Hull Infusion leak

Discussion in 'Boatbuilding' started by eckmuhl, Jul 27, 2005.

  1. eckmuhl
    Joined: Oct 2004
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    Location: France

    eckmuhl Junior Member

    Hye, i'm doing trial in order to infuse a 40ft hull. During my trial everything is going right until i cut off the resin inlet. The full part is well infuse but then bubbles start to appear. I've got a good vaccum (0.88 bar of pressure)but there is some leak certainly that i can't detect. When the resin is stop the vaccum continue to suck the resin up the hull and bubles appears.
    Because of the complexity of the hull with its stringers i don't think i could do a better baging to avoid every leak. When i cut the vaccum pump i loose around 1mBar per minutes.
    Is there any possibility to avoid this. I think about stop the resin inlet and the vacuum at the same time... could it be a good solution?
    As big boat yard do like 100ft hull i suppose they must have the same issue with some tiny leak , so ther must be an answer.
    Thanks for your help.
     
  2. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Never cut off vacuum untill the resin is cured. Due to the vacuum, the fiberglass is compressed. When you cut off the vacuum, the fiberglass will spring back and the laminate will have voids.

    The leak must be somewhere. Common defects:
    -porous mold (should be tested beforehand)
    -defects in tackytape seal (fiber trapped underneath is a popular defect...)
    -porous vacuum film. Welded films can present problems on the seams. Use only good welders and TEST. Polyethylene films are no good for infusion, too porous.
    -appendages can leak too, but you will notice directly.

    One way of preventing leaks in the perimeter (tackytape) is to run a double line of tape, and pull a higher vacuum in between. Any leaks will compromise the high vacuum, and not the product vacuum.

    If your molds and your film is OK, then the above trick should do.
     
  3. Thunderhead19
    Joined: Sep 2003
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    Location: British Columbia, Canada

    Thunderhead19 Senior Member

    Also, make sure that the film is not being streched into some areas (small wrinkles are okay). The film should pull into all areas easily...loosely. Try cutting back the amount of vacuum you're using during infusion, possibly .6 bar). Any low pressure under a stretched film will make any microscopic air bubbles expand to an enormous size. You can get air entrapped during the mixing of your resin and possibly from leaks or entrapped air pockets in your inlet lines. Also this could happen if the cloth is not wetting out perfectly (you may just be not seeing the dry spots).
     
  4. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Gas in resin is another one. Degassing the resin with a low level vacuum pump is a good idea (at least with epoxy resins, do not do this with polyester, you will cook the styrene out).

    And indeed, a stretched film is more likely to be porous. Use low stretch film, and use generous amounts to prevent bridging in corners. This also relieves the tackytape, with less risk for leaks.
     

  5. nic martin
    Joined: Sep 2005
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    Location: uk

    nic martin New Member

    vacuum baging

    you could always use a peelply break onthe flange this consists of a breather fabric coverd with peelply this works by allowing resin movment until it hits the breather fabric this then slows the flow down and making sure the vacuum is maintained untile the resin is cured
     
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