F1 Brake Discs

[strad]

Usually with brakes when you see CER in the name it means ceramics...are they using ceramics?
Usually on road cars ceramic wears well but doesn't have the friction coefficent of organic.

[FW17]

Isn't AP and Brembo are the same group?

[olefud]

Hello
I want to do a demonstration on carbon fiber Forumla 1 brake discs. I was thinking why the carbon fiber has much more rubbing with higher heat and what the molecular structure and cause was regarding this.

Carbon fiber brakes are not a friendly subject for show and tell. They’re formed from a carbon-rich binder such as pitch and carbon fibers that are sintered to drive off or oxidize the noncarbon constituents. Since carbon is not volatile and doesn’t burn under these conditions, the end product is carbon. Keep in mind that carbon can be graphite, diamond, soot etc. The brakes are mostly graphite but this can change with temperature during use. When cold, wear is rather high, perhaps due to abrasive particles at low temps. However, at higher temperatures the sheet-like graphite functions as a lubricant between the carbon pads and the carbon rotor. Normally friction between like materials is a prime no no.

The high temperatures are because they can and need to. Besides wear at low temperature, carbon rotors have low thermal mass and are unable to sink heat energy for later rejection as cast iron rotors do. Heat is rejected essentially through radiation from the rotors that operate around 600 degrees F hotter than cast iron. You might want to review radiant cooling to appreciate that the heat rejection is a fourth order function of temperature.

The manufacturers are a bit closed mouth about the subject. Don’t argue if someone says the above is in error.

[cemax]

Hi all! one question. Do you know the reason why carbon brakes don't work at low temperatures? We know to optimal operating temperature is 650º, but not the cause. Thanks!

[Drewd11]

Hi all! one question. Do you know the reason why carbon brakes don't work at low temperatures? We know to optimal operating temperature is 650º, but not the cause. Thanks!

If you weren't just being lazy, had seen the post above, and wanted a more in depth explanation of what causes the difference between low temperature and high temperature wear then I am not the guy to give it. But look in this video from I think the 2010 season when carbon discs were newer than they are now:
https://www.youtube.com/watch?v=kqAQpj44kw0
at 1:29 you'll see brake dust coming at what looks like the entry to t17 in Valencia. This is before teams had the optimal disc temps nailed down, and before I think some advances in caliper material tech (this isn't my area). In essence, what used to happen was that carbon discs would just be ruined after a very short time, and they still lose alot of thickness over the course of a race.
The main change that I know of for sure is that they've gone from layering sheets composed of graphite strands for the disc to depositing individual molecules of carbon based material (again, beyond my expertise to guess what specifically) on some initial disc surface, which has brought the abrasiveness of the disc down significantly (avoiding the brake dust in all but the most demanding corners), and stopped them from shattering as they used to when overstressed.

[riff_raff]

Hi all! one question. Do you know the reason why carbon brakes don't work at low temperatures? We know to optimal operating temperature is 650º, but not the cause. Thanks!

CRC brakes work at low temps. It's just that they perform better at elevated temps. This is due to a peculiar characteristic of carbon where its friction coefficient actually increases with higher temperatures.

[cemax]

Thank you. Here I found an article that explains
http://angelesenlacabeza.blogspot.com.e ... ionan.html

[stefan_]

[youtube]http://www.youtube.com/watch?v=C4aO5mw0V7g[/youtube]

[bigpat]

F1 doesn't use ceramic as its heavier than carbon. Also not only do carbon brakes lack modularity of the pedal compared to ceramics., but Ceramics are also happier to work at lower temperatures while still giving good friction co-efficients, where carbon brakes will glaze, unless they' re kept at an elevated bulk temperature, which isn't practical on a road car, and would affect bearings, and seals over time, not an issue over a race instance...

Don't believe that carbon brakes wear quickly, as categories like the DTM mandate them, and although initially expensive to buy and engineer, typically last a number of race meetings, unlike cast iron rotors and their pads, which in many sedan classes are replaced every meeting.

It's a fallacy that carbon brakes stop a car faster than cast iron brakes. It has been repeatedly shown that an iron brake can produce higher friction figures than carbon, but exhibits fade quicker. In 1999, Williams installed cast iron brakes from PFC on Alex Zanardi's car for practise at Monza. Braking performance and lap times were similar, but there as a 16 kg weight penalty, which meant less ballast in the car.....

[Lycoming]

It's a fallacy that carbon brakes stop a car faster than cast iron brakes. It has been repeatedly shown that an iron brake can produce higher friction figures than carbon, but exhibits fade quicker. In 1999, Williams installed cast iron brakes from PFC on Alex Zanardi's car for practise at Monza. Braking performance and lap times were similar, but there as a 16 kg weight penalty, which meant less ballast in the car.....

But in a racecar, braking should always be traction (read:tire) limited, should it not? Then, if that's the case, all friction coefficient really effects is how much pedal force is required, right? Obviously there are other aspects to brake performance (wear, fade, etc.) but assuming that none of those are issues, they should both be capable of locking the tires, in which case the only reason a carbon brake will stop a car faster is because it weighs less.

[olefud]

It's a fallacy that carbon brakes stop a car faster than cast iron brakes. It has been repeatedly shown that an iron brake can produce higher friction figures than carbon, but exhibits fade quicker. In 1999, Williams installed cast iron brakes from PFC on Alex Zanardi's car for practise at Monza. Braking performance and lap times were similar, but there as a 16 kg weight penalty, which meant less ballast in the car.....

But in a racecar, braking should always be traction (read:tire) limited, should it not? Then, if that's the case, all friction coefficient really effects is how much pedal force is required, right? Obviously there are other aspects to brake performance (wear, fade, etc.) but assuming that none of those are issues, they should both be capable of locking the tires, in which case the only reason a carbon brake will stop a car faster is because it weighs less.

Ignoring all the real life problems, it's more that carbon brakes will stop longer at an optimal efficiency than iron brakes. This primarily has to do with much greater heat rejection with carbon brakes.

[bigpat]

Agree that the reduced unstrung weight, and smaller gyroscopic effect of the lighter carbon discs will help lap time, but not ultimate braking power. As i said, cast rotors and their pads produce higher friction values.At high speed with their downforce F1 cars are not traction limited. it is physically impossible to lock the wheels, that's why the drivers stamp on the pedal as hard as they can. Once the grip and speed wash off, and the cars are grip limited, it doesn't matter what brakes you use, as you can't harness all their stopping power. In this case or when there is low grip, iron brakes are more drivable as they exhibit better modularity.....

As for heat rejection, that's not right. Carbon has better insulating properties than iron brakes. As they need higher bulk temperatures, the brakes themselves need less cooling, but the hubs and bearings need to be considered as well.

As mentioned elsewhere, carbon brakes will start to oxidise at 1000 deg C, so while they can take that temp as a peak, you can't keep them elevated. The carbon pad and disc wear together, and as they do, there is physically less mass to absorb the heat, and wear accelerates. This is what happened to Kimi Raikonnen at Spa this wear, when a helmet tear off blocked a brake duct. Cast iron brakes on the other hand can sustain high temperatures peak temperatures, but the pads taper easier, and can fade. When Champcars raced at street circuits, they regular saw 900 deg C brake temps, and drivers still had good pedals, due to advancements in caliber and pad technology.

[olefud]

Agree that the reduced unstrung weight, and smaller gyroscopic effect of the lighter carbon discs will help lap time, but not ultimate braking power. As i said, cast rotors and their pads produce higher friction values.At high speed with their downforce F1 cars are not traction limited. it is physically impossible to lock the wheels, that's why the drivers stamp on the pedal as hard as they can. Once the grip and speed wash off, and the cars are grip limited, it doesn't matter what brakes you use, as you can't harness all their stopping power. In this case or when there is low grip, iron brakes are more drivable as they exhibit better modularity.....

As for heat rejection, that's not right. Carbon has better insulating properties than iron brakes. As they need higher bulk temperatures, the brakes themselves need less cooling, but the hubs and bearings need to be considered as well.

As mentioned elsewhere, carbon brakes will start to oxidise at 1000 deg C, so while they can take that temp as a peak, you can't keep them elevated. The carbon pad and disc wear together, and as they do, there is physically less mass to absorb the heat, and wear accelerates. This is what happened to Kimi Raikonnen at Spa this wear, when a helmet tear off blocked a brake duct. Cast iron brakes on the other hand can sustain high temperatures peak temperatures, but the pads taper easier, and can fade. When Champcars raced at street circuits, they regular saw 900 deg C brake temps, and drivers still had good pedals, due to advancements in caliber and pad technology.

Heat rejection involves several mechanisms, conduction, convection and radiation. Iron brakes rely primarily on convection (mostly through internal fins after the heat is sunk in the rotor). Conduction is largely undesirable beyond the rotor. And radiation is marginal in that heat checking and warping occur at temps at which radiation becomes effective. The Champcars may have seen 900° C at some limited location, but iron is not at all happy at that temp, i.e. shows warping and heat checking at maybe 700°C on a good day when heat soaked. I don’t claim to know but suspect the Champcar improvements involve a more effective heat rejection and maybe a bit of nickel in the rotors.

Long term, carbon brakes actually require somewhat greater heat rejection for a given heat load than iron since, having a low heat capacity, they reach higher temps with a given heat input. However, since carbon functions fairly comfortably at 900° to 1000° C, the radiant heat rejection mechanism becomes exponentially (to the fourth order) more effective with increased temps. Carbon brakes reject heat primarily through a differing mechanism relative to iron brakes,

Heat rejection has been discussed in a bit more detail at;
http://www.f1technical.net/forum/viewto ... brake+heat

[bigpat]

Fair enough, well posted!

[riff_raff]

As olefud noted, there are many differences between iron, ceramic and CRC brakes that must be considered in total when deciding which system is best for a given application. First of all, we should remember the old saying "Brakes only stop the wheels. It's the tires that stop the car."

While CRC brakes are lightweight and can provide huge amounts of braking capacity, they are also very expensive, and have high wear rates. CRC brake rotors and pads also tend to wear equally, unlike other brake systems. This means CRC rotors and pads must both be replaced at the same time.