FRITSCH PULVERISETTE 7 premium line - Manual (Page 29)

5.1.2 Overpressure relief of the grinding bowls
The grinding bowl seals have a sealing effect but are also for overpres-
sure relief. If the pressure increases gradually during grinding, the special
seals open at a certain pressure and release the overpressure in a
defined manner.
DANGER!
This overpressure release does not work in the event of
sudden pressure surges (e.g. explosions).
A half-round notch with a diameter of 2 mm is punched onto the outer
diameter of the flat seal. The grinding bowl's pressure release works with
flat seals made of fluororubber above a static internal grinding bowl
pressure of about 10 bar. Flat seals made of silicone open above a static
internal grinding bowl pressure of about 18 bar.
DANGER!
If flat seals are used without this defined notch, very high
pressures will develop in the grinding bowl that could cause
it to burst (resulting in damage and injuries).
The application of high energy during grinding results in high tempera-
tures in the grinding bowl. An 80 ml grinding bowl filled with 60 ml water
results in the development of the following pressures and temperatures:
Temperature of grinding bowl
wall [°C]
Pressure in the grinding bowl
[bar]
101 1
109 2
127 4
141 6
152 8
159 10
166 12
171 14
177 17
180 19
183 21
If water is used as an additive, the overpressure release with fluoror-
ubber flat seals is triggered at 159 °C, and with silicone flat seals at 180
°C an. Any effects by the ground material are not taken into account.
Using the device
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