FRITSCH PULVERISETTE 23 - Manual (Page 23)

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’
on page 19).
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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