Sieving or screening is a method of categorizing a
powders particle size by running the powder through
a specific sized screen.
A powder can be separated into two or more size
fractions by stacking the screens, thereby determining
the powders particle size distribution.
Sieves and screens are usually used for larger
particle sized materials, greater than 44 micron (325
Two scales are used to classify particle sizes; US Sieve Series and Tyler
Mesh Size. A
powders mesh size can at times be somewhat
-6 mesh powder contains particles that pass through a
6 mesh screen. A
-6 mesh powder has particles that measure less than
A powder that is -325 mesh has particles that
measure less than 44 micron.
As you can see, the larger the mesh number the
smaller the particle size of the powder.
Lets assume for the moment you were interested in tantalum powder and
it had a description of:
Tantalum Powder, -325 Mesh, 3N8 Purity
You would know that this powder passed though a 325
mesh screen. You
could be confident that the powders particle size
was less than 44 micron.
However, much of the powder could be
considerably less than 44 micron and still qualify as
a -325 mesh powder.
It could be 1 micron and qualify as -325 mesh,
it could even be sub-micron and meet the -325 mesh
designation -325 mesh is simply saying the powder
passed through a 325 mesh screen.
If you needed a powder that was closer to size you
would need to specify two mesh sizes.
Tantalum Powder, -40+100 Mesh, 3N8 Purity
This powder would have particles that were smaller
than 40 mesh (420 micron) but larger than
100 Mesh (149 micron).
The powder passed through the 40 mesh screen
but was trapped in the 100 mesh screen.
Larger particles were trapped above in the 40
mesh screen and smaller particles passed through the
100 mesh screen. As
a result the larger particles were eliminated from the
distribution by the 40 mesh screen and smaller
particles were eliminated by the 100 mesh screen.