Sieve electroformed

Sieves are often referred to by their mesh size, which is the number of wires per hnear unit. The U.S. Standard Sieve Series as described by the American Society of Testing and Materials (ASTM) document E-11-87 Standard Specification for Wire-cloth Sieves for Testing Purposes addresses sieve opening sizes from 20 [Lm (635 mesh) to 125 mm (5.00 in). Electroformed sieves with square or round apertures and tolerances of 2 [Lm, are also available. 

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. 

A downward air flow has been found to improve sieving rate for 10, 25 and 45 pm electroformed sieves using a sonic sifter operating at 107 dB and 78 Hz [102]. The sieving rate also increased with decreasing feed rate, especially for sub-10 pm sieves [103]. 

More accurate sieving surfaces than the wire woven material have been developed to improve precision of powder fractionation by sieves. One of these more precise surfaces is known as an electroformed sieving surface. These are created by drawing a grid pattern on a surface and then electroplating the pattern using appropriate tech-... 

Figure 3.6. Optical methods can be used to discover damaged apeitures in a sieving surface [22, 23, 24]. a) Diffraction pattern of an undamaged sieve mesh, b) Optical spatial filtering system used to detect sieve damage, c) Photogtaph of a damaged electroformed sieve surface, d) Spatially filtered image of the damaged sieve of (c).

Electroformed sieves are available from Buckbee-Mears Company, 245 East Sixth Street, St. Paul, Minnesota, 55101. 

Figure 6.2. In the IITRl improved resistazone counter, a metal electroformed sieve acts as one electrode and prevents oversize fineparticles from enterii the sensii zone or extremely large fineparticles from blocking the orifice. The hole through the Teflon block between the electrodes acts as a flow straightener.

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