DEF PROSPETTO spazzole - Timcal Graphite

Powder
Properties:
Electrical resistivity
Measuring method
The electrical resistivity is measured on defined
compacted test bars (50x12x6 mm, compacting pressure:
2.5 t/cm 2).
In order to be able to distinguish between the various
graphites a very accurate and reliable method has
to be used. The four-point method applied for these
measurements greatly reduces the possibility of errors
due to poor contacts.
Conclusion
Information about the electrical resistance of compacted
graphite powders is helpful for raw material
selection from different graphite types. The T and KS
types and mixtures of T and KS are mostly used for
medium and highly ohmic brushes.
SFG and GB types provide best performance in
semi-metallic and sintermetallic brushes, where a high
electrical conductivity is required.
B
A
D
A = Measuring electrodes
B = Current carrying electrodes
C = Silver contact adhesives
D = Ohmmeter
C
www.timcal.com
3
2.5
2
1.5
1
0.5
Electrical resistivity of graphite compacts
Bar: 50 x 12 x 6 mm
GB
SFG
0
0 20 40 60 80
Particle size d90 (µm)
T
KS
The results of resistivity measurement of KS 75 and
T 75 are somewhat misleading. It has to be taken into
consideration that the compactability of the graphite
affects the electrical resistivity because of microcracks
and porosity. As already shown, these two graphites are
relatively difficult to compact due to the coarse particle
size.
Other investigations have shown that in compounds
containing a high amount of graphite the resistivity
decreases with increasing particle size.
Pressure: 2.5 t/cm 2
100 120 140 160