Train Wheel Tribology

MolaKule

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I thought this time we would venture back to a general tribology question.

When turning a curve we know that on modern drive axles the differentials allow the outer wheel to turn faster than the inner wheel in order to avoid dragging/scuffing/slipping that outer wheel.

Train cars have solid axle sets which means the wheels rotate at constant velocity.

Question: How do train wheels avoid this problem?
 
I believe its due to the taper of the wheel set but I could be wrong on that.
My understanding also. Its why train tracks are tapered and so are the wheels. In turns the inner wheel uses a smaller part of the taper than the outside.

I know thats true on the cars. I have no idea on the locomotive if its the same with the traction wheels?
 
The taper of the wheel/flange, profile of the railhead, and also track greasers that help ease friction on particularly tight radius curves. Some locomotives have steerable radial trucks that move traction motor wheel sets at small angles around curves to maintain maximum effective tractive effort.
 
I thought this time we would venture back to a general tribology question.

When turning a curve we know that on modern drive axles the differentials allow the outer wheel to turn faster than the inner wheel in order to avoid dragging/scuffing/slipping that outer wheel.

Train cars have solid axle sets which means the wheels rotate at constant velocity.

Question: How do train wheels avoid this problem?
This is the best video I've ever found giving a great visual on how they work. Train wheels how they work.
 
Regarding the tribology reference in the title, the Swiss company Igralub specializes in rail lubrication: https://igralub.com/en/home-en/


I am "almost" positive that Igralub makes/made the (original) Bendix high solids purple Ceramlub based on speaking with the owner of this automotive supplies distributor in Florida: http://www.gwrauto.com/gwrmain.html

I use their Patelub 2400 high solids moly paste, but the new formulation is not as good in my opinion : https://goodson.com/products/bpl-2400-pastelub-brake-lubricant
 
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Wow, I figured it would take more time for responses but this is great. Thanks to all who responded.

All of the answers are right on.

It all has to do with wheel geometry. The train wheel is a conic section, or more specifically, a truncated conic section. The figure below is a truncated cone on its side, the left wheel. Put a shaft through its center and connect it to another cone to form the right wheel. Add a flange to each of the larger radii and we have a wheel set.

The radius of the left side is smaller than the right side so when contacting the rails on a right turn, the right side of the cone of the left wheel, having a larger radius, cozies up to the inner part of the rail on its larger radius and thus keeps both wheels and axle turning at the same tangential velocity. That is even though the left wheel is running a longer distance, the larger radii compensates for that longer distance.

Obviously, the actual train wheel is an exaggerated, truncated conic section with a flange.

That flange is usually lubricated by dispensing an oil or grease film on the inside of the rail curve or the flange to reduce friction and wear.

As an aside, when two conical sections are connected with a belt/chain, one can see the concept of a CVT transmission arising.


Truncated-Cone.jpg
 
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