EDUCATE YO MOMMA: Roller bearing trucks, and how they work

[mtrpls]

We keep hearing about "roller bearing truck" all the time on freight cars, so I wanted to investigate what they were exactly. Here is the Physics 101 answer:

http://en.wikipedia.org/wiki/Roller_bearing

Something that's often overlooked on rolling stock, eh?

Matt

[jbaakko]

Never knew that? That "bearing failure" they talk about is why you head some nasty "thud thud thud thud..." coming from rolling stock.

[RCH]

Never knew that? That "bearing failure" they talk about is why you head some nasty "thud thud thud thud..." coming from rolling stock.

That thud you're hearing is more likely a flat spot on a wheel than a bad bearing. A wheelset won't last long with a bad bearing, but the flattened wheel can keep going for quite a while.

[jbaakko]

Thats true, I thought of that after I posted and just didn't go through the work to edit the reply.

[OldGettysk]

Bearings greased plenty of them in my day or maybe i forgot my bearings.

[HaggisKennedy]

I've heard that friction bearings actually are a bit more forgiving at the point of failure. They're hard to get rolling from a start, but once going, they're OK. When the bearing fails, it's gradual.

The roller bearings start with way less friction, and roll well. But, it's said that when they fail, they fail catastrophically, and suddenly. There's not a whole lot of grace period. They can overheat and fail between hotboxes, while the friction ones will go by at least one hotbox before the axle is burned through.

Kennedy

[HaggisKennedy]

Never knew that? That "bearing failure" they talk about is why you head some nasty "thud thud thud thud..." coming from rolling stock.

My Dad was an Ordnance Engineer for the Navy back during WWII. This came up during the war; battleship turrets were having a vibration as they rotated. At 15mi gunnery ranges, this could be bad.

Turns out that every time they fired a salvo from a turret, the recoil would put a microscopic flat spot on the turret bearings/race. Enough salvos meant that the bearings/race was filled with little dents, which meant that when the turret rotated, it'd bounce along (if only slightly).

They ended up going to a better bearing and more hard races...

Kennedy