Vacuum Infusion of Lightweight Materials

Discussion in 'Fiberglass and Composite Boat Building' started by packsail, May 10, 2012.

  1. packsail
    Joined: Feb 2012
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    packsail Junior Member

    I'm having a bit of trouble trying to get my laminate schedule properly wet out in vacuum infusion test panels. I'm using a 24 ounce biaxial glass on both sides of a Divinycell foam core which is grid cut with scrim.

    We have done plenty of tests and have been successful when adding layers of continuous filament mat to aid flow, but that is too heavy for the design.

    Does anyone have any ideas or lessons learned for getting difficult biaxial fiberglass to fully wet out?
     
  2. CatBuilder

    CatBuilder Previous Member

  3. groper
    Joined: Jun 2011
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    groper Senior Member

    Please provide full details of your infusion setup, otherwise we cant help... with infusion, the devil is in the details, everything must be perfect... so you need to tell us EVERYTHING :)
     
  4. packsail
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    packsail Junior Member

    Details of Infusion

    Yeah, I lacked quite a few details. We may have been successful today with a test infusion using Compoflex on both the mold side and bag side of the part. Here is our laminate schedule:

    Compoflex 150
    EBX 2400 (24 ounce biaxial glass, +-45)
    5/8" Divinycell Foam Grid cut with scrim back
    EBX 2400
    Compoflex 150

    The compoflex acts as a flow media and a peel ply in one. I'm guessing this is similar to combining a peel ply with a green flow maybe?

    We've had some racetracking in initial tests but know how to avoid that now. The biggest problem is the 45 degree glass and the grid cut foam. The glass does not like to fill in completely in each square. I'm attaching an image to show.

    The only success we have had so far is adding layers of continuous filament mat, but this will add more weight than we are willing to accept. Has anyone ever put removable flow media on both sides of the laminate? laminate.jpg

    peel top.JPG
     
  5. groper
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    groper Senior Member

    ok, in the first pic, when you try to curve the grid cut foam, the cuts open up creating large channels and racetracking pathways. You will find it impossible to design a strategy like this. You need to bog up the grid with a lightweight filler once its in place and do a single sided infusion only with flow media over the top - i use 30% shade cloth as a cheap flow media costs approx $1 per m^2. You can fair the core after bogging it up to get rid of some of the "blocky" surface it will have.

    In the second pic, incomplete wetout between grooves, tell us how fast is the resin front flowing? If things go too quickly, you will get this effect, you might need to slow the resin front down to give it time to wetout the glass between channels. Adding a flow media over the top, whilst it shouldnt be nessesary, will certainly fix the dry patches between blocks if you cannot control the size of the channels in the core...

    How much vacuum can you achieve with your pump?
    Whats the viscosity and type of resin and the temperature of the resin?
     
  6. CatBuilder

    CatBuilder Previous Member

    One quick way to fix your problem would be to put a skim coat of bog on the foam so that you can create a proper (unscored) surface for your infusion. That would allow it to wet out completely.

    My decks are balsa blocks (just like your foam blocks) with scrim backing. I skim coated the balsa to keep weight down and to provide a better surface for infusing.

    Alternately, you could thermoform your foam (using cheaper, regular foam instead of scored), arriving at a perfect surface for infusing immediately with no bog.

    A scored foam like you have is not the best core for infusion. Getting the core right from the start makes the infusion easy.

    What I think happened on the test piece with the dry spots is your entire infusion was racetracking. The resin went up the scored channels quickly and wet out in a sort of "v" pattern between each channel as it went, then each side of the leading wet edge tried to join but the resin was racetracking through those scores too quickly for them to join in the middle of each block. You need to get rid of the scored surface.

    Are you using special infusions resin with low viscosity?

    When doing flat panels, I have always put removable flow media on both sides (green flow and peel ply combo only, not the all-in-one product you are using). However, if infusing both sides in that fashion, you need to have perforated foam (holes in the foam), so both sides infuse properly and completely.

    PS: Don't put fiberglass on your couch!!!! It will be soooo itchy later when you go to rest on it!!! And you will never get all the fiberglass out of the cushions. Don't let your wife see that if you have one. :)
     
  7. groper
    Joined: Jun 2011
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    groper Senior Member

    Packsail, I know you have a male deck mold... This is how i would approach getting the deck finished using your scrim backed grid cut foam. Otherwise, a different core material might be a better option

    1. Hand laminate the bottom skin onto the mold using coarse peelply over the top so you can tear it off ready for bonding (no sanding)

    2. Once the peeply is off, trowel on a thick thickened resin bog mixture to the glass skin using a very slow resin / hardener combo to give you ample working time.

    2. Place the foam core scrim onto the bog and vacuum bag it down with very light vacuum pressure using peelply and flow media over the top to allow even compression. The excess bog will fill the grooves in your foam when its sucked down.

    3. after its cured, remove peelply again and do a top surface infusion with flow media to get the top skin done.

    You would have the core all precut and numbered so the jigsaw of pieces fits nicely on the mold before you started... Alot of work huh? defeats the simplicity of a single shot infusion too doesnt it... compound curves are a tough one, double cut foam would probably be better and give a much more even wetout and no racetracking, but still i dont know how you would hold it down onto your curvy male mold whilst you setup everything for a 1 shot infusion...

    How did Shuttleworth suggest you do this? Surely he gave some building instruction/ methodologies?
     
  8. packsail
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    packsail Junior Member

    Cat Builder,

    Haha! My wife already caught me bringing my materials into the house and yelled at me:) Luckily she is a sailor so it wasn't so bad.

    Our epoxy resin is designed for infusion. We never infuse below 80 degrees F for both the part and the resin. We've even used a turkey fryer to heat up the resin.

    We are using Robinair vacuum pumps and Airtech resin traps and are able to achieve a full vacuum.

    Your guess on what happened with the dry spots seems exactly correct. I think the test we did today with the removable flow media on both sides worked. Since we are working on our first boat using a one off male mold, I think we will just infuse the entire thing with the removable flow media on both sides. Do you see any issue with this?

    I have a facebook page called packsail and a website called packsail.com. Feel free to friend me on facebook. Your advice just in the last two days has been better than what we've gotten from our supplier in the last 6 months.
     
  9. groper
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    groper Senior Member

    No issue besides the surface finish on the mold side...

    How will you control the racetracking through the open grid channels where the highly curved part of the mold is?

    If you reduce the temp of the resin, you will increase its viscosity and slow things down, you might try another test doing this first...
     
  10. AndrewK
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    AndrewK Senior Member

    De-gasing the resin will eliminate your problem, if yor gel time does not allow for this then the flow media on the top alone should be enough. Do more experiments.
     
  11. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    Your glass is not the issue, its the combination of block core and dissolved gas and mixed in air.
     
  12. packsail
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    packsail Junior Member

    Successful Test

    We're doing everything we can to reduce dissolved gas in the resin by hand stirring and heating it. We're also reducing the vacuum pressure after the part is fully infused to 18 inches of mercury to help prevent voids. Here's a picture of yesterday's test with flow media on both sides.
     

    Attached Files:

  13. CatBuilder

    CatBuilder Previous Member

    That looks better. You are going to need to try it with the real curve next... That will be the hard part.
     
  14. packsail
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    packsail Junior Member

    The direction of our resin flow will be perpendicular to the large cracks in the foam. This, I think, would eliminate the racetracking.
     

  15. groper
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    groper Senior Member

    Make sure you test this first...

    In your deck mold, you have tight curvature in various places such as up in the bow and where it turns down the sides... if the resin front gets to any of these areas first and race tracking occurs, it could shoot resin anywhere around your part where these cracks are and to whereever the cracks join other cracks etc ... youll have to plan the stretegy carefully...
     
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