How do train wheels not skid or lose traction?

Question

Basically the title. Considering that train wheels are made of metals and run on metal tracks, how do they prevent wheelslip or loss of traction especially when starting with heavy loads or when going uphill? I’ve heard of sandboxes which can be used to provide more grip by spraying sand onto the track but I’m not sure if they’re still prevalent.

Thanks!

In: 72

Answer 1

The friction coefficient of steel on steel is quite good.

https://www.engineersedge.com/coeffients_of_friction.htm

I suppose the idea that metal on metal is slippery comes from having seen some lubricated linkage. Remove the lube and it grinds bad.

Or maybe from ball bearings. Which are lubricated too. But regardless. Ball bearings have no friction. All contacts are rolling contacts.