Particle size analysis by sieving
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Particle size analysis by sieving


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In many industries, particle size measurements have been carried out 
historically by sieve analysis and light scattering instruments are 
increasingly replacing this. In order to correlate with historic data banks 
some manufacturers have software to manipulate the data so as to present 
the size distribution in terms of sieve diameter. 
Table 4.7 Particle size distribution of BCR 68 by four laboratories 
Equivalent volume 
diameter (|xm) 
160 
250 
320 
400 
500 
630 
Mass percentage undersize 
Lab. 1 
4.7 
21.9 
44.0 
68.6 
89.6 
96.8 
Lab. 2 
4.4 
24.6 
45.4 
70.0 
88.6 
98.1 
Lab. 3 
4.3 
23.0 
44.5 
70.6 
87.7 
97.0 
Lab. 4 
4.4 
24.5 
47.6 
66.9 
88.5 
96.0 
Tests carried out on pneumatically conveyed salt particles showed that 
Insitec data gave size distributions that were over 30% coarser than sieve 
data, the difference being attributable to particle shape effects. The results 
for both instruments showed that the particles attrited with number of 
passes through the system, with the Insitec being more sensitive than 
sieving [118]. 
4.24 Conclusions 
According to Hey wood [1] sieving is the Cinderella of particle size 
analysis methods; it does most of the hard work and gets little 
consideration. This was reiterated by Leschonski [119] who also quotes 
the chairman of the Institution of Mining and Metallurgy as stating, in 
1903, that screening is not a scientific means of measurement. 
However, measuring particle size distributions by sieving is simple and 
inexpensive and can give reproducible results, even when using different 
sets of sieves, if proper care is taken. Although most of the problems 
encountered in sieving have been known for years and solutions proposed, 
reproducibility is rarely achieved, owing to the failure to take advantage of 
this knowledge. 
246 Powder sampling and particle size determination 
For accuracy, it is necessary that the sieves be calibrated and, if the sieves 
are dedicated to a single powder, the calibration should be carried out with 
the powder under test. It is also necessary that the sieves be checked, on a 
regular basis using a calibration powder, so that worn sieves can be 
rejected. Normally, if a sieve analysis is plotted on log-probability paper, a 
smooth curve results; any points lying off the curve should be viewed with 
suspicion. 
For reproducibility, a standard operating procedure should be adopted. 
Table 4.7 illustrates the reproducibility that can be attained using 
calibrated sieves. The data is taken from the certification report on 
reference materials of defined particle size issued by the Commission of 
the European Communities and refers to data generated by four 
laboratories with BCR 68. 
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