Retsch DM 400 - Manual (Page 36)

Working with the disc mill
36
3. The hardness of the zirconium oxide grinding disc is MOHS 8.5
(HV1350). No sample material that is harder may be ground
because this causes the outer edges of the grinding disc to chip.
Chipping of the edges can also occur with a sample material with
MOHS hardness of 6 or 7.
4. Proceed very carefully when grinding using zirconium oxide
grinding discs. You should pre-grind your sample material with a
large gap width in the first run before achieving the desired fine-
ness with the smallest gap in a second run. You should proceed
in a similar way if you have no information about the grindability
of your material. The grinding discs have a progressive chipping
geometry. Coarse grinding takes place in the inner area, and fine
grinding in the outer area of the grinding disc. The strain is
greatest in the fine grinding area. The chipping described may
occur here with very hard sample material.
5. The adhesive used to adhere the securing bolts in the grinding
disc has a temperature resistance up to 80°C. The grinding discs
should therefore not be heated above 80°C in order to guarantee
the secure fit in the support.
6. Please observe the chapter “Replacing the grinding discs (5 + 6)”
in the Operating Manual when assembling and removing the
grinding discs!
NOTICE!
Retsch GmbH guarantees that only zirconium oxide
grinding discs of the highest quality leave our company.
Used grinding discs which are cracked, chipped or
completely broken on the perimeter, cannot be accepted
as complaint.
5.9 Material feed
DANGER
Risk of explosion
There is a risk of spontaneous ignition (dust
explosion) when grinding substances which oxidise
(e.g. metals or coal) if the fine fraction exceeds a set
percentage. Special safety precautions must
therefore be taken when grinding such materials and
the work must be supervised by a specialist.
The device does not have an ex-protected design
and is not suitable for grinding explosive materials.