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PULVERISETTE 7
4.1 Choice of Grinding Bowls and Grinding Balls
Caution!!!
No warranty or claims shall be accepted in case of damages caused on ac-
count of using grinding bowls and grinding balls that are not original accesso-
ries of the appliance.
In order to prevent excessive abrasion, the hardness of the grinding bowl used
and of the grinding balls must be higher than that of the material used.
Material
(bowl and balls)
density
*
in g/cm
3
restistance to
abrasion
Agate
(99.9% SiO
2
)
2.65
Good
Sintered corundum 1
(99.7% Al
2
O
3
)
3.8
Fairly good
Zirconium dioxide
(95% ZrO
2
)
5.7
Very good
Stainless steel
bowl:
(17-19% Cr + 8-10% Ni)
ball:
(12,5-14,5% Cr + 1% Ni)
7.8
Fairly good
Tempered steel
bowl: (11-12% Cr)
ball: (1,0-1,65% Cr)
7.9
Good
Tungsten carbide
(93%WC+6% Co)
14.7
Very good
Silicon nitride (Syalon)
(90% Si
3
N
4
)
3.1
Extremely good
The grinding bowls and grinding balls of zirconium dioxide are resistant to acids
with the exception of hydrofluoric acid.
Normally, grinding bowls and grinding balls of the same material should be
chosen.
Exeption:
Tungsten carbide balls may be combined with steel bowls.
The size of the grinding bowls and grinding balls should be determined experi-
mentally.
4.1.1
Size of the Grinding Balls
Type of feed material
Ball diameter
Hard samples feed with a piece size be-
tween 2mm and 5mm
15 mm
Fine material (0.5 mm)
10 mm / 5 mm
Homogenisation of dry or liquid samples
10 mm /
These are just clues: the size of the grinding bowls and grinding balls
should be determined experimentally if necessary.
Attentione:
Mixing
balls
with
different
diameters
is
not
recommended.
(If different ball diameters are used there is the danger of higher abrasion
of the balls!)
*
High density means high impact energy