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Thread: Liquid Urethane Foam

  1. #1
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    Default Liquid Urethane Foam

    I've been using store bought pink foam for projects and have been disappointed by the cutting characteristics of that material. For my latest project, I used liquid urethane foam. What a difference!

    Liquid urethane foam comes in two parts that are mixed equally, stirred for a short time, poured into a mold, or whatever, then allowed to rise to completion. From the start of the process to when the foam can be machined is about 20 minutes, a bit more for very thick pours. Multiple pours can be combined for really thick or complex parts. No prep is required to pour another layer.

    This foam is incredibly easy to machine. No tear out, very stiff, strong in compression and pretty good in tension. The waste turned out by machining is more like little bits than dust. It doesn't stick to everything like the pink stuff does and since it's heavier, tends to settle and not be airborne.

    This material comes in various densities from 1/2 lb. per cubic foot to 16 lbs. per cubic foot. The 1/2 lb. foam isn't that durable and is less useful for machining. From my experience, 4 lb. foam is the lower limit and machines beautifully. For thinner pieces or more detailed work, up that to 8 lb. foam. That stuff is incredibly strong and will take detail beautifully.

    To finish, coat with epoxy (urethane resins will melt this foam) and fiberglass to turn it into an indestructible piece.

    I'd include pictures but the project I'm working on is NDA.
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  2. #2
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    Default

    What about cost vs HDU??

  3. #3
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    Default

    Since for me, cost isn't a factor, I can't comment on one material vs. another. I do know that high density foams for machining aren't available in my area and shipping them from where they are available costs more than the material itself. I can make the exact shape I need with a minimum of waste by casting liquid urethane using a crude mold made from scrap materials and saran wrap. That's the real advantage.
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  4. #4
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    Here's something I cast today using a mold made from aluminum foil and Saran Wrap...

    IMG_20191127_164717.jpg

    Here's the original:

    IMG_20191127_143401.jpg

    I made this post on my blog that goes into more detail.

    https://www.coryat.org/2019/11/copyi...-urethane.html
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  5. #5
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    Default

    Would this work for out door signs? about 1 1/2 --2 in.

  6. #6
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    Default

    The foam is closed cell, so won't absorb water and once coated with fiberglass, would be like a boat. However, signs are special and I have no experience with them.
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  7. #7
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    Default

    an excellent post John. I don't know if I will ever have a use for it but it is filed away for future reference.

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