Particle size analysis by sieving
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Particle size analysis by sieving

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feed (Figure 4.8). For coarse aggregates, 
sieving is deemed complete when the rate falls below 1% per min [22]. 
2i2 Powder sampling and particle size determination 
End point 
End-point criteria 
BS 1796 0.2% in 5 min. 
ASTM D452 0.5% in 10 min. 
\u2022 I I I I I I 11 I \u2022 I I I I I I I I I I I I \u2022 \u2022 I l l 
1 10 100 1000 
Sieving time in minutes 
4.8 Amount passing through a sieve as a function of time. 
It is generally recommended that if losses during sieving exceed 0.5% of 
the total feed, the test should be discarded. Preliminary hand sieving on 
the finest sieve should be carried out for the removal of dust. This dust 
would otherwise pass through the whole nest of sieves and greatly prolong 
the sieving time; it would also percolate between sieves in the nest and 
increase powder loss. Extreme care needs to be taken when weighing the 
sieve residue. The powder retained on each sieve should be emptied on to 
a sieving paper and the underside of the sieve brushed lightly to remove 
any particles adhering to the sieve. 
In BS 1796 [14] which applies to the sieving of material from 3350 to 
53 |im in size, it is suggested that the sieving operation be carried out in 5 
min. stages at the end of which the sieves should be emptied and brushed 
in order to reduce aperture blockage. This procedure can however lead to 
excessive powder loss. 
While developing a protocol for a system that will serve as a standard, 
NIST recommend sieving a given quantity of the material for varying 
amounts of time, e.g. 10 min. to 30 min. at 5 min. intervals. Sieving time is 
selected based on the time period after which no significant difference in 
mass change is observed. Sieving for a fixed period of time is more 
convenient than sieving until less than a certain fraction of the total mass 
passes through the sieve in a given period of time. The time and effort 
required, if the latter procedure is adopted, can be considerable and would 
Sieving 233 
prove to be too onerous if numerous samples were to be analyzed. Test 
sieving procedures covering a broad band of materials are also described in 
ISO 2591 test sieving procedures [82]. The sieving action of many 
commercial machines is highly suspect and frequently subsequent hand 
sieving will produce a sieving rate far greater than is produced on the 
machine. For the vibratory test sieve shaker a rapid vertical movement is 
needed to help keep the apertures clear and prevent blinding. The best 
type of sieving action is found with the types of shakers exemplified by the 
Pascal Inclyno and the Tyler Ro-tap, which combine a gyratory and a 
jolting movement, although the simpler vibratory sieves may be suitable in 
specific cases. ASTM B214 suggests 270 to 300 rotations per min. for 
granular materials combined with 140 to 160 taps to reduce blinding of 
sieve apertures. Tyler also markets a sieve enclosure to reduce noise levels 
from approximately 85 dB to 60 dB. 
The Endecott Octagon digital sieve shaker has a controller, which is 
used to set the sieving time and amplitude of vibration. These laboratory 
shakers are fitted with a clamping device to ensure that the nest of sieves is 
held firmly without over tightening. The Endecott EFL 2000 series are 
rugged shakers ideal for heavy-duty applications. The Endecott Star 2000 
is a dedicated sieve test analyzer and recorder that incorporates a precision 
balance linked to a microprocessor and printer. The Star memorizes the 
sieve weight before and after sieving and makes the necessary calculations 
to generate a size distribution. The test results can be stored for future 
reference as a master. Current test results can then be compared with stored 
data for up to five masters. Modifications to the methods may be 
necessary for materials that are not free-flowing, are highly hygroscopic, 
very fragile, have abnormal particle shapes or have other properties that 
cause difficulty in sieving. For example, in ASTM C92 the fines are first 
removed by washing through the finest sieve; the residue is then dried and 
analyzed in the dry state. 
Vorti-siv manufacture gyratory and ultrasonic lab sieves that include a 
de-blinding kit for sieving powders as small as 5 |Lim. Units operate at 
1,750 or 3,450 rpm and have an 8, 10 or 12 in diameter screen. Options 
include stainless steel or explosive proof construction and continuous 
discharge chutes. 
Large-scale sieving machines, to take a charge of 50 to 100 kg, are 
needed for the coarse range [83]. A wide range of commercial sieve 
shakers is available for the medium range and these usually classify the 
powder into five or six fractions with a loading of 50 to 100 g. Special 
sieving techniques are used with the finer micromesh sieves. 
234 Powder sampling and particle size determination 
4.13 Wet sieving 
4.13.1 Manual 
Several manual methods of wet sieving using micromesh sieves have been 
described. Mullion [84] uses an 80 kHz, 40 W ultrasonic bath in which the 
micromesh sieve rests on a support, which, in turn, rests on a beaker in the 
bath. Sieving intervals are 5 min. with an initial load of 1 g. and the 
operation is deemed complete when no further powder can be seen passing 
through the sieve. 
Colon [85] rinses the fines through the sieve aperture with a suitable 
liquid after 0.5 to 1 g of sample has been dispersed in a small volume of 
the liquid. Sieving continues by moving the sieve up and down in a glass 
beaker filled with the same liquid so that the direction of flow through the 
sieve is continuously reversed. If necessary, ultrasonics may be used. 
After a standardized time, the operation is repeated using a second beaker 
containing fresh sieving liquid. Sieving is deemed complete when the 
amount passing through the sieve is visibly negligible. 
Niedick [86] disperses about 1 g of powder in 1 liter of liquid and pours 
this through a sieve in a retort stand. The suspension passing through is 
channeled with a funnel into a second container. For woven wire and 
coarse micromesh sieves, the sieves may be mechanically rapped to 
facilitate sieving. The residual powder is then rinsed off the sieve and 
weighed or the pre-tared sieve is dried and weighed. With fine micromesh 
sieves and water as the dispersant, surface tension prevents the suspension 
from passing through the sieve, so that after filling the sieve with 
suspension an ultrasonic probe is used to initiate flow. Alternatively, a low 
surface tension liquid may be used. The procedure is then repeated with 
sieves of increasing fineness. 
Daescher [87] describes a method using a set of tared sieves mounted 
on a special funnel held in a filter flask. 1 to 3 g of powder are placed on 
the top sieve and washed through each sieve in turn with a suitable polar 
liquid or hydrocarbon containing a trace of dispersant. At the same time, 
alternate pulses of pressure and suction are applied to the filter flask. This 
pulsating action orientates the particles in such a way as to speed up the 
sieving action. A full analysis can be completed in less than an hour. 
Sieving 235 
Separating funnel 
Non-rigid tube 
Shower head 
or spray nozzle 
Sieving machine 
li Fi FUter unit 
Low pressure 
Fig. 4.9 The Retsch wet sieving machine. 
loos [88] describes a device that makes it possible to carry out particle size 
analysis from 60 |Lim down to 5 |j.m by means of sieves arranged vertically 
above one another and subjecting this nest of sieves to ultrasonics. 
A method of wet sieving clays is described in ASTM C325 [89] in 
which the fines are washed out first and the rest are washed through a nest 
of sieves. In ASTM D313 and CI 17 washing through a 200-mesh sieve is 
suggested for the removal of fines and in D185-72 the use of a camel-hair 
brush is recommended to facilitate passage through a 325-mesh sieve. 
Other investigators have described similar methods. [90,91]. Ultrasonic 
agitation is also required for cleaning fine