Brake Disc Materials - EU Sources?

[Stocky Fast 1]

A good material, not sure if you can get it in the UK is G2 Durabar(Gray Cast Iron), Google it and you may find a distributer in the UK.

[Richard Pare]

I'd advise that you stick with Ductile iron for your disks. In comparison to Grey CI, they are much less prone to heat-stress cracking because of the spherical graphite. Unfortunately, the heat transfer rate is a bit less, but for the most part, since you are not heat soaking the disks to their max all the time, you won't really notice the difference.

The most common alloy used (in Ductile) is 85-55-06 (also commonly caller Ductile 80).

Steel is used on many karts and motorcycles only because the manufacturer doesn't want the liability of rotors breaking. Stainless gets used on motorcycles only because riders really hate the sight of rusty rotors after a rain. Both are crappy rotor materials from the performance standpoint.

If you can find a source, Compacted Graphite Iron ( a modified form of ductile that has a worm-like graphite structure) is the best CI rotor material available, and seems to be more in use commonly on your side of the pond.

If push comes to shove, I can supply disks of D80 sliced from 10.5" bar stock - I usually have them in stock.

[Adambomb]

Looking at Matweb, here's what I came up with (granted Matweb isn't gospel...but is the best "internet bench racing" reference I know of):

Ductile Iron (80-55-06):
Brinnell hardness: 187-269
Yield strength: >= 55 ksi
Elongation at break: 6%
Specific heat: 0.506 J/g-C
Thermal conductivity: 13-32 W/m-K
Max service temp: 649 C

1018 steel, 16-22 mm round:
Brinnell hardness: 143
Yield strength: 60 ksi
Elongation at break: 18%
Specific heat: 0.486 J/g-C
Thermal conductivity: 51.9 W/m-K

Did a little high-temp strength studying too, looks like up to 500 C there's not much effect on yield strength of low-carbon steel (same for gray iron). Performance-wise, DI looks to have slightly higher specific heat, although much lower thermal conductivity. Strength gives a slight advantage to steel (although if you use Grade 50 steel like we do, in this case iron is slightly better). Also, Ashby's materials charts actually show low-carbon steel to have a slightly higher coefficient of friction (for steel on steel or iron on iron...haven't found anything on steel vs. brake pad or iron vs. brake pad, outside of generic brake pad specs). DI has significantly higher hardness, which I'm assuming would mean longer life.

So basically, the only real differences worth worrying about that I can see (from what I've looked at) is that ductile iron is much harder, and steel has much higher thermal conductivity and ductility. Aside from that, low-carbon steel is available for next to nothing from almost everywhere, and anyone with a laser cutter will gladly carve them into whatever shape you want.

So.....what am I missing? Why should I run ductile iron?

[Richard Pare]

The Cf of steel against pad material is about 1/2 that compared to CI. Since the idea behind brakes is to be able to slow the car as rapidly as possible with the least amount of pedal effort - along with the fact that most brake pads are formulated for use with CI and not steel - what other reason would you have for going to an inferior performing material other than possibly cost?

CI (of various types) is the most common rotor material for street cars, trucks, trains, and race cars, up to and including (but only on rare occasions nowadays) F1.

PS - Standard laser cutting of rotor material is not a good idea unless you plan to cut or grind off the layer of martensite that is left over on the surface. SOME of the latest high-wattage pulsed lasers CAN vaporize the material fast enough to not leave that brittle layer behind, but good luck finding a company that has one. Waterjetting is a better process for this purpose.

[Adambomb]

Good to hear on the Cf, I have heard rumors of CI being higher but haven't found any hard data on it. Haven't had a chance to do testing yet either, what with not having random bits of CI laying around. Also with the laser cutting...feel dumb now for not having thought of that; didn't give it much consideration in the past since low-carbon steel isn't hardenable. Water jetting sounds good. Thanks!

[Vlado]

for my project car, which is a bigger version of a FSAE car, I bought 4 brembo solid discs from alfasud.... as a "blank" to be machined..

http://bremboaftermarket.com/I...?ModelIDMaster=11733

I had them CNC machined into floating disc of a slightly smaller diameter.. I'll have some pics of that when I get them back from the machine shop..

project log:
http://www.locostusa.com/forum...=7683&p=85389#p85389

[Chapo]

Here is an idea from Claude...

Go to the wreckers, find some cars that use carbon clutches, but the clutch plates and machine them down to the right size, hey presto carbon discs.

Might not be as simple as that but could be something worth looking at.

We just use a low carbon steel that is given the correct profile through wire cutting and NC milling, and then is ground to the final thickness. Never had a problem with them and we run quite small rotors.