[compost_tea] Mesh and micron a conversion chart
Some one on this list serve pointed us to this information some time ago.
Don't confuse MESH with MICRON
Contrary to the accepted norm; mesh size, by itself, means nothing!
Remove the concept of trying to equate an arbitrary number (mesh) to a fixe=
d number (micron)
Stick with a micron retention in particle removal
What is mesh?
It refers to the number of openings in a lineal inch measured from the cent=
er of one wire to a point 1" distant. It has nothing to do with the size of=
the hole and this is where confusion reigns. Someone gives you a mesh size=
(and this happens all the time) and through some hocus-pocus, a size in mi=
crons is given. How it ever evolved is beyond me and has caused more proble=
ms than people realize.
A simple example:
A 40 mesh filter screen has 40 holes per lineal inch - so what? Depending o=
n which manufacturers catalog you use, you can end up with, and I hate doin=
g this as a comparison, a micron retention ranging from 307 microns to 435 =
microns. For some applications, the difference is minimal, but for most com=
panies, it can mean rejection of product or contamination.
What determines the disparity when you convert to microns?
That's a good question, and I will answer it as simply as I can. The reason=
is this: manufacturers use different wire diameters. Why? My guess is due =
to the structural integrity of the screen, and a need to please everyone (y=
ou know what happens when you try that!).
Using our 40-mesh example, a manufacturer will use a wire diameter of 0.013=
", which results in smaller holes per linear inch. This calculates to a wid=
th opening of 0.012". The same manufacturer will then use a 0.008" wire dia=
meter, which produces bigger holes and corresponds to a width opening of 0.=
017". Remember, we still have 40 holes per linear inch but our micron size =
has changed from 307microns to 435 microns.
What can a company do?
Well, the first thing you need to do is think in terms of microns. I know, =
your thinking what is a micron? For those who are not sure or forgot, a mic=
ron is 0.000039". How is it applied? In an ideal world, a particle distribu=
tion count would be taken - this breaks down the size and quantity of suspe=
nded particles in a sample liquid. Unfortunately, most companies do not hav=
e the budget or time to do this (the cost can run anywhere from $300 to ove=
r a $1000). So the next best thing is to evaluate (guess) or contact a filt=
er specialist. To help, use the mesh /micron chart provided - the most comm=
on are listed. It isn't complete by any means, but it will get you pointed =
in the right direction.
As a general rule of thumb, anything below 40 microns cannot be seen with t=
he eye. Keep in mind that a mesh screen you're presently using, may not cor=
respond to our chart. If this occurs, you will need to look at the nearest =
mesh/micron size and evaluate which is better (above or below). Better yet,=
determine which micron size is needed for particle removal.
Conversion Chart
Mesh
Nominal Particle Retention
Micron Rating
10
.065"
1666
20
.035"
897
30
.023"
590
40
.015"
384
50
.011"
282
60
.009"
230
70
.008"
205
80
.007"
180
90
.0051"
130
100
.0055"
141
150
.0046"
118
200
.0033"
84
250
.0024"
60
400
.0018"
45
700
.0012"
30
Received on Sun Sep 21 2003 - 10:50:57 EDT
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