Hot box

A hot runner is unacceptably high temperatures of an axle in a rail vehicle. Is sometimes wrongly assumed that it also is a hot box with a heat generation by a fixed brake. The term hot box but is only understood inadmissible heating of the axle box. However, a solid brake lead to a hot runner, namely, if the heat generated is transferred to the wheel set bearings and cause damage there. A hot runner is classified as operating dangerous damage, so the vehicle must be taken out of service.

Causes

Flats

A flat spot develops on the Radsatzlauffläche when the axle is blocked on the brakes before the train has come to a halt. The wheels of the wheelset are blocked pulled by the inertia of the train in the non-rotating state on the rail (this process is referred to as a slide ), which due to the increased friction leads to the resting place of the Radsatzlauffläche to increased material removal. The ensuing flat part ( flat spot ) generated at each wheel revolution a beat which is heard as noise and routed through the wheel center also acts on the components of the axle box. If the flat spot is not removed for a long time, so the load on the axle box guide you through these blows to a bearing failure.

Defective grounding

Special grounding contacts, also called "Frost contacts " in the jargon ( derived from the name of a manufacturer who produces such contacts ) prevent currents that are derived via bogie wheel and rail to the ground, to flow through the wheel set bearing and cause sparking. If, due to a broken ground contact to such sparks, weld deposits occur in wheelset bearings and thus also bearing damage.

Grease discharge

The bearing grease has the task to reduce the friction in the wheel set bearing. One hand, by leakage of bearing grease by insufficient sealing of the bearing friction be increased so that the bearing eventually becomes damaged. On the other hand, a grease leakage but also point to an existing bearing damage, which produces an increased heat generation, thereby reducing the viscosity of the bearing grease. The heat source may also be a fixed brake, the heat carries over to the camp. Due to this effect, a cycle of heat generation can develop through lack of lubrication by a bearing failure (or by a fixed brake), resultant increased lubricant leaks and deterioration ( formation ) of the bearing damage that accelerates the harmful detention Will the camp. If the grease drain slightly, so the fat is removed and the wheel will continue to be monitored. With renewed grease leakage or heavy grease leakage ( the fat has spread to the entire wheel disk or even on the truck ) must be taken out of service the vehicle.

In summary, the reasons above lead to bearing damage due to lack of lubrication. Due to the increased friction, the wheel is heated more than the others.

Consequences of a hot runner

When a hot axle wheelset bearings in high temperatures can occur, which can reach nearly 1000 ° C in extreme cases. This is for a fire hazard, on the other hand, the strength properties of the material take so strongly that it thus may lead to derailment and the broken axle. Also, in a hot runner stops, weld the irreversibly block the wheel bearing axis.

Recognizing a hot runner

At many railway lines HABD ( HOA ) are installed, the register unusually high heat radiations on the vehicles and trigger an alarm. The measurement results of the HOA (hot runner or hot runner ) decide on the place where the train is stopping. Then the driver along the train has to determine the affected axis using the so-called back of the hand sample. If a vehicle is investigated, which is already parked for some time, no heat radiation is clear in the rule. But you can then identify the hot runner paint burn through the bearing housing.

It is also important to pay attention to damage that can lead to a hot box, such as abnormal driving noises, which indicate a bearing damage, grease leakage at the axle bearings, flat spots or damaged grounding contacts.

• Railway operation