Here - Polyurethanes - Bayer

Baydur ®/Bayflex ® – Polyurethanes for Design and Functionality
ELECTRONIC EYES FOR
FLOATING TRAINS
Regardless of whether or not it comes into
service in Germany in the foreseeable future,
the Transrapid is internationally recognized
as an outstanding achievement of German
engineering. As with all modes of mass
transportation, it is vital that all the system
components in this “maglev” (magnetic
levitation) train be totally reliable. That goes
for the moving parts as well as the fixed
system components, which also require
effective protection from the specific environmental
conditions they will encounter when
the train goes into service in China.
The GST 24 VT voltage sensors in the Transrapid
linear motor produced by Duromer Kunststoffverarbeitungs-GmbH
of Ottendorf-Okrilla,
Germany, on behalf of the Transrapid Consortium
are encapsulated in Baydur ® E, a
specially designed polyurethane molding
system using two liquid components. Despite
its appearance, the Transrapid has little in
common with a conventional high-speed train.
Rather than running on rails, it “floats” to its
destination on strong magnetic fields without
coming into contact with the ground. This makes
for a very smooth, energy-efficient action.
Unlike conventional trains, the drive assembly
on the maglev train is located in the track rather
than in the train itself. The magnetic fields
which “carry” the train are switched on and off
in a fraction of a second by a system of linear
motors. To ensure that the control electronics
in these motors have an accurate picture of
the condition of the railway track at all times,
high-performance sensors are built into the
track at regular intervals to relay vital information
about factors such as the voltage and
current conditions. “These sensors play a
key role in the drive assembly of the Transrapid,
so it’s vital that they are totally reliable,” says
Dr. Axel Georgi, Managing Director of Duromer
Kunststoffverarbeitungs-GmbH. “That’s why
these modules are encased in polyurethane
cast resin. This material not only isolates the
electrical components, it also prevents dust,
dirt and water penetrating the modules under
sub-tropical conditions, thereby ensuring high
operating reliability.” The casting compounds
used are extremely resistant to hydrolysis, a
factor which is important in the often warm,
humid climate of Asian countries, and offers some
clear technical advantages over epoxy resins.
Polyurethane molding systems:
Reliability is key to the drive concept
“Polyurethane cast resins can be processed at
comparatively low temperatures of around 100
degrees Celsius,” explains Friedhelm Fähling,
an expert in electrical casting compounds at
Bayer MaterialScience AG. “That allows even
large parts like the cylindrical sensor, which
measures around 150 x 250 mm, to be produced
quickly without lengthy heating uptimes.”
Vacuum technology is used to create a bubblefree
casting which will not cause any unevenness
in the magnetic field. There is no need to anneal
the casting compound afterwards. The moderate
casting temperature also means that only
slight shrinkage pressure is exerted on the
delicate sensor electronics. This allows even
components made of electrical conductors and
semi-conductors with widely divergent thermal
expansion coefficients to be sealed without
sustaining any damage. The excellent flow
properties of the polyurethane and the fact
that it will adhere to a wide range of materials
also ensure gap-free bonding. Moreover, when
used with the appropriate fillers, these
polyurethane resins conduct heat away very
effectively.
Polyurethanes have significant economic
advantages over epoxy resins, shorter cycle
times, lower energy costs and easier storage
because different degrees of hardness can be
achieved using one and the same raw material
system.
Foto: Transrapid Int. GmbH & Co. KG
For further information go to:
www.duromer.de