FRITSCH PULVERISETTE 25/19 - Manual (Page 5)

Cutting mill combination „pulveristte19“ – „pulverisette 25“ page 2
1.3 Fine crusher p-19
In view of the similar principle of functioning, the same applies to the fine
crusher as in the case of pre-crusher. On the other hand, a narrow sieve
mesh can lead to obstructions in the sieve. If the sieve gets pegged, the air
current is interrupted and may result in total breakdown of the system.
Therefore, the condition of the sieve must always be monitored. As the con-
stant flow of air has a certain drying effect, moderately moist mill feed of
approximately 20% humidity can also be fed without causing pegging in the
sieve. Experiments to crush oil-contaminated ground samples have failed.
1.4 Suction unit
A 1.1 kW fan drives the suction unit. Air is suctioned into a simple cyclone
and released into the external air through a 2-step filter. The air quantity
(speed) and hence also the cyclone's degree of cutting depends on the
condition of the filters and that of the sieves. Gradually, the increasing ob-
struction in the sieves and filters diminishes the transported quantity of air
and consequently the speed of the air. This deteriorates the degree of cut-
ting, which means; more and more rough particles find their way to the filter
and do not drop into the sampling jar. On an average, the cutting limit is
approximately 10µm, whereas the cutting limit of the first step of filtering is
approximately 1µm and that of the second step of filtering, i.e. the Hospital
filter is approximately 0.3µm. This makes sure that no bacteria or particles
that may affect lungs are blown into the surrounding space.
2 Operational safety
The safety precautions as described in Chapter 2 of the Operating Man-
ual for p-19 and p-25 are applicable.