Stacking of sieves

Screening. A 100-g sample of mica is usually used for this test, plus a rack of six Tyler sieves and a pan. The stack of sieves containing the sample is rotated, and after screening, the mica remaining on each screen is weighed and the percentage retained is calculated. A combination of wet and dry screening may also be used to determine particle size distribution of fine mica (<0.147 mm ( — 100 mesh)). 

Machine sieving is carried out by stacking the sieves in ascending order of aperture size and placing the powder on the top sieve. A closed pan, a receiver, is placed at the bottom of the stack to collect the fines and a lid is placed at the top to prevent loss of powder. A stack usually consists of five or six sieves in a root two progression of aperture size. The stack of sieves is clamped on to a test sieve shaker that is vibrated for a fixed time and the residual weight of powder on each sieve is determined. Results are usually expressed in the form of a cumulative percentage of the nominal sieve aperture. 

Several writers have proposed automated wet sieving procedures [92,93]. In most of these methods, a stack of sieves is filled with a liquid and the... 

The cascadograph consists of a stack of sieves of the same nominal aperture size in a shaking device (a Tyler Ro-Tap sieve shaker). Each stack consists of twenty 8 in diameter sieves specially made by the Newark Wire Cloth Company Newark sieve cloth is claimed to have very uniformly sized apertures and a low tendency to blind. ... 

In sieve analysis, standard screens with precise screen openings are arranged in a stack from the coarsest to the finest with a pan below the bottom sieve to collect the fines. The material is introduced on the top screen and the stack of sieves is vibrated such that the material will stratify by particle size through the sieves. 

Thus, using a stack of sieves with an ascending order of aperture sizes one can separate the powder sample into the various sizes. By weighing the amount of powders... 

Figure 27. Diagrams depicting different analytical screening methods, (a) Stack of sieves (vibratory screening machine, dry), (b) air jet screen, (c) wet screening (vibratory screening machine, wet)...

Figure 37-25 shows a stack of sieves on a shaker. The sieves are stacked with the smallest number on top and the highest on the bottom. The bottom pan is for collecting the very fine particles, and the top sieve has a cover. The crushed, pulverized, and/or ground sample is placed in the top sieve, the cover put in place, the clamp closed, and the shaker turned on. Each particle will fall until it can go no farther. After 10 to 15 minutes, the shaker is turned off, the sieves are separated, and each is examined. If you want the 60 to 80 fraction, as for most chromatography column packings, you collect those particles that passed through the 60 mesh screen, but not the 80 mesh screen. 

PartiCiO Size Distribution. The particle size distribution is determined by sieving. The Rotap sieving, similar to the ASTM method used for polymer powders (33) is typically used. The method consists of placing a known quantity of the powder in a stack of sieves that are shaken horizontally while being hit at the top with a hammer (34). Alternatively, vibrating sieve sets may be used. The mass of polsrmer on each sieve is measured gravimetrically. From this data, the size distribution may be plotted and the mass-median particle size calculated. 

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