FRITSCH PULVERISETTE 7 premium line - Manual (Page 35)

5.2.4 Calculated weight of a ball
Ball diameter in mm 5 10 15 20
Material Density
in g/cm 3
Calculated weight of a ball in g
Agate 2,65 0,17 1,39 4,68 11,1
Silicon nitride 3,25 0,20 1,16 5,48 12,99
Sintered
corundum
3,9 0,25 1,99 6,72 15,92
Zirconium oxide 5,7 0,37 2,98 10,07 23,88
Stainless steel 7,8 0,51 4,08 13,78 32,67
Tempered steel 7,9 0,52 4,14 13,96 33,09
Tungsten car-
bide
14,9 0,96 7,40 25,98 61,58
To determine the weight of the required balls, the "calculated weight of
a ball" is multiplied with the "amount" of balls required.
Example: A 45 ml agate bowl is to be filled with 185 agate balls with a
diameter of 5 mm.
Calculation: 0.17 g x 185 St = 31.45 g
31.45 g grinding balls can be weighed and inserted in the grinding bowl,
thus avoiding the time required for counting the balls.
5.3 Impact of the ball size and the material during grinding
Large balls with a diameter of 10 mm – 20 mm will result in high
mechanical system stress. The combination of the heavy weight of the
balls and high acceleration result in high mechanical stress ￫ impact
effect.
The higher the density of the material to be ground, the
higher the mechanical stress is.
The highest mechanical stress is achieved with balls made of tungsten
carbide with a diameter of 20mm.
If large agate balls are used, they could destroy themselves and the
grinding bowls.
That is also the case with sintered corundum and silicon nitride balls.
Balls with a diameter of 5 mm and less result in high thermal system
stress.
Using the device
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