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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorcjard
    • CommentTimeOct 5th 2015
     
    @peter I did consider a normal compressor and circa 120 psi but genuinely didn't think it would push the liquid through the hoses. I'm fully prepared to be proven wrong though, and it'd be wonderful to be able to refill the touch'n'foam cylinders and whack a compressor on them. I'll have a bit more time coming up soon, will give it a shot

    I was initially thinking a high pressure to get adequate mixing and ejection of the foam, and a consistency of delivery as the pressure drops during use. Remember that a cylinder X percent full can have quite a high pressure e.g. 3000 psi, but by the time the gas has propelled the liquid it shares the volume with it will have expanded 1/(1-x) times and suffered a commensurate pressure drop..

    You can also get machines that fire touch n foam, but they're insanely expensive.. Not averse to buying kit I can sell on afterwards, or sell as a service, but I don't think there's much call for one

    @ringi - There enters the skill of the operator: don't fill the entire cavity with foam from the (aerosol) gun - get acquainted with how much the foam will expand (foam dispensed faster expands more) and fill partially so that expansion does the rest.

    pretty sure that most of my joints don't waste 50% of the foam..
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 5th 2015 edited
     
    I used to be involved in moulding PU foam (mainly flexible and integral skin, but also some structural as well).
    We used pumps, generally pistons, but some gear ones too, to get the polyol and isocyanate to the mixing head.
    The viscosity of each was different, as was the ratios quite often. Viscosity also changed a lot with temperature, so what worked at start of day often did not work later on.

    We had a selection of mixing heads, for the large stuff it was a paddle mixer with a large electric motor on it. We has a simple atomiser type, but was not of much use to us as we were mainly moulding stuff (gaskets, arm rests, gear knobs, steering wheels and cushions). I seem to remember that it was pretty uncontrollable and never gave the results we hoped for.
    The last sort we had was a screw type, you get these with some cans, just a tube with a perforated Archimedes screw in it. Was alright for prototyping, but not much use in production (though it did save on cleaning time and 'shots to waste').

    If you get covered in PU resins, methylene chloride is what you need.
    Be warned, some resins can stain your skin black and it takes about 3 weeks to go (we did a Black and White Minstrel show routine when to happened).
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