FRITSCH PULVERISETTE 7 premium line - Manual (Page 39)

5.8.1 The effect of high temperature
DANGER!
During wet grinding in the grinding bowls, the high internal
temperature, the increase in size of the surface of the parti-
cles due to crushing and any chemical reactions in the bowl
may result in the development of a very high pressure.
This pressure can get so high that the hooks that hold the
lid on the bowl crack, resulting in the lid "flying off". During
grinding tests, chemical reactions of steel parts (tempered
steel and stainless steel) and tungsten carbide parts with
water suspension were determined. After a grinding period
of 20 minutes, the increase in pressure could tear off the
locking hooks. The grinding bowl temperature may be rela-
tively low.
DANGER!
Explosion hazard! Ignition hazard! Burn hazard!
In the event of a longer grinding duration, apply cooling
pauses to reduce the internal pressure. For certain material
to be ground, it may also be necessary to release the pres-
sure after the cooling phase, otherwise it could be retained
in the bowl in spite of cooling. That is in particular also the
case in the event of a chemical reaction in the grinding
bowl. See Ä Chapter 5.3 ‘Impact of the ball size and the
material during grinding’ on page 35, Ä Chapter 5.8.2
‘Safety measures against an excessively high pressure’
on page 40 and Ä Chapter 5.12.10 ‘Cooling the grinding
bowl’ on page 58.
NOTICE!
If the permissible maximum temperature in the bowl is
exceeded during grinding, then the device must not be
switched off with the lid closed. That could lead to heat
accumulation in the machine, which could cause damage to
the device.
Provide sufficient cooling by letting the mill continue to run
at a speed of 100 rpm for approx. 20 - 30 min. or by shut-
ting off the mill with the lid open.
The bowl may get stuck on the holder if the bowl temperature gets too
high. In such a case, wait until the bowl has cooled down sufficiently in
order that it is released by the holder.
Using the device
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