Measurement, control and enhancement of friction/traction in a simulated wheel/rail contact.

The focus on rail transportation has shifted in recent years to be a viable alternative to road based
means of travel and freight distribution. With a finite stockpile of the world's natural hydrocarbon
based fuels and ever increasing road congestion, rail research has become a prime topic of late. In this
thesis the focus has been on the wheel/rail contact and the measurement of rail head
friction.
The initial project was the development of an alternative technique to measure railhead friction.
Adhesion loss is a major problem on railways around the world and is common during the autumn, at
times for no obvious reason. Currently there are hand-pushed Tribometers which are used by rail
networks to periodically measure and record friction on their rails. These devices however, are large
bulky items and due to their design can only measure friction over a relatively large distance.
However, most adhesion loss problems are caused by localised phenomena. A pendulum tester was
chosen as a potentially viable alternative to the Tribometer as it could measure over shorter lengths of
track (i. e. 13 cm compared to 3 in as in the case of the Salient Systems Tribometer). The pendulum is
also relatively small and hence is convenient to transport. After a series of laboratory and field based
tests the pendulum has been shown to match very well with Tribometer and twin-disc data.
Friction modifiers are commonly used on railways around the world and are promoted to have many
benefits such as reduced fuel consumption, reduced wear and damage to wheels and rails and
reductions in operating noise. These products have been adopted in many different countries. It was
noticed in the literature that very little study had been done on how the performance of these products
is affected by varying atmospheric conditions or levels of railhead contamination. Another aspect of
this thesis has been the measurement of one of the leading brands of top of rail friction modifier using
a pin-on-disc tester with attached atmospheric chamber. It was found that humidity and the presence
of iron oxide have a far greater effect on the friction modifier than temperature.
In the final two chapters a study was carried out to measure the performance of traction enhancing
products. These are intended to restore traction in cases of adhesion loss from, for example, leaves on
the line. It is critical that correct levels of adhesion/traction are maintained for braking and
acceleration purposes. A twin-disc tester was used in this study and a technique for forming a crushed
leaf layer on the discs was developed. The traction enhancers consist of sand particles of uniform size
suspended in a water based gel. There were four products tested each using a different sand grain size.
The first series of tests measured the performance of each product in terms of traction compared to
that of a leaf layer alone. It was found that the smaller particles showed the best performance by
restoring the traction to uncontaminated levels in the shortest time. The second series of tests focused
on the impact these products had on wheel and rail wear and track signalling. Wear was also
measured in terms of mass lost from the discs. An A. C. circuit operating at 2 kHz was used to
simulate a T121 track circuit which is used in the UK as part of the signalling system. Impedance
caused by each product was measured and compared to impedance levels for uncontaminated discs. It
was found that the impedance of a leaf layer plus the product was lower than the impedance of the
leaf layer alone. There also seemed to be no correlation between particle size and impedance. The
impedance levels seen with the products were not deemed to be enough to cause a significant issue to
the signalling system.