Hot box - AbsoluteAstronomy.com

A hot box is the term used when an axle bearing overheats on a piece of railway rolling stock

Rolling stock

Rolling stock comprises all the vehicles that move on a railway. It usually includes both powered and unpowered vehicles, for example locomotives, railroad cars, coaches and wagons...

. The term is derived from the journal-bearing trucks

Bogie

A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...

used before the mid 20th century. The axle bearings were housed in a box that used oil-soaked rags or cotton (collectively called packing) to reduce the friction of the axle against the truck frame. When the oil leaked or dried out, the bearings overheated often starting a fire that could destroy the entire railroad car (and cars coupled to it) if not detected early enough.

The packing and bearing had to be regularly inspected, and packing was often added at major stops. The journal was replaceable, but if neglected it would heat to a temperature where the alloy would melt away and leave the brass carrier riding on the steel axle. This would eventually lead to the axle fracturing and the car above falling onto the wheel, which could cause a major derailment

Derailment

A derailment is an accident on a railway or tramway in which a rail vehicle, or part or all of a train, leaves the tracks on which it is travelling, with consequent damage and in many cases injury and/or death....

of the train. Train worker duties consisted partly of inspecting the train as it ran by, looking for smoke, sparks, or fire. They would then sound the audible report "All Black" to mean the train was not giving off any light energy that would indicate combustion or destruction of the wheel bearings. If the train worker saw "Red" or smoke, he would alert other crew members, or else make an emergency stop to the train to prevent further damage.

When this type of axle box was used, any diesel exhaust

Diesel exhaust

Diesel exhaust is the exhaust gas of a diesel engine....

smells had to be tracked to their source, as a hot-box sometimes smells similar. Most of the larger railroads use defect detector

Defect detector

A defect detector is a device used on railroads to detect axle and signal problems in passing trains. The detectors are normally integrated into the tracks and often include sensors to detect several different kinds of problems that could occur...

s to scan passing trains for hot box conditions. Some of these detectors also have "automated mile posts" which send an automated radio signal to the train crew listing the train number, track number, and train speed.

Modern ball

Ball bearing

A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...

, roller or tapered bearings

Tapered roller bearing

Tapered roller bearings are bearings that can take large axial forces as well as being able to sustain large radial forces.-Description:...

can also overheat, but the likelihood of a roller bearing overheating is usually far smaller than it was with journal bearings. When modern bearings do go wrong, the balls or rollers and their races

Race (bearing)

The rolling-elements of a rolling-element bearing ride on races. The large race that goes into a bore is called the outer race, and the small race that the shaft rides in is called the inner race.-Manufacture:...

fail, generating heat which can ignite fires or be the ignition source of a dust explosion

Dust explosion

A dust explosion is the fast combustion of dust particles suspended in the air in an enclosed location. Coal dust explosions are a frequent hazard in underground coal mines, but dust explosions can occur where any powdered combustible material is present in an enclosed atmosphere.- Conditions for...

in grain, coal, sawdust, etc.

See also