Composites 101: Carbon Fiber, Fiberglass, etc.

Discussion in 'Some Assembly Required' started by HickOnACrick, Jul 14, 2011.

  1. HickOnACrick

    HickOnACrick Groovinator

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    Do you have this backwards? I am under the impression that the greater the surface area exposed to air, the shorter the pot life??
  2. bxr140

    bxr140 Flame Bait

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    He might have been talking thermal runaway? Dunno.
  3. redprimo

    redprimo Been here awhile

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    Not for polyester resin. Polyester resin is an exothermic reaction and heat is also an accelerant to the reaction. if you contain the heat it will go off faster. That is why resin in any bucket always goes off before the lay up. Likewise if you use a large diameter bucket and increase the surface area and minimize the thermal mass you will extend the pot life. My tip about pre weting the cloth is also a way to extend the pot life. The pre wetted cloth if left flat will not go off as fast as the resin in the bucket.

    I used to have my own pattern and mold business and before I had any employees large layups would get a bit crazy. I would mix resin and paint some on the mold then wet out a piece of cloth and fold it up and transfer it to the mold and un-fold it but not roll it out, then pre wet another layer and leave it on the table while I rolled out the first piece of cloth.

    I have never used a paint roller to apply resin, it is too slow. I aways pre-weted the cloth by pouring the resin on and then using a bondo spreader to move it around. When I mention rolling out the cloth I am refering to using a ribed metal roller to get rid of any air bubbles.

    All that I have written also applies to epoxy but the effect of using a shallow bucket on 40 minute epoxy is less than on polyester resin.

    You may be refering to high humidity reacting with epoxy resin and making it kick faster. I live in California and have no experiance with this so some one who does will have to chime in.
  4. HickOnACrick

    HickOnACrick Groovinator

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    Cool. Thanks for clearing that up. Do you think one could pre-wet some layers, then toss them in a fridge for 30 minutes or so until he got all the layers ready, then lay up he piece?
  5. ebrabaek

    ebrabaek Long timer

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    There are a lot of good user input in this thread. A subject that most books....dvd's or course's don't cover..... "The spills and thrills" But as with many people trying their own phase of work..... they venture out to try new things.....and all are not good.... and so it goes that mis information.... Or things that is not necessary the way things work correctly can be misinterpret, and discourage others that thought this is the way. So with all these different advises......available....I encourage all to test new methods ( wherever they are found) on a test batch of any kind.... Before moving onto the piece you are making.......as you are running a risk of destruction and failure...... Which to the newcomer can be detrimental. Many things work great...but perhaps not for each project... So that goes for every project.... Test your methods on a ....uuuummm test bed before moving on to your project...... That said.... Onward with the layups.....:thumb:thumb

    Erling
  6. redprimo

    redprimo Been here awhile

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    Most production shops store their MEKP in a refrigerator but I have never used chilled resin. With polyester I have always followed the old school schedule of applying half the weight of what has already been laid, kicked, and cooled. by the time I get to the point of laying up more than a couple layers of cloth I switch to heavy choped mat, core mat, or woven roving. So I never end up needing to layup more than a couple of layers at a time.

    With epoxy I suppose chilling the pre weted cloth might help but I have never tried it, or needed to.
  7. tmotten

    tmotten Lefthand ride Dutchy

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    Funny you should say that. Tried the pre-wetting technique and found it didn't work for me. Sure, maybe I'm not doing it exactly right, but it frustrated the crap out of me. Think I'll stick to the paint roller method.
  8. redprimo

    redprimo Been here awhile

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    Sorry you had problems, what cloth and resin did you use and what in particular was your problem? I learned this at the first shop I worked in which was an FRP mold shop and the next shop I went to which was a model shop they were using it there with epoxy.
  9. tmotten

    tmotten Lefthand ride Dutchy

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    I used 9oz glass twill with epoxy resin on a curved surface. I taped some news paper onto a bench and wetted out the glass with that. Firstly I struggled to get an even spread of resin partly due to the glass moving around when I tried to spread it. Then laying the wet glass out on the shape. It was very messy and couldn't really get it to conform as well as laying it out on a tacky surface dry and roll the glass into the surface with a paint roller. Any subsequent layer dry after that gets pushed into the old resin which secures it, but this was more difficult to achieve with the other method.
  10. harcus

    harcus Long timer

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    9 oz fabric of any weave is rather inflexible. Depending on the part configuration (size, contour, etc) it is preferable to use a much lighter product like 5 oz. Also, it may be preferable to orient the weave relative to the part corners on a bias (at 45 deg angles) for better draping.
    The prewetting technique works particularly well when placing plies on vertical surfaces. Get a piece of window glass .25 in thick. Lay the fiberglas on the glass & wet it out. Let it sit a few minutes to dissolve the sizing then move the f'glass to the part & roll it in place.

    :D
  11. tmotten

    tmotten Lefthand ride Dutchy

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    Ultimately I'll be using 5.4oz carbon/kavlar which has the same strand widths as 9oz glass though. Have to check the bias angle though. That's a good point, one that I always forget.
  12. Throbbing Missile

    Throbbing Missile Stuck in a rut

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    Thanks for the guidance HickOnACrick - I've just made my first serious attempt at a fibreglass part - the airbox for my project bike.

    [​IMG]

    I was particularly pleased with my pressurised mould release system:
    [​IMG]

    It forced warm water into the base of the mould to break down the release agent and push the airbox out. It worked perfectly despite the mould having no draft.

    Some bits didn't work as well as planned but on the whole I'm pleased with the result and the minor cosmetic defects aren't a problem for this hidden part.

    Full details are on my blog:
    http://www.throbbingmissile.com/2012/02/airbox-of-tricks.html
  13. jesusgatos

    jesusgatos fishing with dynamite

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    This is another great thread. Will add it to the list. Have compiled a lot of helpful links here.
  14. Dustodust

    Dustodust Long timer

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    Noticed this thread just now and thought I would pile on sorry Im late to the party
    Good stuff here
  15. jesusgatos

    jesusgatos fishing with dynamite

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    Why did you edit your post?
  16. beechum1

    beechum1 Grimace Soup

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    I've several years using epoxy and hand layup, this is my first real delve into polyester and bagging.

    I laid up 2 layers of 7.5oz plain weave, 0° off axis, with fiberglast 77 resin, mixed .0125% MEKP with a spray can primer on the mold surface. Vacuum bagged with release, .125" breather and stretchlon 800 bagging and 99.99% sealed, the only leak was the breach at the air connector an inch outside the part.

    Before I bagged it, I made sure it was wetout a bit more than what I would if I was just doing a handlayup part. I figured the breather would absorb the extra, but.... it took a little too much. or.... I did something else wrong?

    The part came out with pin holes in nearly the entire part. The fabric was wetted out, but the space between the fabric was dry, which good news, made for a nice flexible part, but absolutely unacceptable part and would be very difficult to fix the part. i.e. Trashbin.

    What I know I didn't do was lay the 2nd layer up at 45° axis and the spray can primer is obviously a single stage and is not optimal for "production" but for the first few parts may work. I'd like to think the primer isn't the problem, but I don't want to go out a buy a 75$ gallon of pain, 10$ gallon of thinner and acetone, and a new needle and tip for the gun, just to get the first few parts out while I learn. I don't want to have to learn 5 things, when I could just learn 4.... and especially when I don't need more than about 6oz of primer at a time.

    Suggestions to start tracing the problem first with the pin holes?
  17. therivermonster

    therivermonster Been here awhile

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    beechbum, check out compositecentral.com. Open an account there and you'll get the help you need.
  18. HickOnACrick

    HickOnACrick Groovinator

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    The only difference I see is that I use brushes and squeegees for applying the resin, rather than blowing it on. What temp is your shop? It may be curing too fast?
  19. beechum1

    beechum1 Grimace Soup

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    que? I apply with a brush. I put more than I thought I should because I though the breather would soak it up. Maybe I need more???
  20. KungPaoDog

    KungPaoDog Been here awhile

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    Degas the resin. This won't solve all your problems with bucket & brush, but it's a start.

    It's tough to get great parts with bucket & brush in a vacuum bag. You'll pretty much always have some voids since the process tends to make bubble in your part that then grow under vacuum.

    You can try to cure under higher pressure, or use a VPI/VARTM method. (Vacuum Pressure Impregnation/Vacuum Assisted Resin Transfer Method) Suck the resin through your glass inside a vacuum bag.