2 vibration frequency, 3 number and size of the balls, 4 weight of the balls (type of material) – FRITSCH PULVERISETTE 23 User Manual
Page 23: 4 dry grinding, Using the planetary mill

6.3.2 Vibration frequency
Higher vibration frequencies shorten the grinding time and increase the
share of fine particles.
6.3.3 Number and size of the balls
Pre-grind course, hard material with large balls:
Reduced percentage of fine material!
Many small balls increase the percentage of fine material during
extended running time.
6.3.4 Weight of the balls (type of material)
A higher mass (specific weight) of the grinding balls accelerates grinding.
(see table in Ä Chapter 6.1 ‘Choice of grinding bowls and grinding balls’
6.4 Dry grinding
During dry grinding a bed of material with a fineness of approx. 20 µm
forms on the balls and the walls of the grinding bowl after approx. 5-10
minutes, which prevents further comminution. The grinding stock begins
to stick because the surface forces become too big.
If surface-active substances are added to the grinding stock, comminu-
tion can be carried out for longer and it is possible to achieve a higher
share of fine material.
Examples (maximum amount to be added in mass%):
n
Stearic acid 2-3%
n
Aerosil (fine-particle silicic acid) 0.5-2%;
n
Quartz sand 2%
n
Glass powder 2%
Highly flammable and flammable liquids such as ketone and benzine
with boiling points <80°C must not be used.
Using the planetary mill
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