Flat spot

A flat spot is an undesirable phenomenon wear on the wheels of rail vehicles.

Formation

A flat area formed as the wheel of the moving vehicle is not more rolls, but slides on the track. This phenomenon is also called sliding. This can occur by a non -fixed brake noticed by a normal braking operation, in which the coefficient of adhesion between wheel and rail is not big enough, or too strong braking either ( as in an emergency brake ). Through institutions such as the anti-slip or the gritters slipping should be avoided. Since the wheel is not much harder than the steel rail, the material is abraded to the point where the wheel slides on the rail. In addition to the wheel and the rail is worn, only that the rail wear is minimal, since the locked wheel sliding over the rail and this therefore wears relatively uniform. In contrast, the area of ​​contact remains with the wheel and are carried on the wheel itself, uneven wear ( including the sliding rail across acts as an abrasive tape on the stationary wheel). As a result, a flat spot on the wheel tread, which is not infrequently burned out because of the large temperature development forms. In addition, it can also lead to so-called plots. This polished end of the rail surface and usually applied directly in front of the flat spot, or elsewhere material can result in the worst case the wheels to lock, because it can tilt the brake blocks.

Follow

If the flat is small enough, the vehicle can continue to run without restrictions. While the ride is then in the frequency of wheel rotation periodically occurring noise heard. The affected wheel is then turned until the next maintenance on a wheel lathe again. The flat area is too large, there is a (mainly in frost) the risk that a rail break is caused when driving the occurring " strokes ". The vehicle is then fed to a low speed, sometimes on an auxiliary bogie, the next maintenance work.

However, even small flat spots can cause secondary damage. This concerns mainly the wheel itself from the beating it can lead to a change in structure, so that the wheel will wear unevenly. In the further consequence may lead to deviations from the circular shape at the wheels. This is observed especially for wheels with disc brakes because there takes place no material on the wheel tread through the brake blocks. Also wheels are braked with plastic brake blocks are more at risk. This resulting lack of roundness are also called singular flattened. Also may result in microcracks and thus breakouts on the wheel treads. Overall, a flat spot is the mileage of a wheelset massively reduced.

The blows caused by flat spots, act on the components of the axle box. This can lead to bearing failure and ultimately to a hot runner.

According to AVV ( old RIV ) are car " suspend " with flat spots on the following border dimensions, that is, to take from the operation: When a wheel with a diameter greater than 630 mm, if the flat reaches a length of more than 60 mm. If the wheel diameter less than 630 mm, a length of only 30 mm is allowed. Generally, cars suspend with limited -roundness of more than 1 mm, regardless of whether they are flats or material deposits. For smaller flats are allowed to assign the car after unloading the workshop ..

Locating

The diagnosis of a flat spot occurs not only in the workshop by a roundness diagnosis, but can also be made directly on the open road while the train passes with flat detector systems. All such flat detection systems have in common that they measure the wheel forces during one or more Radumläufe. If a wheel has no wheel defects, the rail is evenly loaded during the crossing. Is a flat spot on the wheel, take very different forces during a Radumlaufs.