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Author: Subject: Making a .5 micron filter?

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[*] posted on 30-12-2010 at 21:51
Making a .5 micron filter?

Does anyone know the micron rating of a typical coffee filter or a pair of nylons? How many coffee filterer layers or nylon leggings does it take to make a 6 a 1 and a .5 micron filter? Is there simple formula to figure this out like if we find out our coffee filter is about 30 microns (is that a o.k guess) for one?
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[*] posted on 31-12-2010 at 06:24

You aren't going to improve the micron rating by stacking the filters deeper (well, not much, I realize that for statistical reasons there may be some improvement).
The internets give different values for coffee filter pore sizes, I see 15-30 micron as well as 100 microns; I don't doubt that there is substantial variation in manufacture so both values may be correct
Automotive oil filters will stop 95+% of 40 micron particles but only 10-15% of 10 micron particles. I suppose in principle this means that you could stack twenty of them to achieve ~95% trapping of 10 micron particles, but as you can see this approach is hardly practical as a way of decreasing the minimum particle size. Assuming a similarly shaped curve (trap % versus particle size) for coffee filters as for oil filters (a dubious assumption, especially for small particles!), you'd need, oh, about 500 coffee filters to get to 1 micron.
So really, just buy a filter paper with the pore size you need.
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