Operating the Device
62
6.9.2 Cryogenic grinding with the optional cryokit
WARNING
W9.0000
Risk of injury caused by liquid nitrogen
Use of liquid nitrogen during cryogenic grinding
−
Liquid nitrogen has a boiling point of
– 196 °C and causes burn-like
injuries and frostbite if there is skin and eye contact.
•
Take note of the liquid nitrogen safety data sheets.
•
Always wear goggles and protective gloves when using liquid
nitrogen.
WARNING
W10.0000
Risk of injury caused by liquid nitrogen and dry ice
Use of liquid nitrogen and dry ice in closed grinding jars
-
Liquid nitrogen and dry ice expand and generate high pressure in closed
receptacles. This high pressure bursts grinding jars and leads to serious
injuries.
•
Under no circumstances should you put liquid nitrogen or dry ice
into the grinding jar and then close the jar.
•
Only undertake indirect embrittlement for cryogenic grinding.
Materials that are difficult or impossible to grind at normal temperatures must be ground cold.
Indirect pre-brittleness with liquid nitrogen (- 196 °C) improves the fracture behavior of, for
instance, thermoplastics, rubber products, fatty foods, pharmaceuticals, etc.
For cold grinding, the MM 500 control offers a cryokit (order number: 22.354.0003) for
cooling the grinding jars with liquid nitrogen.
Perform a pre-embrittlement of elastic and tough sample material as follows:
Pre-embrittlement of sample material for grinding must be done indirectly.
Use only grinding balls and grinding jars made of stainless or hardened steel for
cryogenic grinding with the cryokit. Grinding balls and grinding jars made of
zirconium oxide or tungsten carbide are not suitable for direct contact with liquid
nitrogen.
The rapid cooling may cause cracks or fractures.
For this purpose, the sample material must be filled into a grinding jar (steel) together with
the grinding balls (steel) and the grinding jar (steel) must be tightly closed.
Subsequently, the tightly closed grinding jar (steel) with the grinding jar supports of the
cryokit is immersed in a bath of liquid nitrogen until it stops bubbling.
Thus, the sample material inside the grinding jar (steel) is also chilled and ready for
grinding.
Under no circumstances liquid nitrogen or dry ice should be filled into the grinding jar and
then close it. The resulting overpressure in the grinding jar would burst it open.
Summary of Contents for Mixer Mill MM 500 control
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