Retsch ZM 200 - Manual (Page 21)

08.02.2012 Retsch GmbH
21
0003
Comminution by cold grinding
X
Material that cannot be ground at normal room
temperatures, or not at all, must be cold ground. Prior
embrittlement with liquid nitrogen ( -196°C) improves the
breakage behaviour of materials such as thermoplastics,
rubber products, fatty foodstuffs, pharmaceuticals etc.
Embrittlement with liquid nitrogen is not necessary in the
majority of cases. Mixing with dry ice also produces good
results, as does storing the comminution material in a
freezer for 24 hours at a temperature of least -19°C.
When cold grinding with liquid nitrogen, always install the anti-
rebound fitting X in the filling hopper.
Danger of injuries to eyes and skin from extreme freezing.
Wear safety gloves and goggles. Temperature of the liquid nitrogen
–196°C
Danger of injuries to eyes and skin from extreme freezing.
When cold grinding, do not forcibly remove the plug-on rotor,
which jams easily for physical reasons, but rather wait for the
temperature to level out.
Forced removal causes damage to the motor shaft and the
rotor.
Comminution with distance ring sieves
The
deployment of distance ring sieves is
recommendable when materials with a low melting point
are to be ground, or wherever the rise in temperature
caused by comminution needs to be kept as low as
physically possible.
The ring sieve's low friction quotient due to the larger
distance to the rotor means that the grinding result will
be slightly coarser than if a standard ring sieve of the
same hole size is used.
Comminution of extremely small volumes
Grinding tools made of corrosion-resistant steel 1.4404
(316L) are available for grinding small sample volumes of
up to 50 ml.
The figure on the left shows the collecting vessel, ring sieve
and rotor for extremely small volumes.
The cassette cover, which is included in the scope of supply,
is not depicted here.