In doing some recent research, we came across the image below from 1935. While most railroads did something similar, the photo is for the New York Central Railroad. What service is the worker providing? As a hint, the location is the entry to a passenger station located in the distance.

The image above is of the work pit of a railroad “hot box” inspector! Passenger trains, as well as freight trains coming into the station complex, had to slow sufficiently for the switching ahead. They had been running at a much higher speed prior to coming to the location pictured, which meant wheel bearings had been operating at higher speeds, creating more friction. A bearing without sufficient lubrication would be smoking if not on fire, and it was the inspector’s job to spot the smoke/fire from a “hot box” and report it so that the train could be stopped and the problem dealt with.

Depicted in the image below is a typical railroad friction bearing such as was used for locomotive, freight, and passenger cars during the 1800s and into the mid-1900s before roller and ball bearings saw widespread use. The olive part is the rotating axle attached to the railroad wheel. The yellow is the mechanical bearing made of brass. Under the axle and contained within an iron casting box-like structure with a door at the end is the waste packing, which amounts to cotton and wool materials in contact with the underside of the olive axle and saturated with oil. The turning axle picks up a thin layer of oil on the axle’s cylindrical surface and carries the oil as the axle turns to the contact area between the yellow bearing material and the olive axle. That thin layer of oil molecules keeps the axle and bearing from direct contact by forming a thin oil sheet between the two. Without metal-to-metal contact between the bearing and axle, there is little heat generated, offering a low-friction interface between the turning axle and stationary bearing.

Should oil in the packing become depleted, the oil film on the axle is reduced, and metal -to-metal contact between the bearing and axle generates heat from increased friction. With sufficient heat, the oil begins to smoke, and in an extreme situation, the oil can catch fire. As the bearing assembly is within an enclosure resembling a rectangular box, the term hot box came into use when a bearing was found smoking.