DEF PROSPETTO spazzole - Timcal Graphite

Graphites for
Carbon Brushes and
Carbon Parts

Who are we?
TIMCAL Group has a strong tradition
and history in graphite manufacturing. Its
first manufacturing operation was founded
in 1908. Today, TIMCAL Group facilities
produce and market a large variety of synthetic
and natural graphite powders and
dispersions of consistent high quality.
Adhering to a philosophy of Total Quality
Management and continuous process
improvement, all TIMCAL manufacturing
plants comply with ISO 9001-2000.
TIMCAL is committed to produce highly
specialized graphite materials for today’s
and tomorrow’s carbon brush and carbon
parts industries.
TIMCAL has an international presence
with facilities and commercial offices
located in the key markets around the
Globe. The Group’s industrial and commercial
activities are implemented by an experienced
multi-national team of nearly 300
employees from seven countries on three
continents.
TIMCAL Group is a member of
IMERYS, a world leader in adding value to
minerals.
www.timcal.com
TIMREX ® Graphites combine technical
and economic advantages: their optimal
price/performance ratio helps maintain a
high quality level in the finished carbon
part while, at the same time, reducing
manufacturing costs.
Bodio, Switzerland
Lac des Îles, Canada
Changzhou, China
Fuji, Japan
About carbon
brushes
This document is devoted to the complex
field of manufacturing carbon shapes such
as brushes, seals and engineering components.
The variety of products are as different
as the many procedures involved in their
production.
The “carbon parts world” is a unique
industry having to comply with many and
sometimes contradictory requirements such as:
• Electrical and thermal conductivity.
• Lubricity and hardness.
• Mechanical strength and wear protection.
• Corrosion resistance in - very often-
aggressive environments.
These circumstances and the exacting
technical demands of this industry call for
very well defined high performance raw
materials of outstanding consistency.
To help our customers make the best
selection of raw materials for their needs,
TIMCAL Group has produced this document
to describe the full range of TIMREX ®
Graphite grades available for this application

Graphite in
carbon brushes
and carbon parts
Powders for carbon brushes
and carbon parts
Carbon brushes
Sliding contacts
Current collectors
Resin-bonded
Pitch-bonded
Semi-metallic
Sinter-metallic
Carbon parts
Mechanical seals
Bearings
Erosion electrodes
Electrical resistors
TIMREX ® Graphites offer
many advantages
Predictable synthetic and natural
graphites with narrow specifications and
unequalled consistent quality due to:
monitoring of all production and processing
stages, strict final inspection, and
clearly defined development processes.
Unique properties thanks to the combination
of a consistent purity, perfect crystalline
structure and well defined texture.
Market oriented product development.
Application support by TIMCAL engineers.
BASIC CHEMICAL, PHYSICAL AND APPLICATION-
RELATED PROPERTIES
The carbon brushes manufacturers require a carbon with consistent electrical
resistance (for high as well as low conductivity purposes), high lubricity, consistent
compressibility and predictable absorption level of binder.
Electrical conductivity
The electrical conductivity is strongly
influenced by the crystallinity and particle
size. A high anisometry of the particle shape
leads to an anisotropic behaviour of the
electrical conductivity.
Absorption behaviour
of binder
The absorption behaviour is determined by
particle size distribution, surface porosity,
particle shape and surface tension between
graphite and binder. The knowledge of these
properties helps to make the correct selection
of graphite and therefore reduces development
time. Good processability and constant
quality of the final product presuppose
a high consistency of the absorption properties
of the powders used.
Compressibility
Compressibility is dependent on particle
size as well as on crystallinity. Other parameters,
however, which are related to the texture
of the particle also influence compressibility
and can be correlated with mechanical
properties.
Lubricity
Coefficient of friction
Wear reduction
High crystallinity and high chemical purity
of the graphite powder lead to good lubrication
properties. Low friction coefficient
and low wear of the commutator are the
consequence of these powder characteristics.
The hardness of the graphite influences
the wear of the carbon brushes. Lifetime of
the brushes and the commutator is very
often extended by mixing the high purity
TIMREX ® Graphite with small quantities
of well-defined polishing additives.

TIMREX ®
Graphites for
carbon parts
T Graphite T 44
T 75
T 15-75
T 150
KS Graphite
SFG Graphite
GB Natural
Graphite
0 50 100 150
Particle size range d (µm)
0 50 100 150
Particle size range d (µm)
0 50 100 150
Particle size range d (µm)
0 50 100 150
Particle size range d (µm)
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Typical values
SFG 6
SFG 15
SFG 44
SFG 75
SFG 150
GB 99/6
GB 98/75
New
KS 15
KS 5-25
KS 44
KS 5-44 New
KS 75
KS 5-75 TT
KS 150
New
Ash
(%)
0.07
0.07
0.03
0.09
0.05
0.03
0.06
0.02
0.07
0.09
0.06
0.07
0.07
0.07
0.07
0.03
0.6
1.3
Moisture
(%)
0.1
0.1
0.02
0.05
0.1
0.1
0.1
0.03
0.1
0.02
0.05
0.1
0.1
0.1
0.1
0.01
0.1
0.1
Crystallite height
Lc (nm)
> 100
> 100
> 100
> 100
> 80
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 150
> 200
> 200
> 200
> 400
> 400

Particle shape
angular flakes, microporous
irregular spheroids
strong anisometric flakes,
needles
flakes
Tribological
and mechanical properties
- high toughness
- good lubrication properties
- medium toughness
- good lubrication properties
- low toughness
- very good lubrication
properties
- very good lubrication
properties
Advantages and applications
- low friction coefficient
- low wear of the counterpart and low self-wear
- good transfer-film formation
- medium electrical conductivity
- medium density of brushes and parts
- suitable for pitch-bonded and resin-bonded brushes
- low friction coefficient
- low wear of the counterpart
- good transfer-film formation
- high electrical conductivity
- suitable for pitch-bonded and resin-bonded brushes
- very low friction coefficient
- low wear of the counterpart
- extreme good formation of transfer-film
- very high electrical conductivity
- excellent wettability with organic binders
- excellent compressibility
- high transverse rupture strength
- suitable for pitch-bonded, resin-bonded and metallic brushes
- very low friction coefficient
- low wear of the counterpart
- very high electrical conductivity
- suitable for semimetallic and metallic brushes

Powder
Properties
Graphite powders and their
influence on carbon parts
TIMCAL Group is in the position to provide
analytical and test results for graphite
powders and the corresponding graphite
compacts. Based on this information, conclusions
can be drawn from the properties of
the final products and vice versa.
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Powder properties
Purity
Ash content
Moisture
Trace elements
Crystalline structure
Crystallinity
Texture
BET surface area
Xylene density
Scott density
Oil absorption
Particle size
Particle size distribution
Laser diffraction, sieving methods
Thermal stability
Properties of final products
Wear
Compact/brush
Commutator/counterpart
Friction coefficient
Transfer film
Brush temperature
Density
Commutation
Electrical properties
Properties of binder-free
graphite compacts
Compact density
Springback
Mechanical strength
Electrical resistivity
Oil absorption
In the following pages there are some of
the results of experimental work carried out on
TIMREX ® Graphite at our Technical Centre.

Powder
Properties:
Compact density
Compact density is a parameter describing the
structure density available at given pressing conditions.
The density of compact obtained is influenced by
spring back and expansion of the compact after shaping
and demoulding from the press.
The difference between xylene density and compact
density indicates the degree of interparticular porosity
in the compact and compressibility of the powder. The
minimum binder quantity required to achieve porefree
dense composite materials can be calculated.
As the figures show, compact density is influenced
by pressure, particle size, crystallinity and other physical
properties of the graphite particles. At high pressure
values (p>5t/cm 2) the compact density becomes nearly
pressure independent.
For a small particle size, the compact density is
hardly influenced by the particle structure. A high
crystallinity results in a high compact density.
W
Pressure
Die: L = 30 mm W = 20 mm
Mass = constant
L
Density of compacts
Density (g / cm 3 ) Density (g / cm 3 )
2.2
2.0
1.8
1.6
1.4
1.2
GB
SFG
KS
1.0
0 20 40 60 80
Particle size d90 (µm)
2.2
2.0
1.8
1.6
1.4
1.2
Density of graphite compacts
Die: 30 x 20 mm
Pressure: 2.5 t/cm 2
100 120 140 160
1.0
0
Pressure (t / cm
2 4 6 8
2 )
SFG 44
KS 44
T 44
T
10

Powder
Properties:
Springback
Measuring method
The springback is a reading giving the resilience of
compacted graphite powder. A defined amount of dry
powder is poured into a die. After inserting the punch
and sealing the die, air is evacuated from the powder.
Pressure is applied (p=0.477 t/cm 2 ) and the powder sample
thickness is measured. Thickness is measured again
after pressure has been released.
Conclusion
Springback and compact density of graphite powders
are physically connected parameters, which give
information about the compactibility of powders and
dimensional stability of compacts in any pressing
direction. Springback is influenced by pressure, particle
size, crystalline structure ad other properties.
Crystalline structure is the main parameter.
A high crystalline structure results in low springback.
Compacts produced from powders having a low
springback can be easily formed and pressed with
greater accuracy.
Punch
Seal
Die
Compact
Vacuum line
Pressure
Pressure meter
H(p)
H(0)
Spring back
Metering
element
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Springback (%) Springback (%)
25
20
15
10
5
GB
KS
0
0 20 40 60 80
Particle size d90 (µm)
25
20
15
10
5
Springback of graphite compacts
Die diameter: 20 mm
Pressure: 0.477 t/cm 2
100 120 140 160
0
0
Pressure (t/cm
0.2 0.4 0.6 0.8
2 )
H (0) - H (p)
SB = x 100 %
H (0)
SFG
T
T 44
KS 44
SFG 44
1

Powder
Properties:
Transverse rupture strength
Measuring method
The transverse rupture strength is measured on
graphite compacts pressed to bars with size of 50x12x6
mm and 30x20x10 mm without binder. Other measurements
carried out on test pieces with dimensions of
50x12x8 mm show comparable results.
Conclusion
The transverse rupture strength corresponds to the
compressibility of powders, characterised by compact
density, springback and expansion. Compact density
and internal cracks influence the measured mechanical
strength.
The mechanical strength can be enhanced by
increasing the compaction pressure and by using
graphites of smaller particle size.
With the increase of the degree of crystallinity the
mechanical strength also increases.
Compact
Load
L
L = Distance between the supporting rods (20 mm)
Transverse rupture strength (Arbitrary units) Transverse rupture strength (Arbitrary units)
10
8
6
4
2
GB
SFG
KS
0
0 20 40 60 80
Particle size d90 (µm)
7
6
5
4
3
2
1
Transverse rupture strength of compacts
Bar: 30 x 20 x 10 mm
Pressure: 2.5 t/cm 2
100 120 140 160
0
0
Pressure (t / cm
2 4 6 8
2 )
SFG 44
KS 44
T 44
T
10

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
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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

Powder
Properties:
Oil absorption (DBP)
Measuring method
The oil absorption test is a special centrifugation
method showing high reproducibility, developed by
TIMCAL.
A special centrifuge tube is filled with 0.5g of
TIMREX ® graphite powder and then covered with
dibuthylphthalate (DBP). After centrifuging for 90
minutes at a relative acceleration of 453g, the tube is
weighed and the oil absorption of 100g of powder is
calculated (based upon the weight increase of the 0.5 g
sample).
Conclusion
The oil absorption is a very useful tool to estimate
the binder requirement. Various fundamental properties
such as:
• Particle size
• Bulk density
• BET
• Crystalline structure
as well as the wetting angle affect the absorption properties.
Tube
DBP
Sample
Filter
Sieve
Centrifugation
Acceleration
Oil absorption (g DBP / 100 g graphite)
200
150
100
50
Oil absorption of graphite powders
Oil: dibuthylphthalate DBP
KS 5-44
T 15-75
KS
SFG
0
0 20 40 60 80
Particle size d90 (µm)
KS 5-75 TT SFG 150
100 120 140 160
TIMREX ® Graphite has found its place in the field of carbon parts
as a reliable, high quality product. Many problems can be solved
thanks to the broad range of TIMREX ® Graphites.
Our specialists will be glad to help you in the selection of the
most suitable product for your application.
T

Commercial Offices
Manufacturing Plants
Distributors / Agents
(full list available on request)
Offered by your local Distributor/Agent:
© 2001 TIMCAL Ltd., CH-Bodio
No part of this publication may be reproduced in
any form without the prior written authorisation
of TIMCAL Ltd.
Printed in Switzerland.
Leading the way.
TIMCAL Ltd.
Head Office of the Group
CH-6743 Bodio, Switzerland
Phone: +41 91 873 20 10
Fax: +41 91 873 20 19
info@ch.timcal.com
TIMCAL America Ltd.
Representative Office
29299 Clemens Road 1-L
Westlake, Ohio 44145, USA
Phone: +1 440 871 7504
Fax: +1 440 871 6026
info@us.timcal.com
TIMCAL Japan K.K.
Representative Office
7F Sagamiya Bldg.
6 Ichibancho Chiyoda-ku
Tokyo 102-0082 Japan
Phone: +81 3 3511 2078
Fax: +81 3 3511 2077
info@jp.timcal.com
TIMCAL in France
Representative Office
Tour Maine Montparnasse
33, avenue du Maine
FR-75755 Paris Cedex 15, France
Phone: +33 1 4538 3850
Fax: +33 1 4538 3851
info@fr.timcal.com
TIMCAL Deutschland GmbH
Representative Office
D-56564 Neuwied, Germany
Phone: +49 2631 890 737
Fax: +49 2631 890 752
info@de.timcal.com
Changzhou TIMCAL Graphite Corp. Ltd.
188# Taishan Road,
Hi-Tech Zone, Changzhou
213022 P.R. China
Phone: +86 519 5100801
Fax: +86 519 5101322
info@cn.timcal.com
STRATMIN Graphite Inc.
2500 Boul. Daniel-Johnson
Suite 906
Laval, Quebec
Canada H7T 2P6
Phone: +1 450 686 8630
Fax: +1 450 686 8725
info@stratmin.com
CB-01 10.2001