Screening sieve dimensions

The data for a plot like Fig. 18-60 are easily obtained from a screen analysis of the total crystal content of a known volume (e.g., a liter) of magma. The analysis is made with a closely spaced set of testing sieves, as discussed in Sec. 19, Table 19-6, the cumulative number of particles smaller than each sieve in the nest being plotted against the aperture dimension of that sieve. The fraction retained on each sieve is weighed, and the mass is converted to the equivalent number of particles by dividing by the calculated mass of a particle whose dimension is the arithmetic mean of the mesh sizes of the sieve on which it is retained and the sieve immediately above it. 

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... 

We have already discussed measurement of particle size by the use of particle dimensions in Section II. where particle shape as relating to particle size was a major concern. Note that even though the shape of the particle may be quite elongated, the stated size wiU be predicated upon a spheroidal shape. The stated (measured) size of a PSD based upon weight will depend upon how well the particles were separated into fractions. For example, if we use a set of sieves to separate particle fractions, the fractions of particles measured may, or may not, be a function of shape. Acicular particles will not pass through a given screen the same way as... 

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 ... 

Disintegrability, namely fragmentation and loss of visibility in the final compost (absence of visual pollution). The standard recommends assessment of disintegration through trials on a pilot or full-scale composting plant. Specimens on the test materials are composted with biowaste for three months. The final compost is then screened with a 2 mm sieve. The mass of test material residues with dimension >2 mm shall be less than 10% of the original mass. 

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