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 typesaccording to the location of the wears. Wear on head of rails are seen wherethe rail head is worn. Due to abrasion of the rolling wheels over rails, theimpact of the heavy wheel loads on small areas, corrosion of metal of railscauses rail wear on top.
In addition, the slipping action during starting and brakingof vehicles cause rail wear on head. Rail wear on side of the rails isanother type of rail wear. This is the most important type because it is seenvery often and affects the service life of rails at most. From another point ofview, it is also very important factor for safety.
Due to crucial importance ofthat wear type, many factors such as road plain, longitudinal profile, rollingstock and road technical conditions, steel quality of rails and wheels, freightintensity 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 fasteningtypes. On the other hand, in Australia engineers concentrate on changing wheelsof vehicles and try to make the wheels and rails aligned especially at curvessections that has radius smaller than 600 meters. 1 If you can prevent thattype of wear, the maintenance cost will be decreased considerably. It is seen atthe inner face of outer rails at the curves. Main reason for side wears is thefriction between wheel flanges and inner side of outer rail due to centrifugalforce along the curvature. Additionally, the difference between the directionof rails and wheels at the curve sections cause rail wear on side. Also, we cansee side wear at inner rails.
Since the length of outer rail is longer thaninner rail, wheel will slip on the inner rails and causes extra friction actionresulting side wear.Using special alloy is one of the alternative solution forreducing rail wear. When the steel of wheel flange is harder than the steel ofthe rails, it causes rail wear and we can solve this problem by having hardersteel at rails.
However, that comes with a price. As much as it increases theexpanses of rails, it will decrease substantially the cost of maintenance.Another solution is to reduce the expansion gap. The wheelsmust jump while passing over the expansion gap between bars and during thisjump, it causes strike at the end of rails and resulting as rail wear. Byregularly tightening the bolts, we can prevent the extension of expansion gapand we would reduce the rail wear by this way.One of the important aspects of railway engineering ismaintenance.
Good maintenance of track and tightening joints if they are loose wouldreduce the rail wear. Also, the maintenance of wheels are important. If thereis any imperfection on the wheels, it causes the rail wear. Furthermore, thefrequency of maintenance is critical because if the grinding process is notdone at the right time, wear process will be faster and later, it will be hardto fix the problem. Interchanging the inner and outer rails on curves is anothersolution to the rail wear problem.
That process is performed at curves. Exchangeof inner rails which have the top wear and outer rails which have the sidewear, would increase the service life of rails.Lubrication is anotherway to reduce rail wear. Lubrication process is done where the inner side ofouter rails, switches and tongue rails.
This process can be held by person orautomatically. In the regulation of Turkish Railways(TCDD), curve radius versus speed table is given above. From the table, whenthe curve radius increases, the maximum allowable speed also increases.However, the maximum speed is 100 km/h for freight and normal passenger trainseven curve radius increases.
On the other hand, the maximum speed increases upto 280 km/h when curve radius is 5000 meters.Superelevation value can be calculated fromthe formula below: where d=Superelevation (mm) V=Speed (km/h) R=Curve radius (m)During calculation of superelevation, thespeed V illustrates the maximum allowable speed in that area. This standard isalso used in Germany and our Ministry of Public Works approved it.Average sidewear d = rail wearat 90 degreeIn the regulation of U.S. Department ofTransportation Federal transit Administration, the relationship between degreeof curvature, maximum allowable speed and superelevation is given above. Fromthe table, when the degree of curvature increases, radius decreases and maximumspeed decreases. Main reason for why we put this table is toindicate the relationship between the superelevation level and maximumallowable speed at same radius.
For example, at the first line when there is noelevation difference between rail heads, maximum allowable operation speed is93 mph. However, when the elevation difference is 2.5 inches, maximum allowableoperation speed increases to 125 mph. The difference is at speed is 34.4% whichis significantly higher number. Hence, we can increase operating speed withoutincreasing rail wear at same area with just superelevation.
Also, we canincrease maximum allowable operation speed with other techniques like using specialalloy steel, regular maintenance, using less joints and lubrication even more. Rail Wear LimitsAccording to the study of the Ministry ofEducation (MEB), when 100.000 train passes from rail, 1 mm rail wear at therail head is observed.5 According to the type of the rail, allowable railwear limit is between 4-11 mm. The amount of rail wear can be measured byRobel-A, Robel-B devices.