Sieve wire woven

British Standard Specifications BS 410 [13] adopts a primary size of 75 pm (200-mesh) with a fourth root of two progression in size and suggest that alternate sieves should normally be used for an analysis (i.e. a root two progression of sizes). Thus, the specific surface area of particles on consecutive sieves is in a 2 1 progression. BS 1796 describes the methods to be used in sieving with woven wire and perforated plate sieves [14],... 

BS 1796 Test Sieving, Part I, (1989), Method using test sieves of woven wire... 

ISO 2591-1 (1988), Test Sieving-Part I Methods using test sieves of woven wire cloth and perforated metal plate, 233... 

The basic set up for a sieving instrument usually involves a top cover, a stack of 2-6 different sieves with ascending order of opening size and a fines collector. The sieves are often made of wire woven with different aperture sizes and the particle size of the powder is characterized by the size of the sieve aperture. 

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. 

Permitted Variations in Aperture Dimensions for Wire-Woven Sieves Conforming to U.S. Sieve Series (Fine Series) ... 

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.

F uie 3.2. The range of apertures permitted in a wire woven sieving surface are strictly limited by ASTM and similar standaids [10]. Shown above are the ap>erture size distributions derived from two sets of 100 measurements made at the midpoint of the apertures of a 63 mesh ASTM sieve. Note that the aperture size has been normalized by dividing the measurements by the nominal aperture size of the 65 mesh sieve. 

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-... 

Probably the simplest technique for particle size measurement is sieving. Conventional woven-wire screens can be used to analyze powders, most of whose particles fall into the range of 50 jum to 1 cm. The range can be extended downward to 10 fim by using electroformed screens, which are more accurate than woven wire screens up to about 200 m. It is advisable to... 

Sieving Methods and Classification Sieving is probably the most frequently used and abused method of analysis because the equipment, an ytical procedure, and basic concepts are deceptively simple. In sieving, the particles are presented to equal-size apertures that constitute a series of go-no-go gauges. Sieve analysis presents three major difficulties (1) with woven-wire sieves, the weaving process produces three-dimensional apertures with considerable tolerances, particularly for fine-woven mesh (2) the mesh is easily damaged in use (3) the particles must be efficiently presented to the sieve apertures. 

Strainers are usually made from woven wire gauze, like a sieve, and though today the pre-size can be made very small indeed (BSI 300 mesh gauze separates particles of roughly 50 microns) they are mainly included for the exclusion of large particles. Filters deal with the removal of very much smaller particles. 

DRY SIEVING OR SCREEN ANALYSIS WOVEN WIRE SIEVES... 

Fine Series1 — Nominal Dimensions, Permissible Variations, and Limits for Woven Wire Cloth of Standard Sieves... 

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. 

In addition to the y/2 and y/2 series, it is also possible to utilize a series whose successive differences are in the ratio of 3. This series includes both the English inch and the metric millimeter, and should have had a certain amount of international acceptance. Unfortunately, it has never been practical to work out a series of such meshes and sizes of wire that could be woven satisfactorily. In addition to this objection, the cube root of the series does not include any of the sieves now in general use. 

Many methods are available for determining particle size in pharmaceutical practice, including microscopy, sieving, sedimentation, and determination of particle volume [19]. Sieve analysis with U.S. standard sieves is widely used to determine the particle size distribution based on powder weight. Sieves are classified according to the number of openings (Table 14) and are generally made of wire cloth woven from brass, bronze, or other suitable wire. 

A variety of sieve apertures is currently available, and these are classified as coarse (4 mm to 100 mm), medium (0.2 mm to 4 mm) and fine (less than 0.2 mm). The fine range extends down to 37 pm with woven wire sieves but the tolerances are liberal and this has limited their acceptance. 

The French AFNOR Standard NFX 11-501 [18] is based on a woven wire sieve opening of 1 mm in a tenth root of ten progression of size. 

Table 4.1 Nominal apertures and permissible variations for a selection of US woven wire sieves...

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