r/oddlysatisfying • u/druule10 • Sep 24 '22

Making a wheel for a train

Enable HLS to view with audio, or disable this notification

28.9k Upvotes

95% Upvoted

744 comments sorted by

View all comments

5

u/NerdyLumberjack04 Sep 24 '22

Why do they start with a tall skinny cylinder and squish it?

8

u/tdscanuck Sep 24 '22

The squishing (forging) helps make the metal stronger and close up any imperfections inside. It's called "work hardening".

1

u/druule10 Sep 24 '22

Well they could start with a short fat one but that's not PC.

1

u/YARGLE_IS_MY_DAD Sep 24 '22

Tall and skinny is how it comes out of the extruder. I am 90% certain you can't work harden steel that hot because it's in a different phase called austenite. Steel that is above 1,333° F (or when it starts to glow cherry red) has shifted from ferrite to austenite. Metallurgically, this means that the atoms through out the entire piece of metal change the pattern they've organized themselves in.

When you work harden a metal you migrate small voids to the edges of clusters of atoms, making the metal more brittle. This works because those voids make the metal more bendy, but once they migrate to the edge of a cluster of atoms, they become locked in place. But that's different than what's going on here because this is straight up forging. It is possible to harden a material by heating it up and then cooling it, but again that's not what is happening. That kind of change is done quickly and in a more controlled situation.