Vacuum Leaks

Discussion in 'Fiberglass and Composite Boat Building' started by Johnfirstime, Aug 31, 2017.

  1. Johnfirstime
    Joined: May 2017
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    Johnfirstime Junior Member

    I am planning a rather large infusion and wanted to get some prospective on the acceptable amount of vacuum leakage you would accept for an infusion. To date I have only been infusing small (approx 10 sqft) specimens and I have never really been able to get a perfectly sealed bag. I am worried with a larger part the leaks will be to great to get a tolerable result. I look at these large boat hulls many members have been producing and I wonder how they are able to get an acceptable vacuum over such a large part? Are there any tips, tricks, or resources you can guys can recommend to help me improve my bagging technique?

    Thanks for the help guys.
     
  2. jorgepease
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    jorgepease Senior Member

    You can plug pinhole leaks that open up as you infuse, these are often in the pleats that are folded over and blocking air entrance until the bag relaxes but your drop down test should hold vacuum for at least 15 minutes or you are risking that part.

    Do you have an ultrasonic leak detector? It's worth having one if you are doing larger parts.
    Where are your leaks showing up on your smaller parts?
    Are you sure they are leaks and not just humidity flashing off? Let the pump run for a couple of hours prior to infusing.
    Are you using real vacuum film and the proper tacky tape.
     
  3. Tungsten
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    Tungsten Senior Member

    The tacky tape is where all my leaks where.I didn't use the yellow stuff, i bought what was available at a reasonable price.1/2"x 1/8 is what i used.It wasn't until i used two rows of tape( yes twice as many pleats ) before my leaks stopped.The leak detector would not find these leaks as there just too small.I always infused outwards because of this,kept the air away from the part.
    So if you don't have the right tape(very sticky) its worth the cost.
     
  4. ondarvr
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    ondarvr Senior Member

    As mentioned, use the correct materials for the job, they cost a bit more, but are easily worth it.

    I've worked with hundreds of companies that have moved some, or all of their production to infusion, they quickly find out it's far more profitable to use the correct products than the lower price substitutes.

    What are you using as a mold surface.
     
  5. Johnfirstime
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    Johnfirstime Junior Member

    I appreciate the advice guys.

    I did purchase the yellow vacuum tape and proper vacuum bag which I have been told are the correct products for vacuum infusion. I am infusing on a wooden mold but I have put two coats of epoxy over all joints and coated the mold with 3 coats of latex paint. I have meticulously gone around my vacuum bag several times pressing the tape and trying to seal leaks but I still cannot hold an acceptable vacuum. I am inclined to believe the leaks are in my bag because I vacuum tested my mold prior to placing of the fabrics and a stable vacuum was achieved.

    I would be interested in trying a leak detector, are there any specific models you would recommend? For the time being perhaps I will try the two rows of vacuum tape.
     
  6. ondarvr
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    ondarvr Senior Member

    That surface isn't going to be very leak proof, you need to seal the all of the wood with epoxy or a sealer designed for that purpose.
     
  7. jorgepease
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    jorgepease Senior Member

  8. ondarvr
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    ondarvr Senior Member

    I hear that frequently, but there aren't any places I know of that use latex paint over wood thinking it's a reliable surface to hold a vacuum, leaky wooden tooling is part of the learning curve. The stresses on the mold are increased during the loading of the glass and infusion, so what may have held vacuum at one time, doesn't when it counts.

    If he's using the correct bagging film and tacky tape, then there's no reason for leaks except in the wooden shape.
     
  9. Johnfirstime
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    Johnfirstime Junior Member

    I haven't mocked up anything for an infusion just yet but I have been doing small scale samples to test the vacuum. I recognize your concern about the use of latex paint so in order to help rule that out I lined the mold with vacuum bag and then sealed another layer of vacuum bag overtop. While doing this I still was unable to sustain an adequate vacuum and my rate of vacuum loss was virtually identical to when I tested atop of the latex paint.

    Looking in my records I found out that I am using sealant tape AT-200Y from the airtech catalogue. My vacuum bag is also from that same catalogue (green and does not stretch) although I don't have the name of it with me. I'm inclined to believe I am using adequate materials and my colleague and I are very meticulous about laying the bag down flat with no creases. We have been using pleats to ensure there isn't excess pull on the vacuum bag and we always press firmly on the vacuum tape to full seat it to the mold after everything is laid down. I've air tested the resin catch pot alone and it holds a stable vacuum with nothing attached to it. At this point I am pulling my hair out trying to find these leaks and Im loosing faith that the perfect vacuum everyone here talks about is even possible.

    The only thing I feel may be a problem is the integrity of the vacuum tape. I have purchased this case of tape over 3 years ago, it has been stored at room temp and in the box but perhaps it's tack has decreased over time (the manufacturer suggests an 18 month self life). My colleague originally used the tape and he claims he notices no difference in the tack of the tape, have you guys had any issues with using old tape?
     
  10. jorgepease
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    jorgepease Senior Member

    3 years. :eek:.. I'd buy one roll of new tape and test it before chasing more leaks. Also check your hose connections
     
  11. jorgepease
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    jorgepease Senior Member

    Post a pic next time
     
  12. Tungsten
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    Tungsten Senior Member

    A little heat on the tape will make it more sticky
    I here your pain and have been there. Ive even pumped air into the resin inlet to fill the bag to about 2 psi. Then put weight on top to see if i could make the leak louder so my detector could here it.
     
  13. Johnfirstime
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    Johnfirstime Junior Member

    Although I had some faith in them, my hose connections could also be an issue. Currently for both my resin inlets and and air outlets I use the resin infusion connectors shown below which are sold by airtech as well. I simply smooth the bag film over the connector and I pierce the film as I push the hose into the connector. The hose is wrapped with vac tape and it seals to the bag making what I believe to be an air tight connection. The bag does tend to wrinkle when I do this and I would not be surprised if this was a source of leaks.

    I am looking at making a trip to the get some new vacuum tape next week, if you guys would not recommend this hose connection detail, I would be interested in what you can suggest that is perhaps a little more robust and air tight?

    Thanks again for all the help, my colleague is my only contact with infusion experience so I appreciate the fresh insight.
     

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  14. jorgepease
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    jorgepease Senior Member

    Those are fine, I use them too. Wrinkles will get you in trouble so try not to let that happen.
     

  15. SamSam
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    SamSam Senior Member

    At the bottom of this page is a bunch of other vacuum bag threads. In this one vacuum bag leak detector https://www.boatdesign.net/threads/vacuum-bag-leak-detector.58335/ there was this
     
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