Performing The Sieve Analysis; Determination Of Bulk Volume - HAVER & BOECKER W.S. TYLER Ro-Tap RX-29 Notice D'utilisation

7. Performing the sieve analysis

In order to receive precise sieving results, the kind of procedure should be determined before
starting the sieve analysis. The bulk volume, the feeding quantity, the sieving time and the
desired sieving precision should be pre-determined. The RO-TAP has been constructed for
dry sieving. For wet sieving with the RO-TAP a special wet-sieving-kit is available.

8. Determination of bulk volume

The optimum bulk volume can be determined by regarding several factors: the weight of bulk
material and its material properties such as sieving capacity, particle size and distribution.
For example a sieve analysis of a solid material with a coarse particle distribution needs a
feeding with bulk material of about 25 to 100 grams.
Often too large feeding quantities are filled in. To receive uniform results it is better to fill in
smaller, well taken sample quantities. During a reliable sieve analysis each solid particle
must have the possibility to be retained or to pass the sieve openings to the smaller ones of
the following sieve. In a test sieve set of six or seven sieves a small particle must repeat this
operation six or seven times. If the test sieves are overloaded a small particle may not have
the chance to drop down to the right sieve bottom. However the feeding quantity has to be
large enough to enable the first test sieve to retain enough particles, that are representative
for the good to be analyzed.
The weight of the sieving material should be limited to a size that no sieve in the sieve set
shall be overloaded. Overloading of test sieves may arise when sieving analyses are
effectuated with a high degree on cut-point-close particles in the sieving material. To avoid
overloading the capacities of the test sieves should be taken into account, especially the
capacity of the sieve that has to retain the largest residue. Any overloading leads to uncertain
results, because a lot of meshes may be blocked by particles.
The following procedure is recommended to determine the feeding quantity for test sieves:
Divide the material to be analyzed with a sample splitter into samples with different weights:
approx. 25, 50, 100, 150 and 200 grams. Analyze these samples on the test sieve set for
about 5 minutes. When comparing the results it should be obvious, which feeding quantity
leads to an optimum result. If the results, defined in percent of the residue, of a 100 gram
sample are the same as the 50 gram and 150 gram sample and show a smaller mass
fraction on the finest test sieve, 100 gram is the right feeding quantity to perform a sieving
analysis.
Cut-point-close particles are particles, that show a particle size approaching the cut point of a
test sieve. To achieve correct analyzes this test sieve should be fed slightly to enable each of
the cut-point-close particles to meet the openings as often as possible.
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