Feeling the Heat: Railway Defect Detection [Hackaday]

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On the technology spectrum, railroads would certainly seem to skew toward the brutally simplistic side of things. A couple of strips of steel, some wooden ties and gravel ballast to keep everything in place, some rolling stock with flanged wheels on fixed axles, and you’ve got the basics that have been moving freight and passengers since at least the 18th century.

But that basic simplicity belies the true complexity of a railway, where even just keep keeping the trains on the track can be a daunting task. The forces that a fully loaded train can exert on not only the tracks but on itself are hard to get your head around, and the potential for disaster is often only a failed component away. This became painfully evident with the recent Norfolk Southern derailment in East Palestine, Ohio, which resulted in a hazardous materials incident the likes of which no community is ready to deal with.

Given the forces involved, keeping trains on the straight and narrow is no mean feat, and railway designers have come up with a web of sensors and systems to help them with the task of keeping an eye on what’s going on with the rolling stock of a train. Let’s take a look at some of the interesting engineering behind these wayside defect detectors.

Friction Is The Enemy

At the risk of stating the obvious, trains have two essential characteristics that make monitoring systems necessary: they’re heavy, and they’re long. The weight of a train is a problem because even though the basic architecture of a railway reduces rolling friction between a wheel and the ground, it does nothing to reduce friction between the railcar’s axles and the trucks that carry them. That’s the job of the wheel bearings, which like any other mechanical component are subject to wear, damage, and eventual failure, with the potential for catastrophic consequences.

As for the length of a train, that becomes a problem when it puts most of the rolling stock out of the direct visual range of the people running the train. Back in the day, limitations on locomotive power tended to keep trains relatively short, making it possible for conductors and engineers to keep an eye on every car. This was made easier by the invention of the caboose; in its classic configuration with a windowed cupola jutting up over the roof of the car and from its position at the very end of the train, conductors were able to observe the entire length of a train, especially on curves. Given that the wheel bearings of the day were often plain bushings in journal boxes stuffed with oil-soaked fibers, it was generally easy to spot a “hot box” bearing failure by the smoke and flames they emitted, as unsubtle an indicator of trouble as there ever was.

Engineering advances, like replacing plain bearings with roller bearings, made it possible to build ever-larger railcars. Freight cars operating on North American railways these days can have a gross weight of 315,000 pounds (143 tonnes), a mind-boggling amount of weight that’s carried by as few as eight roller bearings. Improvements in locomotive design have also allowed trains built from these supersized cars to get ever longer; the average freight train in 2017 was between 1.2 and 1.7 miles (1.9 to 2.7 kilometers) long, with some railroads regularly operating trains 3 miles (4.8 km) in length. On a train like that, anything more than a dozen or so cars back from the head-end locomotives is out of direct visual range of the engineer and conductor, and is effectively operating completely unobserved.

Eyes On The Rails

Wayside monitoring is the answer to the problems presented by scaling trains up to such massive dimensions. Collectively known in the railroad business as “defect detection,” the sensors and systems installed periodically along railroad tracks automatically scan for any problems with the rolling stock of a train that might result in an accident.