How does he do this? (Resin Infusion)

Discussion in 'Materials' started by catenahalf, Sep 9, 2010.

  1. catenahalf
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    catenahalf Junior Member

    I'm about ready to make a set of female molds from a high aspect rudder build.
    Although I've done some vacuum bagging, resin infusion sounds pretty interesting. I have a basic understanding of it, but this is a head-scratcher for me.

    The designer is describing the pitfalls of controlling precise foil thickness, alignment and straightness when joining the layups of two rudder halves.
    I've seen some pretty awful foils from beautiful female CNC cut molds halves come out with wild thickness inconsistencies. Something I want to avoid; carbon is a terrible thing to waste.

    So, instead of joining them from the outside, he does it from the inside while they are fully clamped, aligned and being resin infused. But, these have a maximum outside dimension of 1.5", taper down to less than .5" and are over 4ft long.

    I can't imagine there being any room for infusion gear in there. And how do you get it out?

    I don't get it.

    Anyone?
     
  2. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    Sorry, somethings missing, a link perhaps?
     
  3. catenahalf
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    catenahalf Junior Member

  4. Bglad
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    Bglad Senior Member

    Resin transfer molding

    If you search resin transfer molding you will find information on companies that use the process and a company that sells equipment to perform the process. I learned of the process because it is used to produce the carbon water ski I use. Basically all the materials are laid in a mold where the orientation of the materials can be precisely laid out to insure proper structural performance. The mold is closed then resin is drawn through the part from one end to the other (probably a simplification of what actually happens). I don't know how the manufacturer's insure proper wetting in a closed mold except to monitor the volume of resin being used then possibly finish with enough pressure to collapse any remaining air bubbles. When the mold is opened the part is complete.
     
  5. apex1

    apex1 Guest

    I would ask Herman "howto" instead of searching the net and receiving platitudes.

    Regards
    Richard
     
  6. Herman
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    Herman Senior Member

    2 simple ways of making similar rudders:

    -1. Fill the moulds with dry laminate, put a piece of (CNC) machined foam in, clamp the moulds, apply vacuum, and fill with resin. Probably 2-4 bars of pressure. This is called RTM (resin transfer molding) and can be pretty efficient. Cycle times of 14 minutes are no exception. (even with epoxy!)

    -2. Fill the moulds with wetted laminate, pour in epoxy foam, wait for it to rise a bit (the viscosity or at least the "hanging power" goes up then) so you can turn one mould half onto the other. Clamp and wait, preferably heat up. Many paddle blades are made this way. (or variants of this method)
     
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  7. apex1

    apex1 Guest

    What I say..........................
     
  8. Herman
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    Herman Senior Member

    Oh, one other thing:

    Most rudders are made by laminating 2 halves, use some mat to keep the rudderpost in position, clamp the 2nd half on it, and fill with PU foam.

    No overlapping fibers ( "the PU will keep it together" )
    No structural connection between rudderpost and the only other structural part of the rudder, the skin. ( "PU foam is structural, sir" )
    No use of water resistant foam ( "PU foam is watertight, and we protect the fill hole with a layer of gelcoat" )

    The PU foam gets water logged, loses its already low structural properties, and if boats end up on shore in winter (normal situation in NL) then the rudder freezes and damages.

    Only good thing about it is that it keeps the boat repair yards busy.
     
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  9. susho
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    susho Composite builder

    [​IMG]

    PU ruddercores.... you could probably make a living on repairing those things alone. :D
     
  10. Herman
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    Herman Senior Member

    I know people that do...
     
  11. catenahalf
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    catenahalf Junior Member

    Thanks Herman.

    Trying to avoid CNC cores and elaborate mfg'g processes for cost reasons.

    Is there a good way to allow an excess of the bond material to exit the same molds used for vacuum bagging the two halves?

    My assumption is that I would bag both halves which would include a high density foam spar (nearly half the section width) in the layup covered with peel-ply. Fully cure. Fill the voids below the center line with foam, bonded to the inside skin. With a router on a sled, take it down to just under the center line. Add a bonding adhesive and clamp/vacuum them together.

    How do you keep the bond from getting between the mold flanges and affecting the thickness?

    After clamping, to fill in the center gap, can the bond be drawn in one end of the mold and out the other by porting the mold ends?

    We're talking very low production. The goal is light and strong.

    I haven't yet done any of this. I'm just trying to work it out in my head.
     
  12. Herman
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    Herman Senior Member

    What is low production?

    I might just glue PVC or SAN core around the post, and start shaping. Then cover in glass.

    If you have a good quality set of moulds, you could laminate skins and bag them if wanted. Then bag foam into the moulds, glue them with epoxy with foaming agent added, for more gap fill properties.
    Sand or route the whole structure flat, make a recess for the rudder post and fingers (plan on high density foam in that aread) and glue all together with epoxy foam.

    If you want, you can apply some 0,5 or 1mm wax sheet on the nose of the profile, in the mould. This will make a recess in the part, which you can use to apply some biax tape over the nose, reinforcing this area dramatically, and without spoiling the shape.
     
  13. catenahalf
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    catenahalf Junior Member

    Production, if you can call it that, may be 4 per year.

    What I'm after is a perfect as possible section shape and light weight and, of course, strong. They will use biaxial carbon and a lot of unidirectional. There is no need for a post, they are more like a daggerboard with an elliptical shape.
    Each half will be bagged with a high density foam and uni between at least three layers to form the skin.

    When laying up the half, should the dry stack never overlap the flange?

    Henry, can you provide a source for epoxy foaming agent? Any idea what size void this can bond at once while being strong?

    If the bond is expanding, does it have to be relieved?

    Will it, as a bond for the two halves, be anywhere as strong as thickened epoxy in keeping the two halves together? Or perhaps the LE rebate takes care of my foam bond concerns.
     
  14. susho
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    susho Composite builder

    For the exces on the flange you can use a router for the most stuff, and cut off the last, (watch out for your mould). I have used an anglegrinder too, you can use it quite precise, but if you slip you have some more work to do. I wouldn't suggest to use that last method in a mould though.. so release the halfs first, trim, place in a glueing mould(could be the same) and finish.
     

  15. Herman
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    Herman Senior Member

    What I would to then is to apply the wax sheet I mentioned, so you have a recess in the part to bond the front, blunt end later with some carbon biax tape.

    There is no need for overlapping of the skin onto the flange. You will need to cut it off anyhow.

    Epoxy foaming agent? Hmmm, difficult. I have it here in NL, but that is of no help to you. Huntsman provides it, Sicomin does, but I do not know of suppliers in the USA.

    About strength: Nothing as strong as unfoamed epoxy. However, if you are bonding foam (the core) you are bonding relatively weak material, and epoxyfoam is stronger than that anyhow. The trailing edge I would bond with classic epoxy paste, the front needs some laminate anyhow.
     
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