Micromesh Sieving

Micromesh sieves are produced by photoetching and electrodeposition techniques. Electrodeposition nickel produces precise square openings with planar surfaces. This thin mesh is supported by a coarser square-etched grid of nickel-plated cupronickel. These sieves are mounted in 75 or 203 mm (3 or 8 in.) stainless steel rings.

Sieve openings may be as small as 3 /'m at frequent intervals. ASTM E 161 specification permits a maximum deviation of only ±2.0 /Jm for sieves ranging from 125 to 5 /'m.

Sieving techniques include the same mechanical shakers and vibrators used for wire cloth sieving. However, for sieves finer than 325 mesh (45 /''in), most dry sieving techniques are inadequate. For these smaller size sieves, a vacuum-

type siever can be used (Fig. 2). This type of apparatus uses suction coupled with a rotating blowback nozzle. Fine particles are suctioned through the mesh, while the blowback nozzle redistributes the powder sample on the sieve, thus breaking up agglomerates and purging the mesh openings.

Fig. 2 Micromesh vacuum siever. (a) Apparatus. (b) Sectional view

The sieving operation is rapid and allows sieving down to 10 /' m. Due to the smaller sieve diameter (75 mm, or 3 in.) and the smaller amount of open area of the finer micromesh sieves, samples of only 1 or 2 g (0.035 or 0.070 oz) are used to prevent overloading. It is also possible to perform wet sieve analyses using micromesh sieves.

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