Biaxial Glass Cloth strength

Discussion in 'Materials' started by mrdebian, Apr 27, 2021.

  1. mrdebian
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    mrdebian Junior Member

    Sorry wrong link, this is the proper one
     
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  2. mrdebian
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    mrdebian Junior Member

    Thanks for the useful comments to all.
    Here is a picture of the mould (deck)
     

    Attached Files:

    Last edited: May 1, 2021
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  3. fallguy
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    fallguy Senior Member

    Can you tell us where you got the mould and whether any vac is used or any more details. It is worse than I expected as far as the demands on the cloth.

    But I cannot help more because it is really out of my wheelhouse. I think I did offer some benefit in suggesting the mould was demanding too much of the cloth.

    There are other forum members that can offer more.

    You might also want to discuss the current strategy as to how you have been laying the fabric a bit.

    @ondarvr comes to mind
    @rxcomposite as well
     
  4. mrdebian
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    mrdebian Junior Member

    I build the mould myself. No vac used.
     
  5. rxcomposite
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    rxcomposite Senior Member

    THAT is a very complex mold. I don't think you can do it in one piece. 2 to three sections maybe to prevent certain sections from bunching up. And you need all the tricks in the trade. Bog for sharp corners, Lots of cutting and patching.

    You can start with a lightweight cloth, something in the 10 oz variety. Do a dry run fitting and see where you will cut and paste. On non critical areas where it is going to be cut out anyway, we use a light CSM to patch. Just to hold the shape.

    During the first trial, do not be afraid to cut the cloth while wet. Messy but if it solves the problem, why not? Start from the center and move outward.
    I have used style 7781 cloth. It is very light and drapeable. In fact we have problem laying it up wet. We pre wet it on a plastic sheet and remove the sheet when it is laid down. It is an industry standard but it is an aircraft supply. Not found in boat supplies.
     
  6. mrdebian
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    mrdebian Junior Member

    @rxcomposite, what is bog?
    Why are you suggesting to start from the middle?
    I found it easier to start from the bow & stern with a few patches in the very narrow part of the hull and then move on with the rest.
    I took already one item out of the mould. I used cutting & patching as you outlined but even with that is tricky many times around the deck fittings with the bubbles. I used 195gr (7 oz) cloth for the patches (twill).
    The cloth I'm using is no more than 300-450gr (10-16 oz).
     
  7. rxcomposite
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    rxcomposite Senior Member

    A paste mixture of cab o sil and resin.

    Whatever suits you. I always start at the middle and move outward. Cut the excess cloth after.

    10 oz cloth is good enough. that is already thin.
     
  8. fallguy
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    fallguy Senior Member

    Bog will help a lot...a must here...that much I can assure you. The trouble will be if it kicks too fast, so I'd want the bog to be as slow as possible, but it will allow you to have less creasing.

    I would probably start on the larger, easier area first and drive the errors to the harder places. But no expertise so take me with a grain of salt.

    I would also be curious as to whether you could do all the fittings separately. And then cutout the cloth around them. I have found in my work that reducing the operator's stress level generally results in a better product. Of course, infusion is that ultimate goal which is not always achievable.

    I am also surprised you flanged the mould which looks like you could use vacuum, but are not. It would help I'd say as well. A lot.
     
  9. mrdebian
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    mrdebian Junior Member

    @fallguy I did indeed the flange for vacuum but due to been newbie to the building process I will do a couple manually to gain experience and then I will move at some point to vacuum.

    From your reply and also from @rxcomposite I'm not sure where it will benefit to use resin with cabosil? I cut patches and put them on top of the fittings and can't see how the cabosil will help but obviously I'm missing something?
    The fittings are not sharp, they are very smooth and round. The cockpit rim is a nightmare.
     
  10. Dejay
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    Dejay Senior Newbie

    Very nice mould! And if you can get good product from it you're already doing a good job. From what I gather from the responses (newbie myself) there is not that much you can do to make work easier at the "cutting edge".

    You'd use bog / thickened epoxy to fill out the corners with paste and make them even more smooth. To reduce the amount of stretch needed for the cloth.

    If you accept higher weight and thickness you could use just a lot of CSM.

    If you want faster production rate maybe you could make a cutting pattern to have cloth pre cut. Not sure if that saves that much time compared to doing it by hand once you get practice in how to lay it out.

    In professional production you'd probably use a CNC laser cutter to precut all cloth so they lay out nicely and then vacuum bag with a reusable bag.

    Maybe you could also 3D print inserts around the corners and fittings to smooth them out, as a kind of core. But that is just an idea.
     
  11. fallguy
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    fallguy Senior Member

    You need to dart or tear csm at the top edge of the cockpit rim a lot. You can't put a flat piece there. The unfold geometry is not flat. Think about unfolding and you'll perhaps better see where to make cuts.

    I have enough experience to know where you will find trouble.

    Rx is a wise fellow. Take his advice and do the layups in sections where you tackle the hard parts and then come back and do the rest later.

    Just today, I had to lay a single tape on a part because if I try to lay more; the part won't be as good. Tomorrow, another tape. Slow, but right.
     
  12. fallguy
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    fallguy Senior Member

    Also, bog is like a good friend in building. If you have fabric pulling away from interior edges; you won't with bog.

    I realize the downside is weight, exotherm, etc., but it can provide a clear advantage if the fabric is not holding well on inside radiuses especially. I have also used it on outside corners if having trouble keeping the laminate tight, but is trickier on outside.

    A good example is all your fittings. And a way to tell if you could benefit from bog is super easy. Just run a 3/4" diameter semicircle around the mold and if it is gapping, a 3/8" radius bog fill would help (where you are having trouble). The bog gives you a few degrees of freedom with the cloth. If you have a 6mm radius now and you step to a 10mm radius, then you have 4mm of less trouble with the glass in that area...
     
  13. mrdebian
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    mrdebian Junior Member

    @fallguy what do you mean by saying "dart or tear chopped strand mat"?

    I must mention that the temperatures here are quiet high. Mid day temperature inside the work area goes up to 27oC. How low I can go safely with the catalyst? I'm using the M50 Butanox.
    I'm using all the techniques that mentioned in the thread apart from the bog.

    Thanks a lot for all the feedback.
     
  14. fallguy
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    fallguy Senior Member

    Did you build the model with a cad program?

    If you unfold the 3d shapes with cad software, you would see that the patterning of the 3d object in two dimensions is not a flat piece of fabric. An unfold feature done on sections would actually show you where to cut fabric for the mould.

    And this is your issue, not simple bubbling.

    If you don't have the ability to use cad software, you have to unfold using the real fabrics as you go.

    When I say dart, I refer to the woven. Rx and others recommend lightly tearing the csm. Csm lays down nicer with torn edges, but you cannot tear the woven.

    For the cockpit rim, in order to get enough fabric into the bottom, you have an excess on the vertical portion and on the flange or what would be the flange if the rim were built alone.

    Darting is merely a relief, so the excess fabric can lay over itself. Darting in sewing is done with a seam to make round contours, like over a shoulder perhaps. In textile work like glassing, your woven glass is no different, it is unable to make round shapes in 3 dimensions because it is a 2 dimensional object. The good news is because of the resin, you don't need to seam it as would a dressmaker.

    But you must dart or tear in the right places or you will get bunching which you started off calling bubbling. In those places you had bubbling, quite sure you had bunching and did not relieve the fabric properly with cutting.

    As rx says, even wet glass can be snipped with a scissors if you discover it won't lay down well. Just be ready to clean the scissors well at the end.

    I am sorry I cannot comment on the resin question. I do not like to answer questions if I am not qualified to do so.
     
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  15. rxcomposite
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    rxcomposite Senior Member

    It is called a caul plate and is used in vaccum bagging. Usually made out of silicon rubber. It is molded roughly to the desired inside shape and presses on the mold to ensure a void free section of high definition surfaces without the use of bog. Edges are rounded but much tighter, usually 1/16" to 1/8". Sometimes it is flat and can be circular or rectangular in shape to define flanged openings.

    I first saw this application in Beechcraft Starship in late 80's, early 90's. We used flat rigid caul plate for a smooth inside and outside finish for our vacuum bagged pieces.
     
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