Multiple brake pads on one disc

[scarbs]

Aaah Aluminium is mandated, I stand corrected.

As you point out there is a rule on 40Gpa for car construction, although the rules are confusing, brake callipers appear to be an exception at 80Gpa.

11.2 Brake calipers :
11.2.1 All brake calipers must be made from aluminium materials with a modulus of elasticity no greater than
80Gpa.
11.2.2 No more than two attachments may be used to secure each brake caliper to the car.
11.2.3 No more than one caliper, with a maximum of six pistons, is permitted on each wheel.
11.2.4 The section of each caliper piston must be circular.



ARTICLE 15 : CAR CONSTRUCTION
15.1 Materials :
15.1.1 The use of magnesium sheet less than 3mm thick is forbidden.
15.1.2 No parts of the car may be made from metallic materials which have a specific modulus of elasticity greater
than 40 GPa / (g/cm3). Tests to establish conformity will be carried out in accordance with FIA Test
Procedure 03/02, a copy of which may be found in the Appendix to these regulations.

[DaveKillens]

On the other hand, I wonder if heat can be pumped quickly enough from them if they are in a vacuum.

A novel concept, but sadly a vacuum is the best form of insulation possible. (vacuum thermos?)
A non-contact brake is wonderful in theory, but the old, trusted and true hydraulic disk brake is powerful, and darn reliable. Personally, I lean towards using electric motors/generators for both propulsion and braking. These units have incredible stopping power, but they would have major heat issues in a racing environment.

[Ciro Pabón]

Vacuum on the surface of the brakes implies you have to pump the heat through diffusion, not convection.

On the other hand I'm not totally sure everybody understood me: one of the most corrosive materials in the world is monoatomic oxygen (when oxygen molecules reach 3 to 5 ev, they dissociate from O2 to O).

You can check here for its effects on the shuttle, where the light it creates when it impacts the shuttle can be easily observed:

http://www.spenvis.oma.be/spenvis/help/ ... osion.html

http://pdf.aiaa.org/jaPreview/JSR/1988/PVJAPRE25965.pdf

Oxygen glow on the engine pods of the Shuttle


Of course, the effect on the shuttle materials is tremendous: the oxygen flow impacts the vehicle at 18.000 kph, magnifying its effect. Carbon fiber is particularly affected by it: losses of up to 13% of material in a few days have been measured when in space. That was one of the problems that kept the Galileo vehicle from being "parked" for too long at low earth orbit: the craft was "melting" away.

This free oxygen is created in many instances, one of them by high temperatures, like in the brake pads of F1 cars.

For example, you could check the way Bessemer converters are handled: you literally throw lumps of clay to the bottom of the oven to avoid holes in it, holes that are caused on the refractary materials by heat and free oxygen. These holes, of course, would be catastrophic: the molten steel escaping from the Bessemer converter would explode on contact with any humidity. This was the cause of many accidents in the beginnings of Bessemer oven use. Next time you visit a Bessemer installation, talk with the guy in charge of the oven.

The monoatomic oxygen erodes the brake pads, I assume. That's why I suggest to investigate if its effects can be avoided.

Dave thinks that if you put the pads in a vacuum they could not be cooled. I do not agree: there are many instances of materials cooled by diffusion.

For example, that's the way the heat sink in your PC works. It's irrelevant that the fins themselves are cooled by convection and radiation: the CPU is cooled by diffusion through contact with the base of the fins.

Finally, to clarify my suggestion, if you somehow are able to avoid air in contact with the pads, you could use materials that react with oxygen, that, by chance, are the most useful to transmit heat and that are the ones that keeps better their strength when heated.

I hope somebody gets it.

[checkered]

You're, in essence, describing

a radiant cooling system for F1 brakes if I get you correctly, designed to work in a complete absence of atmospheric gases which traditionally act as an immediate convective medium. The thermal loads being what they are in F1 brakes, an adjacent absorbent surface would have to be in place, complete with a very potent cooling arrangement to maintain adequate efficiency. Some man made radiant cooling systems are pretty big and/or usually designed to achieve very uniform thermodynamic gradients and very slight variations in temperature by comparison. I couldn't immediately find more "aggressive systems" described online, though I suspect they're entirely possible.

My first thought was that what you're suggesting would propably be achieved more easily by immersing the discs in a noble gas, coupled with a circulative cooling arrangement the parts of which are less susceptible to oxidation than carbon at certain temps. My second thought was, if you create an environment where there's virtually no risk of catastrophic oxidation to begin with, to what extent is cooling the actual discs an issue at all? (I can imagine some fairly obvious answers to that, but won't go there myself so as not to muddy the waters too much.) Anyhoo, I found ample evidence that people are very aware of the effects of oxygen on carbon in brakes and that there are people investigating ways to avoid and/or manage it. I think I won't have to descibe teams using heat sensitive paint on their pads to any great detail here, but

here's a link (read "Monitoring Temperatures")

which describes the use of such paints, just in case. The F1 procedure doesn't differ from that much as far as I can tell (there was also a pretty good Matchett feature on Speed on the subject a while ago). Of course it's a less than favourable tradeoff when more cooling is required and you have to channel more air in as a result - Canada is one track that has traditionally required modifications to both discs and air ducts. I suspect the equations do not offer simple solutions when the loads increase but it's been a while since I last remember brake discs actually disintegrating so I think the teams are on top of it.

Apart from F1, there are evidently people doing basic research on the issue ( "Thermal Characterisation of Brake Pads" (link to abstract) ) and also suggesting innovative approaches ( "Small Worlds: Safeguarding carbon at the nanoscale" (link) ) such as ceramic crystals, insulating the material from a chemical "chain reaction oxidation" while the material retains its positive aspects such as the heat absorbing properties. Whether F1 brake discs make use this technology already, I don't know.

To me, the "nanoscale" solution (while awaiting energy recovery) sounds like the best available compromise.

Edit: I can distinctly remember discussing twin brake pads on a Williams (80's/90's?) with Carlos a while ago ... I think the current regulations that prevent this arrangement also came up as a result. Couldn't find the thread immediately, though, as it was originally about a road going car brake innovation or something.