Electroformed micromesh sieves

Micromesh sieves [11] were first described by Daescher et. al. [35] and are available in standard sizes ranging from 500 pm down to 3 pm. Etched sieves usually have round or square apertures, ranging in size from 500 to 1200 pm, but other aperture shapes are available. They are available in 3, 8 and 12 in diameter frames, as well as custom-made sizes. Other aperture sizes are also available and Zwicker reports using a 1 pm sieve [36]. 

The tolerances with micromesh sieves are much better than those for woven-wire sieves the apertures being guaranteed to 2 pm of nominal size apertures except for the smaller aperture sieves. Each type of sieve has advantages and disadvantages [38] e.g. sieves having a large percentage open area are structurally weaker but measurement time is reduced. 

5 Effective aperture width distribution with increasing sieving time. 

Niklas [42] discusses edge weaknesses in nickel electroformed sieves due to acute angle comers. Additives used during photo-etching increases these defects [43] Stork [44] also describe sieve preparation by electrodepositing a thin metal skeleton on to a substrate, removal of the skeleton from the substrate, followed by deposition of two or more layers of metal on both sides of the substrate. Additives encourage growth perpendicular to the surface of the skeleton. 

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The common sieves are made of woven wire cloth and have square apertures. The sizes of the sieve openings have been standardized, and currently two different sets of standard series, the Tyler Standard and the U.S. Series ASTM Standard, are used in the United States. The mesh number of a sieve is normally defined as the number of apertures per unit area (square inch). Thus, the higher the mesh number the smaller the aperture. Typical mesh numbers, aperture sizes, and wire diameters are given for the lyier sieves and the U.S. ASTM sieves in Table 1.3. Sieve analysis covers the approximate size range of 37 pm to 5,660 pm using standard woven wire sieves. Electroformed micromesh sieves extend the range down to 5 pm or less while punched plate sieves extend the upper limit. 

Electroformed micromesh sieves extend the range down to 5 pm or less, and punched plate sieves extend the upper range. 

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