic the dread white streak revealed itself. So what's going on with that??
     
  10. JRL
    Joined: May 2007
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    JRL Im with stupid

    After looking at your custom made resin sock picture I think I might have your answer.

    Your problem may be as simple as NOT doubling up on ANY of your flow medium that comes in contact with part. When you do this you create areas of low pressure that will attract any vapor/gas left in the resin. Since the areas to the right and left of the sock have more "pressure" your gas will migrate to the sock because of its lower pressure (essentially a bridge because the bag can not pull through double stacked FM). If you look closely at your pics there are signs of trapped air in the FM sock.

    Heres an example of my old nightmare. The part on the left was infused at 27.5 hg. All FM was butted instead of over lapped. The part on the right was layed up identically, only difference was over lapping FM. Both bags had absolutely ZERO leakage. This was a relatively thin layp.... 9 layers of 8.8oz glass, and max thickness of 13 layers at the base.

    [​IMG]
     
  11. otseg
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    otseg Junior Member

    The green thing you are seeing was used as a pre feeder to the primary omega flow resin feed. It was a spiral wrap, wrapped in flow media. We were trying to let the gas diffuse before it got to the primary feed line, fill the primary feed line and then have both open. It was one of a hundred things we tried. Didn't work.

    When the resin hits that big empty feed line, it foams. once it foams, there is no getting the foam out. We use the moving resin front to fill the next feed line before opening it, and that works ok for the follow on feed lines.

    What is happening to your part? It looks like the feed line was closed off and the part got sucked dry.
     
  12. Stumble
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    Stumble Senior Member

    Otseg,

    How tied to this resin supplier are you? It sounds like their tech support people can't give you any ideas of how to solve this problem, which is usually the point where I start looking for other suppliers.
     
  13. Stumble
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    Stumble Senior Member

    It looks like lead is going for around 70 cents a pound on the world market so you will probably get about half that for a keel at a scrap yard. For this much in a mass it would probably be worth calling around to a couple of yards to get prices though.

    Add in the ebay value of the winches and deck hardware, and if you are willing to take a chainsaw to the boat it might be able to help fun a more reasonable project boat.
     
  14. AndrewK
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    AndrewK Senior Member

    Otseg,

    If the problem is only in the first distribution line then at the end of the infusion turn this into a vacuum line and suck all of the gas out.

    I do not think your issue is dissolved gas but something in the resin mix boiling at the low pressure, same as what I get with the fast hardener.
    Check all of your components as I described, could also be due to wet resin and water boiling off.
     

  15. otseg
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    otseg Junior Member

    If the problem is only in the first distribution line then at the end of the infusion turn this into a vacuum line and suck all of the gas out.

    Thats effective when someone kicks a hose loose or the feed line runs out of resin. The part gets a big gulp of air, and if there is a flow media it tends to stay on top. You can suck it back out.

    This foam is the first resin to hit the part and it has shown no inclination to migrate once it is in the laminate. Prove this as you shoot a part switch to a tinted resin and you will see that the follow on resin does not push the first resin along the part, but takes the path of least resistance and wets out the dry stack, leap froggin over the first resin.

    I do not think your issue is dissolved gas but something in the resin mix boiling at the low pressure, same as what I get with the fast hardener.
    Check all of your components as I described, could also be due to wet resin and water boiling off
    .

    I think this is fair to say, however we take great pains to keep the materials dry and the part always has a bag over it if not immediately being worked on.

    The question may be are we over doing the vacuum achieved? Is there test data for laminates shot at 200, 400 or 600 millibars instead of 20-30 millibars we achieve?
     
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