Mold support

Discussion in 'Fiberglass and Composite Boat Building' started by mrdebian, May 5, 2022.

  1. Kayakmarathon
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    Kayakmarathon Senior Member

    This picture shows a center wall made from styrofoam, which provides flotation and supports the deck.

    upload_2022-5-9_19-35-24.png
     
  2. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    I've got 3 bulkheads on the kayak so there is support for the deck.
     
  3. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    @wet feet did you spray the gelcoat in once? Due to large amount of gelcoat will be better to spray it with a small gap but I'm not sure how much time to wait between the 1t and 2nd layer of gelcoat to avoid the second attack to the 1st and vice versa. Is it like 20 minutes at 20oC enough or what?

    Also regarding the coremat framing, do you mean that you used many layers of coremat together and on top just a cloth to keep them in place?

    Thanks a lot
     
  4. wet feet
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    wet feet Senior Member

    I don't normally spray gelcoat as it makes a huge sticky mess in the workshop as well as leaving a thin coat of the material.Whether you brush or spray,I would expect 40-50 minutes between coats to be typical in normal temperatures.The coremat I have used for the purpose of framing was applied to the mould laminate and them covered with CSM and in this way it provided enough stiffness for the framing to provide a foundation of support.The framing was MDF and was attached to the mould with Sikaflex to retain it.The mould had sufficient stiffness to stay the correct shape and the MDF simply stabilised it so that it didn't fall over.If you store the mould outside,it is a good idea to use moisture resistant MDF and give it a good coating of resin for extra protection.
     
  5. rxcomposite
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    rxcomposite Senior Member

    This is an old thread but I feel I have to clarify things.

    In my book of moldmaking, the rule of thumb is just to make the mold as thin as practicable so as not to absorb much heat from the laminate being molded. The mold is a heatsink. About 1.3 to 1.5x of the part that is going to be pulled out of the mold. But there is a caveat. The book goes on detailing how to compute the stiffness of the mold by spacing the stiffeners and frames. So much for practical use. In short, the mold must be robust, stiff, and dimensionally stable.

    In marine, parts are usually 5 to 8 mm thick so expect the mold to be 7 to 12 mm thick plus flanges. Thick you might say but it is heavily reinforced with carton tubings or plywood plus maybe steel framing if we have to move it around or keep it rotating.

    In contrast, we also do high temperature aircraft molds. The parts are thin, about 2 to 3 mm but the molds are 5 to 8 mm thick, plus flanges, plus metal framings. This is to make it dimensionally stable as parts accuracy is a must. The mold itself is built up with almost all woven fabric and very little CSM. The metal frames does not hug the mold, only support it at some points 40 mm wide spaced at about a meter apart. If the parts are very long, bolts located at strategic points support it. we call it "floating support".

    Now if you want to make it cheap, use lots of CSM or even coremat to build up bulk. Thickness always makes it stiff. A few stiff plywood cradles tabbed at certain points so it does not print thru. Remember, molds with high percentage of resin tends to warp when kept outdoors.
     
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  6. rxcomposite
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    rxcomposite Senior Member

    One coremat on top of each other then finish with a WR. This a cheap substitute for a "sandwich" laminate. Makes it stiff.
     
  7. Scuff
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    Scuff Senior Member

    I'd like to read your book on mold making. Could you tell me where I could find a copy?
     
  8. rxcomposite
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    rxcomposite Senior Member

    Advanced Composite Mold Making- John Morena

    Everything from steel to plaster.
     
  9. Scuff
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    Scuff Senior Member

    Ordered a copy. Thanks.
     
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  10. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    @rxcomposite thank. you for the valuable info. I've ordered also a copy of the book.
    May I ask please what is the recommended technique on laminating this particular mold (the kayak mold).
    I am thinking of laminating like below the new mold:

    The 1st layer with 200gr chopped max (to take easier the curves and take the bubbles out)
    2nd layer 300gr mat
    3rd layer a 1.4mm coremat (this is what I got handy at the moment)
    4th layer 300gr mat
    5th layer 1.4mm coremat
    6th layer 450gr mat
    7th layer 450gr mat
    Then on at least 3 maybe in 4 places in the mold I will do what you recommended for reinforcement; that is 4-5 layers of 1.4mm coremat and a woven roven or a 450gr mat on top of them.

    The actual kayak (this is for the deck) that will be produced it will have 3 layers of cloth.

    Also, is there a benefit of not putting all layers in once (I mean same day)?
     
    Last edited: Nov 25, 2022
  11. wet feet
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    wet feet Senior Member

    You definitely should not put all the glass down on the same day.A maximum of 1800g is a good working limit,even with tooling resin.You can push it a little higher once you have confidence in the stability of the resin and your experience of the shrinkage characteristics.
     
  12. rxcomposite
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    rxcomposite Senior Member

    Here is the sequence for a female mold

    1. Gelcoat
    2. Veil cloth- Laminate shiny, nor dry looking. This is to tie up the gelcoat to the next layer. Others omit it.
    3. Light CSM- 280 to 300 gr/m2 Glass content 0.30 or less
    4 Heavy CSM - 450 g/m2. Glass content 0.33 The 300 +450 is the minimum I use to prevent print thru. This depends on the resin you are using.
    5. Heavy CSM or coremat or any approved felt type material. If 1.1 mm, you can just lay one on top of another.
    6. Light CSM in between coremat of 2 mm or thicker. 200 gr is best, 300 gr is good. This is to increase adhesion between layers, As many coremat you need to build up bulk. Can be 4x the thickness of ist set of laminate. Follow manufacturer's instruction.
    7. Light CSM
    8. WR- 600 gr. This to have a dense outer layer and promote stability.

    Ideally lamination is a continous process. Lay up the next layer when the first layer is "tacky dry". About 45 mins to 1 hour in between coats. This ensure a good chemical bond. Watch out for exotherm. If laying up too fast, there is going to be thermal runaway and the mold is going to be progressively hotter and crack the underlying layer. Should be comfortably hot to touch. If you cannot finish in a day, lightly sand the cured resin to remove slivers and promote adhesion of next layer, Agree with Wet feet.

    If this a large mold, You can add stiffeners, otherwise just eggcrate it with plywood or MDF, tabbing only at a few points with CSM. If you need longitudinal strength, insert a steel tube along the bulkheads. Glass only the mid part to allow for the difference in thermal expansion of different materials.

    A better alternative is to weld a box frame of steel tube and attach to the mold at several points using only CSM. This is just to support it.
     
  13. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Senior Member

    Layers are too thin, barcol development will be poor. Mold will shrink over production use, possibly twisting the mold.

    For GP resin, modified GP, mod VE, or VE unfilled;
    Day 1;
    Tooling gelcoat ; 0.5mm
    allow to cure until no longer transfer to gloved finger
    Option 1;
    900g CSM (split in to two applications of 450g), wet-on-wet. Initiate via low hydrogen 9% active oxygen MEKP, low reactivity. A 9% MEKP / CHP blend can also be utilized in hot temperatures. Maintain >20c ambient

    Option 2;
    Veil + 450g CSM (wet on wet). Initiate via low hydrogen 9% active oxygen MEKP, high reactivity. Maintain >20c ambient.

    Day 2;
    900g CSM. Initiate via low hydrogen 9% active oxygen MEKP, low reactivity. Maintain >20c ambient.
    allow to cure until exotherm drops back to ambient
    900g CSM. Initiate via low hydrogen 9% active oxygen MEKP, low reactivity. Maintain >20c ambient.

    Day 3;
    450g CSM
    4mm polyester mat (Spheretex SP 4mm or Coremat Xi 4mm)
    900g CSM
    allow to cure until exotherm drops back to ambient
    900g CSM
    Combination WR/Mat or 0/90 noncrimp

    This will yield a relatively balanced & well cured laminate.

    ///

    For low-profile tooling resin (Polynt Optiplus, AOC LPT68000, Unimold, RM2000, etc)
    Day 1;
    Tooling gelcoat ; 0.5mm
    allow to cure until no longer transfer to gloved finger
    Use 100% VE resin or modified VE resin for this stage;
    Option 1;
    900g CSM (split in to two applications of 450g), wet-on-wet. Initiate via low hydrogen 9% active oxygen MEKP, low reactivity. A 9% MEKP / CHP blend can also be utilized in hot temperatures. Maintain >20c ambient

    Option 2;
    Veil + 450g CSM (wet on wet). Initiate via low hydrogen 9% active oxygen MEKP, high reactivity. Maintain >20c ambient.

    Day 2;
    Low profile tooling resin
    1800g CSM wet-on-wet. Initiate via low hydrogen 9% active oxygen MEKP, low reactivity.
    allow to cure until exotherm drops back to ambient
    450g CSM
    4mm polyester mat (Spheretex SP 4mm or Coremat Xi 4mm)
    1800g CSM
    Combination WR/Mat or 0/90 noncrimp
     
  14. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    That is a detailed spec! I don't believe I've ever known anybody insist on that particular variety of MEKP,they just order a drum of catalyst in my experience and since it is a catalyst that by definition isn't part of the reaction,the details don't seem to make a huge amount of difference.could we be advised on why this precise formulation makes a difference?I don't think too many commercial concerns have even half decent environmental control of their premises and that may not hold up if a door is opened to allow a delivery of materials in.It is comforting to be reminded that some applications require careful monitoring of materials and application.Too often I hear about slapdash methods,often out of sight of the management,to maximise bonus earning opportunities for the people applying the materials and at that level they deserve the appellation dreamt up by L Francis Herreshoff and popularised since.
     

  15. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Senior Member

    Barcol development is a function of the promoter working properly with the initiator, which is affected by;

    Temperature
    Percentage initiator
    Promoter & initiator system

    low hydrogen ; most VE resins react negatively with the hydrogen peroxide found in common 9% MEKP. If you mix a cup, it will foam like a latte. It can introduce “aeration” in to the laminate that is difficult to remove.

    reactivity simply slides the geltime around slightly without needing to alter percentage.

    We mainly use AzkoNobel initiators now.
    MEKP 9% active oxygen;
    L50 = low reactivity
    D50 = medium reactivity
    M50 = high reactivity

    All things equal, simply changing from M50 to L50 can give you 10-15+ minutes of extra working time at the expense of slightly slower Barcol development.

    during the summer (>25C), we usually change to Trigonox 263 which is a blend of MEKP with 35% cumene hydroperoxide. Still 9% active oxygen. Extends gel times by about 10 min longer than L50, and reduces peak exotherm by -50F (-28C). Slows Barcol development slightly.

    Thin laminates are ultra sensitive to temperature, proper initiator dispersion, and reactivity.

    Initiator percentage should be kept 1.75 to 2.25% for most resin / initiators. If higher or lower percentage is “required”, changing the initiator would be preferred instead.
     
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