Steel Brake Rotors

[chart21]

For teams who make their own rotors, has anyone heat-treated their steel rotors? If so, what was your experience with it and would you recommend it?

[Charles Kaneb]

I'm not sure of the wisdom of heat-treating a part that's going to glow white-hot several times a minute for its entire service life if properly designed. Seems to me that you're either partially annealing or hot-quenching it every time you get on the brake, depending on how well your brake cooling system works.

[MCoach]

White hot? White hot is the edge or point of melting.

Good luck with thermal cycling and cracks on those little guys.
Cherry...mmmm...now that is a beautiful color to see.

[onemaniac]

May I ask why you want to heat treat your rotor? Wear resistance?

[Rex Chan]

Melbourne Uni uses mild steel (laser cut) as backups, and machined cast iron (from OEM/passenger cars) as primary.

We do not heat treat.

[Owen Thomas]

We make our own rotors, and do not heat treat them. Also, I think you used the word "steel" a little too liberally. What KIND of steel are you thinking of heat treating for your rotor? Annealing? Tempering? It may or may not be a good idea based on a number of things.

I wouldn't go through the trouble, as it seems there are enough things that could go wrong and not very much (if any) gain.

[chart21]

I would be using 4140 steel and heat treating to increase the yield strength.

[Charles Kaneb]

Originally posted by MCoach:
White hot? White hot is the edge or point of melting.

Good luck with thermal cycling and cracks on those little guys.
Cherry...mmmm...now that is a beautiful color to see.

Yep. White hot.

Make 'em simple and cheap to manufacture, and you'll be able to get to the right lifespan for a brake rotor - one endurance event.

[Owen Thomas]

I would be using 4140 steel and heat treating to increase the yield strength.

I would not do this. The yield strength of 4140 is typically far higher than the stresses you (should) see in your rotors. In addition, most types of 4000 series are heat treated already, so you may be messing with a good thing (unless you welded your rotors?). I believe the reason people use high carbon (high strength) steels is not for thier strength, but for the heat transfer properties. A ductile rotor is much safer for our application, especially since temperatures above 800C (re-crystallization temp, ie when heat treating begins) are typically not seen for very long. Sorry Charles, gonna need some pictures to back up that one http://fsae.com/groupee_common/emoticons/icon_razz.gif

[onemaniac]

Originally posted by Charles Kaneb:

Yep. White hot.



Then it's too hot. Isn't it?
I think the optimal temperature for most brake pads is in 500F-1000F range depending on the compound.

[MCoach]

Charles,

I disagree with this design theory that things should be made 'just to last one endurace'.

Why not bring a spare car to competition? Seems reasonable if those are your design goals.
The cost is not worth the benefit, especially for smaller teams. To take this point further, how many parts do you go through during testing? If you minimize testing because parts are likely to fail, then the chance of them failing during competition is quite a bit higher than that of a car designed with a slightly higher safety factor.


I'd rather do testing and make sure things are safe rather than toast them to white hot colors of the rainbow.

Take your disposable car theory elsewhere.

[Charles Kaneb]

If your laser-cutting supplier or sponsor doesn't want to make them by the dozen "for the same price, it won't take any longer" your design's too complicated. Minimize the laser travel length, and, yes, make them so they're shot after a few hours. Make enough that you can throw them away frequently.

[kcapitano]

the right lifespan for a brake rotor - one endurance event.

Charles,

Have you actually implemented this strategy before? I'm less concerned about the cost of manufacturing brake rotors in bulk then I am concerned about the time it would take to keep replacing them.

A good team with a reliable car should be able to do at least four endurance events on a single day of testing. So you expect your team to swap four sets of rotors four times a day? And how long do you think it will take to remove all four tires, all four calipers and put everything back on?

In an ideal world the car would work perfectly up until you cross the finish line of the endurance event, at which point everything on the car would simultaneously fall to bits. Unfortunately we live in the real world.