Standard screen sizes

Example 3 Calculating Sample Weight for Screen-Size Measurement Weight W of bulk sample for screen analysis is calculated by the Gayle model for percent retained on a specified screen with relative standard error s.e. in percent... 

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. 

Tlie average screen size of a fraction is the mean arithmetical value of the average size of the screen mesh through which a fraction passes and the mesh that retains the fraction. Finally, the United States standard screen series is used (mesh size) for expressing the particle size. In Table 3.14, the conversion from mesh size to (cm) is given. 

Contracts for acetylene-grade carbide are usually based on size and gas yidd specification, and indude penalties for carbide that fails to meet specified gas yidd. The sizes generally available in the trade are based on established U.S. Government specifications. In general gas yidds range from 280—300 L/kg and depend on the screen size of the carbide. The most important standard is the method of expressing gas yidd, which in the United States is at 15°C and 101 kPa (1 atm). Gas impurities are typically 0.05% by volume phosphine, 0.15% by volume hydrogen sulfide, and 0.001% arsine. 

Data analysis would normally commence with the calculation of means and standard deviations for each column of numbers where this was appropriate. Next, tests would be performed to establish whether or not the data were normally distributed. The data could then be grouped according to a particular variable (e.g., year of manufacture, oscillator screen size, or assay method) and compared statistically for differences between the mean and standard deviations. For ease of review by the validation team, a table should be printed summarizing the statistics calculated and the conclusions reached as a result of these data manipulations. 

Most synthetic resins are granular with a spherical diameter of 0.04-1.0 mm. In the United States, the particle sizes are listed according to standard screen sizes or mesh values. Table 8.2 shows a comparison of mesh sizes and metric sizes the most common size ranges used in large-scale applications are 20-50 and 50-100 mesh [4]. 

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... 

Supports are usually sized by screening through standard ASTM screens. Mesh numbers refer to the number of openings per linear inch. Particles that will pass through 60 mesh, but not through 80 mesh, are referred to as 60/80 mesh. 

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. 

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

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