Brake rotor material selection

[mgomezz116]

I am in the midst of deciding what material to use but was not on our Drivetrain Team last year so missed out on the decision process.

Last year we used A2 tooling steel for our rotors. The minimum amount of mass needed to dissipate the heat was calculated and the rotors designed accordingly. This material was selected primarily because we could get it in the right thickness. So the rotor was just water-jetted out of the off the shelf material.

However, according to Carol Smith and others Cast Iron is a superior brake rotor material. If we take this route we will not be able to get the material in the thickness desired, which will lead to higher manufacturing costs. I am imagining that Cast Iron is better because it is a harder material and dissipates heat better. I haven't been able to find any sort of definitive backing in my internet searches.

So basically what kind percent weight reduction would we see by switching material? Also, what do we really gain by switching material? Would there be a better steel to use that we could still easily get in a sheet of the correct thickness?

Any help would be great.

M Gomez
U of Illinois at Urbana-Champaign
Dtrain Team Leader

[Buckingham]

First, kudos for putting in some effort/thought before posting.


I am imagining that Cast Iron is better because it is a harder material and dissipates heat better.

There are three modes of heat transfer. Conduction, convection, and radiation. Which one is the primary path for heat to leave the brakes? How do the mass and material properties of the rotor affect this path?


This material was selected primarily because we could get it in the right thickness

12" Round Cast Iron is available in whatever thickness you want.

[Ben K]

Cast Iron can store a lot of energy as well as hold it closer to the surface due to its low conductivity. Therefore it dissipates the energy quickly and doesn't heat soak as much.

Tool steels are an option--but frankly cast iron is so darn easy to deal with you might as well stick with it unless you have a laser cutter somewhere.....

Ben

[coastertrav]

And if you use cast iron you get to astonish the judges with the fact that you actually have iron rotors. I have no idea why, but our guy explaining the braking system to the judge had the hardest time convincing him that they were actually iron. (The judge also threw a fit about our steel brake buttons, apparently "anything less than titanium couldn't possibly work." It's been an ongoing joke around our shop since May).

[theTTshark]

Originally posted by coastertrav:
And if you use cast iron you get to astonish the judges with the fact that you actually have iron rotors. I have no idea why, but our guy explaining the braking system to the judge had the hardest time convincing him that they were actually iron. (The judge also threw a fit about our steel brake buttons, apparently "anything less than titanium couldn't possibly work." It's been an ongoing joke around our shop since May).
Personally we like to use solid gold rotors with platinum brake buttons, but to each their own.

[Buckingham]

but frankly cast iron is so darn easy to deal with you might as well stick with it unless you have a laser cutter somewhere.....

What's wrong with laser cutting cast iron? http://fsae.com/groupee_common/emoticons/icon_wink.gif

[mgomezz116]

[/QUOTE]12" Round Cast Iron is available in whatever thickness you want.[/QUOTE]

Where are you finding cast iron in thicknesses of your choice? For the most part all i have been able to find is some sort of bar or massive billets.

[Buckingham]

For the most part all i have been able to find is some sort of bar or massive billets.

So you're half way there... now all you need is a saw. http://fsae.com/groupee_common/emoticons/icon_smile.gif

A good metal distributor can actually saw off the disks for you for what is known as a "cut charge". Besides, their saw is probably better than yours (if not, find a better distributor).

[sbrenaman]

Should you call either one of these vendors, PLEASE tell them Portland State University's FSAE team sent you. Thanks

Both of the following vendors were able to cut the round stock into discs for us. 5/16-3/8" discs are what we usually got. They don't really seem to like cutting less than that.

Ductile Iron:
Encore Metals - Tigard, OR
http://www.encoremetals.com/
503-620-8810

Gray Cast Iron:
Scot Industries - Centralia, WA
http://www.scotindustries.com
360-623-1305