Here - Polyurethanes - Bayer

Baydur ®/Bayflex ® – Polyurethanes for Design and Functionality
THE WHISPERING
STREETCAR
Streetcar systems are a wonderful thing.
Many city centers are much easier to reach
by streetcar than by car. The streetcar takes
you straight to where the action is, and
there’s no need to worry about finding somewhere
to park. Unfortunately, however,
streetcars have their downside too. It’s not
uncommon for people living along the
routes to be bothered by the noise of streetcars
squeaking and rumbling past their
homes, particularly at night, and stray current
from the tracks can cause corrosion damage
to water and gas pipes.
Fortunately, there’s an effective means of solving
these problems. The underside of the tracks can
be encased in an elastic, non-conducting plastic
foam, a technique mastered by Polyplan GmbH
of Strasslach, Germany. The materials used are
polyurethane systems with tailor-made cell
structures formulated specially for this application
by Büfa Polyurethane GmbH & Co. KG
of Oldenburg, Germany, a systems house of
Bayer MaterialScience AG. They boast outstanding
mechanical performance in long-term
use and are very easy to work with.
“There are two main sources of noise from streetcars,”
says Lutz Ohmstede, who was part of the
team at Büfa which developed the polyurethane
system for this unusual application. “Firstly,
there’s the rolling noise from the wheels and
secondly, there’s the impact noise produced
when the streetcar hits weld joints and points
on the track. Both sources of noise can be re-
duced by dampening the rail webs which emit
the noise to provide effective acoustic insulation.
Elastic plastics are perfect for the job.”
Compared to conventional solutions using filled
solid plastics, rigid polyurethane foams offer
particular advantages. “Instead of controlling
the dampening effect, and in turn the noise
reduction performance of the grouting material
by altering its hardness, we can optimize both
properties using a tailor-made pore structure
that literally swallows up sound,” continues
Lutz Ohmstede “Moreover, using polyurethanes
here means that we can completely do
away with plasticizers. That’s particularly
important, since these auxiliary substances
are known to leach out of many other noisereducing
materials over time, which can cause
the material to become brittle.” The Büfaflex ®
systems, which are based on Bayflex ® systems
from Bayer MaterialScience AG, boast excellent
long-term stability and maintain their vital
dampening properties very well. Foams produced
using these systems are highly weatherresistant
and are also suitable for use in
groundwater protection zones. Even adverse
environmental conditions don’t affect them.
Foam-coated rails minimize running
noise and problems with stray current
Büfaflex ® is also more cost-effective to process
than conventional rail grouting systems. The
rail is simply “floated” in a special framework
on site and then encased in the foamed polymer
material using a mobile, computer-controlled
polyurethane grouting system so that the grout
comes up to the lower edge of the rail head.
The foam automatically expands to fill any space.
“Grouting the rail in this way provides it with
complete support,” explains Jürgen Huber from
Polyplan GmbH, which specializes in rail grouting.