I need a 0.5mm Coremat

Discussion in 'Materials' started by fpjeepy05, Apr 29, 2016.

  1. fpjeepy05
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    fpjeepy05 Senior Member

    Does anyone know if a product like this exists? the 1mm Coremat Xi absorbs 21.2oz per square meter. I need something that is going to absorb about half of that. Its for the construction of an ultralight stand-up paddleboard.

    I understand I could wide belt sand down some sheets of H60 Divinycell, but I don't really feel like doing that.
     
  2. upchurchmr
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    upchurchmr Senior Member

    Just use cedar. It won't absorb as much.
     
  3. wet feet
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    wet feet Senior Member

    I haven't checked,but I find it hard to believe it would be worth a company's time to make 0.5mm coremat.I have been surprised to find even 1mm used as the inner and outer skins are barely separated.I know you can obtain 1mm syncore for use with prepregs,but again I doubt there is a great demand for anything thinner.Good luck with pushing the boundaries as you pursue your project.
     
  4. fpjeepy05
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    fpjeepy05 Senior Member

    I don't really want to try to fit the cedar to the compound bends

    Is there a sprayable high build epoxy fairing compound. I know of the polyester products, but I would like to stay all epoxy if possible.
     
  5. fpjeepy05
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    fpjeepy05 Senior Member

    [​IMG]

    One layer of 6oz carbon deflects pretty easy, and 1.5# density EPS foam dents pretty easy. Bad combination. Two layers of 3.75oz carbon over a thin layer of higher density core is much stiffer, and makes a much more durable board at close to the same weight.
     
  6. upchurchmr
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    upchurchmr Senior Member

    At 0.5 mm (0.020") the cedar will form with hand pressure.
    You really ought to try it

    Your illustration doesn't match what you are talking about.
    Is the core-mat supposed to be the "stiff high density PVC foam"?

    What is an epoxy hot coat to you?

    Why would you have two different "high density" foams? What is the purpose?
     
  7. waikikin
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    waikikin Senior Member

    Are you building one or many?
    Why not invest in a higher quality blank if one off, the sandwich construction over a eps foam blank looks overly complex. If you're headed for multiple molded production boards blowing a high quality foam inside the moldings while still in the matched tooling may be the go.
    Jeff.
     
  8. fpjeepy05
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    fpjeepy05 Senior Member

    I don't have any cedar on hand, but I do have some paulownia. I might just use that because I have it.

    Yeah I would be replacing the PVC foam with coremat, because my board has a recessed deck, so there are is a lot of shape and my thought was coremat would make the compound shapes a lot easier.

    I'm not following that image. It was just the best reference image I could find. I'll prob use a Duratec polyester primer, and an Polyurethane automotive paint, because I'm cheap.

    One layer of 6oz carbon deflects pretty easy, and 1.5# density EPS foam dents pretty easy. Bad combination. Two layers of 3.75oz carbon over a thin layer of higher density core is much stiffer so it less likely to dent the foam. That is my purpose. A combination of lightweight, durable, and cheap.
     
  9. fpjeepy05
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    fpjeepy05 Senior Member

    I agree that it complex, but it appears to be a necessary evil at this point.

    By higher quality do you mean higher density? Weight is the concern. Heavy foam with heavy single skins makes a heavy board, and heavy boards don't sell.

    I don't think that anyone is doing tooling for boards yet. Everything is cnc cut from blanks. I'm planning on going the custom route, so everything will be one off.

    Maybe I can use a combination of paulownia and coremat. Paulownia in the flat sections and coremat in the shapley areas. Now the next question is there anywhere in the US to get 1mm coremat by the yard?
     
  10. rxcomposite
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    rxcomposite Senior Member

    I don't know where you got that image but in calculations, the shear is greatest at midpoint or NA and diminishes towards the edge. This is where sizing of cores are important. Therefore, if you want to use multiple core densities, the one in the middle should be highest.

    If you design the laminate with the outside skins and webs supporting, then you can use a low density core just to keep things stable without the core bearing the shear load.

    By the way, 0.5 mm core is just about the thickness of CSM 225 loaded at 30% glass content.
     
  11. fpjeepy05
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    fpjeepy05 Senior Member

    Loading and failure modes are a little unique for a displacement raceboard. At 23" wide it is unlikely that even the most talented paddler over 225#'s could stand on this board. And it is rarely in surf so impact loading is minimal. So the amount to shear that the core sees is pretty minimal. So really where failure is going to occur is outside of its designed use. E.i. falling on the board with a knee, hitting docks, taking it on and off of a car. For these things having a tough skin is important. So how do you make a tough skin that is lighter than just CSM? Two layers of glass sandwiched around a layer of Coremat. That's the best idea I have come up with.
     
  12. rxcomposite
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    rxcomposite Senior Member

    Carbon is brittle. WR glass is more forgiving and will stand up to abuse than Uni's. Usually, there is an interface between the skin and the foam. A layer of light CSM, maybe 225 gr/m2. Hotcoat on the low density foam might not be enough so a csm is used to prevent delamination.

    Try this stacking sequence. Light foam, hot coat (optional),CSM 225, WR laid up at 0/90 degree, WR bias cut, laid up at 45 degree.

    If you lack longitudinal stiffness, insert a layer of uni, maybe 150 mm wide longitudinally after the foam, top and bottom.

    If you want good finish, top off with surfacing mat 30 or 50 gr/m2 then sand. Or give it a light coat of resin loaded with micro balloons, then sand.

    A client of mine once tried 1/8" laminated molded plastic with a UV layer on top, top and bottom half, premolded styrofoam core, then glued together with industrial urethane.

    Try to contact Steve W, a member of this forum. I recall he made a lot of surfboards before.
     

  13. fpjeepy05
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    fpjeepy05 Senior Member

    Too Heavy. Two layers of 4oz glass over 2 pcf eps foam would result is a 14' board weighing roughly 35# I would say that is "traditional surfboard construction."

    Race boards on the market are ranging from 19# to 25# I don't think a 35# board would be that much slower, but regardless people are not buying them. So anything heavier than 2 layers of 4oz cloth is not worth considering.
     
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