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PULVERISETTE 7
4.2 Filling the Grinding Bowl
Grinding bowl
Min. filling
max. filling
45ml
3ml
20ml
12ml
0,5ml
5ml
Using less sample material than recommended will cause
higher abrasion!
It is imperative that the following sequence be observed:
1. Place the grinding balls in the empty bowl.
2. Fill the material to be ground on the balls.
Never use the mill without sample material!
Danger of badly damage of the grinding balls and bowl!
4.3 Influencing Quantities During Grinding
Running time (grinding time)
A longer grinding time will increase the fine fraction.
Speed
A higher speed will reduce the grinding time and increase the fine fraction.
Reversing operation (regular reversal of the direction of rotation)
May improve the grinding; useful for mechanical alloying.
Number and size of the balls
Pregrinding coarse, hard material with large balls:
small fine fraction.
Use of many small balls will increase the fine fraction if the running time is in-
creased.
Mass of the balls (type of material)
A higher mass (density) of the grinding balls will accelerate the grinding.
(See the table in section 4.1.)
4.3.1
Dry Grinding
Below a particle size of approx. 20 µm, surface forces predominate and the
material will start to "stick".
Further dry grinding can be achieved if surface-active substances are added to
the material.
Examples (maximum quantity to be added in % by mass)
Stearic acid 2-3%
Aerosil (microdispersed silicic acid) 0.5-2%
Silica sand ~ 2%
Glass powder ~ 2%
filling = sample material