Re: Friction Bearings – How Old Is This Term?



It's back.

The term bearing in the broad sense means a method to support the relative motion of one surface against another - a bearing surface, usually under some manner of "load" that need to be transferred from one surface to the other..

The vast majority of bearings are designed to reduce friction, but they are not "anti-friction". Outside of roller bearings, pretty much ALL bearings have some amount of friction.

In the case of railroad journal bearings of the original types (you can do patent searches back to the early 1800's on railroad bearings as friction bearings, to include a number of British patents), when first starting the train, the axles and bearings are truly in direct contact and suffering from significant sliding friction between the axle and the bearing.

Within a few axle revolutions, with enough oil and some manner of helping spread the oil, if the speed was high enough (I suspect at least one and maybe two mph), an oil film between the two surfaces would be established that turned the bearing into a hydrodynamic bearing, where there was no longer direct contact between the axle and bearing. But with one side of that oil film "stuck" to the axle, and the other side of that oil film "stuck" to the bearing, there is significant shear within that fluid, and shear in fluid is itself, by nearly every properly trained mechanical engineer I have ever known, referred to as "friction", which is why the oil in your car engine, which also has hydrodynamic bearings on the crank shaft, also gets hot (from the friction!) (And that same shear friction is why pressure drops along a pipe moving fluids - that is also friction.)

Which is why it was so hard to start a train with "friction bearings" and why engineers, especially steam locomotive engineers, would "take slack" so that only a few cars at a time were starting, otherwise the direct contact friction in the cars that have not yet established the hydrodynamic oil film was so high it would stall the locomotive, or exert so much drawbar pull to cause the drivers to slip.

A roller bearing can properly be called an "Anti-friction" bearing because there is NO sliding between the contact surfaces inside the roller bearing that transmit the load (weight of the car) from the truck sideframe to the axle - the contact is just like the wheel rolling on the rail.

Bottom line, there is significant friction occurring in the original railroad journal bearings, and almost no "friction" in today's modern roller bearings (there is some friction in the bearing cages, but that friction is not related to transmitting the weight of the car to the axle.)

What I really don't understand is where does this seemingly "hate" for Timken come from? Roller bearings, especially Timken's tapered roller bearings, where a vast improvement in safety and economy of freight rail. The fact that Timken stuck with it for nearly 50 years before wide spread adoption is amazing to me. The real tragedy is the refusal of railroad line engineers to adopt the technology. That refusal to accept change is not unique - having studied "disruptive" technologies one finds this to be quite common across many industries - a current example being SpaceX's Falcon 9 taking over the commercial satellite launch market from aerospace companies that refused to modernize their rockets (effectively derivatives of late 1950 ICBM's.)

The 1929 report of a test train of 100 roller bearing equipped hoppers on the PRR helps illustrate the inability of the PRR's engineering staff to understand how roller bearings work. There is a copy of the draft report in the PA state Archives that I hope to copy and analyze some day but a quick review of it about 5 years ago highlighted the almost irrational resistance to the roller bearing concept by a number of PRR engineers (that draft has a LOT of pencil'd markups.)

If there is ANY criticism due, it is of the RR's line engineers (not the locomotive engineers), refusal to change to a safer and more efficient technology (although there were economic dis-incentives to adopt roller bearings in freight service.)

Dave Evans

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