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additional minute. The data can be plotted
as percentage throughput versus time for
each data point you calculate.
change in the percentage of fines passing
in the 1 minute period drops below 1%, the
test can be considered complete.
the
total
testing
analyses.
Another type of sieve analysis is the wet
sieve test. In this method, the sample is
weighed and then washed through the
finest sieve in the stack with water, a
wetting agent (water based), or some
other compatible solvent. After thoroughly
washing the fines from the raw sample, the
residue is dried either over a hot plate or in
an oven. The temperature of the sieve
should
be
maintained
3
(300°F)
to avoid loosening of the sieve
cloth or failure of the solder joint. After
drying, the residue is then sieved normally
on the balance of the sieve stack. The loss
in weight not accounted for on the coarse
screens is assumed to be fines or soluble
material.
Wet sieve analysis is especially helpful
when working with naturally agglomerated
materials, ultra-fine powders with severe
static changes and in samples where fine
particles
tend
to
fractions in the blend. The disadvantages
associated with wet sieving are primarily
the time period required to perform the
analysis due to the additional washing and
drying time and the possible damage to the
sieve mesh by overloading. A common
practice with wet sieving operations is
brushing or forcing the sample through the
mesh while the liquid medium is directed
on the sieve. This pressure can distort the
sieve openings or tear the mesh at the
solder joint through stress. Therefore, this
procedure is not recommended. Once the
sieving interval is complete, whether dry or
wet sieving is used, the residue on each
sieve is removed by pouring the residue
into a suitable weighing vessel. To remove
material wedged in the sieve's openings,
the sieve is inverted over a sheet of paper
or suitable collector and the underside of
the wire cloth brushed gently with a nylon
paint brush with bristles cut to a 25.4 mm
(1") length. The side of the sieve frame
3
Advantech metal framed sieves should not exceed 261° F
(127° C). Solder will begin to soften at this point.
When the
Record
time
for
subsequent
below
149°C
cling
to
the
coarse
may be tapped gently with the handle of
the brush to dislodge the particles between
brush strokes. At no time should a needle
or other sharp object be used to remove
the particles lodged in the wire cloth.
Special
care
should
brushing
sieves
finer
Brushing
can
cause
irregularities in the sieve openings. The
procedure is repeated for each sieve in the
stack and contents of the pan.
The individual weights retained on the
sieves should be added and compared to
the starting sample weight. Wide variations
or sample losses should be determined
immediately. If the finished sample weight
varies more than 2% from the initial
weight, the analysis and sample should be
discarded and the test performed another
sample.
If
the
acceptable, complete the calculations and
report the individual weights retained on
each sieve.
Presentation
and
resulting data is frequently made easier by
plotting on one of a number of graph
formats.
The
most
presentation
is
the
cumulative percentage of material retained
on a sieve (plotted on a logarithmic scale)
versus percentage (plotted on a linear
scale). The resulting curve allows a quick
approximation of the sieve size at the fifty-
percentile point of accumulation. The curve
also
shows
the
distribution by revealing the presence of
bimodal
blends
in
plotting techniques include log-log and
direct
plotting
of
percentage retained.
be
taken
when
than
80
mesh.
distortions
and
sample
weights
are
analysis
of
the
common
graphic
plotting
of
the
smoothness
of
the
the
sample.
Other
micron
size
versus
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