Disc Brakes

[B]

Hi all. My name is Brett and I'm designing the braking system for the 2005 Curtin Motorsport Team car as my finial year project.

I'm having trouble finding info regarding the design of the disc itself i.e what material, how to fabricate it etc. I'm aware of aluminium metal matrix composites that have been tested with promising results but am unsure of where to purchase such material and how to fabricate the disc from it. Any ideas? There is also the possibility of using Titanium, but which titanium alloys are appropriate for the job? And once again how would you fabricate a rotor from such a material?

Also does anyone know how to calculate with any reasonable accuracy what temperature the rotor and pads will operate at given the boundary conditions and material properties?

Does anyone know where I can access such information or know of someone that might know a bit about it?

Please... anything!

[Cement Legs]

I think a popular material for disc brakes is grey cast iron.

[Marshall Grice]

and i think titanium is just about the worst material you could use for a rotor.

[jpventuri]

Alright,after a few pints, i'll do my best here...

Okay, like someone said, titanium bad choice. The aluminum matrix composite is your best bet in terms of "high technology". It comes cast, and you need to finish it off yourself.

This is good stuff, it's light, strong, good temperature characteristics, but it's a real problem to machine. Imagine machining a gringing wheel...yah, same deal. Where to get it? Google search...

So, steel is the next choice. Cast iron is good, of course so is stainless, then again, so is good ol regular steel. Research on this, look at what they make motorcycle rotors out of.

Once you got that down, your biggest problem is finishing the disc. They have to be perfectly true and flat, devoid of any runout, and they must spin in the plane of the pads, perfectly.
This is the tricky part. This is what i'm still working on.

My first disk experiment ended horribly, when my discs warped slightly. So, surface grinding, laser/water jet cutting, and careful turning are your best options.

To calculate heats and stuff like that, you can approximate by using an energy method, calculating the energy that must be dispersed to stop the car, and all this goes to the brake disc. A good book is BRAKE DESIGN AND SAFETY, rudolph limpert, from the sae.

Anything else, email me,

cheers

[rjwoods77]

jpventuri,

blanchard grinding is the right way to finish it.

[ben]

When I first started at Birmingham we had AL MMC rotors but I never liked the low friction coefficient or the quality of the castings we were getting. Also we got free pads and calipers off AP but they wouldn't give us a pad like Ferodo DS3000 or PFC that would have been best on the MMC.

For this reason I switched last year to cast iron discs at the front and stainless steel discs at the rear simply because we had a bike caliper at the rear with pads designed for stainless steel discs (Jap bike manufacturers don't like rust hence all discs are SS) and a car caliper at the front with pads designed for cast iron. If you can't do lots of testing it's a good pragmatic argument for settling on that choice.

Ben

[Schwanger]

HOT ROLLED mild steel seems to work well. It is very import that you use hot rolled otherwise your disk will warp horribly when machining and during use.

[Alastair Clarke]

We're using grade 15 grey cast iron (we're actually using a "special" grade from one of our sponsors, who make racing brakes, but I've been told that grade 15 is the nearest equivalent).

We've water-jet cut the part and then surface ground to achieve a flat disk. I'm sure laser cutting would work as an alternative to water jet, but we went for water-jet as it doesn't heat up the material and hence less chance of thermal distortion etc. If you're machining them down, be sure to take a bit off each side, to avoid distortion.

Cheers

Alastair

[Jarrod]

we have used cast iron in the past, it can be very difficult to work with. We were put onto a steel alloy called bisalloy 80, available in plate form, we had the rotors laser cut, then wash ground to get them flat. The material is fairly easy to get in australia, and is commonly used as a brake material on motorbike rotors(for custom stuff, don't know about production)

[Richard Pare]

The vast majority of racing brake disks are made from various types of grey cast iron, with varying levels of manganese, nickle, and carbon, depending on the particular company. Two that you can use that are readily available is either Type 30 or Type 40, with rough disks available from places like McMaster-Carr. I also have cast Type 30 disks (5.0 id x 10.4 od ) available that we supply to some SAE teams.

Whatever you use, you should have it stress relieved before final machining (easy to do on the lathe), and then do an easy "bedding in" before hard use.

To keep the rotors running true, and to reduce drag to the minimum, you will want to "float" the rotors on their hats (mounting disks).

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