KET050 Carbon Strip Challenge
Department of Chemical Engineering, Faculty of Engineering, Lund University
Final Report
on
Carbon Strip Challenge
Designing new carbon strips for better railing
Presented to Bombardier
Brussels, Belgium
6/17/2010
Investigators:
Supervisors:
Viktor Björk
Johan Edfeldt
Mikael Edmundson
Nina Håkanson
Tomas Nelander
Dipti Shinde
Prof. Hans T Karlsson
Prof. Reine Wallenberg
PhD Christian Hulteberg
MSE Filip Nilsson
i
Summary
The objective of this project is to increase the durability and lifetime of the carbon strip while
maintaining, or lowering, the price. Two important aspects of increasing the lifetime would be to
increase resistance to flash-overs and decreasing the friction between the strip and the catenary.
At the same time the conductivity should be maintained at a reasonable level and ideally the solution should be patentable.
The main focus for this project has been on keeping the existing structure of the pantograph and
instead to study the material of the carbon strip, the carbon fragment, and its disposition. To fulfill the project objectives several different solutions have been approached.
The project has two different goals with possible synergy effects and the first aims to find an
existing low friction material to use in a new application as a replacement of the carbon fragment
to make the fragments more durable and flash over resistant with lowered or maintained conductivity and cost. The second goal was to find a straightforward coating solution to decrease the
arcing damage on the current carbon strips in order to extend their service life.
Three different solutions have been considered. The first solution, which is preferred, is to coat
parts of the carbon strip with silicone to increase its resistance to damages caused by electric
discharges. This solution is easy and cheap to implement since the existing carbon strips can be
used. If the silicone is placed mainly upon the aluminum carrier it could be possible to reuse the
carrier and only change the carbon fragment in order to reduce costs. Another solution would be
to replace the carbon fragment with a MAX phase material which is very hard, has high electrical conductivity and low frictional coefficients. Since the material is so much harder it would
however risk increasing the wear of the catenary. The third solution considered is to replace the
carbon fragment with a composite material consisting of the advanced binder Thermic 1100
mixed with silver flakes. The Thermic 1100 is a cheap inorganic binder based on silicates. The
silver flakes are to increase the conductivity; however more testing is required to optimize the
mixing ratios.
i
Table of Contents
1
2
3
4
5
Problem definition ................................................................................................................................ 1
1.1
Project focus ................................................................................................................................. 1
1.2
Project goals .................................................................................................................................. 1
1.3
Disposition .................................................................................................................................... 1
Background ........................................................................................................................................... 3
2.1
Catenary (Overhead wires) ........................................................................................................... 3
2.2
The pantograph ............................................................................................................................. 5
2.3
The aluminum carrier.................................................................................................................... 6
2.4
The carbon fragment .................................................................................................................... 6
2.5
Microscopy .................................................................................................................................... 8
2.6
Wear of the carbon strip ............................................................................................................. 11
2.7
Technical workshop visit ............................................................................................................. 16
2.8
Ice creation on the catenary ....................................................................................................... 17
Existing solutions................................................................................................................................. 18
3.1
Auto-drop detection system (A.D.D.) ......................................................................................... 18
3.2
Glycerol solution ......................................................................................................................... 21
3.3
Brass on carbon strip .................................................................................................................. 23
New solutions ..................................................................................................................................... 24
4.1
LEGO ............................................................................................................................................ 24
4.2
Silicone ........................................................................................................................................ 27
4.3
MAX Phase .................................................................................................................................. 28
4.4
Advanced binder ......................................................................................................................... 33
Laboratory tests .................................................................................................................................. 36
5.1
Silicone application ..................................................................................................................... 36
5.2
Micro hardness ........................................................................................................................... 38
5.3
Advanced binder ......................................................................................................................... 40
6
Conclusions ......................................................................................................................................... 41
7
Referenser ........................................................................................................................................... 42
7.1
WebPages: .................................................................................................................................. 42
7.2
Litterature ................................................................................................................................... 42
7.3
Personal contact ......................................................................................................................... 43
ii
Appendix A .................................................................................................................................................. A1
iii
Word-list
ADD
DC
HV
MHV
RC-locomotive
RMS current
SEM
TEM
WLD
Aluminum carrier
Auto-drop detection system/
Automatic Dropping Device
Carbon fragment
Carbon strip
Catenary
Flash-over/Arcing
Fog frost
Hoar frost
Ice bark
Pantograph
Pylons
Automatic Dropping Device
Direct Current
Vickers hardness
Micro Vickers hardness
Most commonly used electric
train in Sweden
Root Mean Square current
Scanning Electron Microscope
Transmission Electron Microscope
Wear Limit Detection
The aluminum supporting the carbon fragment
A safety system that automatically lowers the pantograph should it be damaged
The material that has contact with the catenary
The sum of the carbon fragment and the aluminum carrier
The copper wire carrying the current
An ongoing electrical discharge
Supercooled water droplets from the fog deposits on an
object
Ice crystals trough precipitate of steam on an object that
is cooled below the freezing point
When rain hits an object, with a temperature below the
freezing point, it instantly causes the water to freeze to
ice
The device on top of the trains that collect the electrical
current from the catenary
Poles carrying the catenaries
iv
1 Problem definition
The objective of the project is to increase the durability and the lifetime of the carbon strip in
order to lower the maintenance costs of running the trains. An important part of achieving this,
and another objective of the project, is to improve the resistance to flash-overs, thereby reducing
the risk of damaging both the carbon strip and the catenary. The price of the carbon strip should
be maintained or preferably lowered. The current price of a carbon strip ranges from € 189 to €
275. The friction between the carbon strip and the catenary should not increase. Also the conductivity of the suggested solution cannot be less than 15 % lower than in the currently used carbon
strips, i.e. the resistivity the material used may not exceed 1000 μΩcm. Finally it would be preferable if the new solutions suggested can be protected through patents.
1.1 Project focus
The main focus for this project has been on keeping the existing structure of the pantograph and
instead to study the material of the carbon strip, the carbon fragment, and its disposition. To fulfill the project objectives several different solutions have been approached. The expenses can be
kept at a low level if as little changes as possible are made to the commonly used system. The
project has targeted existing materials with multiple high-quality properties and has not been
searching for new ones. This ensures the possibility of a full follow through in the production
phase and previously made errors with the materials need not to be repeated. (Harryson Consulting 2009)


Changing the material and keeping the existing pantograph and carbon strip structure to
minimize modification costs.
Using an existing material in a new way, not “inventing” an entirely new material.
1.2 Project goals
The project has two different goals with possible synergies and the first aims at finding an
existing low friction material to use in a new application, as a replacement of the carbon
fragment to make the fragments more durable and flash-over resistant, with lowered or
maintained conductivity and cost.
The second goal was to find a straightforward coating solution to decrease the arcing damage
on the current carbon strips in order to extend their service life.
1.3 Disposition
The report is disposed by first formulating the problem and reviewing all constraints and demands that has to be fulfilled. The layout of the existing current transmission of the train including the pantograph, the carbon strip and the catenary was studied and is described in the background. In chapter 3, Existing solutions, different techniques currently being used in order to
decrease the wear of both the carbon strip and the catenary is presented. The new solutions sug1
gested are described in chapter 4, these solutions include the LEGO-solution, coating with silicone and exchanging of carbon fragment with either a MAX phase material or the advanced
binder Thermic 1100. A few laboratory tests have been performed and in chapter 5 the reports
from these tests can be found. Finally, different aspects of the solutions are discussed in the conclusion.
2
2 Background
As a background to project the existing solutions were investigated. This investigation included a
literature review in order to attain a basic understanding of the problems surrounding the electrical supply system. Also pieces from different carbon strips were investigated with microscopy
to investigate the structure and composition of carbon strips currently in use. Furthermore a
technical workshop visit was undertaken to attain a sense of the everyday practical work being
performed to keep the trains in operation.
2.1 Catenary (Overhead wires)
The catenaries are the overhead wires used to transmit electrical energy to trains, trams and trolleybuses at a distance from the energy supply point. A self bearing wire (direct suspended system) is used for tramways and industrial railway track while normal railway tracks require an
indirect suspended system where the catenary is suspended with a second wire with vertical
wires between the two known as droppers. (Nationalencyklopedin 2010)
The contact wire is made of copper or (for high speed routs) copper alloyed with silver and has
an area of 100 mm2, 109 mm2 or 120 mm2 (high speed). The second wire is a multiple threaded
round copper or bronze wire (50-70 mm2). The contact wire standardized height above the track
is 5.5 m or 5.3 m depending on if the route has level crossings or not. The contact wire can be
allowed to go up to 5.9 m or down to 4.8 m in tunnels and bridges. (Nationalencyklopedin 2010)
The pylons carrying the wires are often made from steel coated with zinc through galvanization
with a lifetime expectancy of about 40 years. In general, they are placed with a distance of 60
meters from each other but in narrow curves and particularly vulnerable locations the distances
are reduced. The largest allowed distance is 75 m and the contact wire is installed in a zigzag
formation with a deviation of ±400 mm from the center of the track. The reason behind the zigzag formation is to allow for an even wear on the carbon strips and pantographs of the trains.
The contact wire must have a regulated and evenly distributed tension because the pantograph
causes oscillations in the wire. In general, a higher tension means a higher allowed speed. The
tension varies between 4.9 kN and 15 kN. To manage an even tension the contact wire system is
split into 1.2-1.5 km sections which are anchored in the middle and tensioned in both ends. The
wires are tensioned with weights independent of the temperature (Nationalencyklopedin 2010).
A section of 1200 meters has a thermal expansion of 2 meters in the temperature interval -40 oC
to +50oC. (Gudojc 2004)
The track is also a part of the electrical system because one of the two (catenary and track) works
as a neutral wire and a reconnector. When using altering current, the asymmetry between the
system and the ground can lead to interfering induction with telephone wires. This problem can
partly be solved by the use of isolating reconnector, often double aluminum wires.
3
In Sweden as well as in Norway, Germany, Switzerland and Austria 15 kV 1-phase altering currant with the frequency 16 2/3 Hz is used. The electricity is taken from the common grid and
must not just transform to the correct voltage but also reform because of the difference in frequency. The reform stations, with either a rotating reformer or static inverter, are placed about
100 km from each other. They are connected electrically via section stations, or coupling station
at hubs between the reform stations. Because of this the traction on the catenary is often done
both ways along the route.
The Swedish electrified railroad has a total installed effect of 1200 MW and the energy usage for
the train management is about 1.550 TWh/year. (Nationalencyklopedin 2010) The entire Swedish electricity consumption amounts to 138.3 TWh/year, which means that the electrified railroads constitute 1.12 % of the total Swedish electricity consumption. (Energimyndigheten 2009)
2.1.1
Oxidation of the catenary
The used catenary, received by Bombardier, is covered with a black surface layer supposedly in
the form of copper(II)oxide. The oxidation from copper to copper(II)oxides occur when copper is
heated in air:
Copper oxide is a semiconductor which has lower conductivity than a metallic conductor. (Barrans, 2001)
A semiconductor is an electronic conductor with a resistance that decreases as the temperature is
increased, whereas a metallic conductor is an electronic conductor with a resistance that increases as the temperature is increased. (Jones & Atkins 2003)
The two images below show the oxidized and the non-oxidized catenaries.
Figure 1a & b. Oxidized and non-oxidized catenaries
4
2.2 The pantograph
The pantograph is the device on top of trains and trams that collects electric current from the
overhead wires. It pushes a contact shoe up against the overhead wire to draw electricity. The
lifetime of a pantograph is limited to 1.5·1030 km or 30 years (Bombardier 2010). The image
below shows a real life pantograph with two carbon strips from a train. The pantographs and the
carbon strips may be constructed slightly different depending on whether their to be used on a
train or a tram because of the difference in speed. A tram has an average speed of 30 km/h and a
max speed of 70 km/h while a train has an average speed of 100 km/h and a max speed of 160
km/h.
Carbon strips
Figure 2. The image shows a pantograph with carbons strip from the Locomotive garage in Malmö.
5
2.3 The aluminum carrier
The carbon fragment is supported on an aluminum carrier. The appearance of the carrier may
differ depending on the type of pantograph and how it is suspended. The image below shows five
different carbon strip designs and the one to the left has the horns attached to the ends.
Figure 3. Different types of aluminum carriers with carbon strips (Schunk 2004)
2.4 The carbon fragment
Between the pantograph and the contact wire above is the carbon fragment (sometimes called the
carbon strip; however “carbon strip” is also used for the sum of the carbon fragment, copperlayer, adhesive layer and aluminum carrier). The carbon fragment is made out of approximately
85% carbon and 15 % copper attached to the pantograph and slides along the wire. (Harryson
Consulting 2009)
The minimum thickness allowed for the carbon fragment on trams and trains depends on type of
train and varies between 3 mm and 12 mm in summer and 11 mm and 18 mm in winter. (Bombardier 2010)
The images below show two different structures of the carbon strip. In Figure 4 there is the carbon fragment followed by a solid copper layer attached to the aluminum carrier with an electrically conductive adhesive layer. In the bottom image the carbon strip is followed by a thinner
copper layer with the non-conductive adhesive layer on the sides. Because of the thin copper
layer there is a need for an electrically conductive strip between the aluminum carrier and the
copper. The carbon strip supplied by Bombardier has the structure of Figure 4 while the carbon
6
strips retrieved from “Lokverkstaden” (a locomotive garage in Malmö where maintenance and
repairs are carried out upon Swedish trains) has the structure as in Figure 5. (Schunk 2004)
Figure 4. Structure on a carbon strip (Schunk 2004)
Figure 5. Structure on a carbon strip (Schunk 2004)
7
2.5 Microscopy
With the help from Professor Reine Wallenberg, at the Division of Polymer & Materials Chemistry at Lund University, Faculty of Engineering, several images were taken with an electron microscope in order to study the composition of the presently used carbon strips. Two pantographs
received from the train maintenance workshop called “Lokverkstaden” in Malmö were also investigated with the same microscope. All pantographs were made by Schunk and had an alumina
carrier with a carbon fragment containing copper.
2.5.1
Train, carbon strip without A.D.D.
Figure 6 shows the carbon fragment of a carbon strip without the A.D.D. (a system which automatically lowers the pantograph should the carbon strip be damaged) received from Lokverkstaden. An analysis of the elements in the material made by SEM was also carried out on the studied piece. As expected the analysis revealed that the piece consisted mostly of carbon with
small amount of copper. It also showed other elements, such as calcium, chlorine, phosphor and
aluminum. The distribution of these elements can be seen in Figure 7. The copper appears to be
consisting of many very small well dispersed particles. The calcium, chlorine, phosphor and
aluminum are probably impurities.
Figure 6. SEM-image of the carbon fragment from a pantograph without ADD received from ”Lokverstaden”
8
Figure 7. Distribution of different elements in carbon strip without ADD from ”lokverkstaden”. Cu=copper, C=carbon,
Ca=calcium, Cl=chlorine, P=phosphor, Al=aluminum.
2.5.2
Train, carbon strip with A.D.D.
A piece from the carbon strip with automatic dropping device was also investigated. It was expected to have the same composition and structure as the strip without. The picture can be seen
in Figure 8. However, the elemental analysis showed that there barely were any copper present,
but the same impurities as in the strip without the ADD was present. Also, some iron could be
found, but it has possibly come from the saw during the preparation of the sample. The distribution of the elements can also be seen in Figure 8.
9
Figure 8. SEM image and elemental distribution of a carbon strip with ADD from “Lokverkstaden”. C=carbon, O=oxygen,
Al=aluminum, P=phosphor, Fe=iron, S=sulfur, Ca=calcium.
2.5.3
Tram, carbon strip sent from Bombardier
The SEM-spectrum shows that the carbon strip is made from carbon with 10wt% copper and
0.6wt% sulfur and oxygen. Underneath the carbon strip a layer of copper holds the carbon strip
in place and acts as a conductor for the electricity. This is followed by some sort of epoxy glue
composed of carbon and oxygen which is a poor conductor. The epoxy glue attaches the copper
layer to the aluminum carrier composed of pure aluminum.
Carbon current collector
Cu
Carbon based glue
Al
m
m
m
m
m
m
m
m
ou
nt
Figure 9. A SEM image of the provided carbon strip.
10
2.6 Wear of the carbon strip
The main degradation of the carbon fragment and contact wire is based on friction caused as the
train/tram operates along the line. The carbon strip may also be subjected to flash over damages
which can make dents in the carbon strip and the contact wire. If these damages are not repaired
immediately the wire or the strip can influence each other in a negative way which is both costly
and time consuming. (Harryson Consulting 2009)
Stefan Östlund from the Royal Institute of Technology in Stockholm has shown that the wear of
the carbon strip differs during the year. The figure below shows the number of change contact
strips on Green Cargo locomotives during the year of 2004.
Figure 10. Number of changed contact strips on Green Cargo locomotives Rc2, Rc3, Rc4 and Rm during 2004
The number of replaced contact strips varies heavily over the year and needs to be changed more
often during the winter part of the year. The problem is not only that the contact strips wears
more on the winter but that the wear varies over the year. The main difference between ”winter
operation” and ”summer operation” is that arcing is more common during the winter.
2.6.1
Monitoring and estimation of specific wear
The wear of the carbon strip can be estimated with the following equation:
W is the wear of the contact strip, s is the distance of the pantograph,
and
are the specific wear of the contact strip.
is the arcing time,
11
Figure 11. The specific wear in mm per kkm during the year
is the specific wear of the contact strip in [mm/km],
strips,
is the distance of a locomotive [km]
is number of changed contact
It is desirable to separate the mechanical- from the electromechanical wear, this is done by studying the difference in wear depending upon the season. The mechanical wear is based on an average wear (May-July) that has a value of 0.064 mm per km with the absence of electric arcs.
Figure 12. Wear mm carbon per kkm Rc/Rm locomotives based on data from 2004
12
Field tests have been conducted by Stefan Östlund to verify the relation between the discharges
(DC) and the arcs. The image below shows the distribution of DC versus arc light intensity.
Figure 13. Distribution of DC versus arc light intensity
Figure 14. Distribution of mean DC > 3.5 versus arc light intensity
Figure 15. Distribution of st. dev. DC > 3.5 versus arc light intensity
13
‘
Figure 16. Distribution of DC-level during test runs
Figure 17. Distribution of DC > 3.5. A versus RMS train current both mean and st. dev.
14
The following image shows how the discharges depend on the speed of the locomotive.
2.6.2
Conclusions of field tests
The normal DC level at non-icy overhead line is less than 2 A and when there is ”ice” on the
overhead line the lowest DC level increases to about 3.5-4 A. The DC levels between 3.5-4 A
and 7-8 A occurs when the locomotive is coasting and there is ice on the overhead line. DC levels above 7-8 A occurs at load and ice on the overhead line. On average there is proportionality
between the intensity of the arc and the DC level. The DC level increases with increasing RMS
current. There is no clear indication of the relation between DC level and train speed. The trigger
level does not have to be precisely selected. There are ”false indications”, that is DC current but
no arcing, and arcing but no DC. However their portion of the total is relatively small. There is a
dependency between the RMS value of the locomotive current and the DC component. The DC
component increases with increasing RMS current. The study shows that the main problem of
wear is arcing.
15
2.7 Technical workshop visit
To examine the structure of existing pantographs a visit to the locomotive garage in Malmö was
made. Several worn out carbon strips were shown where either entire parts were torn off or the
wear had created a carbon strip out of use. There were various profiles of used carbon strips; on
some the wear was located mainly in the middle of the strip whereas others were damaged by
indentations along the strip.
An employee working in the garage answered numerous questions that were prepared before the
visit. The price of a carbon strip was for instance estimated to €50-100 by the employee and had
to be changed approximately after 6000 km for a RC-locomotive (most commonly used electric
locomotive in Sweden). However, depending on the season, the wear of the carbon strips differ.
Hence, during the winter the carbon strips have to be changed more frequently. The time for
changing the carbon strip was approximated to 20 minutes since merely the screws beneath the
strip had to be removed. Once the carbon strips were removed they were discarded. The carbon
strips are considered to be out of use when they are worn down to 5 mm during the summer and
7 mm in the winter. The strips are especially damaged during the winter when the temperature
changes and causes melted snow on the catenary to freeze again, creating sharp needles of ice.
Furthermore, although the arcing primarily affects the aluminium carrier, the carbon strip is also
damaged to a certain extent. Also, frost that is created by fog wear the carbon strips which is why
the carbon strips are changed with shorter intervals during the winter. The catenary on the other
hand has a much longer lifespan and is changed after approximately 30 years.
Different types of train use different types of carbon strips which the employee believed could
depend on the supplier. The pantograph however differs between accommodation trains and cargo trains where the latter carries a “double axed” pantograph. Each train has two pantographs,
one in the front and one at the end. According to the employee both are never used at the same
time but one of them is used as a back-up, if the other one is worn out completely. However both
can be used at the same time in order to temporarily reduce frost problems where the first one
acts as an ice scraper. Questions regarding the orientation of the copper in the carbon strip and
the temperature the strips are exposed to, while the train is mobile and stationary, remained unanswered. (Påhlsson)
16
2.8 Ice creation on the catenary
There are mainly three different types of ice creation on the catenary during the winter.



Fog frost is created when supercooled water droplets in clouds and fog are deposit on an
object. The condition demands heavy mist or fog together with temperatures below freezing. The frost is created on the wind side of an object when either the fog droplets freeze
to ice or when steam sublime into ice crystals.
Hoar frost is deposits of ice crystals trough precipitate of steam on an object that is
cooled below the freezing point. Hoar frost is created out of fog free air, especially during clear nights, when the object is cooled.
Ice bark is the hardest type of ice creation. When rain hits an object, with a temperature
below the freezing point, it instantly causes the water to freeze to ice.
Figure 18. The catenary affected of ice creation, mostly ice bark. This is an extreme case where the ice layer is approximately
1-2 cm.
2.8.1
Consequences of ice creation
Poor contact between the catenary and the carbon strip due to ice creation generates arcs. The arc
heats up the aluminum carrier making the glue, which connects the carbon fragment with the
carrier, detach. When the glue joint starts to crack, a small mechanical stress can knock off large
carbon fragments of the strip. During the winter, an ice granulated catenary can result in a severe
lifetime reduction of the carbon strip.
The ice creation also affects the pantograph on the train. Ice storage on the pantograph increases
the weight on the construction, resulting in a reduced force upwards from the carbon strip towards the catenary. The reduced contact force deteriorates the entire dynamic of the pantograph
which induces more arcing. (Personal contact, Jan-Eric Gudojc, Swedish Transport Administration 2010-03-20)
17
3 Existing solutions
Several different solutions to minimize wear of the catenary and the carbon strip are currently
available on the market. A few of these solutions have been investigated further.
3.1 Auto-drop detection system (A.D.D.)
The carbon strip and pantograph can be damaged in several ways, sometimes so badly that the
catenary risks to be harmed. In order to prevent more extreme types of damage to the catenary a
form of impact detection system can be incorporated. A form of impact detection is the so called
auto-drop detection system whichs drops the panhead away from the wire, preventing further
damage. The pantograph head is kept in place against the overhead wire by pneumatic pressure
and when the slot in the carbon fragment wears down to a particular level or is broken by an
obstruction on overhead wire the air pressure is lost and the pantograph is lowered. The figures
below shows schematic images of the A.D.D. (Morgan Carbon 2010)
Figure 19. Schematic image of ADD (Morgan Carbon 2010)
18
Figure 20. A type of Automatic Dropping Device (Schunk 2004)
Figure 21. A type of Automatic Dropping Device (Schunk 2004)
Figure 22. A real life carbon strip with A.D.D. As seen in the picture some parts of the carbon
fragment have been removed in order to show the air duct.
19
Tube ADD
Tube WLD
Figure 23. Automatic dropping device (ADD)
and Wear Limit Detection (WLD). (PanTrac 2005)
20
3.2 Glycerol solution
Glycerol is an organic liquid with excellent anti-freeze properties. The minimum freezing point
is at approximately -40 °C corresponding to complacently 65 % glycerol in water (The Soap and
Detergent Association Glycerine & Oleochemical Devision 1990). Figure 24 shows the freezing
point of glycerol in water and depending on weather conditions a suitable glycerol concentration
can be chosen.
Figure 24.Freezing point of glycerol in water. Glycerol
solutions show a minimum in freezing point, corresponding to complacently 65 % glycerol in water.
21
Stockholm’s local traffic in Sweden has tested glycerol solutions in order to remove frost and ice
from catenaries. The tests have been made in Arvidsjaur in northern Sweden. The water melts
and it also makes it harder for water to freeze later. A type of working vehicle is used to apply
the solution on the catenaries. One treatment with this technique lasts for about three days before
it has to be revised (Ekström 2008). Other advantages are that it is inexpensive (0.14 EUR/kg, 80
% glycerol solution, ALIBABA 2010) and biodegradable.
Figure 25. Working vehicle applying the glycerol solution on the catenary
22
3.3 Brass on carbon strip
To overcome the difficulties with ice creation on the catenary, carbon strip manufacturers around
the world are investigating the beneficial properties of a carbon strip with an ice scrape. The construction of the strip is presented in Figure 26, with a plate made of brass additional to the regular
carbon fragment. Brass is a soft metal with relatively low friction. The carbon strip with brass
will be placed on a train in the front pantograph detached from current transmission, scraping the
iced catenary.
Figure 26. A carbon strip with a plate of brass
23
4 New solutions
4.1 LEGO
It was requested from Bombardier to investigate the possibility of using carbon strips built up
with “LEGO pieces”. To do this, three alternatives was considered. The first alternative is a carbon strip divided into several pieces where it is possible to change only worn-out parts. Another
solution could be that the carbon fraction could be removed from the aluminum carrier. The last
alternative is a carrier built up by several pieces.
Figure 27. Shows the three alternatives. Alternative one is most
likely a bad solution since there will be differences in height when
pieces are changed. If there was a way to protect the aluminum
carrier it would be possible to use alternative two or three.
The advantage of using this construction is that it would facilitate the maintenance since it would
then be possible to change only small pieces that are worn out. However, changing a carbon strip
only takes about 20 minutes. This means that the cost for stoppage is in that case larger than the
cost for changing the carbon strip. Therefore the only advantage is that the material costs would
be lowered since it is possible to reuse the aluminum carrier.
24
For alternative one we believe that it is hard to come up with a solution where you can easily
remove the pieces, but at the same time maintain the strength. Another disadvantage is the differences in height that will occur when changing only worn out pieces. Figure 28 and Figure 29
shows a picture of a worn out carbon strip and that the main wearing occurs in the middle of the
strip. The “lego pieces” method would then create a new profile with uneven parts at the ends of
the strip where the catenary may be trapped, Figure 30.
Figure 28. A worn out carbon strip, the main wearing has occurred in the middle of the strip.
Figure 29. A sketch over a worn out carbon strip.
Figure 30. Alternative one where some worn out pieces are changed.
25
Figure 31 - Pictures of carbon strips with torn off pieces.
The differences in height would contribute to new wears and it is then most likely that the new
piece would be torn off entirely as we have seen several times before. The difference in height
would probably also increase the amount of flash over since no contact between the catenary and
strip occur in the ends. If the pieces are changed frequently though it would not be a severe
problem but then the entire concept appears pointless.
The Lund team considers alternative two and three to be very useful provided that the
aluminum carrier can be protected in some way. A suggestion of protection is the use of
silicone as described later in chapter 4.2. Our recommendation though is to keep the current construction because the change will result in higher costs.
26
4.2 Silicone
A major contributor to the wear of a carbon strip is the arcs of electricity that forms between the
catenary and the carbon strip. This is especially the case during winter, when ice on the catenary
increases the occurrence of arcs substantially. The arcs damages the aluminum carriers more
severely than they do the carbon fragment and large holes can appear on the aluminium carrier as
a consequence of the arcs. In order to protect the aluminum carrier from arcs, a design were the
exposed parts of the carrier is covered by carbon has been developed and patented (Schunk Kohlenstofftechnik GmbH and Hoffman & Co., Elektrokohle AG 2004). The arc heats up the aluminum carrier making the glue (which connects the carbon fragment with the carrier) detach.
Another way to protect the carrier could be to cover it with an electrically insulating material.
Silicone is a material that is both cheap and can be electrically insulating. It is also resilient, remains unaffected at temperatures ranging from approximately -40 to 260 °C and resistant to aging and degradation from sunlight and ozone. (Stockwell Elastomerics 2009) By coating with
silicone the carrier is also protected against moisture, corrosion and thermal shock. The dielectric
strength is 80 kV/mm and the volume resistivity 1·1020 µΩcm, which indicates that it is a very
good electrical insulator. (MG Chemicals 2010)
The silicone can protect the aluminum carrier and glue against arc effects, by reducing the
possibilities for torn off pieces prolonging the carbon strips life span. According to Östlund
(2004) the main problem of wear is arcing and the silicone can solve this problem. The silicone coating leaves the aluminum carrier unharmed to be reused in future applications.
27
4.3 MAX Phase
MAX phases are a class of hexagonal-structure ternary ceramics consisting a transition metal, an
A-group element and carbon or nitrogen. Figure 32 shows which components can be included in a
MAX phase material. The most commonly used are titanium, silicon and carbon.
Figure 32. Elements that can be included in a MAX Phase.
There are about 60 MAX phases with at least nine discovered in the last five years alone (2009).
The research on MAX phases has been accelerated by the introduction of thin-film processing
methods. A Swedish company, Impact coatings, uses Max phase as a replacement for electroplated gold on contacts.
This might be a little bit confusing because the terms MaxPhase and Maxfas in Swedish are trade
names used by impact coating. These names do not necessarily refer to a MAX phase but to a TiSi-C based coating. (The trade name Maxphase originates from the first generations of such coatings, which were synthesized by sputtering from targets which was a Max phase).
The right picture in Figure 33 shows the hexagonal unit cells of the different MAX phases. The
difference between the three structures is the number of M-layers separating the A-layers. In the
211 phases there are two, in the 312 phases there are three and so on. In the left picture there is a
high resolution TEM (transmission electron microscope) image showing a MAX phase. The zigzag pattern corresponds to the different layers in the unit cells.
28
Figure 33. The left picture shows a high resolution TEM image of a MAX Phase, the picture us taken from the 110 direction.
The right picture shows the hexagonal unit cells. The red dots correspond to the A-layers and the blue the transition metal.
4.3.1
Properties
What makes this class of materials so interesting are their combination of chemical and physical,
but also electrical and mechanical, properties which often combine the desired characteristics of
metals and ceramics. Some of the MAX phases properties are their excellent thermal and electrical conductivity combined with superb machineability, which is almost as good as graphite.
Some Max phases also exhibit extremely low friction coefficients. They are also typically resistant to oxidation and corrosion (Eklund et al. 2009).
Different studies have shown that the Ti3SiC2 nanocomposite has some form of self-lubricity of
the material. The layered structure of the material with strong bonds along the layer and weaker
in-between the layer is the explanation of this behavior. The nanocomposite structure has many
similarities to graphite. The friction coefficient along the planes is the lowest coefficient ever
measured to date and is maintained even after six month exposure the atmosphere. However, the
low friction coefficient is not retained with polycrystalline samples. For larger polycrystalline
samples the steady state friction coefficient from a pin-on-disc test is approximately 0.8 against
stainless steel (Barsoum 2000).
29
4.3.2
MAX phase improvements
The MAX phase nanocomposite coating is often produced using magnetron sputtering onto electrical components. The contact resistant was measured between the nanocomposite and Ag
coated Cu cylinders, illustrated in Figure 34. By varying both the sputtering temperature and the
contact force from 0 to 300 N different contact resistances were measured. Figure 35 describes the
result from the previously mention test. The figure shows that the Ti-Si-C coating has somewhat
higher contact resistant than Ag against Ag, especially at a low contact force. On the other hand,
it has a very low resistance considering that it is a ceramic material. Also, the nanocomposite has
other favorable mechanical properties like preventing welding and potentially minimizing wear.
Furthermore, the material is rather hard (nanoindentation hardness of 20 GPa) with a ductile deformation behavior. It is the rotation and gliding of the TiC grains in the matrix that explains the
ductile behavior of the material. The overall properties of the material make it a good candidate
for many types of different electrical components (Eklund 2006).
Figure 34. Schematic description of the crossed cylinders in the contact resisters test, (Eklund 2006).
30
Figure 35. Contact resistances of Ti-Si-C films deposited on Ni plated Cu cylinders. Ag/Ag contact resistance is included for
comparison, (Eklund 2006).
By adding noble-metals like Ag to nanocomposite coatings, various microstructure and electrical
properties of the material can be improved. Different contents of Ag were encrusted in the MAX
phase morphology and the resistivity was measured. Furthermore, the metallic, Ag particles in
the nanocomposite have been examined with X-ray diffraction, scanning electron microscopy
and transmission electron microscopy.
Pure nanocrystalline titanium carbide in an amorphous Si matrix, known as MAX phase 312, has
a measured resistivity of 340 μΩcm. By adding Ag to the material the resistivity decreased to as
low as 40 μΩcm.
The same dense microstructure of MAX phase was retained by adding moderate amounts of Ag
(10-11 wt-%). In this range the Ag forms approximate 10 nm large crystallites that are homogenously disturbed in the film. For higher Ag content the Ag particles increase in size to about 100
nm and become islands on the film surface and affects the morphology by making it more rough
and porous. However, the change in structure indicates to have beneficial impact and tribological properties, e.g like reducing friction. (Eklund 2006).
31
Figure 36. SEM image of the surface of Ti-Si-C samples (a) low Ag content (6 %) and (b) high Ag content (15 %). Note the
different scale, (Eklund 2006)
4.3.3
Maxthal
Maxthal is a material produced by Kanthal among others. The material is a MAX phase, but instead of being applied as a nanocomposite coating it is produced as a bulk material. Two types of
Maxthal have been studied for the project:
MAXTHAL® 312 (Ti3SiC2) has a maximum operating temperature of 900-1000 °C in air, however this can be exceeded in vacuum or hydrogen up to 1600 °C. The material is very inert, withstands corrosions and has a low coefficient of thermal expansion. MAXTHAL® 312 also has a
high resistance to thermal shocks with excellent structural properties at high temperatures.
MAXTHAL® 211 (Ti2AlC) has aluminum as one of its components which leads to a protective
aluminum oxide layer making it suitable for use in the air and atmospheric temperatures up to
1450° C. (Kanthal 2006). Figure 37 shows the two different Maxthal types.
Figure 37. MAXTHAL ® 211 on the left and MAXTHAL ® 312 on the right
There are two ways of using MAX phase in carbon strips. The first one is to coat the existing
carbon strip with a thin layer of MAX phase and another alternative is using Maxthal instead of
the carbon. A problem with the coating is that magnetron sputtering (technique for making thin
32
films) needs vacuum and the carbon is porous. Also the films are very thin and could therefore
be worn down quite quickly.
MAX phase in bulk, Maxthal, is quiet cheep (the cost of Ti3SiC2 is roughly equal to Ti
powder, 16-32 EUR/kg, Barsoum 2001) but does not exhibit as low frictions coefficients as
MAX phase in thin films were the structure is more organized. It is however harder than
the currently used carbon so the wear should be decreased. On the other hand, there is a
risk that the wear of the catenary will increase. If the frictional coefficient is lower this
could counter the effect. It has to be investigated more before we can request manufacturing methods.
4.4 Advanced binder
In order to improve the lifespan of both the “carbon strip” and the catenary an alternative could
be to replace or coat the carbon with an advanced binder, e.g. Thermic 1100. Thermic 1100 is an
advanced binder based on water with several inorganic compounds, mainly silica. Normally it is
used to bind for instance inorganic materials, such as insulators, to metallic or non-metallic surfaces (Culimeta 2010). However, the surface of the binder, once it has cured, appears to be very
smooth and also the binder becomes very strong after curing. The binder contains mainly sodium
silicate, except for water which evaporates during the curing process, see Table 1.
Table 1. Chemical composition of the advanced binder; Thermic 1100 before curing (Culimeta 2010).
Chemical Composition % uncured and cured
34,55
SiO2
8,41
Al2O2
0,26
Fe2O2
0,02
MgO
0,02
CaO
0,27
K2O
6,65
Na2O
49,82
H2 O
68,95
16,76
0,52
0,04
0,04
0,54
13,25
-
Due to the large amount of sodium silicate, the advanced binder has a low cost and can have high
resistance to temperatures and chemicals. It is also easy to handle and different additives can be
used to improve specific properties such as toughness and conductivity (SpecialChem 2006).
Also, the sodium silicates are environmentally friendly, non toxic and non flammable (PQ corporation 2010). These properties make the advanced binder an interesting candidate to replace the
carbon fragment.
The resistivity of Thermic 1100 has not been measured and it was therefore estimated to approximately 1.37·1014 µΩcm based on the value for silicate glass of similar composition. As mentioned earlier, the advanced binder consists mainly of sodium silicate and alumina oxide and the
electrical properties have therefore been assumed to share numerous characteristics with sodium
33
silicate glasses. The electrical conductivity in silicate glasses is believed to be caused by ionic
motion in the glass network. This mechanism is influenced by many factors, such as the number
and charge of the moving alkali ions and the molecular structure of the glass. Different ways of
improving the conductivity exist. One way is to replace some of the oxygen anions in the sodium
silicate with smaller anions, for instance sulphide anions. Furthermore, doping the glass with an
alkali oxide may also enhance the conductivity. The conductivity increases with increasing temperature due to the increased mobility of alkali ions. Also, the conductivity is greater for smaller
alkali ions such as K+ compared to larger ones such as Na+. Moreover, the conductivity of a silica glass increases with the NaO-concentration and also with the amount of Al2O3. To achieve
maximum conductivity the NaO/Al2O3 ratio should be close to one. However, the electrical conductivity remains too low for all options mentioned above (Ezz Eldin and El Alaily 1998).
Instead of manipulating the structure of the glass a second phase could be added in order to
create a composite material. The current in this case would be carried by the electrons instead of
by the significantly slower ions which is the case in a silicate glass. Studies have shown that sodium silicate can be blended with graphite powder and mould pressed into an appropriate shape.
The conductivity of such a composite varies depending upon the grain size of the graphite, the
graphite content and the pressure at which the moulding process was carried out. The greater the
graphite content the greater the conductivity becomes because the chance of two graphite flakes
having contact increases and the risk of the acid silica gel to cut the contact between graphite
flakes decreases, Figure 38. The conductivity also increases with increasing size of the graphite
flakes, this is probably because when the size of the flakes increases fewer flakes need to be in
contact to form a line of contact through the material. Also, the surface area of the flakes increases, thereby increasing the chance of contact between flakes. When increasing the pressure
during the moulding process the conductivity will increase and reach a maximum value at around
10 MPa pressure; at the same time the density of the material will not change much. The reason
for the increase in conductivity is probably because the contact resistance between the graphite
flakes decreases when the pressure is increased. Also the mould pressure time can be increased
to increase conductivity; longer mould pressure time means the contact resistance between graphite flakes decreases (Chunhui, Mu, Qin, and Runzhang 2006).
34
Figure 38. The conductivity increases with the graphite content where 1 s/cm equals 1 (Ωcm)-1.
The electrical resistivity of silver is 1.60 µΩcm and should therefore be very effective as an additive to increase conductivity. Silver is well-known for its special properties including the softness
and the high thermal conductivity. If a silver catalyst in the form of silver flakes were to be added to the carbon strip it would provide a desired enhancement of the conductivity while still remaining relatively inexpensive due to its high specific surface area. Moreover, the silver flakes
have a low bulk density and consequently less silver needs to be added (K. A. Rasmussen Norway 2008).
By mixing silver flakes with a very high surface-to-weight ratio into the Thermic 1100 and
then forming it to an appropriate shape and curing it, a replacement for the carbon fragment can be created. This replacement has the potential to be cheaper than the currently
used carbon strip and with the added silver flakes the electrical conductivity should be
maintained at a satisfactory level. Electrical resistivity tests have been made at the Department of Measurement Technology and Industrial Electrical Engineering at LTH which
unfortunately shows very high resistivity, almost an isolator. In order to solve this problem
more silver needs to be added which will increase the price.
35
5 Laboratory tests
The different solutions were tested in order to evaluate their performance and qualities.
5.1 Silicone application
On Mars the 21st 2010 a laboratory test on how to apply the silicone on to the sides of the carbon
strips to prevent arcing damages was done at LTH Chemical centre’s laboratory. There were
three different options of how the silicone should be applied, the first way was to only cover the
aluminum edge, the second was to only cover the carbon on the sides and the last one was to
cover both the aluminum edge and the carbon on the sides. Pictures of the applied silicone can be
viewed in Appendix A. Unfortunately, the silicone applied to the carbon alone was very easy to
remove. Therefore covering the aluminum edge together with the glue, which binds the carrier to
the strip, became the main interest.
The laboratory test was performed to study the appropriate quantities of silicone that could be
applied to the entire carbon strip and to improve the procedure. The time required for it to dry,
the technique with which the silicone was to be applied and the adhesiveness were studied.
Electrical discharges developed between the catenary and the carbon strip can cause severe damages to the aluminum carrier. When the arcs hits the aluminum or the carbon close to the glue
binding the carbon to the aluminum large fractions of carbon can as a consequence be torn off
and rapidly shorten the lifetime of the carbon strip.
Silicone has a good electrical resistance and the idea is that applying it to the carbon strip will
protect the aluminum carrier and the glue from being hit from electrical discharges. Therefore
avoiding large fractions of carbon to be torn off and making the carbon strips lifetime longer.
5.1.1
Results from the silicone test performed by Bombardier
The idée to apply silicone on the sides of the carbon strip to prevent arcing damage to the carrier
was forwarded to Bombardier for testing. It was tested on trams with two different carbon strips
with the silicone application and two carbon strips without the silicone applied. The silicone application was tested 200 km/day and after one day they were examined and pictures were taken,
the same procedure was done after three days of testing.
A picture after one day of testing without the silicone application can be seen in and a carbon
strip with the silicone is depicted in Figure 39.
36
Figure 39. Carbon strip without the silicone applied after one day of testing. The red circle marks a severe burn spot trough
the glue.
Figure 40. Carbon strip with silicone applied after one day of testing.
Figure 41. The schematic untreated carbon strip on the top has several burn spots whereas the silicone treated has none.
37
The results from the testing indicate that the silicone fulfills the function of protecting the aluminum carrier and the glue joining it to the carbon fragment. The welding sparks to the sides of the
carbon strips near the aluminum carrier has completely ceased. However, the results is as earlier
mentioned only from one day of testing so to fully appreciate the effects of longer testing periods
are required. The tram will keep running in order to acquire more data concerning the durability
of the silicone applied.
5.2 Micro hardness
On April the 5th a micro hardness test was performed on Maxthal, both on the 321 and the 211
sample. This was done at the LTH department of Mechanical Engineering, with the help of the
Associate Professor Srinivasan Iyengar. The tests were made in order to estimate how hard this
material was in comparison with the carbon on the carbon strip. The result from the test showed
that Maxthal is a very hard material and the hardness is more like a metal than the carbon used
on the carbon strip today.
The micro hardness test is a static indentation made with loads not exceeding 1 kgf and with the
intender as a Vickers diamond pyramid. The procedure for testing is a Vickers hardness test done
on a microscopic scale with high precision instruments. The surface of the sample being tested
generally requires a fine metallographic finish. To measure the indentations, a precision microscope is used with a magnification of X500.
The Vickers Diamond Pyramid is shaped in the form of a squared pyramid with an angle of 136o
between the faces (Figure 42) and the Vickers Diamond Pyramid harness number is the applied
load (kgf) divided by the surface area of the indentation (mm2).
The equation below is used to calculate the hardness.
Where F is the load in kgf, d is the arithmetic mean of the two diagonals, d1 and d2 in mm and
HV is the Vickers hardness. (Gordon England 2008)
38
Figure 42. A Vickers Diamond Pyramid used to determine the Vickers microhardness, (Gordon England 2008)
5.2.1
Results from the Micro Vickers hardness test
The results from the Micro Vickers hardness (MHV) test for a sample Maxthal 211 (Ti-Al-C) are
shown in the table below. Four tests were carried out and the weight of the load causing the
Vickers diamond pyramid to create an indentation was measured to 400g.
Table 2. The Vickers hardness of Maxthal 211
1
2
3
4
diagonal1
(µm)
diagonal2
(µm)
56.54
53.30
44.87
46.94
55.80
53.94
56.29
53.87
Mean value of
the diagonals
(mm)
0.056
0.054
0.051
0.050
MHV
236
258
291
292
Mean MHV: 269
A test similar to the one mentioned above was performed with a sample of Maxthal 312 (Ti-SiC). Again, the same weight of the load was 400g.
Table 3. The Vickers hardness of Maxthal 312
1
2
3
4
diagonal1
(µm)
32.05
36.97
32.76
32.53
diagonal2
(µm)
30.45
32.70
29.97
32.91
Mean value of the
diagonals (mm)
0.031
0.035
0.031
0.033
MHV
762
612
757
694
Mean MHV: 706
39
Maxthal 312 is significantly harder than Maxthal 211 according to performed tests. (Gordon
England 2008)
5.3 Advanced binder
Several samples of the advanced binder were made in different molds in order to determine how
the binder cured and how long time it took for the curing process. Thick molds that dried in room
temperature seemed to have problems with the curing below the surface of the advanced binder.
If the top surface of the advanced binder was ground off, the properties changed. For instance,
the sample became soluble in water once the top layer was removed. The curing process was
therefore tested in a heated oven. However, cured in a heated environment pores and small holes
in the molds of the advanced binder appeared. To avoid this problem, the next sample was made
as a thin layer of the advanced binder so that the curing process would not only be done on the
surface but throughout the whole sample. When it was complete, another thin layer was applied
on the first layer and then dried, this procedure continued until the desired thickness of the sample was achieved. To get an overview of how thick these layers should be different layer thicknesses was applied on different samples.
Samples with 10 wt% and 20 wt% silver flakes mixed into the binder before the curing were also
made. Silver flakes were added in order to enhance the electrical conduction since the electrical
conduction of the advanced binder itself was not as good as the carbon mixed with copper in the
carbon strips. Figure 43 shows the molded samples of the advanced binder Thermic 1100 on aluminum plate.
Figure 43. Molded samples of the advanced binder Thermic 1100 on aluminum plate
40
6 Conclusions
Three different solutions have been considered and the Lund Team prefers solution number 1;
the silicone solution:
1. The silicone solution: The silicone can protect the aluminum carrier and glue
against arc effects, by reducing the possibilities for torn off pieces prolonging the
carbon strips life span. The silicone coating leaves the aluminum carrier unharmed
to be reused in future applications. Silicone has the possibility to increase the wearbased lifetime by increasing the resistance towards flash overs thus increasing the
lifetime based on resistance against flash overs. Furthermore, the silicone is a very
cheap solution which can be implemented immediately and applied quickly and
easily. This solution is most certainly patentable. Finally, the silicone solution has
been tested under real conditions with great success by Bombardier during a limited
time span.
2. The Max Phase solution: MAX phase in bulk, Maxthal, is quiet cheep (the cost of
Ti3SiC2 is roughly equal to Ti powder, 16-32 EUR/kg, Barsoum 2001) but does not exhibit as low frictions coefficients as MAX phase in thin films where the structure is more
organized. It is however harder than the currently used carbon so the wear on the strip
should be decreased. On the other hand, there is a risk that the wear of the catenary will
increase. If the frictional coefficient is lower this could counter the effect. It has to be investigated more before we can request manufacturing methods.
3. The Advanced binder solution: By mixing silver flakes with a very high surface-toweight ratio into the Thermic 1100 and then forming it to an appropriate shape and curing
it, a replacement for the carbon fragment can be created. This replacement has the potential to be cheaper than the currently used carbon strip and with the added silver flakes the
electrical conductivity should be maintained at a satisfactory level.
41
7 Referenser
7.1 WebPages:
Morgan Carbon (2010) Morgan Carbon Current Collector – Sharing Knowledge, 100301,
www.morgancarbon.com/applications/pdf/currentcollector2.pdf
Schunk AB (2004) Carbon Sliding Strips, 100115, http://www.schunksbi.com/sixcms/media.php/1702/16_10_en_CarbonSlidingStripsPantographsTrolleyPoleSystems
.pdf
Nationalencyklopedin (2010) Kontaktledning, 100206,
http://www.ne.se.ludwig.lub.lu.se/lang/kontaktledning
Richard E. Barrans Jr. (2001) CuO Conduction, 100206
http://www.newton.dep.anl.gov/askasci/eng99/eng99154.htm
PanTrac (2005) PantoDrive, 100205, http://www.karma.se/uploads/pantracinfo.pdf
Kanthal (2006) Maxthal, 100511, http://www.kanthal.cz/produkty/kanthal-maxthal.html
SpecialChem (2006) Sodium Silicate Adhesive,
http://www.specialchem4adhesives.com/resources/articles/article.aspx?id=1495
PQ corporation (2010) Adhesives and binders
http://www.pqcorp.com/applications/adhesivesandbinders_application.asp
ALIBABA (2010), glycerol, 100511,
http://www.alibaba.com/product-tp/104563161/Crude_Glycerine_80_.html
Energimyndigheten (2009), 100520
http://www.energimyndigheten.se/sv/press/Pressmeddelanden/Sverige-blev-nettoimportor-av-elunder-2009/
7.2 Litterature
Harryson consulting (2009), distributed documents
Atkins P. and Jones. L. (2003) Chemistry: Molecules, Matter, and Change, Freeman, USA, 442443
Gudojc (2004), Banverket, Kontaktledningsteknik för dummies
Bombardier (2009), distributes documents
42
The Soap and Detergent Association Glycerine & Oleochemical Devision (1990) Glycerine: an
overview, 17
Chunhui, S. Mu, P. Qin, Y. and Runzhang, Y. (2006). Studies on Preparation and Performance of
Sodium Silicate/Graphite Conductive Composites. Journal of Composite Materials 40, 839-848.
Ezz Eldin, F.M. and El Alaily, N.A. (1998). Electrical conductivity of some alkali silicate
glasses. Material Chemistry and Physics 52, 175-179.
Culimeta (2010) High temperature glue Thermic 1100°, Bersenbrück/Germany
Stockwell Elastomerics (2009) Silicone Sponge and Silicone Rubber Gaskets, Seals, Cushions,
and Materials, Philadelphia/USA
MG Chemicals (2010) Silicone Conformal Coating, Surrey B.C. /Canada
Schunk Kohlenstofftechnik GmbH and Hoffman & Co., Elektrokohle AG (2004) Carbon Sliding
Strip for Pantographs and Trolley Pole Systems, Heuchelheim/Germany and Steeg/Austria
K. A. Rasmussen Norway (2008) Silver Catalyst, Hamar/Norway
Ekström (2008) Kontaktproblem I frostig miljö, ROSLAGET, 2/3
Eklund, Beckers, Jansson, Högberg, Hultman (2009) The Mn+1AXn phases: Materials science
and thin- film processing, Thin Solid Films 518, 1851–1878
Barsoum, M. (2000) The MN+1AXN Phases: A New Class of Solids; Frog. Solid St. Chem. Vol.
28, 201-281.
Barsoum, M. (2001) The scientific Research Society, The MAX Phases: Unique New Carbide
and Nitride Materials, Vol 89, 9.
Eklund. P (2006) Novel ceramic Ti–Si–C nanocomposite coatings for electrical contact applications, Surface Engineering, VOL 23, NO 6, 406-411.
Eklund et al. (2009) Microstructure and electrical properties of Ti–Si–C–Ag nanocomposite thin
films, Surface & Coatings Technology 201, 6465–6469
Gordon England (2008) Microhardness Test, 100511
7.3 Personal contact
Ulf Påhlsson, EuroMaint Rail AB
Jan-Erik Gudojc, Swedish Transport Administration 2010-03-20
43
Appendix A
How to apply silicone to a carbon strip
1. Make sure that the surface of the carbon strip on which the silicone is to be applied to is
clean and dry.
2. Open the tube containing silicone according to the instructions on the tube.
3. Releasing the tab on the gun and pulling the pressure rod back allows the user to insert
the silicone tube. The pressure rod should then press against the base of the tube when the
trigger on the gun is gently squeezed. Keep squeezing until the desired amount of silicone is received. Finally, to prevent silicone from leaking out of the nozzle when the procedure is done, the tab should again be released and the pressure rod pulled back.
4. Apply a 3 mm thick layer of silicone along the entire aluminum carrier on both sides of a
carbon strip (aluminum edge). Approximately 5 mm of the carbon near the carrier shall
also be coated with a thinner layer of silicone, however it is more important that the carrier is properly coated, Figure A1 (carbon side up).
5 mm
Aluminum edge
Figure A1. Silicone coated carbon strip
5. Smoothen the silicone surface with a flat object or another appropriate tool in order to obtain an evenly thick layer. The silicone layer should be left to dry for a minimum of 24
hours before the carbon strip can be assembled on a pantograph.
A1
Laboratory report
Objective
The purpose of this laboratory was to examine appropriate quantities of silicone that can be applied to an entire carbon strip. The time required for drying, the technique with which the silicone is to be applied and the adhesiveness were also studied in order to improve the procedure.
Background
Electrical discharges between the catenary and a carbon strip can cause severe damages on the
aluminum carrier surrounding the carbon strip. Large fractions of carbon can as a consequence
be torn off which results in a substantially shorter lifetime. Carbon has a greater resistant to discharges than aluminum and it is therefore desirable to protect the carrier which is why silicone is
applied on it.
Material
The laboratory was performed using a carbon strip, silicone- Bostik Silikon Bygg & Sanitet, a
silicone gun, a flat object for smoothening and a scale.
Method
Different approaches were tried in applying the silicone, in one end of the carbon strip the silicone was applied to the aluminum carrier only (1), in the middle the silicone was applied to both
the carbon and the aluminum carrier (2) and finally, in the other end silicone was applied to the
carbon alone (3), Figure A2 and A3.
1
2
3
Figure A2 and A3. Silicone applied to a carbon strip using three different approaches
A2
The length of the part of the strip coated with silicone was measured. Furthermore, the tube containing silicone was weighed before and after silicone had been applied. This was done to determine the amount of silicone used and to enable the calculation of the amount required for an entire carbon strip. The part where silicone was applied to the carbon alone there was a slight slope
of the carbon strip because it was so close to the edge. Hence, the amount applied there was determined by dividing the area with the weight.
Results
The aluminum carrier
Weight of silicone tube before coating (g)
Weight of silicone tube after
coating (g)
Difference (g)
Length 6 cm
Amount silicone = 0.33 g/cm
721
719
2
The carbon and the carrier
Weight of silicone tube be718
fore coating (g)
Weight of silicone tube after 715
coating (g)
Difference (g)
3
Length = 4.8 cm
Amount silicone = 0.625 g/cm
The carbon
Weight of silicone tube be714
fore coating (g)
Weight of silicone tube after 713
coating (g)
Difference (g)
1
2
Area = 7 cm
Amount silicone = 0.14 g/cm2
The carbon strip was carefully observed 48 hours after it had been coated with silicone. The
layer was firm, dry and tightly bonded to the aluminum carrier. However, the silicone applied to
the carbon was unfortunately easy to remove.
A3