Hot runner
In a rail vehicle, a hot runner is an impermissibly high level of heating of a wheel set bearing . It is sometimes mistakenly believed that any heat generated by a stuck brake (a stuck brake ) is also a hot runner. However, the term “hot runner” only refers to impermissible heating of the wheelset bearing. However, a fixed brake can lead to a hot runner, namely when the resulting heat is transferred to the axlebox bearing and causes damage there. A hot runner is classified as hazardous damage, which is why the vehicle must be taken out of service immediately.
causes
Flats
A flat spot occurs on the wheelset tread when the wheelset locks up when braking before the train has come to a standstill. The wheels of the blocked wheel set are pulled over the rails by the inertia of the train when it is not rotating (this process is known as sliding ), which leads to increased material removal at the contact point of the wheel set running surface due to the increased friction. The resulting flattened point (flat point) generates a blow with every revolution of the wheel, which is audible as a noise and which is transmitted through the wheel center and also acts on the components of the wheelset bearing. If the flat spot is not removed over a longer period of time, the load on the axlebox bearing from these impacts can lead to bearing damage.
Broken earthing
Special earthing contacts , also known as “frost contacts ” in technical jargon (derived from the name of a company that makes such contacts), ensure that currents are diverted to earth via the bogie , wheelset and rail . In this way, you prevent currents from flowing through the axlebox bearing and causing sparks there. If such sparks occur due to a defective earth contact, bearing damage will result from welds in the axlebox bearing.
Grease leakage
The task of the bearing grease is to reduce the friction in the axlebox bearing. On the one hand, the leakage of bearing grease due to insufficient sealing of the bearing can increase the friction to such an extent that the bearing will eventually become damaged. On the other hand, leakage of grease can also indicate existing bearing damage, which generates increased heat generation and thereby reduces the viscosity of the bearing grease. The heat source can also be a fixed brake, the heat of which is transferred to the bearing. As a result of this effect, a cycle can develop from heat generation through bearing damage (or through a fixed brake), the resulting increased grease leakage and aggravation (formation) of the bearing damage due to lack of lubricant, which accelerates the deterioration of the bearing. If the grease leakage is minor, the grease should be removed and the wheelset should be observed. If the grease leaks again or if there is heavy grease leakage (the grease has spread over the entire wheel disc or even on the bogie), the vehicle must be taken out of operation immediately.
In summary, the causes mentioned lead to bearing damage due to insufficient lubrication. Due to the increased friction, the wheelset heats up more than the others.
consequences
In the case of a hot runner, high temperatures can arise in the axlebox bearing, which in extreme cases can reach almost 1000 ° C. On the one hand, this creates a risk of fire and, on the other hand, the strength properties of the material decrease so much that an axle breakage and thus derailment can occur. In the case of a hot runner that comes to a standstill, the wheel bearings can weld irreversibly and block the axle.
Detect
Many railway lines are HABD (HOA) installed, register the unusually high heat emissions of the vehicles and set off an alarm. The measurement results of the HOA (hot runner or warm runner) decide on the place where the train is to stop. The driver then has to determine the affected axle along the train using the so-called back hand test. If a vehicle is examined that has been parked for some time, there is usually no more heat radiation to be detected. But you can then recognize the hot runner by burning off the paint on the bearing housing.
It is also important to watch out for damage that could lead to an overheating, e.g. B. abnormal driving noises that indicate bearing damage, grease leakage on the axle box, flat spots or damaged grounding contacts.