Apertures woven cloths

To allow for these practical difificulties it is usually necessary to rigidly specify and adhere to sieve fractionation study protocols. One also may fix limitations on the permitted variations in sieve apertures and sieving times according to empirical limits. In the manufacturing of sieve surfaces using wire woven cloth most major industrial nations have established specifications for sieves used in test studies [3, 7—10]. See Table 3.1. 

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. 

Woven wire sieves, having apertures ranging from 20 pm to 125 mm, are readily available in 100, 200, 300 and 450 mm diameters frames as well as 3, 8, 12 and 18 in diameters. Microplate sieves are available in 100 and 200 mm diameters with round or square apertures ranging from 1 to 125 mm. Endecottes test sieves have at least five intermediate and one final inspection in which wire cloth dimensions are inspected by projector. 

Sieve cloth is woven from wire and the cloth is soldered and clamped to the bottom of cylindrical containers [10,13]. Although the apertures are described as square, they deviate from this shape due to the three-dimensional structure of the weave. In the weaving process, the weft wires are crimped on to the warp wires for added strength vigorous cleaning, for example with a wire brush, can separate the wires leading to oversize apertures. Fine sieves are usually woven with phosphor bronze wire, medium with brass, and coarse with mild steel. 

The cylindrical sieve cloth containers (sieves) are formed in such a way that they will stack, one on top of the other, to give a snug fit (Figure 4.3). Due to the method of manufacture, woven wire sieves have poor tolerances, particularly as the aperture size decreases. Tolerances are improved and the lower size limit extended with electroformed mieromesh sieves. 

Most countries have standard sieve specifications and sieve analysis procedures. These specifications and procedures are usually generic and can be used for a wide variety of products, including fertilizers. The ISO has a series of international standards for test sieves [10] including (1) Test sieves - Woven metal wire cloth and perforated plate - Nominal sizes of apertures (ISO 565) ... 

A wide variety of screens and meshes are available, ranging from fine photoetched or electroformed perforated screens to the heavy duty wedge wire screens used in centrifuge and high pressure screw press construction. Simple sieves and coarse screens were used as early as the sixteenth century for processing metal ores. Modern woven wire screens are precision made cloths with aperture sizes as small as 20 pm (smaller aperture sizes are supplied by some manufacturers) for industrial separations in filtration, clarification and extraction. Plastic meshes and plastic coated metal meshes are finding an increasing number of applications in separation processes. 

In this section we will concern ourselves with the manufacture and characterization of sieving surfaces. The first type of sieving surface to be widely used in powder technology was woven wire. In the manufacture of sieves for analytical studies, it is usual to have the wire used to weave the cloth forming the surface of the sieve the same diameter as the aperture created by the weaving process. The sieve apertures created by such a process have the appearance shown in Figure 3.1(a). The aperture defined... 

Figure 3.1. Various measurements used to define the operative size of an aperture in a woven wire sieve cloth, a) (i) The appearance of an aperture formed by weaving wires, (ii) Measurements possible on an aperture in a wire woven sieve, b) Appearance of a wire woven sieve as viewed with a microscope.

Woven wire cloth for test sieves Width of apertures ... 

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