Rail wear is a phenomenon caused by friction and heavy load.
It is a change in the cross section of rails. We can classify rail wear types
according to the location of the wears.
Wear on head of rails are seen where
the rail head is worn. Due to abrasion of the rolling wheels over rails, the
impact of the heavy wheel loads on small areas, corrosion of metal of rails
causes rail wear on top. In addition, the slipping action during starting and braking
of vehicles cause rail wear on head.
Rail wear on side of the rails is
another type of rail wear. This is the most important type because it is seen
very often and affects the service life of rails at most. From another point of
view, it is also very important factor for safety. Due to crucial importance of
that wear type, many factors such as road plain, longitudinal profile, rolling
stock and road technical conditions, steel quality of rails and wheels, freight
intensity and axial loads are considered to prevent wear. In that situation,
countries try to solve that problem in different ways. For instance, in U.S.
engineers concentrate on improving steel quantity and create new fastening
types. On the other hand, in Australia engineers concentrate on changing wheels
of vehicles and try to make the wheels and rails aligned especially at curves
sections that has radius smaller than 600 meters. 1 If you can prevent that
type of wear, the maintenance cost will be decreased considerably. It is seen at
the inner face of outer rails at the curves. Main reason for side wears is the
friction between wheel flanges and inner side of outer rail due to centrifugal
force along the curvature. Additionally, the difference between the direction
of rails and wheels at the curve sections cause rail wear on side. Also, we can
see side wear at inner rails. Since the length of outer rail is longer than
inner rail, wheel will slip on the inner rails and causes extra friction action
resulting side wear.
Using special alloy is one of the alternative solution for
reducing rail wear. When the steel of wheel flange is harder than the steel of
the rails, it causes rail wear and we can solve this problem by having harder
steel at rails. However, that comes with a price. As much as it increases the
expanses of rails, it will decrease substantially the cost of maintenance.
Another solution is to reduce the expansion gap. The wheels
must jump while passing over the expansion gap between bars and during this
jump, it causes strike at the end of rails and resulting as rail wear. By
regularly tightening the bolts, we can prevent the extension of expansion gap
and we would reduce the rail wear by this way.
One of the important aspects of railway engineering is
maintenance. Good maintenance of track and tightening joints if they are loose would
reduce the rail wear. Also, the maintenance of wheels are important. If there
is any imperfection on the wheels, it causes the rail wear. Furthermore, the
frequency of maintenance is critical because if the grinding process is not
done at the right time, wear process will be faster and later, it will be hard
to fix the problem.
Interchanging the inner and outer rails on curves is another
solution to the rail wear problem. That process is performed at curves. Exchange
of inner rails which have the top wear and outer rails which have the side
wear, would increase the service life of rails.
Lubrication is another
way to reduce rail wear. Lubrication process is done where the inner side of
outer rails, switches and tongue rails. This process can be held by person or
In the regulation of Turkish Railways
(TCDD), curve radius versus speed table is given above. From the table, when
the curve radius increases, the maximum allowable speed also increases.
However, the maximum speed is 100 km/h for freight and normal passenger trains
even curve radius increases. On the other hand, the maximum speed increases up
to 280 km/h when curve radius is 5000 meters.
Superelevation value can be calculated from
the formula below:
where d=Superelevation (mm)
R=Curve radius (m)
During calculation of superelevation, the
speed V illustrates the maximum allowable speed in that area. This standard is
also used in Germany and our Ministry of Public Works approved it.
d = rail wear
at 90 degree
In the regulation of U.S. Department of
Transportation Federal transit Administration, the relationship between degree
of curvature, maximum allowable speed and superelevation is given above. From
the table, when the degree of curvature increases, radius decreases and maximum
Main reason for why we put this table is to
indicate the relationship between the superelevation level and maximum
allowable speed at same radius. For example, at the first line when there is no
elevation difference between rail heads, maximum allowable operation speed is
93 mph. However, when the elevation difference is 2.5 inches, maximum allowable
operation speed increases to 125 mph. The difference is at speed is 34.4% which
is significantly higher number. Hence, we can increase operating speed without
increasing rail wear at same area with just superelevation. Also, we can
increase maximum allowable operation speed with other techniques like using special
alloy steel, regular maintenance, using less joints and lubrication even more.
Rail Wear Limits
According to the study of the Ministry of
Education (MEB), when 100.000 train passes from rail, 1 mm rail wear at the
rail head is observed.5 According to the type of the rail, allowable rail
wear limit is between 4-11 mm. The amount of rail wear can be measured by
Robel-A, Robel-B devices.