Hand sieving

The process is repeated with sieves of increasing fineness and the residue weights collated. Finally, the process is repeated with the finest sieve and the fines are added to the dust collected initially. Brushing is not recommended for sieves with aperture less than 200 pm due to the possibility of damage. Sieves should be washed and dried after use. Ultrasonics should be used to remove particles clogging the apertures or these may be leached out if this can be done without damage to the sieve. 

The results may be expressed in terms of the nominal size, although it is preferable to use calibrated sieves. A reference set of sieves should be used after every fiftieth analysis for comparison purposes in order to detect wear. In essence, the smaller the sieve loading, the more rapid is the sieving operation. The low weights however lead to errors in weighing and intolerable percentage losses. 

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Particle-SiZe Distribution. Particle-size specifications for sugar are not usually a part of the legislated standards, but they are of concern to commercial users and suppHers and are often specified in contracts. Grain-size distribution is determined by using a series of sieves, either hand-sieved or machine-sieved (13). 

ISO 972 1997 Chillies and capsicums, whole or ground (powdered) - specification ISO 7540 1984 Ground (powdered) paprika (Capsicum annuum L.) - specification ISO 3588 1977 Determination of degree of fineness of grinding - hand-sieving method (reference method)... 

Hand sieving is the reference technique by which other sieving techniques should be judged. For instance, in the French standard NFX 11-57, it states ... 

If sieving machines are used, they must be built and used in such a way that the sieve analysis must, within the agreed tolerances, agree with the analysis obtained by hand sieving. 

Different sieves, different methods Different sieves, same method Same sieve, same method Machine sieving Hand sieving ... 

The analyst may wish to remove and record particles naturally larger than a given particle size. Typically, for soils, particles larger than 10 mm or 2 mm are removed by mechanical or hand sieving and their mass recorded as a proportion of the total dry mass of the sample. Care should be taken to avoid removal of aggregates formed during drying. 

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