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Polyurethane Foam

Discussion in 'Molding and Casting' started by 1tahr, Jun 28, 2020.

  1. 1tahr

    1tahr Member

    74
    3
    hi sometimes when i pour a small wallaby mold i have i notice the foam has just stopped and hasnt filled the mold properly other times it works well, i realise alot affects foam preformance , do you guys have small air escape holes, rotate molds after pouring , im wonderinmg weather trapped air is making the foam stop rising so sudden, any tips would be appreciated thanks
     
  2. Frank E. Kotula

    Frank E. Kotula master, judge, instructor

    Having an air hole that can be shut will aid in knowing that your mold got filled plus it does release air but in reality your mold isn’t air tight so air does escape.
    Having the mold not fill up can be
    Not the right amount mixed.
    Not mixing it up properly
    Old foam
    Water or moisture in mold.
    Release not dried properly and causing a chemical reaction.
    If your using the same mold and know that it takes this amount of A-B and it’s not filling look to old foam.
     
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  3. 1tahr

    1tahr Member

    74
    3
     
  4. 1tahr

    1tahr Member

    74
    3
    hi Thanks Frank , im just not sure what the problem was combination of a few things , never thought of the release agent not being dry and causing reaction , its all a learning curve can be an expensive one at times
     
    Frank E. Kotula likes this.
  5. crablover

    crablover Well-Known Member

    175
    416
    Choose the proper density foam for your mold Adding some water to your foam as you mix. You will get better expansion of the foam. Mix until you see a color change in the foam before pouring
     
  6. There's some good tips here. Be careful adding your own extra water. Water is a reactive crosslinker in the world of polyurethanes and will certainly change the ratio, which will change the properties. I think Frank is right on when he suggests maybe mixing up a bit more material, or possibly not mixing with enough shear. A 2-part urethane foam needs energy to properly align the cell structure. A small jiffy-mixer and high speed drill works great. Also, a vent hole is a great addition to your mold. As mentioned, this will allow you to know when the foam is filled into the cavity, and a small hole will help to "pack" the foam to give you more even bubble distribution within the cells and a skin of sorts on the walls making it stronger. If you need any help on product choice, send me a pm. BJB has a bunch of PU rigid and soft foams for use in the taxidermy world.
     
    light, Frank E. Kotula and George like this.