I understand that ribbed back cast wheels were barred from interchange in the late 1950’s. When did introduction of “flat back” (forged?) wheels start?
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Isambard,
I believe the introduction began in the mid to late '30s. The reason for the switch was that the ribbed wheels were used and needed for the older cars that were “handbraked”. The ribs allowed for the air to keep the wheel cool and to keep it from warping. Once air braking came into the scene in the '30s, the ribbed wheels were no longer needed and the advent of the flat wheels (by law) eventually replaced the older ribbed wheels by the '50s.
Tom
While cooling was indeed the reason for the ribs, the type of braking was not the issue (Since Hand brakes and air brakes activate the same shoes) but rather method of manufacture of the wheels. The older methods were more susceptible to heat damage, so the cooling ribs were necessary.
Once air braking came into the scene in the '30s, the ribbed wheels were no longer needed…
Air brakes had “come onto the scene” by the 1880s. The Safety Appliance Act of 1893 made them mandatory - “a sufficient number of cars should be equipped with air brakes so as to control the speed of the train.”
All the best,
Mark.
I don’t know what year smooth backed wheels became mandatory, but the difference between the two types is that the ribbed back wheels were cast iron, which became brittle and could shatter from being overheated by brake application, and the ribs were to help dissipate the heat. Smooth backed wheels are steel.
I remember seeing ribbed back wheels on some rolling stock on the Illinois Central in the 1940s.
Ribbed back wheels were not permitted after the war.
The ribs were simply a strengthening feature of early wheels, which was needed for them to survive the manufacturing process which became favored at the time. These wheels are called “Chilled wheels” because of the method used to manufactor them, which involved quickly dunking the red hot wheels which had been freshly cast in molds, into a tank of chilled water. The rapid temperature change caused the wheels to shrink very rapidly, hardening and strengthening them to a high degree. The ribs were needed to keep the wheels from deforming during this process. If they weren’t there, the wheels would fold over like an omlette. Unfortunatly, this process also makes the metal very brittle, and it is suseptible to cracks after just a short time in service.
Reinforceing ribs like those used on chilled wheels aren’t illegal in and of themselves, rather it is the chilled wheels which are illegal. Ribs can and have been applied occasionally to modern equipment where extra lateral strength is needed in the wheel.
Matthew Imbrogno
-Mechanical Vollenteer, Arizona Railway Museum.
www.azrymuseum.org