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I want to grind flexible polyurethane foam to a size of about 50-100 microns. The feedstock is shredded 1.5 lb/ft^3 polyurethane foam.

I tried a commercial meat grinder, which works but is very slow, and I tried a hammermill, which works, especially if it's mixed with ice, but nothing's really been effective.

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  • $\begingroup$ Liquid nitrogen bath before using any of the other methods? $\endgroup$
    – hazzey
    Nov 26 '15 at 19:40
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    $\begingroup$ It can be quite hard to grind elastomers to a fine size when they are above their glass transition temperature. You will have to either increase the glass transition temperature or reduce the processing temperature to below glass transition. Liquid nitrogen looks like your best bet. $\endgroup$ Nov 27 '15 at 2:49
  • $\begingroup$ Biswajit- I'll try the liquid nitrogen. Great idea. Glass transition of polyurethane is listed as -20C, I think I'll try dry ice as well. Post this as an answer, I'll mark it as 'the' answer. $\endgroup$
    – Anniepoo
    Nov 27 '15 at 19:00
  • $\begingroup$ more reading - plasticizers decrease glass transition temp. Am I being foolish to try dry ice? $\endgroup$
    – Anniepoo
    Nov 28 '15 at 2:16
  • $\begingroup$ @Anniepoo: Your question deserves a more detailed and careful response than I have time for. So I'll skip posting an answer for now. Yes, you don't want to use plasticizers but you could try to increase the cross-link density (to get increased brittleness). Dry ice should help. I'm sure there are patents on similar processes; search Google Scholar. $\endgroup$ Nov 28 '15 at 2:49
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Have you considered a Industrial Plastics grinder? they are typically a series of metal plates that have teeth on them that spin in one axis with two sets in opposite directions. you can typically find them that take things down to i think 1/4 inch but you could probably find one that would take it down even smaller or even use a secondary meat grinder to take it further from your initial grinder size. i have a link to a place that sells them below and a video of an extremely large one crushing a car.

http://www.jordanreductionsolutions.com/plastic-grinder.html : Plastics Grinder

https://www.youtube.com/watch?v=tPDLX0koXFs : Car Crush

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  • $\begingroup$ Thanks, but 50 microns is 0.002 inch, lots smaller than 1/4" sadly. A blender does 0.050 with no problem, a meat grinder somewhat larger. $\endgroup$
    – Anniepoo
    Dec 22 '16 at 19:54
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Have you considered adjusting the nozzle on a pressure washer to create a coaxial (zero degree) exit angle and using it like a fluid powered knife?

https://youtu.be/MATIA-X59ro?t=3m23s

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  • $\begingroup$ That sounds slow. Have you seen anything similar in use? $\endgroup$
    – Anniepoo
    Nov 26 '15 at 2:50
  • $\begingroup$ @Anniepoo: youtu.be/MATIA-X59ro?t=3m21s $\endgroup$
    – Mowzer
    Nov 26 '15 at 2:57
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    $\begingroup$ Your youtube video seems to demonstrate that I can cut the foam with a pressure washer. I'd certainly believe that - it's basically scraps of old foam rubber seat cushions. A household blender will take it to 3000 microns pretty quick - it's getting a fine grind that's the problem. $\endgroup$
    – Anniepoo
    Nov 26 '15 at 3:07
  • $\begingroup$ @Anniepoo: Agreed. $\endgroup$
    – Mowzer
    Nov 26 '15 at 3:12
  • $\begingroup$ @Anniepoo: What is your application? What's your goal? $\endgroup$
    – Mowzer
    Nov 26 '15 at 3:14

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