Nomex Honecomb Panels without Prepreg?

Discussion in 'Fiberglass and Composite Boat Building' started by CloudDiver, May 31, 2018.

  1. CloudDiver
    Joined: Jun 2014
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    CloudDiver Senior Member

    Is there a method for vac infusion/wet lay-up bagging to laminate both sides of a Nomex Honeycomb panel with a thin layer of fiberglass/carbon?

    I ask because I have only seen the process done with pre-preg. I am assuming that if you tried to make a panel by vac-inufsion or vac-bagging a wet layup it would pull the resin into and all over the surface area of the the cells, adding weight, and possibly suck the laminate down into the cells (at least on the top layer.

    I suppose it may be possible to do one side at a time, the laminate layer on the bottom against the table with honeycomb on top, then flip and repeat after cure. It would be nice to avoid a two step process for each panel since the time/labor might out weigh the cost of just using pre-preg in the first place. Then again, I don't think I want to build a giant oven either!
     
  2. rob denney
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    rob denney Senior Member

    Assuming it is aflat panel: Wet out a layer of glass on the table and lay the nomex on it. Wet out the other skin on a sheet of melanie or similar. Flip it and lay it on the core.Just enough vacuum tokeep the top in contact
     
  3. upchurchmr
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    upchurchmr Senior Member

    Aerospace typically makes one prepreg skin, then bonds on the core, makes another prepreg skin, and then bonds on the second skin.
    This is so the core cells don't fill with the prepreg resin. And because you need pressure on both sides of a skin to get good skin properties.
    There still is a concern with using too much bonding adhesive and filling up the cells, starving the bond line - a delicate balancing issue.
    Also the bonding adhesive is foaming, so that the adhesive will climb up the cell walls a short distance - increasing the skin to core bond strength.

    One way that was used to make a one cure sandwich, was to force Rohacell foam into the core cells. This was a step to prepare the core before sandwich construction.
    The Rohacell prevented the skin resin from pooling in the cells. The Rohacell was forced just using vacumn pressure. Might take some experimentation to get it to work for you.
    One good thing was that under heat, the rohacell expanded a little, providing pressure on the laminate from inside to consolidate the skins.

    All that is probably too much work/ development for a one off.
    Have fun.
     
  4. ondarvr
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    ondarvr Senior Member

    You can buy it with skins on it already.
     
  5. rxcomposite
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    rxcomposite Senior Member

    It cannot be done by infusion. The resin will fill up the voids in the cell.

    With prepreg honeycomb, an adhesive film is laid up in between the core and the prepreg to promote adhesion. A caul plate is laid up on the top and bottom of the prepreg to prevent the skin from dimpling. The caul plate has several tiny holes to evacuate trapped air inside the cells during vacuum. If the air is not evacuated, the trapped air expands causing poor bonding or delamination.

    Can it be duplicated by wet bagging technique? Yes it can but you have to experiment to get best results.
     

  6. CloudDiver
    Joined: Jun 2014
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    CloudDiver Senior Member

    Thanks everyone for you respones and suggestions. It pretty much confirms what I have learned so far, working with honeycomb is much different and presents special challenges vs. perforated foam cores. My 4 x 8 CNC router kit should be delivered by mid July (the electronics, controls, and motors). In the mean time I am working on the design and features of the frame using 80/20 extrusion and the dust collection system. I work in an Aviation Repair facility, but my job is procurement. I have recently discovered several outlets to purchase composite materials that are 'de-certified' for aviation use. These are materials like pre-preg that are beyond the 'expiration date', but fundamentally nothing wrong it and fine to use for marine or hobby applications. I won't be messing with the pre-pregs in the immediate future, but I might if I can cobble together a small oven for curing (space is an issue). For now, I can get nomex honeycomb sheets pretty cheap. I want to experiment with making some flat panels and then cutting things out like chairs and coffee tables. I will just do them in fiberglass because I had the idea that semi-transparent layups of thin fiberglass with clear resins should make the honeycomb structure somewhat visible with back-lighting. I think this would look sweet on certain decorative furniture type creations. Eventually I can add a single very light layer of carbon just for the carbon look if that is desired. So moral of the story is, a wet lay up and vac bagged one side at a time will probably do the trick. Extra steps yes, but that's why I'm doing this learning/experimenting process.
     
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