Mesh number, sieve

It is found that the rate is only feebly dependent on the sieve mesh number. This is unlike a steep rise in rate expected for diffusion-rate limited situation (in this case, the rate can be improved by modifying catalyst s physical features) or independent as expected for reaction-rate limited situation (rates can be improved by changing chemical features of the catalyst). In the present case with Ti02 (SD) there is need to optimize both chemical and physical features of the catalyst to a certain extent. Further work in this direction is currently in progress. 

Table I. U.S. Standard Sieves, Mesh Numbers, Phi and Wentworth Class...

US Standard Sieve. Mesh number is the number of standard diameter wires per inch of wire mesh. 

The mesh number is the number of apertures per unit length of sieve. 

Mascheci-draht, m. screeQ wire, netting wire, -grSsse,/. size of mesh, -sieb, n. mesh sieve, mesh screen, -weite,/. width of mesh, -werk, n. network, -zahl,/. mesh number, mesh. 

Screen sizes are defined in two ways by a mesh size number for small sizes and by the actual size of opening in the screen for the larger sizes. There are several different standards in use for mesh size, and it is important to quote the particular standard used when specifying particle size ranges by mesh size. In the UK the appropriate British Standards should be used BS 410 and BS 1796. A comparison of the various international standard sieve mesh sizes is given in Volume 2, Chapter 1. 

BS. mesh number Sieve aperture, pm Fractional weight per cent retained Cumulative weight per cent oversize Cumulative weight per cent undersize... 

A series of fine mesh, std test sieves of specification governed by British Standards Spec No 410-1943, available from BSI, Victoria St, London SW1. These sieves with their mesh numbers openings are compared with US,... 

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 order to sieve samples, sets of sieves with increasing mesh number and made of different materials, including very inert ones, can be used. 

SCREEN ANALYSIS STANDARD SCREEN SERIES. Standard screens are used to measure the size (and size distribution) of particles in the size range between about 3 and 0.0015 in. (76 ram and 38 pm). Testing sieves are made of woven wire screens, the mesh and dimensions of which are carefully standardized. The openings are square. Each screen is identified in meshes per inch. The actual openings are smaller than those corresponding to the mesh numbers, however, because of the thickness of the wires. The characteristics of one common series, the Tyler standard... 

The sieve openings and mesh numbers for U.S.A. Sieve Series and Tyler Equivalents (A.S.T.M. E-l 1-87) are shown in Table II. 

Mesh number and particle size for standard sieves. 

Woven wire test sieves were formerly designated by a mesh number (the number of wires per inch) but as the important sieve characteristic is the size of its apertures all standard test sieves are now designed, by international agreement, by their aperture size in millimetres or micrometres. The aperture sizes in a standard series are related to one another, e.g. following a fourth root of two (1.189) or a tenth root of ten (1.259) progression. The two most widely used standard sieve scales are the American (ASTM Ell, 1995) and British (BS 410, 2000) both of which are compatible with the international scale (ISO 3310, 2000) (Table 2.11). 

Table 2.11. Comparison between the British and US standard wire mesh sieve scales showing the danger of using the mesh number as a sieve designation...

Sieves are used to separate particles into fractions with different size ranges. The particles are classified according to their ability or inability to pass through an aperture with a controlled size. Sieves are constructed with wire mesh with openings between 20 pm and 10 mm, which are characterized by a mesh size and a corresponding aperture size. The wire mesh has square apertures, whose size is determined by the number of wires per linear dimension and the diameter of the wire. The mesh size is equal to the number of wires per inch linearly of the sieve screen, which is the same as the number of square apertures per inch. The relationships among mesh number M, aperture width a, wire diameter w, and the open area A can be described by the following equations ... 

Each sieve is designated by a number that corresponds to the aperture of the sieve mesh. Sieves used for sieve analysis have apertures of square shape, as specified by CEN EN 933-2 (1995) or ASTM E 11 (2013). They are designated by the edge lengths of the square apertures. 

S. Subramanian, A.S. Ganesh Kumar, and C.T. Goudar, Determine Sieve Opening from Mesh Number, reprinted in Chemical Engineering Buyers Guide (2000), p. 15. 

Equations 2.34 and 2.35 allow for transformations between mesh number and aperture size. Both features of sieves are listed in standard screen scales. Standardized sieve apertures were first proposed by Rittinger (1867). Modem standards are based on either a-Jl or progression. In the United States, the series of sieves with standard opening sizes are called "Tyler" sieves and the openings of successive sieves are based onayfz progression starting at 45 pm. 

Granules and particles are characterized by their size, and possibly size distribution. This character is denominated by sieve or mesh size. Larger particles are recognized by being associated with smaller sieve size numbers. 

Fines n In the classification of powdered or granular materials according to particle size, fines are in portion of the material whose particles are smaller than a stated minimum size. When the particle-size distribution is determined by Sieve Analysis, the fines are those particles passing the finest sieve and found on the pan, usually designated as minus 000 mesh, where 000 is the mesh number of that finest sieve (Provder T, Texter J (eds) (2004) Particle sizing and chacterization. American Chemical Society, Washington, DC). 

Larger sieve openings (1-1/4 in.) have been designated by a sieve "mesh" size that corresponds to the size of the opening in inches. Smaiier sieve "mesh" sizes of 3 1 /2-400 are designated by the number of openings per iinear inch in the sieve. 

Sieve Fraction Tbe mass fraction of a sieve-analyzed powder found between two successive screens in a Sieve Analysis. For example, one might say, The —0.420-, -1-0.250-mm fraction was 15.27 percent. See also Mesh Number. 

---