Sieve Openings — Microns

Size or sieve designation Micron No Sieve opening Inch (approx, equiva- Mm lents) Permissible variations in av. opening (percent = ) Permissible variations in max opening (percent = ) Wire diameter Inch (approx. Mm equivalents) ... 

Plot cumulative weight percent passing (y) as a function of particle size (x) in microns (as denoted by size of sieve opening) on log-log paper, as in Fig. 13.1. 

Particles as small as this cannot, at present, be produced on a commercial scale. It may be noted that the smaller particles found in a fluidized-bed reactor are retained on 400 mesh size, which has a sieve opening of 37 microns. 

Particle size conversion Sieve designation Standard Mesh Nominal sieve opening Inches mm Microns ... 

U.S. Sieve Series The American Society for Testing and Materials in cooperation with the National Bureau of Standards and the American National Standards Institute has further refined the U.S. sieve series, combining the former coarse and fine series into a single series series with a fourth-root-of-2 ratio (Table 19-6). The openings in the individual sieves have remained unchanged except for minor adjustments in sieves coarser than 0.00673 m (6.73 mm). In the revised series, sieves 1 mm and coarser are identified by opening in millimeters, and those finer than 1 mm by their openings in microns. 

For sieves from the 1000 micron (No 18) to the 37 micron (No 400) size inclusive, not more than 5 percent of the openings shall exceed the nominal opening by more than one-half of the permissible variation in maximum opening... 

Note The mesh designation is the number of openings per linear inch in the sieve. Material that passes through a 400 mesh sieve is very fine, but it still can be material that is up to 37 microns in size. Material in the 5-micron range cannot be analyzed with any accuracy using sieves an instrumental method is needed. 

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